Why we need to see the dark matter to understand the dark energy
Kunz, Martin
2007-01-01
The cosmological concordance model contains two separate constituents which interact only gravitationally with themselves and everything else, the dark matter and the dark energy. In the standard dark energy models, the dark matter makes up some 20% of the total energy budget today, while the dark energy is responsible for about 75%. Here we show that these numbers are only robust for specific dark energy models and that in general we cannot measure the abundance of the dark constituents sepa...
Why we need to see the dark matter to understand the dark energy
International Nuclear Information System (INIS)
Kunz, M
2008-01-01
Abstract. The cosmological concordance model contains two separate constituents which interact only gravitationally with themselves and everything else, the dark matter and the dark energy. In the standard dark energy models, the dark matter makes up some 20% of the total energy budget today, while the dark energy is responsible for about 75%. Here we show that these numbers are only robust for specific dark energy models and that in general we cannot measure the abundance of the dark constituents separately without making strong assumptions
Dark matter and dark energy: The critical questions
International Nuclear Information System (INIS)
Michael S. Turner
2002-01-01
Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% ± 1% baryons; 29% ± 4% cold dark matter; and 66% ± 6% dark energy. Now that we have characterized the dark side of the Universe, the challenge is to understand it. The critical questions are: (1) What form do the dark baryons take? (2) What is (are) the constituent(s) of the cold dark matter? (3) What is the nature of the mysterious dark energy that is causing the Universe to speed up
Dark energy and dark matter from primordial QGP
Energy Technology Data Exchange (ETDEWEB)
Vaidya, Vaishali, E-mail: vaidvavaishali24@gmail.com; Upadhyaya, G. K., E-mail: gopalujiain@yahoo.co.in [School of Studies in Physics, Vikram University Ujjain (India)
2015-07-31
Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.
Conformal Gravity: Dark Matter and Dark Energy
Directory of Open Access Journals (Sweden)
Robert K. Nesbet
2013-01-01
Full Text Available This short review examines recent progress in understanding dark matter, dark energy, and galactic halos using theory that departs minimally from standard particle physics and cosmology. Strict conformal symmetry (local Weyl scaling covariance, postulated for all elementary massless fields, retains standard fermion and gauge boson theory but modifies Einstein–Hilbert general relativity and the Higgs scalar field model, with no new physical fields. Subgalactic phenomenology is retained. Without invoking dark matter, conformal gravity and a conformal Higgs model fit empirical data on galactic rotational velocities, galactic halos, and Hubble expansion including dark energy.
Dark Energy and Structure Formation
International Nuclear Information System (INIS)
Singh, Anupam
2010-01-01
We study the gravitational dynamics of dark energy configurations. We report on the time evolution of the dark energy field configurations as well as the time evolution of the energy density to demonstrate the gravitational collapse of dark energy field configurations. We live in a Universe which is dominated by Dark Energy. According to current estimates about 75% of the Energy Density is in the form of Dark Energy. Thus when we consider gravitational dynamics and Structure Formation we expect Dark Energy to play an important role. The most promising candidate for dark energy is the energy density of fields in curved space-time. It therefore become a pressing need to understand the gravitational dynamics of dark energy field configurations. We develop and describe the formalism to study the gravitational collapse of fields given any general potential for the fields. We apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting evolution equations which determine the time evolution of field configurations as well as the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our universe.
The dark side of cosmology: dark matter and dark energy.
Spergel, David N
2015-03-06
A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales. Copyright © 2015, American Association for the Advancement of Science.
On dark energy isocurvature perturbation
International Nuclear Information System (INIS)
Liu, Jie; Zhang, Xinmin; Li, Mingzhe
2011-01-01
Determining the equation of state of dark energy with astronomical observations is crucially important to understand the nature of dark energy. In performing a likelihood analysis of the data, especially of the cosmic microwave background and large scale structure data the dark energy perturbations have to be taken into account both for theoretical consistency and for numerical accuracy. Usually, one assumes in the global fitting analysis that the dark energy perturbations are adiabatic. In this paper, we study the dark energy isocurvature perturbation analytically and discuss its implications for the cosmic microwave background radiation and large scale structure. Furthermore, with the current astronomical observational data and by employing Markov Chain Monte Carlo method, we perform a global analysis of cosmological parameters assuming general initial conditions for the dark energy perturbations. The results show that the dark energy isocurvature perturbations are very weakly constrained and that purely adiabatic initial conditions are consistent with the data
International Nuclear Information System (INIS)
Ellis, Richard S.
2008-01-01
This program is concerned with developing and verifying the validity of observational methods for constraining the properties of dark matter and dark energy in the universe. Excellent progress has been made in comparing observational projects involving weak gravitational lensing using both ground and space-based instruments, in further constraining the nature of dark matter via precise measures of its distribution in clusters of galaxies using strong gravitational lensing, in demonstrating the possible limitations of using distant supernovae in future dark energy missions, and in investigating the requirement for ground-based surveys of baryonic acoustic oscillations.
The dark universe dark matter and dark energy
CERN. Geneva
2008-01-01
According to the standard cosmological model, 95% of the present mass density of the universe is dark: roughly 70% of the total in the form of dark energy and 25% in the form of dark matter. In a series of four lectures, I will begin by presenting a brief review of cosmology, and then I will review the observational evidence for dark matter and dark energy. I will discuss some of the proposals for dark matter and dark energy, and connect them to high-energy physics. I will also present an overview of an observational program to quantify the properties of dark energy.
International Nuclear Information System (INIS)
Comelli, D.; Pietroni, M.; Riotto, A.
2003-01-01
It is a puzzle why the densities of dark matter and dark energy are nearly equal today when they scale so differently during the expansion of the universe. This conundrum may be solved if there is a coupling between the two dark sectors. In this Letter we assume that dark matter is made of cold relics with masses depending exponentially on the scalar field associated to dark energy. Since the dynamics of the system is dominated by an attractor solution, the dark matter particle mass is forced to change with time as to ensure that the ratio between the energy densities of dark matter and dark energy become a constant at late times and one readily realizes that the present-day dark matter abundance is not very sensitive to its value when dark matter particles decouple from the thermal bath. We show that the dependence of the present abundance of cold dark matter on the parameters of the model differs drastically from the familiar results where no connection between dark energy and dark matter is present. In particular, we analyze the case in which the cold dark matter particle is the lightest supersymmetric particle
Dark group: dark energy and dark matter
International Nuclear Information System (INIS)
Macorra, A. de la
2004-01-01
We study the possibility that a dark group, a gauge group with particles interacting with the standard model particles only via gravity, is responsible for containing the dark energy and dark matter required by present day observations. We show that it is indeed possible and we determine the constrains for the dark group. The non-perturbative effects generated by a strong gauge coupling constant can de determined and a inverse power law scalar potential IPL for the dark meson fields is generated parameterizing the dark energy. On the other hand it is the massive particles, e.g., dark baryons, of the dark gauge group that give the corresponding dark matter. The mass of the dark particles is of the order of the condensation scale Λ c and the temperature is smaller then the photon's temperature. The dark matter is of the warm matter type. The only parameters of the model are the number of particles of the dark group. The allowed values of the different parameters are severely restricted. The dark group energy density at Λ c must be Ω DGc ≤0.17 and the evolution and acceptable values of dark matter and dark energy leads to a constrain of Λ c and the IPL parameter n giving Λ c =O(1-10 3 ) eV and 0.28≤n≤1.04
Report of the Dark Energy Task Force
Albrecht, Andreas; Bernstein, Gary; Cahn, Robert; Freedman, Wendy L.; Hewitt, Jacqueline; Hu, Wayne; Huth, John; Kamionkowski, Marc; Kolb, Edward W.; Knox, Lloyd; Mather, John C.
2006-01-01
Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the dark energy properties as well as possible.
Effective dark energy equation of state in interacting dark energy models
International Nuclear Information System (INIS)
Avelino, P.P.; Silva, H.M.R. da
2012-01-01
In models where dark matter and dark energy interact non-minimally, the total amount of matter in a fixed comoving volume may vary from the time of recombination to the present time due to energy transfer between the two components. This implies that, in interacting dark energy models, the fractional matter density estimated using the cosmic microwave background assuming no interaction between dark matter and dark energy will in general be shifted with respect to its true value. This may result in an incorrect determination of the equation of state of dark energy if the interaction between dark matter and dark energy is not properly accounted for, even if the evolution of the Hubble parameter as a function of redshift is known with arbitrary precision. In this Letter we find an exact expression, as well as a simple analytical approximation, for the evolution of the effective equation of state of dark energy, assuming that the energy transfer rate between dark matter and dark energy is described by a simple two-parameter model. We also provide analytical examples where non-phantom interacting dark energy models mimic the background evolution and primary cosmic microwave background anisotropies of phantom dark energy models.
Effective dark energy equation of state in interacting dark energy models
Energy Technology Data Exchange (ETDEWEB)
Avelino, P.P., E-mail: ppavelin@fc.up.pt [Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Departamento de Fisica e Astronomia da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Silva, H.M.R. da, E-mail: hilberto.silva@gmail.com [Departamento de Fisica e Astronomia da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal)
2012-07-24
In models where dark matter and dark energy interact non-minimally, the total amount of matter in a fixed comoving volume may vary from the time of recombination to the present time due to energy transfer between the two components. This implies that, in interacting dark energy models, the fractional matter density estimated using the cosmic microwave background assuming no interaction between dark matter and dark energy will in general be shifted with respect to its true value. This may result in an incorrect determination of the equation of state of dark energy if the interaction between dark matter and dark energy is not properly accounted for, even if the evolution of the Hubble parameter as a function of redshift is known with arbitrary precision. In this Letter we find an exact expression, as well as a simple analytical approximation, for the evolution of the effective equation of state of dark energy, assuming that the energy transfer rate between dark matter and dark energy is described by a simple two-parameter model. We also provide analytical examples where non-phantom interacting dark energy models mimic the background evolution and primary cosmic microwave background anisotropies of phantom dark energy models.
Interacting agegraphic dark energy
International Nuclear Information System (INIS)
Wei, Hao; Cai, Rong-Gen
2009-01-01
A new dark energy model, named ''agegraphic dark energy'', has been proposed recently, based on the so-called Karolyhazy uncertainty relation, which arises from quantum mechanics together with general relativity. In this note, we extend the original agegraphic dark energy model by including the interaction between agegraphic dark energy and pressureless (dark) matter. In the interacting agegraphic dark energy model, there are many interesting features different from the original agegraphic dark energy model and holographic dark energy model. The similarity and difference between agegraphic dark energy and holographic dark energy are also discussed. (orig.)
Directory of Open Access Journals (Sweden)
Ricardo G. Landim
2017-01-01
Full Text Available We build a model of metastable dark energy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable dark energy is also embedded into a model with SU(2R symmetry. The dark energy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the dark energy particle into (cold and warm dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and dark energy, and the model opens a new window to investigate the dark sector from the point-of-view of particle physics.
Precision Photometry to Study the Nature of Dark Energy
International Nuclear Information System (INIS)
Lorenzon, Wolfgang; Schubnell, Michael
2011-01-01
Over the past decade scientists have collected convincing evidence that the expansion of the universe is accelerating, leading to the conclusion that the content of our universe is dominated by a mysterious 'dark energy'. The fact that present theory cannot account for the dark energy has made the determination of the nature of dark energy central to the field of high energy physics. It is expected that nothing short of a revolution in our understanding of the fundamental laws of physics is required to fully understand the accelerating universe. Discovering the nature of dark energy is a very difficult task, and requires experiments that employ a combination of different observational techniques, such as type-Ia supernovae, gravitational weak lensing surveys, galaxy and galaxy cluster surveys, and baryon acoustic oscillations. A critical component of any approach to understanding the nature of dark energy is precision photometry. This report addresses just that. Most dark energy missions will require photometric calibration over a wide range of intensities using standardized stars and internal reference sources. All of the techniques proposed for these missions rely on a complete understanding of the linearity of the detectors. The technical report focuses on the investigation and characterization of 'reciprocity failure', a newly discovered count-rate dependent nonlinearity in the NICMOS cameras on the Hubble Space Telescope. In order to quantify reciprocity failure for modern astronomical detectors, we built a dedicated reciprocity test setup that produced a known amount of light on a detector, and to measured its response as a function of light intensity and wavelength.
Interacting Agegraphic Dark Energy
Wei, Hao; Cai, Rong-Gen
2007-01-01
A new dark energy model, named "agegraphic dark energy", has been proposed recently, based on the so-called K\\'{a}rolyh\\'{a}zy uncertainty relation, which arises from quantum mechanics together with general relativity. In this note, we extend the original agegraphic dark energy model by including the interaction between agegraphic dark energy and pressureless (dark) matter. In the interacting agegraphic dark energy model, there are many interesting features different from the original agegrap...
International Nuclear Information System (INIS)
Wang, Yun
2010-01-01
Dark energy research aims to illuminate the mystery of the observed cosmic acceleration, one of the fundamental problems in physics and astronomy today. This book presents a systematic and detailed review of the current state of dark energy research, with the focus on the examination of the major observational techniques for probing dark energy. It can be used as a textbook to train students and others who wish to enter this extremely active field in cosmology.
Greyber, Howard
2009-11-01
By careful analysis of the data from the WMAP satellite, scientists were surprised to determine that about 70% of the matter in our universe is in some unknown form, and labeled it Dark Energy. Earlier, in 1998, two separate international groups of astronomers studying Ia supernovae were even more surprised to be forced to conclude that an amazing smooth transition occurred, from the expected slowing down of the expansion of our universe (due to normal positive gravitation) to an accelerating expansion of the universe that began at at a big bang age of the universe of about nine billion years. In 1918 Albert Einstein stated that his Lambda term in his theory of general relativity was ees,``the energy of empty space,'' and represented a negative pressure and thus a negative gravity force. However my 2004 ``Strong'' Magnetic Field model (SMF) for the origin of magnetic fields at Combination Time (Astro-ph0509223 and 0509222) in our big bang universe produces a unique topology for Superclusters, having almost all the mass, visible and invisible, i.e. from clusters of galaxies down to particles with mass, on the surface of an ellipsoid surrounding a growing very high vacuum. If I hypothesize, with Einstein, that there exists a constant ees force per unit volume, then, gradually, as the universe expands from Combination Time, two effects occur (a) the volume of the central high vacuum region increases, and (b) the density of positive gravity particles in the central region of each Supercluster in our universe decreases dramatically. Thus eventually Einstein's general relativity theory's repulsive gravity of the central very high vacuum region becomes larger than the positive gravitational attraction of all the clusters of galaxies, galaxies, quasars, stars and plasma on the Supercluster shell, and the observed accelerating expansion of our universe occurs. This assumes that our universe is made up mostly of such Superclusters. It is conceivable that the high vacuum
Weak lensing: Dark Matter, Dark Energy and Dark Gravity
International Nuclear Information System (INIS)
Heavens, Alan
2009-01-01
In this non-specialist review I look at how weak lensing can provide information on the dark sector of the Universe. The review concentrates on what can be learned about Dark Matter, Dark Energy and Dark Gravity, and why. On Dark Matter, results on the confrontation of theoretical profiles with observation are reviewed, and measurements of neutrino masses discussed. On Dark Energy, the interest is whether this could be Einstein's cosmological constant, and prospects for high-precision studies of the equation of state are considered. On Dark Gravity, we consider the exciting prospects for future weak lensing surveys to distinguish General Relativity from extra-dimensional or other gravity theories.
Structure formation in inhomogeneous Early Dark Energy models
International Nuclear Information System (INIS)
Batista, R.C.; Pace, F.
2013-01-01
We study the impact of Early Dark Energy fluctuations in the linear and non-linear regimes of structure formation. In these models the energy density of dark energy is non-negligible at high redshifts and the fluctuations in the dark energy component can have the same order of magnitude of dark matter fluctuations. Since two basic approximations usually taken in the standard scenario of quintessence models, that both dark energy density during the matter dominated period and dark energy fluctuations on small scales are negligible, are not valid in such models, we first study approximate analytical solutions for dark matter and dark energy perturbations in the linear regime. This study is helpful to find consistent initial conditions for the system of equations and to analytically understand the effects of Early Dark Energy and its fluctuations, which are also verified numerically. In the linear regime we compute the matter growth and variation of the gravitational potential associated with the Integrated Sachs-Wolf effect, showing that these observables present important modifications due to Early Dark Energy fluctuations, though making them more similar to the ΛCDM model. We also make use of the Spherical Collapse model to study the influence of Early Dark Energy fluctuations in the nonlinear regime of structure formation, especially on δ c parameter, and their contribution to the halo mass, which we show can be of the order of 10%. We finally compute how the number density of halos is modified in comparison to the ΛCDM model and address the problem of how to correct the mass function in order to take into account the contribution of clustered dark energy. We conclude that the inhomogeneous Early Dark Energy models are more similar to the ΛCDM model than its homogeneous counterparts
Evaluating dark energy probes using multidimensional dark energy parameters
International Nuclear Information System (INIS)
Albrecht, Andreas; Bernstein, Gary
2007-01-01
We investigate the value of future dark-energy experiments by modeling their ability to constrain the dark-energy equation of state. Similar work was recently reported by the Dark Energy Task Force (DETF) using a two dimensional parameterization of the equation-of-state evolution. We examine constraints in a nine-dimensional dark-energy parameterization, and find that the best experiments constrain significantly more than two dimensions in our 9D space. Consequently the impact of these experiments is substantially beyond that revealed in the DETF analysis, and the estimated cost per 'impact' drops by about a factor of 10 as one moves to the very best experiments. The DETF conclusions about the relative value of different techniques and of the importance of combining techniques are unchanged by our analysis
Coupling q-Deformed Dark Energy to Dark Matter
Directory of Open Access Journals (Sweden)
Emre Dil
2016-01-01
Full Text Available We propose a novel coupled dark energy model which is assumed to occur as a q-deformed scalar field and investigate whether it will provide an expanding universe phase. We consider the q-deformed dark energy as coupled to dark matter inhomogeneities. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions. The attractor solutions imply that the coupled q-deformed dark energy model is consistent with the conventional dark energy models satisfying an acceleration phase of universe. At the end, we compare the cosmological parameters of deformed and standard dark energy models and interpret the implications.
Quantum Field Theory of Interacting Dark Matter/Dark Energy: Dark Monodromies
D'Amico, Guido; Kaloper, Nemanja
2016-11-28
We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory. Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations.
Gravitational collapse of dark energy field configurations and supermassive black hole formation
International Nuclear Information System (INIS)
Jhalani, V.; Kharkwal, H.; Singh, A.
2016-01-01
Dark energy is the dominant component of the total energy density of our Universe. The primary interaction of dark energy with the rest of the Universe is gravitational. It is therefore important to understand the gravitational dynamics of dark energy. Since dark energy is a low-energy phenomenon from the perspective of particle physics and field theory, a fundamental approach based on fields in curved space should be sufficient to understand the current dynamics of dark energy. Here, we take a field theory approach to dark energy. We discuss the evolution equations for a generic dark energy field in curved space-time and then discuss the gravitational collapse for dark energy field configurations. We describe the 3 + 1 BSSN formalism to study the gravitational collapse of fields for any general potential for the fields and apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting equations for the time evolution of field configurations and the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our Universe. We also demonstrate the black hole formation as a result of the gravitational collapse of the dark energy field configurations. The black holes produced by the collapse of dark energy fields are in the supermassive black hole category with the masses of these black holes being comparable to the masses of black holes at the centers of galaxies.
Gravitational collapse of dark energy field configurations and supermassive black hole formation
Energy Technology Data Exchange (ETDEWEB)
Jhalani, V.; Kharkwal, H.; Singh, A., E-mail: anupamsingh.iitk@gmail.com [L. N. Mittal Institute of Information Technology, Physics Department (India)
2016-11-15
Dark energy is the dominant component of the total energy density of our Universe. The primary interaction of dark energy with the rest of the Universe is gravitational. It is therefore important to understand the gravitational dynamics of dark energy. Since dark energy is a low-energy phenomenon from the perspective of particle physics and field theory, a fundamental approach based on fields in curved space should be sufficient to understand the current dynamics of dark energy. Here, we take a field theory approach to dark energy. We discuss the evolution equations for a generic dark energy field in curved space-time and then discuss the gravitational collapse for dark energy field configurations. We describe the 3 + 1 BSSN formalism to study the gravitational collapse of fields for any general potential for the fields and apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting equations for the time evolution of field configurations and the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our Universe. We also demonstrate the black hole formation as a result of the gravitational collapse of the dark energy field configurations. The black holes produced by the collapse of dark energy fields are in the supermassive black hole category with the masses of these black holes being comparable to the masses of black holes at the centers of galaxies.
Energy Technology Data Exchange (ETDEWEB)
Binder, Gary A.; /Caltech /SLAC
2010-08-25
In order to make accurate measurements of dark energy, a system is needed to monitor the focus and alignment of the Dark Energy Camera (DECam) to be located on the Blanco 4m Telescope for the upcoming Dark Energy Survey. One new approach under development is to fit out-of-focus star images to a point spread function from which information about the focus and tilt of the camera can be obtained. As a first test of a new algorithm using this idea, simulated star images produced from a model of DECam in the optics software Zemax were fitted. Then, real images from the Mosaic II imager currently installed on the Blanco telescope were used to investigate the algorithm's capabilities. A number of problems with the algorithm were found, and more work is needed to understand its limitations and improve its capabilities so it can reliably predict camera alignment and focus.
Unified picture for Dirac neutrinos, dark matter, dark energy and matter–antimatter asymmetry
Gu, Pei-Hong
2008-01-01
We propose a unified scenario to generate the masses of Dirac neutrinos and cold dark matter at the TeV scale, understand the origin of dark energy and explain the matter-antimatter asymmetry of the universe. This model can lead to significant impact on the Higgs searches at LHC.
Can strong gravitational lensing constrain dark energy?
International Nuclear Information System (INIS)
Lee, Seokcheon; Ng, K.-W.
2007-01-01
We discuss the ratio of the angular diameter distances from the source to the lens, D ds , and to the observer at present, D s , for various dark energy models. It is well known that the difference of D s s between the models is apparent and this quantity is used for the analysis of Type Ia supernovae. However we investigate the difference between the ratio of the angular diameter distances for a cosmological constant, (D ds /D s ) Λ , and that for other dark energy models, (D ds /D s ) other , in this paper. It has been known that there is lens model degeneracy in using strong gravitational lensing. Thus, we investigate the model independent observable quantity, Einstein radius (θ E ), which is proportional to both D ds /D s and velocity dispersion squared, σ v 2 . D ds /D s values depend on the parameters of each dark energy model individually. However, (D ds /D s ) Λ -(D ds /D s ) other for the various dark energy models, is well within the error of σ v for most of the parameter spaces of the dark energy models. Thus, a single strong gravitational lensing by use of the Einstein radius may not be a proper method to investigate the property of dark energy. However, better understanding to the mass profile of clusters in the future or other methods related to arc statistics rather than the distances may be used for constraints on dark energy
Revival of the unified dark energy-dark matter model?
International Nuclear Information System (INIS)
Bento, M.C.; Bertolami, O.; Sen, A.A.
2004-01-01
We consider the generalized Chaplygin gas (GCG) proposal for unification of dark energy and dark matter and show that it admits an unique decomposition into dark energy and dark matter components once phantomlike dark energy is excluded. Within this framework, we study structure formation and show that difficulties associated to unphysical oscillations or blowup in the matter power spectrum can be circumvented. Furthermore, we show that the dominance of dark energy is related to the time when energy density fluctuations start deviating from the linear δ∼a behavior
Cosmic Visions Dark Energy. Science
Energy Technology Data Exchange (ETDEWEB)
Dodelson, Scott [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Heitmann, Katrin [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Hirata, Chris [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Honscheid, Klaus [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Roodman, Aaron [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Seljak, Uroš [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Slosar, Anže [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Trodden, Mark [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2016-04-26
Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.
Cosmic Visions Dark Energy: Science
Energy Technology Data Exchange (ETDEWEB)
Dodelson, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Slosar, A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Heitmann, K. [Brookhaven National Lab. (BNL), Upton, NY (United States); Hirata, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Honscheid, K. [Brookhaven National Lab. (BNL), Upton, NY (United States); Roodman, A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Seljak, U. [Brookhaven National Lab. (BNL), Upton, NY (United States); Trodden, M. [Brookhaven National Lab. (BNL), Upton, NY (United States)
2016-04-26
Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.
Unified Description of Dark Energy and Dark Matter
Petry, Walter
2008-01-01
Dark energy in the universe is assumed to be vacuum energy. The energy-momentum of vacuum is described by a scale-dependent cosmological constant. The equations of motion imply for the density of matter (dust) the sum of the usual matter density (luminous matter) and an additional matter density (dark matter) similar to the dark energy. The scale-dependent cosmological constant is given up to an exponent which is approximated by the experimentally decided density parameters of dark matter and...
Dark energy two decades after: observables, probes, consistency tests.
Huterer, Dragan; Shafer, Daniel L
2018-01-01
The discovery of the accelerating universe in the late 1990s was a watershed moment in modern cosmology, as it indicated the presence of a fundamentally new, dominant contribution to the energy budget of the universe. Evidence for dark energy, the new component that causes the acceleration, has since become extremely strong, owing to an impressive variety of increasingly precise measurements of the expansion history and the growth of structure in the universe. Still, one of the central challenges of modern cosmology is to shed light on the physical mechanism behind the accelerating universe. In this review, we briefly summarize the developments that led to the discovery of dark energy. Next, we discuss the parametric descriptions of dark energy and the cosmological tests that allow us to better understand its nature. We then review the cosmological probes of dark energy. For each probe, we briefly discuss the physics behind it and its prospects for measuring dark energy properties. We end with a summary of the current status of dark energy research.
Measuring the speed of dark: Detecting dark energy perturbations
International Nuclear Information System (INIS)
Putter, Roland de; Huterer, Dragan; Linder, Eric V.
2010-01-01
The nature of dark energy can be probed not only through its equation of state but also through its microphysics, characterized by the sound speed of perturbations to the dark energy density and pressure. As the sound speed drops below the speed of light, dark energy inhomogeneities increase, affecting both cosmic microwave background and matter power spectra. We show that current data can put no significant constraints on the value of the sound speed when dark energy is purely a recent phenomenon, but can begin to show more interesting results for early dark energy models. For example, the best fit model for current data has a slight preference for dynamics [w(a)≠-1], degrees of freedom distinct from quintessence (c s ≠1), and early presence of dark energy [Ω de (a<<1)≠0]. Future data may open a new window on dark energy by measuring its spatial as well as time variation.
Unification of dark energy and dark matter
International Nuclear Information System (INIS)
Takahashi, Fuminobu; Yanagida, T.T.
2006-01-01
We propose a scenario in which dark energy and dark matter are described in a unified manner. The ultralight pseudo-Nambu-Goldstone (pNG) boson, A, naturally explains the observed magnitude of dark energy, while the bosonic supersymmetry partner of the pNG boson, B, can be a dominant component of dark matter. The decay of B into a pair of electron and positron may explain the 511 keV γ ray from the Galactic Center
Dark Mass Creation During EWPT Via Dark Energy Interaction
Kisslinger, Leonard S.; Casper, Steven
2013-01-01
We add Dark Matter Dark Energy terms with a quintessence field interacting with a Dark Matter field to a MSSM EW Lagrangian previously used to calculate the magnetic field created during the EWPT. From the expectation value of the quintessence field we estimate the Dark Matter mass for parameters used in previous work on Dark Matter-Dark Energy interactions.
Interactions between dark energy and dark matter
Energy Technology Data Exchange (ETDEWEB)
Baldi, Marco
2009-03-20
We have investigated interacting dark energy cosmologies both concerning their impact on the background evolution of the Universe and their effects on cosmological structure growth. For the former aspect, we have developed a cosmological model featuring a matter species consisting of particles with a mass that increases with time. In such model the appearance of a Growing Matter component, which is negligible in early cosmology, dramatically slows down the evolution of the dark energy scalar field at a redshift around six, and triggers the onset of the accelerated expansion of the Universe, therefore addressing the Coincidence Problem. We propose to identify this Growing Matter component with cosmic neutrinos, in which case the present dark energy density can be related to the measured average mass of neutrinos. For the latter aspect, we have implemented the new physical features of interacting dark energy models into the cosmological N-body code GADGET-2, and we present the results of a series of high-resolution simulations for a simple realization of dark energy interaction. As a consequence of the new physics, cold dark matter and baryon distributions evolve differently both in the linear and in the non-linear regime of structure formation. Already on large scales, a linear bias develops between these two components, which is further enhanced by the non-linear evolution. We also find, in contrast with previous work, that the density profiles of cold dark matter halos are less concentrated in coupled dark energy cosmologies compared with {lambda}{sub CDM}. Also, the baryon fraction in halos in the coupled models is significantly reduced below the universal baryon fraction. These features alleviate tensions between observations and the {lambda}{sub CDM} model on small scales. Our methodology is ideally suited to explore the predictions of coupled dark energy models in the fully non-linear regime, which can provide powerful constraints for the viable parameter
Interactions between dark energy and dark matter
International Nuclear Information System (INIS)
Baldi, Marco
2009-01-01
We have investigated interacting dark energy cosmologies both concerning their impact on the background evolution of the Universe and their effects on cosmological structure growth. For the former aspect, we have developed a cosmological model featuring a matter species consisting of particles with a mass that increases with time. In such model the appearance of a Growing Matter component, which is negligible in early cosmology, dramatically slows down the evolution of the dark energy scalar field at a redshift around six, and triggers the onset of the accelerated expansion of the Universe, therefore addressing the Coincidence Problem. We propose to identify this Growing Matter component with cosmic neutrinos, in which case the present dark energy density can be related to the measured average mass of neutrinos. For the latter aspect, we have implemented the new physical features of interacting dark energy models into the cosmological N-body code GADGET-2, and we present the results of a series of high-resolution simulations for a simple realization of dark energy interaction. As a consequence of the new physics, cold dark matter and baryon distributions evolve differently both in the linear and in the non-linear regime of structure formation. Already on large scales, a linear bias develops between these two components, which is further enhanced by the non-linear evolution. We also find, in contrast with previous work, that the density profiles of cold dark matter halos are less concentrated in coupled dark energy cosmologies compared with Λ CDM . Also, the baryon fraction in halos in the coupled models is significantly reduced below the universal baryon fraction. These features alleviate tensions between observations and the Λ CDM model on small scales. Our methodology is ideally suited to explore the predictions of coupled dark energy models in the fully non-linear regime, which can provide powerful constraints for the viable parameter space of such scenarios
Unified dark energy-dark matter model with inverse quintessence
Energy Technology Data Exchange (ETDEWEB)
Ansoldi, Stefano [ICRA — International Center for Relativistic Astrophysics, INFN — Istituto Nazionale di Fisica Nucleare, and Dipartimento di Matematica e Informatica, Università degli Studi di Udine, via delle Scienze 206, I-33100 Udine (UD) (Italy); Guendelman, Eduardo I., E-mail: ansoldi@fulbrightmail.org, E-mail: guendel@bgu.ac.il [Department of Physics, Ben-Gurion University of the Negeev, Beer-Sheva 84105 (Israel)
2013-05-01
We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.
Unified dark energy-dark matter model with inverse quintessence
International Nuclear Information System (INIS)
Ansoldi, Stefano; Guendelman, Eduardo I.
2013-01-01
We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future
Cosmic Visions Dark Energy: Small Projects Portfolio
Energy Technology Data Exchange (ETDEWEB)
Dawson, Kyle; Frieman, Josh; Heitmann, Katrin; Jain, Bhuvnesh; Kahn, Steve; Mandelbaum, Rachel; Perlmutter, Saul; Slosar, Anže
2018-02-20
Understanding cosmic acceleration is one of the key science drivers for astrophysics and high-energy physics in the coming decade (2014 P5 Report). With the Large Synoptic Survey Telescope (LSST) and the Dark Energy Spectroscopic Instrument (DESI) and other new facilities beginning operations soon, we are entering an exciting phase during which we expect an order of magnitude improvement in constraints on dark energy and the physics of the accelerating Universe. This is a key moment for a matching Small Projects portfolio that can (1) greatly enhance the science reach of these flagship projects, (2) have immediate scientific impact, and (3) lay the groundwork for the next stages of the Cosmic Frontier Dark Energy program. In this White Paper, we outline a balanced portfolio that can accomplish these goals through a combination of observational, experimental, and theory and simulation efforts.
Possible dark energy imprints in the gravitational wave spectrum of mixed neutron-dark-energy stars
Energy Technology Data Exchange (ETDEWEB)
Yazadjiev, Stoytcho S. [Department of Theoretical Physics, Faculty of Physics, St. Kliment Ohridski University of Sofia, James Bourchier Blvd. 5, 1164 Sofia (Bulgaria); Doneva, Daniela D., E-mail: yazad@phys.uni-sofia.bg, E-mail: daniela.doneva@uni-tuebingen.de [Theoretical Astrophysics, IAAT, Eberhard-Karls University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen (Germany)
2012-03-01
In the present paper we study the oscillation spectrum of neutron stars containing both ordinary matter and dark energy in different proportions. Within the model we consider, the equilibrium configurations are numerically constructed and the results show that the properties of the mixed neuron-dark-energy star can differ significantly when the amount of dark energy in the stars is varied. The oscillations of the mixed neuron-dark-energy stars are studied in the Cowling approximation. As a result we find that the frequencies of the fundamental mode and the higher overtones are strongly affected by the dark energy content. This can be used in the future to detect the presence of dark energy in the neutron stars and to constrain the dark-energy models.
Supplying Dark Energy from Scalar Field Dark Matter
Gogberashvili, Merab; Sakharov, Alexander S.
2017-01-01
We consider the hypothesis that dark matter and dark energy consists of ultra-light self-interacting scalar particles. It is found that the Klein-Gordon equation with only two free parameters (mass and self-coupling) on a Schwarzschild background, at the galactic length-scales has the solution which corresponds to Bose-Einstein condensate, behaving as dark matter, while the constant solution at supra-galactic scales can explain dark energy.
Dark energy: Recent observations and future prospects
International Nuclear Information System (INIS)
Perlmutter, Saul
2003-01-01
Dark energy presents us with a challenging puzzle: understanding the new element of physics evident in the acceleration of the expansion of the universe. Type Ia supernovae first detected this acceleration and have been instrumental in breaking the matter dominated universe paradigm, measuring the current acceleration of the expansion, and probing back to the decelerating phase. To further study the nature of dark energy requires understanding of systematic errors entering into any cosmological probe. Type Ia supernovae provide simple, transparent tracers of the expansion history of the universe, and the sources of systematic uncertainties in the supernova measurement have been identified. We briefly review the progress to date and examine the promise of future surveys with large numbers of supernovae and well bounded systematics
A power-law coupled three-form dark energy model
Yao, Yan-Hong; Yan, Yang-Jie; Meng, Xin-He
2018-02-01
We consider a field theory model of coupled dark energy which treats dark energy as a three-form field and dark matter as a spinor field. By assuming the effective mass of dark matter as a power-law function of the three-form field and neglecting the potential term of dark energy, we obtain three solutions of the autonomous system of evolution equations, including a de Sitter attractor, a tracking solution and an approximate solution. To understand the strength of the coupling, we confront the model with the latest Type Ia Supernova, Baryon Acoustic Oscillations and Cosmic Microwave Background radiation observations, with the conclusion that the combination of these three databases marginalized over the present dark matter density parameter Ω _{m0} and the present three-form field κ X0 gives stringent constraints on the coupling constant, - 0.017< λ <0.047 (2σ confidence level), by which we present the model's applicable parameter range.
A power-law coupled three-form dark energy model
Energy Technology Data Exchange (ETDEWEB)
Yao, Yan-Hong; Yan, Yang-Jie; Meng, Xin-He [Nankai University, Department of Physics, Tianjin (China)
2018-02-15
We consider a field theory model of coupled dark energy which treats dark energy as a three-form field and dark matter as a spinor field. By assuming the effective mass of dark matter as a power-law function of the three-form field and neglecting the potential term of dark energy, we obtain three solutions of the autonomous system of evolution equations, including a de Sitter attractor, a tracking solution and an approximate solution. To understand the strength of the coupling, we confront the model with the latest Type Ia Supernova, Baryon Acoustic Oscillations and Cosmic Microwave Background radiation observations, with the conclusion that the combination of these three databases marginalized over the present dark matter density parameter Ω{sub m0} and the present three-form field κX{sub 0} gives stringent constraints on the coupling constant, -0.017 < λ < 0.047 (2σ confidence level), by which we present the model's applicable parameter range. (orig.)
Dynamics of teleparallel dark energy
International Nuclear Information System (INIS)
Wei Hao
2012-01-01
Recently, Geng et al. proposed to allow a non-minimal coupling between quintessence and gravity in the framework of teleparallel gravity, motivated by the similar one in the framework of General Relativity (GR). They found that this non-minimally coupled quintessence in the framework of teleparallel gravity has a richer structure, and named it “teleparallel dark energy”. In the present work, we note that there might be a deep and unknown connection between teleparallel dark energy and Elko spinor dark energy. Motivated by this observation and the previous results of Elko spinor dark energy, we try to study the dynamics of teleparallel dark energy. We find that there exist only some dark-energy-dominated de Sitter attractors. Unfortunately, no scaling attractor has been found, even when we allow the possible interaction between teleparallel dark energy and matter. However, we note that w at the critical points is in agreement with observations (in particular, the fact that w=−1 independently of ξ is a great advantage).
Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?
Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim
2009-10-09
We show the importance of properly including the perturbations of the dark energy component in the dynamical dark energy models based on a scalar field and modified gravity theories in order to meet with present and future observational precisions. Based on a simple scaling scalar field dark energy model, we show that observationally distinguishable substantial differences appear by ignoring the dark energy perturbation. By ignoring it the perturbed system of equations becomes inconsistent and deviations in (gauge-invariant) power spectra depend on the gauge choice.
Galaxy evolution, cosmology and dark energy with the Square Kilometer Array
Rawlings, S; Abdalla, FB; Bridle, SL; Blake, CA; Baugh, CM; Greenhill, LJ; van der Hulst, JM
2004-01-01
The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics - understanding how galaxies form - and astro-particle physics inferring properties of the dark components. The Square Kilometer Array (SKA)
Dark energy and dark matter in galaxy halos
International Nuclear Information System (INIS)
Tetradis, N.
2006-01-01
We consider the possibility that the dark matter is coupled through its mass to a scalar field associated with the dark energy of the Universe. In order for such a field to play a role at the present cosmological distances, it must be effectively massless at galactic length scales. We discuss the effect of the field on the distribution of dark matter in galaxy halos. We show that the profile of the distribution outside the galaxy core remains largely unaffected and the approximately flat rotation curves persist. The dispersion of the dark matter velocity is enhanced by a potentially large factor relative to the case of zero coupling between dark energy and dark matter. The counting rates in terrestrial dark matter detectors are similarly enhanced. Existing bounds on the properties of dark matter candidates can be extended to the coupled case, by taking into account the enhancement factor
Dark information of black hole radiation raised by dark energy
Ma, Yu-Han; Chen, Jin-Fu; Sun, Chang-Pu
2018-06-01
The "lost" information of black hole through the Hawking radiation was discovered being stored in the correlation among the non-thermally radiated particles (Parikh and Wilczek, 2000 [31], Zhang et al., 2009 [16]). This correlation information, which has not yet been proved locally observable in principle, is named by dark information. In this paper, we systematically study the influences of dark energy on black hole radiation, especially on the dark information. Calculating the radiation spectrum in the existence of dark energy by the approach of canonical typicality, which is reconfirmed by the quantum tunneling method, we find that the dark energy will effectively lower the Hawking temperature, and thus makes the black hole has longer life time. It is also discovered that the non-thermal effect of the black hole radiation is enhanced by dark energy so that the dark information of the radiation is increased. Our observation shows that, besides the mechanical effect (e.g., gravitational lensing effect), the dark energy rises the stored dark information, which could be probed by a non-local coincidence measurement similar to the coincidence counting of the Hanbury-Brown-Twiss experiment in quantum optics.
Thermodynamical properties of dark energy
International Nuclear Information System (INIS)
Gong Yungui; Wang Bin; Wang Anzhong
2007-01-01
We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature T∼a -n and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state w>-1 and the generalized Chaplygin gas, the derived entropy can be positive and satisfy the entropy bound. The total entropy, including those of dark energy, the thermal radiation, and the apparent horizon, satisfies the generalized second law of thermodynamics. However, for the phantom with constant equation of state, the positivity of entropy, the entropy bound, and the generalized second law cannot be satisfied simultaneously
Nonlocal astrophysics dark matter, dark energy and physical vacuum
Alexeev, Boris V
2017-01-01
Non-Local Astrophysics: Dark Matter, Dark Energy and Physical Vacuum highlights the most significant features of non-local theory, a highly effective tool for solving many physical problems in areas where classical local theory runs into difficulties. The book provides the fundamental science behind new non-local astrophysics, discussing non-local kinetic and generalized hydrodynamic equations, non-local parameters in several physical systems, dark matter, dark energy, black holes and gravitational waves. Devoted to the solution of astrophysical problems from the position of non-local physics Provides a solution for dark matter and dark energy Discusses cosmological aspects of the theory of non-local physics Includes a solution for the problem of the Hubble Universe expansion, and of the dependence of the orbital velocity from the center of gravity
Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
Origin of holographic dark energy models
International Nuclear Information System (INIS)
Myung, Yun Soo; Seo, Min-Gyun
2009-01-01
We investigate the origin of holographic dark energy models which were recently proposed to explain the dark energy-dominated universe. For this purpose, we introduce the spacetime foam uncertainty of δl≥l p α l α-1 . It was argued that the case of α=2/3 could describe the dark energy with infinite statistics, while the case of α=1/2 can describe the ordinary matter with Bose-Fermi statistics. However, two cases may lead to the holographic energy density if the latter recovers from the geometric mean of UV and IR scales. Hence the dark energy with infinite statistics based on the entropy bound is not an ingredient for deriving the holographic dark energy model. Furthermore, it is shown that the agegraphic dark energy models are the holographic dark energy model with different IR length scales
Dark Energy vs. Dark Matter: Towards a Unifying Scalar Field?
Arbey, A.
2008-01-01
The standard model of cosmology suggests the existence of two components, "dark matter" and "dark energy", which determine the fate of the Universe. Their nature is still under investigation, and no direct proof of their existences has emerged yet. There exist alternative models which reinterpret the cosmological observations, for example by replacing the dark energy/dark matter hypothesis by the existence of a unique dark component, the dark fluid, which is able to mimic the behaviour of bot...
Unifying dark energy and dark matter with the modified Ricci model
International Nuclear Information System (INIS)
Zhang, Linsen; Wu, Puxun; Yu, Hongwei
2011-01-01
In this paper, two modified Ricci models are considered as the candidates of unified dark matter-dark energy. In model one, the energy density is given by ρ MR =3M pl (αH 2 + βH), whereas, in model two, by ρ MR =3M pl ((α)/(6)R + γH H -1 ). We find that they can explain both dark matter and dark energy successfully. A constant equation of state of dark energy is obtained in model one, which means that it gives the same background evolution as the wCDM model, while model two can give an evolutionary equation of state of dark energy with the phantom divide line crossing in the near past. (orig.)
Entropy-Corrected Holographic Dark Energy
International Nuclear Information System (INIS)
Wei Hao
2009-01-01
The holographic dark energy (HDE) is now an interesting candidate of dark energy, which has been studied extensively in the literature. In the derivation of HDE, the black hole entropy plays an important role. In fact, the entropy-area relation can be modified due to loop quantum gravity or other reasons. With the modified entropy-area relation, we propose the so-called 'entropy-corrected holographic dark energy' (ECHDE) in the present work. We consider many aspects of ECHDE and find some interesting results. In addition, we briefly consider the so-called 'entropy-corrected agegraphic dark energy' (ECADE). (geophysics, astronomy, and astrophysics)
International Nuclear Information System (INIS)
Lobo, Francisco S N
2006-01-01
The gravastar picture is an alternative model to the concept of a black hole, where there is an effective phase transition at or near where the event horizon is expected to form, and the interior is replaced by a de Sitter condensate. In this work a generalization of the gravastar picture is explored by considering matching of an interior solution governed by the dark energy equation of state, ω ≡ p/ρ < -1/3, to an exterior Schwarzschild vacuum solution at a junction interface. The motivation for implementing this generalization arises from the fact that recent observations have confirmed an accelerated cosmic expansion, for which dark energy is a possible candidate. Several relativistic dark energy stellar configurations are analysed by imposing specific choices for the mass function. The first case considered is that of a constant energy density, and the second choice that of a monotonic decreasing energy density in the star's interior. The dynamical stability of the transition layer of these dark energy stars to linearized spherically symmetric radial perturbations about static equilibrium solutions is also explored. It is found that large stability regions exist that are sufficiently close to where the event horizon is expected to form, so that it would be difficult to distinguish the exterior geometry of the dark energy stars, analysed in this work, from an astrophysical black hole
Dark clouds in particle physics and cosmology: the issues of dark matter and dark energy
International Nuclear Information System (INIS)
Zhang Xinmin
2011-01-01
Unveiling the nature of dark matter and dark energy is one of the main tasks of particle physics and cosmology in the 21st century. We first present an overview of the history and current status of research in cosmology, at the same time emphasizing the new challenges in particle physics. Then we focus on the scientific issues of dark energy, dark matter and anti-matter, and review the recent progress made in these fields. Finally, we discuss the prospects for future research on the experimental probing of dark matter and dark energy in China. (authors)
Inflation, Dark Matter, and Dark Energy in the String Landscape
Liddle, Andrew R; Ureña-López, L Arturo
2006-01-01
We consider the conditions needed to unify the description of dark matter, dark energy and inflation in the context of the string landscape. We find that incomplete decay of the inflaton field gives the possibility that a single field is responsible for all three phenomena. By contrast, unifying dark matter and dark energy into a single field, separate from the inflaton, appears rather difficult.
Limits on dark radiation, early dark energy, and relativistic degrees of freedom
International Nuclear Information System (INIS)
Calabrese, Erminia; Melchiorri, Alessandro; Huterer, Dragan; Linder, Eric V.; Pagano, Luca
2011-01-01
Recent cosmological data analyses hint at the presence of an extra relativistic energy component in the early universe. This component is often parametrized as an excess of the effective neutrino number N eff over the standard value of 3.046. The excess relativistic energy could be an indication for an extra (sterile) neutrino, but early dark energy and barotropic dark energy also contribute to the relativistic degrees of freedom. We examine the capabilities of current and future data to constrain and discriminate between these explanations, and to detect the early dark energy density associated with them. We find that while early dark energy does not alter the current constraints on N eff , a dark radiation component, such as that provided by barotropic dark energy models, can substantially change current constraints on N eff , bringing its value back to agreement with the theoretical prediction. Both dark energy models also have implications for the primordial mass fraction of Helium Y p and the scalar perturbation index n s . The ongoing Planck satellite mission will be able to further discriminate between sterile neutrinos and early dark energy.
Dark fluid: A complex scalar field to unify dark energy and dark matter
International Nuclear Information System (INIS)
Arbey, Alexandre
2006-01-01
In this article, we examine a model which proposes a common explanation for the presence of additional attractive gravitational effects - generally considered to be due to dark matter - in galaxies and in clusters, and for the presence of a repulsive effect at cosmological scales - generally taken as an indication of the presence of dark energy. We therefore consider the behavior of a so-called dark fluid based on a complex scalar field with a conserved U(1)-charge and associated to a specific potential, and show that it can at the same time account for dark matter in galaxies and in clusters, and agree with the cosmological observations and constraints on dark energy and dark matter
International Nuclear Information System (INIS)
Piattella, O.F.; Martins, D.L.A.; Casarini, L.
2014-01-01
We consider a cosmological model of the late universe constituted by standard cold dark matter plus a dark energy component with constant equation of state w and constant effective speed of sound. By neglecting fluctuations in the dark energy component, we obtain an equation describing the evolution of sub-horizon cold dark matter perturbations through the epoch of dark matter-dark energy equality. We explore its analytic solutions and calculate an exact w-dependent correction for the dark matter growth function, logarithmic growth function and growth index parameter through the epoch considered. We test our analytic approximation with the numerical solution and find that the discrepancy is less than 1% for 0k = during the cosmic evolution up to a = 100
Voids and overdensities of coupled Dark Energy
International Nuclear Information System (INIS)
Mainini, Roberto
2009-01-01
We investigate the clustering properties of dynamical Dark Energy even in association of a possible coupling between Dark Energy and Dark Matter. We find that within matter inhomogeneities, Dark Energy migth form voids as well as overdensity depending on how its background energy density evolves. Consequently and contrarily to what expected, Dark Energy fluctuations are found to be slightly suppressed if a coupling with Dark Matter is permitted. When considering density contrasts and scales typical of superclusters, voids and supervoids, perturbations amplitudes range from |δ φ | ∼ O(10 −6 ) to |δ φ | ∼ O(10 −4 ) indicating an almost homogeneous Dark Energy component
arXiv Supplying Dark Energy from Scalar Field Dark Matter
Gogberashvili, Merab
We consider the hypothesis that dark matter and dark energy consists of ultra-light self-interacting scalar particles. It is found that the Klein-Gordon equation with only two free parameters (mass and self-coupling) on a Schwarzschild background, at the galactic length-scales has the solution which corresponds to Bose-Einstein condensate, behaving as dark matter, while the constant solution at supra-galactic scales can explain dark energy.
Dark energy: myths and reality
International Nuclear Information System (INIS)
Lukash, V N; Rubakov, V A
2008-01-01
We discuss the questions related to dark energy in the Universe. We note that in spite of the effect of dark energy, large-scale structure is still being generated in the Universe and this will continue for about ten billion years. We also comment on some statements in the paper 'Dark energy and universal antigravitation' by A D Chernin, Physics-Uspekhi 51 (3) (2008). (physics of our days)
Cosmological anisotropy from non-comoving dark matter and dark energy
International Nuclear Information System (INIS)
Harko, Tiberiu; Lobo, Francisco S. N.
2013-01-01
We consider a cosmological model in which the two major fluid components of the Universe, dark energy and dark matter, flow with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is an appropriate combination of the two fluid four-velocities. The energy density of the single cosmological fluid is larger than the sum of the energy densities of the two perfect fluids, i.e., dark energy and dark matter, respectively, and contains a correction term due to the anisotropy generated by the differences in the four-velocities. Furthermore, the gravitational field equations of the two-fluid anisotropic cosmological model are obtained for a Bianchi type I geometry. By assuming that the non-comoving motion of the dark energy and dark matter induces small perturbations in the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker type cosmological background, and that the anisotropy parameter is small, the equations of the cosmological perturbations due to the non-comoving nature of the two major components are obtained. The time evolution of the metric perturbations is explicitly obtained for the cases of the exponential and power law background cosmological expansion. The imprints of a non-comoving dark energy - dark matter on the Cosmic Microwave Background and on the luminosity distance are briefly discussed, and the temperature anisotropies and the quadrupole are explicitly obtained in terms of the metric perturbations of the flat background metric. Therefore, if there is a slight difference between the four-velocities of the dark energy and dark matter, the Universe would acquire some anisotropic characteristics, and its geometry will deviate from the standard FLRW one. In fact, the recent Planck results show that the presence of an intrinsic large scale anisotropy in the Universe cannot be excluded a priori, so that the model presented in this work can be considered as a
Investigating Dark Energy with Black Hole Binaries
International Nuclear Information System (INIS)
Mersini-Houghton, Laura; Kelleher, Adam
2009-01-01
The accelerated expansion of the universe is ascribed to the existence of dark energy. Black holes accrete dark energy. The accretion induces a mass change proportional to the energy density and pressure of the background dark energy fluid. The time scale during which the mass of black holes changes considerably is long relative to the age of the universe, thus beyond detection possibilities. We propose to take advantage of the modified black hole masses for exploring the equation of state w[z] of dark energy, by investigating the evolution of supermassive black hole binaries on a dark energy background. Deriving the signatures of dark energy accretion on the evolution of binaries, we find that dark energy imprints on the emitted gravitational radiation and on the changes in the orbital radius of the binary can be within detection limits for certain supermassive black hole binaries. This talk describes how binaries can provide a useful tool in obtaining complementary information on the nature of dark energy.
Dynamics of interacting dark energy
International Nuclear Information System (INIS)
Caldera-Cabral, Gabriela; Maartens, Roy; Urena-Lopez, L. Arturo
2009-01-01
Dark energy and dark matter are only indirectly measured via their gravitational effects. It is possible that there is an exchange of energy within the dark sector, and this offers an interesting alternative approach to the coincidence problem. We consider two broad classes of interacting models where the energy exchange is a linear combination of the dark sector densities. The first class has been previously investigated, but we define new variables and find a new exact solution, which allows for a more direct, transparent, and comprehensive analysis. The second class has not been investigated in general form before. We give general conditions on the parameters in both classes to avoid unphysical behavior (such as negative energy densities).
Dynamical evolution of quintessence dark energy in collapsing dark matter halos
International Nuclear Information System (INIS)
Wang Qiao; Fan Zuhui
2009-01-01
In this paper, we analyze the dynamical evolution of quintessence dark energy induced by the collapse of dark matter halos. Different from other previous studies, we develop a numerical strategy which allows us to calculate the dark energy evolution for the entire history of the spherical collapse of dark matter halos, without the need of separate treatments for linear, quasilinear, and nonlinear stages of the halo formation. It is found that the dark energy perturbations evolve with redshifts, and their specific behaviors depend on the quintessence potential as well as the collapsing process. The overall energy density perturbation is at the level of 10 -6 for cluster-sized halos. The perturbation amplitude decreases with the decrease of the halo mass. At a given redshift, the dark energy perturbation changes with the radius to the halo center, and can be either positive or negative depending on the contrast of ∂ t φ, ∂ r φ, and φ with respect to the background, where φ is the quintessence field. For shells where the contrast of ∂ r φ is dominant, the dark energy perturbation is positive and can be as high as about 10 -5 .
Advanced Dark Energy Physics Telescope (ADEPT)
Energy Technology Data Exchange (ETDEWEB)
Charles L. Bennett
2009-03-26
In 2006, we proposed to NASA a detailed concept study of ADEPT (the Advanced Dark Energy Physics Telescope), a potential space mission to reliably measure the time-evolution of dark energy by conducting the largest effective volume survey of the universe ever done. A peer-review panel of scientific, management, and technical experts reported back the highest possible 'excellent' rating for ADEPT. We have since made substantial advances in the scientific and technical maturity of the mission design. With this Department of Energy (DOE) award we were granted supplemental funding to support specific extended research items that were not included in the NASA proposal, many of which were intended to broadly advance future dark energy research, as laid out by the Dark Energy Task Force (DETF). The proposed work had three targets: (1) the adaptation of large-format infrared arrays to a 2 micron cut-off; (2) analytical research to improve the understanding of the dark energy figure-of- merit; and (3) extended studies of baryon acoustic oscillation systematic uncertainties. Since the actual award was only for {approx}10% of the proposed amount item (1) was dropped and item (2) work was severely restricted, consistent with the referee reviews of the proposal, although there was considerable contradictions between reviewer comments and several comments that displayed a lack of familiarity with the research. None the less, item (3) was the focus of the work. To characterize the nature of the dark energy, ADEPT is designed to observe baryon acoustic oscillations (BAO) in a large galaxy redshift survey and to obtain substantial numbers of high-redshift Type Ia supernovae (SNe Ia). The 2003 Wilkinson Microwave Anisotropy Probe (WMAP) made a precise determination of the BAO 'standard ruler' scale, as it was imprinted on the cosmic microwave background (CMB) at z {approx} 1090. The standard ruler was also imprinted on the pattern of galaxies, and was first
Constraints on the coupling between dark energy and dark matter from CMB data
International Nuclear Information System (INIS)
Murgia, R.; Gariazzo, S.; Fornengo, N.
2016-01-01
We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both models are found to be compatible with all cosmological observables, but in the case where dark matter decays into dark energy, the tension with the independent determinations of H 0 and σ 8 , already present for standard cosmology, increases: this model in fact predicts lower H 0 and higher σ 8 , mostly as a consequence of the higher amount of dark matter at early times, leading to a stronger clustering during the evolution. Instead, when dark matter is fed by dark energy, the reconstructed values of H 0 and σ 8 nicely agree with their local determinations, with a full reconciliation between high- and low-redshift observations. A non-zero coupling between dark energy and dark matter, with an energy flow from the former to the latter, appears therefore to be in better agreement with cosmological data
Holographic dark energy interacting with dark matter in a closed Universe
International Nuclear Information System (INIS)
Cruz, Norman; Lepe, Samuel; Pena, Francisco; Saavedra, Joel
2008-01-01
A cosmological model of an holographic dark energy interacting with dark matter throughout a decaying term of the form Q=3(λ 1 ρ DE +λ 2 ρ m )H is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenario, without any reference to a specific equation of state for the dark energy. The behavior of equation of state for dark energy is also discussed
The dark side of silicon energy efficient computing in the dark silicon era
Liljeberg, Pasi; Hemani, Ahmed; Jantsch, Axel; Tenhunen, Hannu
2017-01-01
This book presents the state-of-the art of one of the main concerns with microprocessors today, a phenomenon known as "dark silicon". Readers will learn how power constraints (both leakage and dynamic power) limit the extent to which large portions of a chip can be powered up at a given time, i.e. how much actual performance and functionality the microprocessor can provide. The authors describe their research toward the future of microprocessor development in the dark silicon era, covering a variety of important aspects of dark silicon-aware architectures including design, management, reliability, and test. Readers will benefit from specific recommendations for mitigating the dark silicon phenomenon, including energy-efficient, dedicated solutions and technologies to maximize the utilization and reliability of microprocessors. Enables readers to understand the dark silicon phenomenon and why it has emerged, including detailed analysis of its impacts; Presents state-of-the-art research, as well as tools for mi...
Quantum mechanical theory behind "dark energy"?
Colin Johnson, R
2007-01-01
"The mysterious increase in the acceleration of the universe, when intuition says it should be slowing down, is postulated to be caused by dark energy - "dark" because it is undetected. Now a group of scientists in the international collaboration Essence has suggested that a quantum mechanical interpretation of Einstein's proposed "cosmological constant" is the simplest explanation for dark energy. The group measured dark energy to within 10 percent." (1,5 page)
Interacting diffusive unified dark energy and dark matter from scalar fields
Energy Technology Data Exchange (ETDEWEB)
Benisty, David; Guendelman, E.I. [Ben Gurion University of the Negev, Department of Physics, Beersheba (Israel)
2017-06-15
Here we generalize ideas of unified dark matter-dark energy in the context of two measure theories and of dynamical space time theories. In two measure theories one uses metric independent volume elements and this allows one to construct unified dark matter-dark energy, where the cosmological constant appears as an integration constant associated with the equation of motion of the measure fields. The dynamical space-time theories generalize the two measure theories by introducing a vector field whose equation of motion guarantees the conservation of a certain Energy Momentum tensor, which may be related, but in general is not the same as the gravitational Energy Momentum tensor. We propose two formulations of this idea: (I) by demanding that this vector field be the gradient of a scalar, (II) by considering the dynamical space field appearing in another part of the action. Then the dynamical space time theory becomes a theory of Diffusive Unified dark energy and dark matter. These generalizations produce non-conserved energy momentum tensors instead of conserved energy momentum tensors which leads at the end to a formulation of interacting DE-DM dust models in the form of a diffusive type interacting Unified dark energy and dark matter scenario. We solved analytically the theories for perturbative solution and asymptotic solution, and we show that the ΛCDM is a fixed point of these theories at large times. Also a preliminary argument as regards the good behavior of the theory at the quantum level is proposed for both theories. (orig.)
Holographic dark energy interacting with dark matter in a closed Universe
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile); Lepe, Samuel [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4950, Valparaiso (Chile); Pena, Francisco [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de La Frontera, Avda. Francisco Salazar 01145, Casilla 54-D Temuco (Chile); Saavedra, Joel [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4950, Valparaiso (Chile)], E-mail: joel.saavedra@ucv.cl
2008-11-27
A cosmological model of an holographic dark energy interacting with dark matter throughout a decaying term of the form Q=3({lambda}{sub 1}{rho}{sub DE}+{lambda}{sub 2}{rho}{sub m})H is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenario, without any reference to a specific equation of state for the dark energy. The behavior of equation of state for dark energy is also discussed.
International Nuclear Information System (INIS)
Schrempp, L.
2008-02-01
From the observed late-time acceleration of cosmic expansion arises the quest for the nature of Dark Energy. As has been widely discussed, the cosmic neutrino background naturally qualifies for a connection with the Dark Energy sector and as a result could play a key role for the origin of cosmic acceleration. In this thesis we explore various theoretical aspects and phenomenological consequences arising from non-standard neutrino interactions, which dynamically link the cosmic neutrino background and a slowly-evolving scalar field of the dark sector. In the considered scenario, known as Neutrino Dark Energy, the complex interplay between the neutrinos and the scalar field not only allows to explain cosmic acceleration, but intriguingly, as a distinct signature, also gives rise to dynamical, time-dependent neutrino masses. In a first analysis, we thoroughly investigate an astrophysical high energy neutrino process which is sensitive to neutrino masses. We work out, both semi-analytically and numerically, the generic clear-cut signatures arising from a possible time variation of neutrino masses which we compare to the corresponding results for constant neutrino masses. Finally, we demonstrate that even for the lowest possible neutrino mass scale, it is feasible for the radio telescope LOFAR to reveal a variation of neutrino masses and therefore to probe the nature of Dark Energy within the next decade. A second independent analysis deals with the recently challenged stability of Neutrino Dark Energy against the strong growth of hydrodynamic perturbations, driven by the new scalar force felt between neutrinos. Within the framework of linear cosmological perturbation theory, we derive the equation of motion of the neutrino perturbations in a model-independent way. This equation allows to deduce an analytical stability condition which translates into a comfortable upper bound on the scalar-neutrino coupling which is determined by the ratio of the densities in cold dark
Energy Technology Data Exchange (ETDEWEB)
Schrempp, L.
2008-02-15
From the observed late-time acceleration of cosmic expansion arises the quest for the nature of Dark Energy. As has been widely discussed, the cosmic neutrino background naturally qualifies for a connection with the Dark Energy sector and as a result could play a key role for the origin of cosmic acceleration. In this thesis we explore various theoretical aspects and phenomenological consequences arising from non-standard neutrino interactions, which dynamically link the cosmic neutrino background and a slowly-evolving scalar field of the dark sector. In the considered scenario, known as Neutrino Dark Energy, the complex interplay between the neutrinos and the scalar field not only allows to explain cosmic acceleration, but intriguingly, as a distinct signature, also gives rise to dynamical, time-dependent neutrino masses. In a first analysis, we thoroughly investigate an astrophysical high energy neutrino process which is sensitive to neutrino masses. We work out, both semi-analytically and numerically, the generic clear-cut signatures arising from a possible time variation of neutrino masses which we compare to the corresponding results for constant neutrino masses. Finally, we demonstrate that even for the lowest possible neutrino mass scale, it is feasible for the radio telescope LOFAR to reveal a variation of neutrino masses and therefore to probe the nature of Dark Energy within the next decade. A second independent analysis deals with the recently challenged stability of Neutrino Dark Energy against the strong growth of hydrodynamic perturbations, driven by the new scalar force felt between neutrinos. Within the framework of linear cosmological perturbation theory, we derive the equation of motion of the neutrino perturbations in a model-independent way. This equation allows to deduce an analytical stability condition which translates into a comfortable upper bound on the scalar-neutrino coupling which is determined by the ratio of the densities in cold dark
Agegraphic dark energy as a quintessence
International Nuclear Information System (INIS)
Zhang, Jingfei; Liu, Hongya; Zhang, Xin
2008-01-01
Recently, a dark energy model characterized by the age of the universe, dubbed ''agegraphic dark energy'', was proposed by Cai. In this paper, a connection between the quintessence scalar-field and the agegraphic dark energy is established, and accordingly, the potential of the agegraphic quintessence field is constructed. (orig.)
Boddy, Kimberly K.
2017-03-28
Many models currently exist which attempt to interpret the excess of gamma rays emanating from the Galactic Center in terms of annihilating or decaying dark matter. These models typically exhibit a variety of complicated cascade mechanisms for photon production, leading to a non-trivial kinematics which obscures the physics of the underlying dark sector. In this paper, by contrast, we observe that the spectrum of the gamma-ray excess may actually exhibit an intriguing "energy-duality" invariance under $E_\\gamma \\rightarrow E_\\ast^2/E_\\gamma$ for some $E_\\ast$. As we shall discuss, such an energy duality points back to a remarkably simple alternative kinematics which in turn is realized naturally within the Dynamical Dark Matter framework. Observation of this energy duality could therefore provide considerable information about the properties of the dark sector from which the Galactic-Center gamma-ray excess might arise, and highlights the importance of acquiring more complete data for the Galactic-Center exce...
Interacting dark energy models as an approach for solving Cosmic Coincidence Problem
Shojaei, Hamed
Understanding the dark side of the Universe is one of the main tasks of physicists. As there is no thorough understanding of nature of the dark energy, this area is full of new ideas and there may be several discoveries, theoretical or experimental, in the near future. We know that dark energy, though not detected directly, exists and it is not just an exotic idea. The presence of dark energy is required by the observation of the acceleration of the universe. There are several questions regarding dark energy. What is the nature of dark energy? How does it interact with matter, baryonic or dark? Why is the density of dark energy so tiny, i.e. why rhoΛ ≈ 10--120 M4Pl ? And finally why does its density have the same order of magnitude as the density of matter does at the present time? The last question is one form of what is known as the "Cosmic Coincidence Problem" and in this work, I have been investigating one way to resolve this issue. Observations of Type Ia supernovae indicate that we are in an accelerating universe. A matter-dominated universe cannot be accelerating. A good fit is obtained if we assume that energy density parameters are O Λ = 0.7 and Om = 0.3. Here O Λ is related to dark energy, or cosmological constant in ΛCDM model. At the same time data from Wilkinson Microwave Anisotropy Probe (WMAP) satellite and supernova surveys have placed a constraint on w, the equation of state for dark energy, which is actually the ratio of pressure and energy density. Any good theory needs to explain this coincidence problem and yields a value for w between -1.1 and -0.9. I have employed an interesting approach to solve this problem by assuming that there exists an interaction between dark energy and matter in the context of holographic dark energy. This interaction converts dark energy to matter or vice versa without violating the local conservation of energy in the universe. Holographic dark energy by itself indicates that the value of dark energy is related
Dark energy and extended dark matter halos
Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.
2012-03-01
The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even
Dark matter and dark energy a challenge for modern cosmology
Gorini, Vittorio; Moschella, Ugo; Matarrese, Sabino
2011-01-01
This book brings together reviews from leading international authorities on the developments in the study of dark matter and dark energy, as seen from both their cosmological and particle physics side. Studying the physical and astrophysical properties of the dark components of our Universe is a crucial step towards the ultimate goal of unveiling their nature. The work developed from a doctoral school sponsored by the Italian Society of General Relativity and Gravitation. The book starts with a concise introduction to the standard cosmological model, as well as with a presentation of the theory of linear perturbations around a homogeneous and isotropic background. It covers the particle physics and cosmological aspects of dark matter and (dynamical) dark energy, including a discussion of how modified theories of gravity could provide a possible candidate for dark energy. A detailed presentation is also given of the possible ways of testing the theory in terms of cosmic microwave background, galaxy redshift su...
Leptogenesis, Dark Energy, Dark Matter and the neutrinos
International Nuclear Information System (INIS)
Sarkar, Utpal
2007-01-01
In this review we discuss how the models of neutrino masses can accommodate solutions to the problem of matter-antimatter asymmetry in the universe, dark energy or cosmological constant problem and dark matter candidates. The matter-antimatter asymmetry is explained by leptogenesis, originating from the lepton number violation associated with the neutrino masses. The dark energy problem is correlated with a mass varying neutrinos, which could originate from a pseudo-Nambu-Goldstone boson. In some radiative models of neutrino masses, there exists a Higgs doublet that does not acquire any vacuum expectation value. This field could be inert and the lightest inert particle could then be a dark matter candidate. We reviewed these scenarios in connection with models of neutrino masses with right-handed neutrinos and with triplet Higgs scalars
Large-scale instability in interacting dark energy and dark matter fluids
International Nuclear Information System (INIS)
Väliviita, Jussi; Majerotto, Elisabetta; Maartens, Roy
2008-01-01
If dark energy interacts with dark matter, this gives a new approach to the coincidence problem. But interacting dark energy models can suffer from pathologies. We consider the case where the dark energy is modelled as a fluid with constant equation of state parameter w. Non-interacting constant-w models are well behaved in the background and in the perturbed universe. But the combination of constant w and a simple interaction with dark matter leads to an instability in the dark sector perturbations at early times: the curvature perturbation blows up on super-Hubble scales. Our results underline how important it is to carefully analyse the relativistic perturbations when considering models of coupled dark energy. The instability that we find has been missed in some previous work where the perturbations were not consistently treated. The unstable mode dominates even if adiabatic initial conditions are used. The instability also arises regardless of how weak the coupling is. This non-adiabatic instability is different from previously discovered adiabatic instabilities on small scales in the strong-coupling regime
Direct reconstruction of dark energy.
Clarkson, Chris; Zunckel, Caroline
2010-05-28
An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With so few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space. We present a new nonparametric method which can accurately reconstruct a wide variety of dark energy behavior with no prior assumptions about it. It is simple, quick and relatively accurate, and involves no expensive explorations of parameter space. The technique uses principal component analysis and a combination of information criteria to identify real features in the data, and tailors the fitting functions to pick up trends and smooth over noise. We find that we can constrain a large variety of w(z) models to within 10%-20% at redshifts z≲1 using just SNAP-quality data.
Signature of the interaction between dark energy and dark matter in observations
International Nuclear Information System (INIS)
Abdalla, Elcio; Abramo, L. Raul; Souza, Jose C. C. de
2010-01-01
We investigate the effect of an interaction between dark energy and dark matter upon the dynamics of galaxy clusters. This effect is computed through the Layser-Irvine equation, which describes how an astrophysical system reaches virial equilibrium and was modified to include the dark interactions. Using observational data from almost 100 purportedly relaxed galaxy clusters we put constraints on the strength of the couplings in the dark sector. We compare our results with those from other observations and find that a positive (in the sense of energy flow from dark energy to dark matter) nonvanishing interaction is consistent with the data within several standard deviations.
Adiabatic instability in coupled dark energy/dark matter models
International Nuclear Information System (INIS)
Bean, Rachel; Flanagan, Eanna E.; Trodden, Mark
2008-01-01
We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the Universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, which can also be thought of as a type of Jeans instability, is characterized by a negative sound speed squared of an effective coupled dark matter/dark energy fluid, and results in the exponential growth of small scale modes. We discuss the role of the instability in specific coupled cold dark matter and mass varying neutrino models of dark energy and clarify for these theories the regimes in which the instability can be evaded due to nonadiabaticity or weak coupling.
Dark Energy and Spacetime Symmetry
Directory of Open Access Journals (Sweden)
Irina Dymnikova
2017-03-01
Full Text Available The Petrov classification of stress-energy tensors provides a model-independent definition of a vacuum by the algebraic structure of its stress-energy tensor and implies the existence of vacua whose symmetry is reduced as compared with the maximally symmetric de Sitter vacuum associated with the Einstein cosmological term. This allows to describe a vacuum in general setting by dynamical vacuum dark fluid, presented by a variable cosmological term with the reduced symmetry which makes vacuum fluid essentially anisotropic and allows it to be evolving and clustering. The relevant solutions to the Einstein equations describe regular cosmological models with time-evolving and spatially inhomogeneous vacuum dark energy, and compact vacuum objects generically related to a dark energy: regular black holes, their remnants and self-gravitating vacuum solitons with de Sitter vacuum interiors—which can be responsible for observational effects typically related to a dark matter. The mass of objects with de Sitter interior is generically related to vacuum dark energy and to breaking of space-time symmetry. In the cosmological context spacetime symmetry provides a mechanism for relaxing cosmological constant to a needed non-zero value.
Dark energy interacting with two fluids
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile)], E-mail: ncruz@lauca.usach.cl; Lepe, Samuel [Instituto de Fisica, Facultad de Ciencias Basicas y Matematicas, Universidad Catolica de Valparaiso, Avenida Brasil 2950, Valparaiso (Chile)], E-mail: slepe@ucv.cl; Pena, Francisco [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de La Frontera, Avda. Francisco Salazar 01145, Casilla 54-D Temuco (Chile)], E-mail: fcampos@ufro.cl
2008-05-29
A cosmological model of dark energy interacting with dark matter and another general component of the universe is investigated. We found general constraints on these models imposing an accelerated expansion. The same is also studied in the case for holographic dark energy.
Dark Energy Found Stifling Growth in Universe
2008-12-01
WASHINGTON -- For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how dark energy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what dark energy is and what the destiny of the universe could be. This work, which took years to complete, is separate from other methods of dark energy research such as supernovas. These new X-ray results provide a crucial independent test of dark energy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity. Scientists think dark energy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of dark energy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Ghostly Glow Reveals a Hidden Class of Long-Wavelength Radio Emitters Powerful Nearby Supernova Caught By Web Cassiopeia A Comes Alive Across Time and Space To help decide between these options, a new way of looking at dark energy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time. "This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its
Effects of the interaction between dark energy and dark matter on cosmological parameters
International Nuclear Information System (INIS)
He, Jian-Hua; Wang, Bin
2008-01-01
We examine the effects of possible phenomenological interactions between dark energy and dark matter on cosmological parameters and their efficiency in solving the coincidence problem. We work with two simple parameterizations of the dynamical dark energy equation of state and the constant dark energy equation of state. Using observational data coming from the new 182 Gold type Ia supernova samples, the shift parameter of the Cosmic Microwave Background given by the three-year Wilkinson Microwave Anisotropy Probe observations and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, we perform a statistical joint analysis of different forms of phenomenological interaction between dark energy and dark matter
Cosmological acceleration. Dark energy or modified gravity?
International Nuclear Information System (INIS)
Bludman, S.
2006-05-01
We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model ΛCDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)
Cosmological acceleration. Dark energy or modified gravity?
Energy Technology Data Exchange (ETDEWEB)
Bludman, S
2006-05-15
We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)
Non-adiabatic perturbations in Ricci dark energy model
International Nuclear Information System (INIS)
Karwan, Khamphee; Thitapura, Thiti
2012-01-01
We show that the non-adiabatic perturbations between Ricci dark energy and matter can grow both on superhorizon and subhorizon scales, and these non-adiabatic perturbations on subhorizon scales can lead to instability in this dark energy model. The rapidly growing non-adiabatic modes on subhorizon scales always occur when the equation of state parameter of dark energy starts to drop towards -1 near the end of matter era, except that the parameter α of Ricci dark energy equals to 1/2. In the case where α = 1/2, the rapidly growing non-adiabatic modes disappear when the perturbations in dark energy and matter are adiabatic initially. However, an adiabaticity between dark energy and matter perturbations at early time implies a non-adiabaticity between matter and radiation, this can influence the ordinary Sachs-Wolfe (OSW) effect. Since the amount of Ricci dark energy is not small during matter domination, the integrated Sachs-Wolfe (ISW) effect is greatly modified by density perturbations of dark energy, leading to a wrong shape of CMB power spectrum. The instability in Ricci dark energy is difficult to be alleviated if the effects of coupling between baryon and photon on dark energy perturbations are included
Ricci-Gauss-Bonnet holographic dark energy
Saridakis, Emmanuel N.
2018-03-01
We present a model of holographic dark energy in which the infrared cutoff is determined by both the Ricci and the Gauss-Bonnet invariants. Such a construction has the significant advantage that the infrared cutoff, and consequently the holographic dark energy density, does not depend on the future or the past evolution of the universe, but only on its current features, and moreover it is determined by invariants, whose role is fundamental in gravitational theories. We extract analytical solutions for the behavior of the dark energy density and equation-of-state parameters as functions of the redshift. These reveal the usual thermal history of the universe, with the sequence of radiation, matter and dark energy epochs, resulting in the future to a complete dark energy domination. The corresponding dark energy equation-of-state parameter can lie in the quintessence or phantom regime, or experience the phantom-divide crossing during the cosmological evolution, and its asymptotic value can be quintessencelike, phantomlike, or be exactly equal to the cosmological-constant value. Finally, we extract the constraints on the model parameters that arise from big bang nucleosynthesis.
Kinetic k-essence ghost dark energy model
International Nuclear Information System (INIS)
Rozas-Fernández, Alberto
2012-01-01
A ghost dark energy model has been recently put forward to explain the current accelerated expansion of the Universe. In this model, the energy density of ghost dark energy, which comes from the Veneziano ghost of QCD, is proportional to the Hubble parameter, ρ D =αH. Here α is a constant of order Λ QCD 3 where Λ QCD ∼100 MeV is the QCD mass scale. We consider a connection between ghost dark energy with/without interaction between the components of the dark sector and the kinetic k-essence field. It is shown that the cosmological evolution of the ghost dark energy dominated Universe can be completely described a kinetic k-essence scalar field. We reconstruct the kinetic k-essence function F(X) in a flat Friedmann-Robertson-Walker Universe according to the evolution of ghost dark energy density.
Gravitational Waves and Dark Energy
Directory of Open Access Journals (Sweden)
Peter L. Biermann
2014-12-01
Full Text Available The idea that dark energy is gravitational waves may explain its strength and its time-evolution. A possible concept is that dark energy is the ensemble of coherent bursts (solitons of gravitational waves originally produced when the first generation of super-massive black holes was formed. These solitons get their initial energy as well as keep up their energy density throughout the evolution of the universe by stimulating emission from a background, a process which we model by working out this energy transfer in a Boltzmann equation approach. New Planck data suggest that dark energy has increased in strength over cosmic time, supporting the concept here. The transit of these gravitational wave solitons may be detectable. Key tests include pulsar timing, clock jitter and the radio background.
Late forming dark matter in theories of neutrino dark energy
International Nuclear Information System (INIS)
Das, Subinoy; Weiner, Neal
2011-01-01
We study the possibility of late forming dark matter, where a scalar field, previously trapped in a metastable state by thermal or finite density effects, goes through a phase transition near the era matter-radiation equality and begins to oscillate about its true minimum. Such a theory is motivated generally if the dark energy is of a similar form, but has not yet made the transition to dark matter, and, in particular, arises automatically in recently considered theories of neutrino dark energy. If such a field comprises the present dark matter, the matter power spectrum typically shows a sharp break at small, presently nonlinear scales, below which power is highly suppressed and previously contained acoustic oscillations. If, instead, such a field forms a subdominant component of the total dark matter, such acoustic oscillations may imprint themselves in the linear regime.
Dark energy and dark matter perturbations in singular universes
International Nuclear Information System (INIS)
Denkiewicz, Tomasz
2015-01-01
We discuss the evolution of density perturbations of dark matter and dark energy in cosmological models which admit future singularities in a finite time. Up to now geometrical tests of the evolution of the universe do not differentiate between singular universes and ΛCDM scenario. We solve perturbation equations using the gauge invariant formalism. The analysis shows that the detailed reconstruction of the evolution of perturbations within singular cosmologies, in the dark sector, can exhibit important differences between the singular universes models and the ΛCDM cosmology. This is encouraging for further examination and gives hope for discriminating between those models with future galaxy weak lensing experiments like the Dark Energy Survey (DES) and Euclid or CMB observations like PRISM and CoRE
From asymptotic safety to dark energy
International Nuclear Information System (INIS)
Ahn, Changrim; Kim, Chanju; Linder, Eric V.
2011-01-01
We consider renormalization group flow applied to the cosmological dynamical equations. A consistency condition arising from energy-momentum conservation links the flow parameters to the cosmological evolution, restricting possible behaviors. Three classes of cosmological fixed points for dark energy plus a barotropic fluid are found: a dark energy dominated universe, which can be either accelerating or decelerating depending on the RG flow parameters, a barotropic dominated universe where dark energy fades away, and solutions where the gravitational and potential couplings cease to flow. If the IR fixed point coincides with the asymptotically safe UV fixed point then the dark energy pressure vanishes in the first class, while (only) in the de Sitter limit of the third class the RG cutoff scale becomes the Hubble scale.
Third-Order Density Perturbation and One-Loop Power Spectrum in Dark-Energy-Dominated Universe
Takahashi, Ryuichi
2008-01-01
We investigate the third-order density perturbation and the one-loop correction to the linear power spectrum in the dark-energy cosmological model. Our main interest is to understand the dark-energy effect on baryon acoustic oscillations in a quasi-nonlinear regime ($k \\approx 0.1h$/Mpc). Analytical solutions and simple fitting formulae are presented for the dark-energy model with the general time-varying equation of state $w(a)$. It turns out that the power spectrum coincides with the approx...
International Nuclear Information System (INIS)
Huterer, Dragan
2002-01-01
We study the power of upcoming weak lensing surveys to probe dark energy. Dark energy modifies the distance-redshift relation as well as the matter power spectrum, both of which affect the weak lensing convergence power spectrum. Some dark-energy models predict additional clustering on very large scales, but this probably cannot be detected by weak lensing alone due to cosmic variance. With reasonable prior information on other cosmological parameters, we find that a survey covering 1000 sq deg down to a limiting magnitude of R=27 can impose constraints comparable to those expected from upcoming type Ia supernova and number-count surveys. This result, however, is contingent on the control of both observational and theoretical systematics. Concentrating on the latter, we find that the nonlinear power spectrum of matter perturbations and the redshift distribution of source galaxies both need to be determined accurately in order for weak lensing to achieve its full potential. Finally, we discuss the sensitivity of the three-point statistics to dark energy
Clustering properties of dynamical dark energy models
International Nuclear Information System (INIS)
Avelino, P. P.; Beca, L. M. G.; Martins, C. J. A. P.
2008-01-01
We provide a generic but physically clear discussion of the clustering properties of dark energy models. We explicitly show that in quintessence-type models the dark energy fluctuations, on scales smaller than the Hubble radius, are of the order of the perturbations to the Newtonian gravitational potential, hence necessarily small on cosmological scales. Moreover, comparable fluctuations are associated with different gauge choices. We also demonstrate that the often used homogeneous approximation is unrealistic, and that the so-called dark energy mutation is a trivial artifact of an effective, single fluid description. Finally, we discuss the particular case where the dark energy fluid is nonminimally coupled to dark matter
Interacting agegraphic dark energy models in non-flat universe
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Sheykhi, Ahmad
2009-01-01
A so-called 'agegraphic dark energy' was recently proposed to explain the dark energy-dominated universe. In this Letter, we generalize the agegraphic dark energy models to the universe with spatial curvature in the presence of interaction between dark matter and dark energy. We show that these models can accommodate w D =-1 crossing for the equation of state of dark energy. In the limiting case of a flat universe, i.e. k=0, all previous results of agegraphic dark energy in flat universe are restored.
Particle Physics Foundations of Dark Matter, Dark Energy, and Inflation (2/3)
CERN. Geneva
2012-01-01
Ninety-five percent of the present mass-energy density of the Universe is dark. Twenty-five percent is in the form of dark matter holding together galaxies and other large scale structures, and 70% is in the form of dark energy driving an accelerated expansion of the universe. Dark matter and dark energy cannot be explained within the standard model of particle physics. In the first lecture I will review the evidence for dark matter and the observations that point to an explanation in the form of cold dark matter. I will then describe the expected properties of a hypothetical Weakly-Interacting Massive Particle, or WIMP, and review experimental and observational approaches to test the hypothesis. Finally, I will discuss how the LHC might shed light on the problem. In the second lecture I will review the theoretical foundations and observational evidence that the dominant component of the present mass density of the Universe has a negative pressure, which leads to an accelerated expansion of the Universe...
Particle Physics Foundations of Dark Matter, Dark Energy, and Inflation (3/3)
CERN. Geneva
2012-01-01
Ninety-five percent of the present mass-energy density of the Universe is dark. Twenty-five percent is in the form of dark matter holding together galaxies and other large scale structures, and 70% is in the form of dark energy driving an accelerated expansion of the universe. Dark matter and dark energy cannot be explained within the standard model of particle physics. In the first lecture I will review the evidence for dark matter and the observations that point to an explanation in the form of cold dark matter. I will then describe the expected properties of a hypothetical Weakly-Interacting Massive Particle, or WIMP, and review experimental and observational approaches to test the hypothesis. Finally, I will discuss how the LHC might shed light on the problem. In the second lecture I will review the theoretical foundations and observational evidence that the dominant component of the present mass density of the Universe has a negative pressure, which leads to an accelerated expansion of the Universe...
Particle Physics Foundations of Dark Matter, Dark Energy, and Inflation (1/3)
CERN. Geneva
2012-01-01
Ninety-five percent of the present mass-energy density of the Universe is dark. Twenty-five percent is in the form of dark matter holding together galaxies and other large scale structures, and 70% is in the form of dark energy driving an accelerated expansion of the universe. Dark matter and dark energy cannot be explained within the standard model of particle physics. In the first lecture I will review the evidence for dark matter and the observations that point to an explanation in the form of cold dark matter. I will then describe the expected properties of a hypothetical Weakly-Interacting Massive Particle, or WIMP, and review experimental and observational approaches to test the hypothesis. Finally, I will discuss how the LHC might shed light on the problem. In the second lecture I will review the theoretical foundations and observational evidence that the dominant component of the present mass density of the Universe has a negative pressure, which leads to an accelerated expansion of the Universe...
Energy Technology Data Exchange (ETDEWEB)
Abdalla, Elcio, E-mail: eabdalla@usp.br [Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970, São Paulo (Brazil); Graef, L.L., E-mail: leilagraef@usp.br [Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970, São Paulo (Brazil); Wang, Bin, E-mail: wang_b@sjtu.edu.cn [INPAC and Department of Physics, Shanghai Jiao Tong University, 200240 Shanghai (China)
2013-11-04
We discuss a model of nonperturbative decay of dark energy. We suggest the possibility that this model can provide a mechanism from the field theory to realize the energy transfer from dark energy into dark matter, which is the requirement to alleviate the coincidence problem. The advantage of the model is the fact that it accommodates a mean life compatible with the age of the universe. We also argue that supersymmetry is a natural set up, though not essential.
How to distinguish dark energy and modified gravity?
International Nuclear Information System (INIS)
Wei Hao; Zhang Shuangnan
2008-01-01
The current accelerated expansion of our universe could be due to an unknown energy component (dark energy) or a modification of general relativity (modified gravity). In the literature it has been proposed that combining the probes of the cosmic expansion history and growth history can distinguish between dark energy and modified gravity. In this work, without invoking nontrivial dark energy clustering, we show that the possible interaction between dark energy and dark matter could make the interacting dark model and the modified gravity model indistinguishable. An explicit example is also given. Therefore, it is required to seek some complementary probes beyond the ones of cosmic expansion history and growth history.
Dark Energy and the Hubble Law
Chernin, A. D.; Dolgachev, V. P.; Domozhilova, L. M.
The Big Bang predicted by Friedmann could not be empirically discovered in the 1920th, since global cosmological distances (more than 300-1000 Mpc) were not available for observations at that time. Lemaitre and Hubble studied receding motions of galaxies at local distances of less than 20-30 Mpc and found that the motions followed the (nearly) linear velocity-distance relation, known now as Hubble's law. For decades, the real nature of this phenomenon has remained a mystery, in Sandage's words. After the discovery of dark energy, it was suggested that the dynamics of local expansion flows is dominated by omnipresent dark energy, and it is the dark energy antigravity that is able to introduce the linear velocity-distance relation to the flows. It implies that Hubble's law observed at local distances was in fact the first observational manifestation of dark energy. If this is the case, the commonly accepted criteria of scientific discovery lead to the conclusion: In 1927, Lemaitre discovered dark energy and Hubble confirmed this in 1929.
Distinguishing modified gravity from dark energy
International Nuclear Information System (INIS)
Bertschinger, Edmund; Zukin, Phillip
2008-01-01
The acceleration of the Universe can be explained either through dark energy or through the modification of gravity on large scales. In this paper we investigate modified gravity models and compare their observable predictions with dark energy models. Modifications of general relativity are expected to be scale independent on superhorizon scales and scale dependent on subhorizon scales. For scale-independent modifications, utilizing the conservation of the curvature scalar and a parametrized post-Newtonian formulation of cosmological perturbations, we derive results for large-scale structure growth, weak gravitational lensing, and cosmic microwave background anisotropy. For scale-dependent modifications, inspired by recent f(R) theories we introduce a parametrization for the gravitational coupling G and the post-Newtonian parameter γ. These parametrizations provide a convenient formalism for testing general relativity. However, we find that if dark energy is generalized to include both entropy and shear stress perturbations, and the dynamics of dark energy is unknown a priori, then modified gravity cannot in general be distinguished from dark energy using cosmological linear perturbations.
Dark energy and universal antigravitation
International Nuclear Information System (INIS)
Chernin, A D
2008-01-01
Universal antigravitation, a new physical phenomenon discovered astronomically at distances of 5 to 8 billion light years, manifests itself as cosmic repulsion that acts between distant galaxies and overcomes their gravitational attraction, resulting in the accelerating expansion of the Universe. The source of the antigravitation is not galaxies or any other bodies of nature but a previously unknown form of mass/energy that has been termed dark energy. Dark energy accounts for 70 to 80% of the total mass and energy of the Universe and, in macroscopic terms, is a kind of continuous medium that fills the entire space of the Universe and is characterized by positive density and negative pressure. With its physical nature and microscopic structure unknown, dark energy is among the most critical challenges fundamental science faces in the twenty-first century. (physics of our days)
Interacting holographic dark energy with logarithmic correction
International Nuclear Information System (INIS)
Jamil, Mubasher; Farooq, M. Umar
2010-01-01
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Employing this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy
Comparing holographic dark energy models with statefinder
International Nuclear Information System (INIS)
Cui, Jing-Lei; Zhang, Jing-Fei
2014-01-01
We apply the statefinder diagnostic to the holographic dark energy models, including the original holographic dark energy (HDE) model, the new holographic dark energy model, the new agegraphic dark energy (NADE) model, and the Ricci dark energy model. In the low-redshift region the holographic dark energy models are degenerate with each other and with the ΛCDM model in the H(z) and q(z) evolutions. In particular, the HDE model is highly degenerate with the ΛCDM model, and in the HDE model the cases with different parameter values are also in strong degeneracy. Since the observational data are mainly within the low-redshift region, it is very important to break this lowredshift degeneracy in the H(z) and q(z) diagnostics by using some quantities with higher order derivatives of the scale factor. It is shown that the statefinder diagnostic r(z) is very useful in breaking the low-redshift degeneracies. By employing the statefinder diagnostic the holographic dark energy models can be differentiated efficiently in the low-redshift region. The degeneracy between the holographic dark energy models and the ΛCDM model can also be broken by this method. Especially for the HDE model, all the previous strong degeneracies appearing in the H(z) and q(z) diagnostics are broken effectively. But for the NADE model, the degeneracy between the cases with different parameter values cannot be broken, even though the statefinder diagnostic is used. A direct comparison of the holographic dark energy models in the r-s plane is also made, in which the separations between the models (including the ΛCDM model) can be directly measured in the light of the current values {r 0 , s 0 } of the models. (orig.)
Dark energy observational evidence and theoretical models
Novosyadlyj, B; Shtanov, Yu; Zhuk, A
2013-01-01
The book elucidates the current state of the dark energy problem and presents the results of the authors, who work in this area. It describes the observational evidence for the existence of dark energy, the methods and results of constraining of its parameters, modeling of dark energy by scalar fields, the space-times with extra spatial dimensions, especially Kaluza---Klein models, the braneworld models with a single extra dimension as well as the problems of positive definition of gravitational energy in General Relativity, energy conditions and consequences of their violation in the presence of dark energy. This monograph is intended for science professionals, educators and graduate students, specializing in general relativity, cosmology, field theory and particle physics.
The interaction between dark energy and dark matter
International Nuclear Information System (INIS)
He Jianhua; Wang Bin
2010-01-01
In this review we first present a general formalism to study the growth of dark matter perturbations in the presence of interactions between dark matter(DM) and dark energy(DE). We also study the signature of such interaction on the temperature anisotropies of the large scale cosmic microwave background (CMB). We find that the effect of such interaction has significant signature on both the growth of dark matter structure and the late Integrated Sachs Wolfe effect(ISW). We further discuss the potential possibility to detect the coupling by cross-correlating CMB maps with tracers of the large scale structure. We finally confront this interacting model with WMAP 5-year data as well as other data sets. We find that in the 1σ range, the constrained coupling between dark sectors can solve the coincidence problem.
Coupled dark matter-dark energy in light of near Universe observations
Honorez, Laura Lopez; Mena, Olga; Verde, Licia; Jimenez, Raul
2010-01-01
Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified --and thus can be probed by a combination of tests for the expansion history and the growth of structure--, there is a class of dark coupling models where gravity is still GR, but the growth of perturbations is, in principle modified. While this effect is small in the specific models we have considered, one should bear in mind that an inco...
Sapone, Domenico
2010-01-01
In this paper we review a part of the approaches that have been considered to explain the extraordinary discovery of the late time acceleration of the Universe. We discuss the arguments that have led physicists and astronomers to accept dark energy as the current preferable candidate to explain the acceleration. We highlight the problems and the attempts to overcome the difficulties related to such a component. We also consider alternative theories capable of explaining the acceleration of the Universe, such as modification of gravity. We compare the two approaches and point out the observational consequences, reaching the sad but foresightful conclusion that we will not be able to distinguish between a Universe filled by dark energy or a Universe where gravity is different from General Relativity. We review the present observations and discuss the future experiments that will help us to learn more about our Universe. This is not intended to be a complete list of all the dark energy models but this paper shou...
International Nuclear Information System (INIS)
Amendola, Luca; Campos, Gabriela Camargo; Rosenfeld, Rogerio
2007-01-01
Models where the dark matter component of the Universe interacts with the dark energy field have been proposed as a solution to the cosmic coincidence problem, since in the attractor regime both dark energy and dark matter scale in the same way. In these models the mass of the cold dark matter particles is a function of the dark energy field responsible for the present acceleration of the Universe, and different scenarios can be parametrized by how the mass of the cold dark matter particles evolves with time. In this article we study the impact of a constant coupling δ between dark energy and dark matter on the determination of a redshift dependent dark energy equation of state w DE (z) and on the dark matter density today from SNIa data. We derive an analytical expression for the luminosity distance in this case. In particular, we show that the presence of such a coupling increases the tension between the cosmic microwave background data from the analysis of the shift parameter in models with constant w DE and SNIa data for realistic values of the present dark matter density fraction. Thus, an independent measurement of the present dark matter density can place constraints on models with interacting dark energy
International Nuclear Information System (INIS)
Fuezfa, A.; Alimi, J.-M.
2007-01-01
The abnormally weighting energy hypothesis consists of assuming that the dark sector of cosmology violates the weak equivalence principle (WEP) on cosmological scales, which implies a violation of the strong equivalence principle for ordinary matter. In this paper, dark energy is shown to result from the violation of WEP by pressureless (dark) matter. This allows us to build a new cosmological framework in which general relativity is satisfied at low scales, as WEP violation depends on the ratio of the ordinary matter over dark matter densities, but at large scales, we obtain a general relativity-like theory with a different value of the gravitational coupling. This explanation is formulated in terms of a tensor-scalar theory of gravitation without WEP for which there exists a revisited convergence mechanism toward general relativity. The consequent dark energy mechanism build upon the anomalous gravity of dark matter (i) does not require any violation of the strong energy condition p 2 /3, (ii) offers a natural way out of the coincidence problem thanks to the nonminimal couplings to gravitation, (iii) accounts fairly for supernovae data from various simple couplings and with density parameters very close to the ones of the concordance model ΛCDM, and therefore suggests an explanation to its remarkable adequacy. Finally, (iv) this mechanism ends up in the future with an Einstein-de Sitter expansion regime once the attractor is reached
Paths to dark energy theory and observation
Valtonen, Mauri; Chernin, Arthur D; Byrd, Gene
2012-01-01
This work provides the current theory and observations behind the cosmological phenomenon of dark energy. The approach is comprehensivewith rigorous mathematical theory and relevant astronomical observations discussed in context.The book treats the background and history starting with the new-found importance of Einstein's cosmological constant (proposed long ago for the opposite purpose) in dark energy formulation, as well as the frontiers of dark energy.
Reconstruction of the Dark Energy Equation of State from the Latest Observations
Dai, Ji-Ping; Yang, Yang; Xia, Jun-Qing
2018-04-01
Since the discovery of the accelerating expansion of our universe in 1998, studying the features of dark energy has remained a hot topic in modern cosmology. In the literature, dark energy is usually described by w ≡ P/ρ, where P and ρ denote its pressure and energy density. Therefore, exploring the evolution of w is the key approach to understanding dark energy. In this work, we adopt three different methods, polynomial expansion, principal component analysis, and the correlated prior method, to reconstruct w with a collection of the latest observations, including the type-Ia supernova, cosmic microwave background, large-scale structure, Hubble measurements, and baryon acoustic oscillations (BAOs), and find that the concordance cosmological constant model (w = ‑1) is still safely consistent with these observational data at the 68% confidence level. However, when we add the high-redshift BAO measurement from the Lyα forest (Lyα FB) of BOSS DR11 quasars into the calculation, there is a significant impact on the reconstruction result. In the standard ΛCDM model, since the Lyα FB data slightly prefer a negative dark energy density, in order to avoid this problem, a dark energy model with a w significantly smaller than ‑1 is needed to explain this Lyα FB data. In this work, we find the consistent conclusion that there is a strong preference for the time-evolving behavior of dark energy w at high redshifts, when including the Lyα FB data. Therefore, we think that this Lyα FB data needs to be watched carefully attention when studying the evolution of the dark energy equation of state.
Holography and holographic dark energy model
International Nuclear Information System (INIS)
Gong Yungui; Zhang Yuanzhong
2005-01-01
The holographic principle is used to discuss the holographic dark energy model. We find that the Bekenstein-Hawking entropy bound is far from saturation under certain conditions. A more general constraint on the parameter of the holographic dark energy model is also derived
A modified generalized Chaplygin gas as the unified dark matter-dark energy revisited
Energy Technology Data Exchange (ETDEWEB)
Deng, Xue-Mei, E-mail: xmd@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China)
2011-12-15
A modified generalized Chaplygin gas (MGCG) is considered as the unified dark matter-dark energy revisited. The character of MGCG is endued with the dual role, which behaves as matter at early times and as a quiescence dark energy at late times. The equation of state for MGCG is p = -{alpha}{rho}/(1 + {alpha}) - {upsilon}(z){rho}{sup -{alpha}/(1 + {alpha})}, where {upsilon}(z) = -[{rho}0{sub c}(1 + z){sup 3}] {sup (1+{alpha})} (1 - {Omega}{sub 0B}){sup {alpha} {l_brace}{alpha}{Omega}0{sub DM} + {Omega}{sub 0DE} [{omega}{sub DE} + {alpha}(1 +{omega}{sub DE})](1 + z){sup 3}{omega}DE(1+{alpha}){r_brace}}. Some cosmological quantities, such as the densities of different components of the universe {Omega}{sub i} (i, respectively, denotes baryons, dark matter, and dark energy) and the deceleration parameter q, are obtained. The present deceleration parameter q{sub 0}, the transition redshift z{sub T}, and the redshift z{sub eq}, which describes the epoch when the densities in dark matter and dark energy are equal, are also calculated. To distinguish MGCG from others, we then apply the Statefinder diagnostic. Later on, the parameters ({alpha} and {omega}{sub DE}) of MGCG are constrained by combination of the sound speed c{sup 2}{sub s} , the age of the universe t{sub 0}, the growth factor m, and the bias parameter b. It yields {alpha} = -3.07{sup +5.66} {sub -4.98} x 10{sup -2} and {omega}{sub DE} = -1.05 {sup +0.06} {sub -0.11}. Through the analysis of the growth of density perturbations for MGCG, it is found that the energy will transfer from dark matter to dark energy which reach equal at z{sub e}{approx} 0.48 and the density fluctuations start deviating from the linear behavior at z {approx} 0.25 caused by the dominance of dark energy. (author)
Advanced Dark Energy Physics Telescope (ADEPT). Final Report
International Nuclear Information System (INIS)
Bennett, Charles L.
2009-01-01
In 2006, we proposed to NASA a detailed concept study of ADEPT (the Advanced Dark Energy Physics Telescope), a potential space mission to reliably measure the time-evolution of dark energy by conducting the largest effective volume survey of the universe ever done. A peer-review panel of scientific, management, and technical experts reported back the highest possible 'excellent' rating for ADEPT. We have since made substantial advances in the scientific and technical maturity of the mission design. With this Department of Energy (DOE) award we were granted supplemental funding to support specific extended research items that were not included in the NASA proposal, many of which were intended to broadly advance future dark energy research, as laid out by the Dark Energy Task Force (DETF). The proposed work had three targets: (1) the adaptation of large-format infrared arrays to a 2 micron cut-off; (2) analytical research to improve the understanding of the dark energy figure-of- merit; and (3) extended studies of baryon acoustic oscillation systematic uncertainties. Since the actual award was only for ∼10% of the proposed amount item (1) was dropped and item (2) work was severely restricted, consistent with the referee reviews of the proposal, although there was considerable contradictions between reviewer comments and several comments that displayed a lack of familiarity with the research. None the less, item (3) was the focus of the work. To characterize the nature of the dark energy, ADEPT is designed to observe baryon acoustic oscillations (BAO) in a large galaxy redshift survey and to obtain substantial numbers of high-redshift Type Ia supernovae (SNe Ia). The 2003 Wilkinson Microwave Anisotropy Probe (WMAP) made a precise determination of the BAO 'standard ruler' scale, as it was imprinted on the cosmic microwave background (CMB) at z ∼ 1090. The standard ruler was also imprinted on the pattern of galaxies, and was first detected in 2005 in Sloan Digital
The continuous tower of scalar fields as a system of interacting dark matter–dark energy
International Nuclear Information System (INIS)
Santos, Paulo
2015-01-01
This paper aims to introduce a new parameterisation for the coupling Q in interacting dark matter and dark energy models by connecting said models with the Continuous Tower of Scalar Fields model. Based upon the existence of a dark matter and a dark energy sectors in the Continuous Tower of Scalar Fields, a simplification is considered for the evolution of a single scalar field from the tower, validated in this paper. This allows for the results obtained with the Continuous Tower of Scalar Fields model to match those of an interacting dark matter–dark energy system, considering that the energy transferred from one fluid to the other is given by the energy of the scalar fields that start oscillating at a given time, rather than considering that the energy transference depends on properties of the whole fluids that are interacting.
Covariant generalized holographic dark energy and accelerating universe
Energy Technology Data Exchange (ETDEWEB)
Nojiri, Shin' ichi [Nagoya University, Department of Physics, Nagoya (Japan); Nagoya University, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya (Japan); Odintsov, S.D. [ICREA, Barcelona (Spain); Institute of Space Sciences (IEEC-CSIC), Barcelona (Spain); National Research Tomsk State University, Tomsk (Russian Federation); Tomsk State Pedagogical University, Tomsk (Russian Federation)
2017-08-15
We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F(R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy. (orig.)
Covariant generalized holographic dark energy and accelerating universe
International Nuclear Information System (INIS)
Nojiri, Shin'ichi; Odintsov, S.D.
2017-01-01
We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F(R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy. (orig.)
Covariant generalized holographic dark energy and accelerating universe
Nojiri, Shin'ichi; Odintsov, S. D.
2017-08-01
We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F( R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy.
On the geometry of dark energy
International Nuclear Information System (INIS)
Maia, M D; Monte, E M; Maia, J M F; Alcaniz, J S
2005-01-01
Experimental evidence suggests that we live in a spatially flat, accelerating universe composed of roughly one-third of matter (baryonic + dark) and two-thirds of a negative-pressure dark component, generically called dark energy. The presence of such energy not only explains the observed accelerating expansion of the universe but also provides the remaining piece of information connecting the inflationary flatness prediction with astronomical observations. However, despite its good observational indications, the nature of dark energy still remains an open question. In this paper we explore a geometrical explanation for such a component within the context of braneworld theory without mirror symmetry, leading to a geometrical interpretation for dark energy as a warp in the universe given by the extrinsic curvature. In particular, we study the phenomenological implications of the extrinsic curvature of a Friedmann-Robertson-Walker universe in a five-dimensional constant curvature bulk, with signatures (4,1) or (3,2), as compared with the x-matter (XCDM) model. From the analysis of the geometrically modified Friedmann's equations, the deceleration parameter and the weak energy condition, we find a consistent agreement with the presently known observational data on inflation for the de Sitter bulk, but not for the anti-de Sitter case
Dark matter and dark energy from the solution of the strong CP problem.
Mainini, Roberto; Bonometto, Silvio A
2004-09-17
The Peccei-Quinn (PQ) solution of the strong CP problem requires the existence of axions, which are viable candidates for dark matter. If the Nambu-Goldstone potential of the PQ model is replaced by a potential V(|Phi|) admitting a tracker solution, the scalar field |Phi| can account for dark energy, while the phase of Phi yields axion dark matter. If V is a supergravity (SUGRA) potential, the model essentially depends on a single parameter, the energy scale Lambda. Once we set Lambda approximately equal to 10(10) GeV at the quark-hadron transition, |Phi| naturally passes through values suitable to solve the strong CP problem, later growing to values providing fair amounts of dark matter and dark energy.
Variable sound speed in interacting dark energy models
Linton, Mark S.; Pourtsidou, Alkistis; Crittenden, Robert; Maartens, Roy
2018-04-01
We consider a self-consistent and physical approach to interacting dark energy models described by a Lagrangian, and identify a new class of models with variable dark energy sound speed. We show that if the interaction between dark energy in the form of quintessence and cold dark matter is purely momentum exchange this generally leads to a dark energy sound speed that deviates from unity. Choosing a specific sub-case, we study its phenomenology by investigating the effects of the interaction on the cosmic microwave background and linear matter power spectrum. We also perform a global fitting of cosmological parameters using CMB data, and compare our findings to ΛCDM.
Sourcing dark matter and dark energy from α-attractors
Energy Technology Data Exchange (ETDEWEB)
Mishra, Swagat S.; Sahni, Varun [Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007 (India); Shtanov, Yuri, E-mail: swagat@iucaa.in, E-mail: varun@iucaa.in, E-mail: shtanov@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Kiev 03680 (Ukraine)
2017-06-01
In [1], Kallosh and Linde drew attention to a new family of superconformal inflationary potentials, subsequently called α-attractors [2]. The α-attractor family can interpolate between a large class of inflationary models. It also has an important theoretical underpinning within the framework of supergravity. We demonstrate that the α-attractors have an even wider appeal since they may describe dark matter and perhaps even dark energy. The dark matter associated with the α-attractors, which we call α-dark matter (αDM), shares many of the attractive features of fuzzy dark matter, with V (φ) = ½ m {sup 2}φ{sup 2}, while having none of its drawbacks. Like fuzzy dark matter, αDM can have a large Jeans length which could resolve the cusp-core and substructure problems faced by standard cold dark matter. αDM also has an appealing tracker property which enables it to converge to the late-time dark matter asymptote, ( w ) ≅ 0, from a wide range of initial conditions. It thus avoids the enormous fine-tuning problems faced by the m {sup 2}φ{sup 2} potential in describing dark matter.
Sourcing dark matter and dark energy from α-attractors
International Nuclear Information System (INIS)
Mishra, Swagat S.; Sahni, Varun; Shtanov, Yuri
2017-01-01
In [1], Kallosh and Linde drew attention to a new family of superconformal inflationary potentials, subsequently called α-attractors [2]. The α-attractor family can interpolate between a large class of inflationary models. It also has an important theoretical underpinning within the framework of supergravity. We demonstrate that the α-attractors have an even wider appeal since they may describe dark matter and perhaps even dark energy. The dark matter associated with the α-attractors, which we call α-dark matter (αDM), shares many of the attractive features of fuzzy dark matter, with V (φ) = ½ m 2 φ 2 , while having none of its drawbacks. Like fuzzy dark matter, αDM can have a large Jeans length which could resolve the cusp-core and substructure problems faced by standard cold dark matter. αDM also has an appealing tracker property which enables it to converge to the late-time dark matter asymptote, ( w ) ≅ 0, from a wide range of initial conditions. It thus avoids the enormous fine-tuning problems faced by the m 2 φ 2 potential in describing dark matter.
Dark energy from gravitoelectromagnetic inflation?
International Nuclear Information System (INIS)
Membiela, A.; Bellini, M.
2008-01-01
Gravitoelectromagnetic Inflation (GI) was introduced to describe in a unified manner electromagnetic, gravitatory and inflation fields from a 5D vacuum state. On the other hand, the primordial origin and evolution of dark energy is today unknown. In this letter we show using GI that the zero modes of some redefined vector fields B i = A i /a produced during inflation could be the source of dark energy in the Universe.
Dark energy from gravitoelectromagnetic inflation?
Membiela, F. A.; Bellini, M.
2008-02-01
Gravitoectromagnetic Inflation (GI) was introduced to describe in an unified manner, electromagnetic, gravitatory and inflaton fields from a 5D vacuum state. On the other hand, the primordial origin and evolution of dark energy is today unknown. In this letter we show using GI that the zero modes of some redefined vector fields $B_i=A_i/a$ produced during inflation, could be the source of dark energy in the universe.
10th Symposium on Sources and Detection of Dark Matter and Dark Energy in the Universe
UCLA Dark Matter 2012
2012-01-01
These proceedings provide the latest results on dark matter and dark energy research. The UCLA Department of Physics and Astronomy hosted its tenth Dark Matter and Dark Energy conference in Marina del Rey and brought together all the leaders in the field. The symposium provided a scientific forum for the latest discussions in the field. Topics covered at the symposium: •Status of measurements of the equation of state of dark energy and new experiments •The search for missing energy events at the LHC and implications for dark matter search •Theoretical calculations on all forms of dark matter (SUSY, axions, sterile neutrinos, etc.) •Status of the indirect search for dark matter •Status of the direct search for dark matter in detectors around the world •The low-mass wimp search region •The next generation of very large dark matter detectors •New underground laboratories for dark matter search
Can the Existence of Dark Energy be Directly Detected?
Energy Technology Data Exchange (ETDEWEB)
Perl, Martin L.; /SLAC /KIPAC, Menlo Park
2011-11-23
The majority of astronomers and physicists accept the reality of dark energy and also believe that it can only be studied indirectly through observation of the motions of stars and galaxies. In this paper I open the experimental question of whether it is possible to directly detect dark energy through the presence of dark energy density. Two thirds of this paper outlines the major aspects of dark energy density as now comprehended by the astronomical and physics community. The final third summarizes various proposals for direct detection of dark energy density or its possible effects. At this time I do not have a fruitful answer to the question: Can the Existence of Dark Energy Be Directly Detected?
Effect of Dark Energy Perturbation on Cosmic Voids Formation
Endo, Takao; Nishizawa, Atsushi J.; Ichiki, Kiyotomo
2018-05-01
In this paper, we present the effects of dark energy perturbation on the formation and abundance of cosmic voids. We consider dark energy to be a fluid with a negative pressure characterised by a constant equation of state w and speed of sound c_s^2. By solving fluid equations for two components, namely, dark matter and dark energy fluids, we quantify the effects of dark energy perturbation on the sizes of top-hat voids. We also explore the effects on the size distribution of voids based on the excursion set theory. We confirm that dark energy perturbation negligibly affects the size evolution of voids; c_s^2=0 varies the size only by 0.1% as compared to the homogeneous dark energy model. We also confirm that dark energy perturbation suppresses the void size when w -1 (Basse et al. 2011). In contrast to the negligible impact on the size, we find that the size distribution function on scales larger than 10 Mpc/h highly depends on dark energy perturbation; compared to the homogeneous dark energy model, the number of large voids of radius 30Mpc is 25% larger for the model with w = -0.9 and c_s^2=0 while they are 20% less abundant for the model with w = -1.3 and c_s^2=0.
Dynamics of Interacting Tachyonic Teleparallel Dark Energy
International Nuclear Information System (INIS)
Banijamali, Ali
2014-01-01
We consider a tachyon scalar field which is nonminimally coupled to gravity in the framework of teleparallel gravity. We analyze the phase-space of the model, known as tachyonic teleparallel dark energy, in the presence of an interaction between dark energy and background matter. We find that although there exist some late-time accelerated attractor solutions, there is no scaling attractor. So, unfortunately interacting tachyonic teleparallel dark energy cannot alleviate the coincidence problem.
Interacting holographic dark energy in Brans-Dicke theory
International Nuclear Information System (INIS)
Sheykhi, Ahmad
2009-01-01
We study cosmological application of interacting holographic energy density in the framework of Brans-Dicke cosmology. We obtain the equation of state and the deceleration parameter of the holographic dark energy in a non-flat universe. As system's IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as L=ar(t). We find that the combination of Brans-Dicke field and holographic dark energy can accommodate w D =-1 crossing for the equation of state of noninteracting holographic dark energy. When an interaction between dark energy and dark matter is taken into account, the transition of w D to phantom regime can be more easily accounted for than when resort to the Einstein field equations is made.
Baryon acoustic oscillation intensity mapping of dark energy.
Chang, Tzu-Ching; Pen, Ue-Li; Peterson, Jeffrey B; McDonald, Patrick
2008-03-07
The expansion of the Universe appears to be accelerating, and the mysterious antigravity agent of this acceleration has been called "dark energy." To measure the dynamics of dark energy, baryon acoustic oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 10(9) individual galaxies, by observing the 21 cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three-dimensional intensity mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy.
Bouncing Cosmologies with Dark Matter and Dark Energy
Directory of Open Access Journals (Sweden)
Yi-Fu Cai
2016-12-01
Full Text Available We review matter bounce scenarios where the matter content is dark matter and dark energy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence, could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.
Dark energy and key physical parameters of clusters of galaxies
Bisnovatyi-Kogan, G. S.; Chernin, A. D.
2012-04-01
We study physics of clusters of galaxies embedded in the cosmic dark energy background. Under the assumption that dark energy is described by the cosmological constant, we show that the dynamical effects of dark energy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by dark energy: (1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; (2) the halo averaged density is equal to two densities of dark energy; (3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by dark energy: the maximum of the potential is located at the zero-gravity radius of the cluster.
Analysis of pilgrim dark energy models
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Jawad, Abdul [University of the Punjab, Department of Mathematics, Lahore (Pakistan)
2013-04-15
The proposal of pilgrim dark energy is based on the idea that phantom dark energy possesses enough resistive force to preclude black hole formation. We work on this proposal by choosing an interacting framework with cold dark matter and three cutoffs such as Hubble as well as event horizon and conformal age of the universe. We present a graphical analysis and focus our study on the pilgrim dark energy as well as interacting parameters. It is found that these parameters play an effective role on the equation of state parameter for exploring the phantom region of the universe. We also make the analysis of {omega}-{omega}' and point out freezing region in the {omega}-{omega}' plane. Finally, it turns out that the {Lambda}CDM is achieved in the statefinders plane for all models. (orig.)
Statefinder diagnosis for Ricci dark energy
International Nuclear Information System (INIS)
Feng Chaojun
2008-01-01
Statefinder diagnostic is a useful method which can differ one dark energy model from each others. In this Letter, we apply this method to a holographic dark energy model from Ricci scalar curvature, called the Ricci dark energy model (RDE). We plot the evolutionary trajectories of this model in the statefinder parameter-planes, and it is found that the parameter of this model plays a significant role from the statefinder viewpoint. In a very special case, the statefinder diagnostic fails to discriminate LCDM and RDE models, thus we apply a new diagnostic called the Om diagnostic proposed recently to this model in this case in Appendix A and it works well
Dark Energy from structure: a status report
Buchert, Thomas
2008-02-01
The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein’s theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field (“morphon field”) modeling Dark Energy. The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation. The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard model of cosmology; exact solutions and perturbative results modeling this instability lie in the right sector to explain Dark Energy from inhomogeneities. It is fair to say that, even if backreaction effects turn out to be less important than anticipated by some researchers, the concordance high-precision cosmology, the architecture of current N-body simulations, as well as standard perturbative approaches may all fall short in correctly describing the Late Universe.
The CHASE laboratory search for chameleon dark energy
International Nuclear Information System (INIS)
Steffen, Jason H.
2010-01-01
A scalar field is a favorite candidate for the particle responsible for dark energy. However, few theoretical means exist that can simultaneously explain the observed acceleration of the Universe and evade tests of gravity. The chameleon mechanism, whereby the properties of a particle depend upon the local environment, is one possible avenue. We present the results of the Chameleon Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark energy. CHASE marks a significant improvement other searches for chameleons both in terms of its sensitivity to the photon/chameleon coupling as well as its sensitivity to the classes of chameleon dark energy models and standard power-law models. Since chameleon dark energy is virtually indistinguishable from a cosmological constant, CHASE tests dark energy models in a manner not accessible to astronomical surveys.
The CHASE laboratory search for chameleon dark energy
Energy Technology Data Exchange (ETDEWEB)
Steffen, Jason [Fermi National Accelerator Laboratory - Fermilab, P.O. Box 500, Batavia, IL 60510-5011 (United States)
2010-07-01
A scalar field is a favorite candidate for the particle responsible for dark energy. However, few theoretical means exist that can simultaneously explain the observed acceleration of the Universe and evade tests of gravity. The chameleon mechanism, whereby the properties of a particle depend upon the local environment, is one possible avenue. I present the results of the Chameleon Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark energy. CHASE marks a significant improvement over other searches for chameleons both in terms of its sensitivity to the photon/chameleon coupling as well as its sensitivity to the classes of chameleon dark energy models and standard power-law models. Since chameleon dark energy is virtually indistinguishable from a cosmological constant, CHASE tests dark energy models in a manner not accessible to astronomical surveys. (author)
New interactions in the dark sector mediated by dark energy
International Nuclear Information System (INIS)
Brookfield, Anthony W.; Bruck, Carsten van de; Hall, Lisa M. H.
2008-01-01
Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example, two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a dark energy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles
Probing dark energy using convergence power spectrum and bi-spectrum
Energy Technology Data Exchange (ETDEWEB)
Dinda, Bikash R., E-mail: bikash@ctp-jamia.res.in [Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi-110025 (India)
2017-09-01
Weak lensing convergence statistics is a powerful tool to probe dark energy. Dark energy plays an important role to the structure formation and the effects can be detected through the convergence power spectrum, bi-spectrum etc. One of the most promising and simplest dark energy model is the ΛCDM . However, it is worth investigating different dark energy models with evolving equation of state of the dark energy. In this work, detectability of different dark energy models from ΛCDM model has been explored through convergence power spectrum and bi-spectrum.
On the Effective Equation of State of Dark Energy
DEFF Research Database (Denmark)
Sloth, Martin Snoager
2010-01-01
In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation of state of dark energy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of dark energy different from minus one, does not rule out vacuum...... energy as dark energy. It also indicates an interesting possibility that precise measurements of the infrared properties of dark energy can be used to probe the ultraviolet cutoff scale of effective quantum field theory coupled to gravity. In a toy model with a vacuum energy dominated universe...... with a Planck scale cutoff, the dark energy effective equation of state is -0.96....
Searching for dark matter-dark energy interactions: Going beyond the conformal case
van de Bruck, Carsten; Mifsud, Jurgen
2018-01-01
We consider several cosmological models which allow for nongravitational direct couplings between dark matter and dark energy. The distinguishing cosmological features of these couplings can be probed by current cosmological observations, thus enabling us to place constraints on these specific interactions which are composed of the conformal and disformal coupling functions. We perform a global analysis in order to independently constrain the conformal, disformal, and mixed interactions between dark matter and dark energy by combining current data from: Planck observations of the cosmic microwave background radiation anisotropies, a combination of measurements of baryon acoustic oscillations, a supernova type Ia sample, a compilation of Hubble parameter measurements estimated from the cosmic chronometers approach, direct measurements of the expansion rate of the Universe today, and a compilation of growth of structure measurements. We find that in these coupled dark-energy models, the influence of the local value of the Hubble constant does not significantly alter the inferred constraints when we consider joint analyses that include all cosmological probes. Moreover, the parameter constraints are remarkably improved with the inclusion of the growth of structure data set measurements. We find no compelling evidence for an interaction within the dark sector of the Universe.
Interacting holographic dark energy with logarithmic correction
Jamil, Mubasher; Farooq, M. Umar
2010-01-01
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is originally motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Using this new definition, we investigate the model of interacting dark energy and derive its effective equation of s...
Revisit of the interaction between holographic dark energy and dark matter
International Nuclear Information System (INIS)
Zhang, Zhenhui; Li, Xiao-Dong; Li, Song; Li, Miao; Zhang, Xin
2012-01-01
In this paper we investigate the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter. Firstly, we start with two simple models with the interaction terms Q∝ρ dm and Q∝ρ de , and then we move on to the general form Q∝ρ m α ρ de β . The cosmological constraints of the models are obtained from the joint analysis of the present Union2.1+BAO+CMB+H 0 data. We find that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level (CL) region. For all models we find c dm and ρ de is smaller, and the relative increment (decrement) amount of the energy in the dark matter component is constrained to be less than 9% (15%) at the 95.4% CL. By introducing the interaction, we find that even when c < 1 the big rip still can be avoided due to the existence of a de Sitter solution at z→−1. We show that this solution can not be accomplished in the two simple models, while for the general model such a solution can be achieved with a large β, and the big rip may be avoided at the 95.4% CL
Energy Technology Data Exchange (ETDEWEB)
Bernal, José Luis; Cuesta, Antonio J. [Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, Barcelona, E08028 Spain (Spain); Verde, Licia, E-mail: joseluis.bernal@icc.ub.edu, E-mail: liciaverde@icc.ub.edu, E-mail: ajcuesta@icc.ub.edu [ICREA (Institució Catalana de Recerca i Estudis Avançats), Passeig Lluís Companys, Barcelona, E-23 08010 Spain (Spain)
2016-02-01
We perform an empirical consistency test of General Relativity/dark energy by disentangling expansion history and growth of structure constraints. We replace each late-universe parameter that describes the behavior of dark energy with two meta-parameters: one describing geometrical information in cosmological probes, and the other controlling the growth of structure. If the underlying model (a standard wCDM cosmology with General Relativity) is correct, that is under the null hypothesis, the two meta-parameters coincide. If they do not, it could indicate a failure of the model or systematics in the data. We present a global analysis using state-of-the-art cosmological data sets which points in the direction that cosmic structures prefer a weaker growth than that inferred by background probes. This result could signify inconsistencies of the model, the necessity of extensions to it or the presence of systematic errors in the data. We examine all these possibilities. The fact that the result is mostly driven by a specific sub-set of galaxy clusters abundance data, points to the need of a better understanding of this probe.
"Dark energy" in the Local Void
Villata, M.
2012-05-01
The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter (˜5×1015 M ⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an initial "explosion" and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies of the Universe.
Nonlinear spherical perturbations in quintessence models of dark energy
Pratap Rajvanshi, Manvendra; Bagla, J. S.
2018-06-01
Observations have confirmed the accelerated expansion of the universe. The accelerated expansion can be modelled by invoking a cosmological constant or a dynamical model of dark energy. A key difference between these models is that the equation of state parameter w for dark energy differs from ‑1 in dynamical dark energy (DDE) models. Further, the equation of state parameter is not constant for a general DDE model. Such differences can be probed using the variation of scale factor with time by measuring distances. Another significant difference between the cosmological constant and DDE models is that the latter must cluster. Linear perturbation analysis indicates that perturbations in quintessence models of dark energy do not grow to have a significant amplitude at small length scales. In this paper we study the response of quintessence dark energy to non-linear perturbations in dark matter. We use a fully relativistic model for spherically symmetric perturbations. In this study we focus on thawing models. We find that in response to non-linear perturbations in dark matter, dark energy perturbations grow at a faster rate than expected in linear perturbation theory. We find that dark energy perturbation remains localised and does not diffuse out to larger scales. The dominant drivers of the evolution of dark energy perturbations are the local Hubble flow and a supression of gradients of the scalar field. We also find that the equation of state parameter w changes in response to perturbations in dark matter such that it also becomes a function of position. The variation of w in space is correlated with density contrast for matter. Variation of w and perturbations in dark energy are more pronounced in response to large scale perturbations in matter while the dependence on the amplitude of matter perturbations is much weaker.
Laboratory tests on dark energy
International Nuclear Information System (INIS)
Beck, Christian
2006-01-01
The physical nature of the currently observed dark energy in the universe is completely unclear, and many different theoretical models co-exist. Nevertheless, if dark energy is produced by vacuum fluctuations then there is a chance to probe some of its properties by simple laboratory tests based on Josephson junctions. These electronic devices can be used to perform 'vacuum fluctuation spectroscopy', by directly measuring a noise spectrum induced by vacuum fluctuations. One would expect to see a cutoff near 1.7 THz in the measured power spectrum, provided the new physics underlying dark energy couples to electric charge. The effect exploited by the Josephson junction is a subtile nonlinear mixing effect and has nothing to do with the Casimir effect or other effects based on van der Waals forces. A Josephson experiment of the suggested type will now be built, and we should know the result within the next 3 years
Interacting Dark Matter and q-Deformed Dark Energy Nonminimally Coupled to Gravity
Directory of Open Access Journals (Sweden)
Emre Dil
2016-01-01
Full Text Available In this paper, we propose a new approach to study the dark sector of the universe by considering the dark energy as an emerging q-deformed bosonic scalar field which is not only interacting with the dark matter, but also nonminimally coupled to gravity, in the framework of standard Einsteinian gravity. In order to analyze the dynamic of the system, we first give the quantum field theoretical description of the q-deformed scalar field dark energy and then construct the action and the dynamical structure of this interacting and nonminimally coupled dark sector. As a second issue, we perform the phase-space analysis of the model to check the reliability of our proposal by searching the stable attractor solutions implying the late-time accelerating expansion phase of the universe.
International Nuclear Information System (INIS)
Leon, Genly; Saridakis, Emmanuel N.
2010-01-01
We investigate several varying-mass dark matter particle models in the framework of phantom cosmology. We examine whether there exist late-time cosmological solutions, corresponding to an accelerating universe and possessing dark energy and dark matter densities of the same order. Imposing exponential or power-law potentials and exponential or power-law mass dependence, we conclude that the coincidence problem cannot be solved or even alleviated. Thus, if dark energy is attributed to the phantom paradigm, varying-mass dark matter models cannot fulfill the basic requirement that led to their construction.
Black holes in the presence of dark energy
International Nuclear Information System (INIS)
Babichev, E O; Dokuchaev, V I; Eroshenko, Yu N
2013-01-01
The new, rapidly developing field of theoretical research—studies of dark energy interacting with black holes (and, in particular, accreting onto black holes)–—is reviewed. The term 'dark energy' is meant to cover a wide range of field theory models, as well as perfect fluids with various equations of state, including cosmological dark energy. Various accretion models are analyzed in terms of the simplest test field approximation or by allowing back reaction on the black-hole metric. The behavior of various types of dark energy in the vicinity of Schwarzschild and electrically charged black holes is examined. Nontrivial effects due to the presence of dark energy in the black hole vicinity are discussed. In particular, a physical explanation is given of why the black hole mass decreases when phantom energy is being accreted, a process in which the basic energy conditions of the famous theorem of nondecreasing horizon area in classical black holes are violated. The theoretical possibility of a signal escaping from beneath the black hole event horizon is discussed for a number of dark energy models. Finally, the violation of the laws of thermodynamics by black holes in the presence of noncanonical fields is considered. (reviews of topical problems)
Dark energy in systems of galaxies
Chernin, A. D.
2013-11-01
The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.
Supersymmetric theories of neutrino dark energy
International Nuclear Information System (INIS)
Fardon, Rob; Nelson, Ann E.; Weiner, Neal
2006-01-01
We present a supersymmetric model of dark energy from Mass Varying Neutrinos which is stable against radiative corrections to masses and couplings, and free of dynamical instabilities. This is the only such model of dark energy involving fields with significant couplings to any standard model particle. We briefly discuss consequences for neutrino oscillations and solar neutrinos
Constraining dark energy with clusters: Complementarity with other probes
International Nuclear Information System (INIS)
Cunha, Carlos; Huterer, Dragan; Frieman, Joshua A.
2009-01-01
The Figure of Merit Science Working Group recently forecast the constraints on dark energy that will be achieved prior to the Joint Dark Energy Mission by ground-based experiments that exploit baryon acoustic oscillations, type Ia supernovae, and weak gravitational lensing. We show that cluster counts from ongoing and near-future surveys should provide robust, complementary dark energy constraints. In particular, we find that optimally combined optical and Sunyaev-Zel'dovich effect cluster surveys should improve the Dark Energy Task Force figure of merit for pre-Joint Dark Energy Mission projects by a factor of 2 even without prior knowledge of the nuisance parameters in the cluster mass-observable relation. Comparable improvements are achieved in the forecast precision of parameters specifying the principal component description of the dark energy equation of state parameter, as well as in the growth index γ. These results indicate that cluster counts can play an important complementary role in constraining dark energy and modified gravity even if the associated systematic errors are not strongly controlled.
Probing dark energy via galaxy cluster outskirts
Morandi, Andrea; Sun, Ming
2016-04-01
We present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056 definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmological test has the capacity to provide a generational leap forward in our understanding of the equation of state of dark energy.
Signature of the interaction between dark energy and dark matter in galaxy clusters
International Nuclear Information System (INIS)
Abdalla, Elcio; Abramo, L. Raul; Sodre, Laerte; Wang Bin
2009-01-01
We investigate the influence of an interaction between dark energy and dark matter upon the dynamics of galaxy clusters. We obtain the general Layser-Irvine equation in the presence of interactions, and find how, in that case, the virial theorem stands corrected. Using optical, X-ray and weak lensing data from 33 relaxed galaxy clusters, we put constraints on the strength of the coupling between the dark sectors. Available data suggests that this coupling is small but positive, indicating that dark energy might be decaying into dark matter. Systematic effects between the several mass estimates, however, should be better known, before definitive conclusions on the magnitude and significance of this coupling could be established
Holographic dark energy in the DGP model
International Nuclear Information System (INIS)
Cruz, Norman; Lepe, Samuel; Pena, Francisco; Avelino, Arturo
2012-01-01
The braneworld model proposed by Dvali, Gabadadze, and Porrati leads to an accelerated universe without cosmological constant or any other form of dark energy. Nevertheless, we have investigated the consequences of this model when an holographic dark energy is included, taking the Hubble scale as IR cutoff. We have found that the holographic dark energy leads to an accelerated flat universe (de Sitter-like expansion) for the two branches: ε=±1, of the DGP model. Nevertheless, in universes with no null curvature the dark energy presents an EoS corresponding to a phantom fluid during the present era and evolving to a de Sitter-like phase for future cosmic time. In the special case in which the holographic parameter c is equal to one we have found a sudden singularity in closed universes. In this case the expansion is decelerating. (orig.)
Holographic dark energy in the DGP model
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Universidad de Santiago, Departamento de Fisica, Facultad de Ciencia, Santiago (Chile); Lepe, Samuel [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Facultad de Ciencias, Valparaiso (Chile); Pena, Francisco [Universidad de La Frontera, Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Avda. Francisco Salazar 01145, Casilla 54-D, Temuco (Chile); Avelino, Arturo [Universidad de Guanajuato, Departamento de Fisica, DCI, Codigo Postal 37150, Leon, Guanajuato (Mexico)
2012-09-15
The braneworld model proposed by Dvali, Gabadadze, and Porrati leads to an accelerated universe without cosmological constant or any other form of dark energy. Nevertheless, we have investigated the consequences of this model when an holographic dark energy is included, taking the Hubble scale as IR cutoff. We have found that the holographic dark energy leads to an accelerated flat universe (de Sitter-like expansion) for the two branches: {epsilon}={+-}1, of the DGP model. Nevertheless, in universes with no null curvature the dark energy presents an EoS corresponding to a phantom fluid during the present era and evolving to a de Sitter-like phase for future cosmic time. In the special case in which the holographic parameter c is equal to one we have found a sudden singularity in closed universes. In this case the expansion is decelerating. (orig.)
Ryuichi, TAKAHASHI; Department of Physics and Astrophysics, Nagoya University
2008-01-01
We investigate the third-order density perturbation and the one-loop correction to the linear power spectrum in the dark-energy cosmological model. Our main interest is to understand the dark-energy effect on baryon acoustic oscillations in a quasi-nonlinear regime (k≈0.1h/Mpc). Analytical solutions and simple fitting formulae are presented for the dark-energy model with the general time-varying equation of state w(a). It turns out that the power spectrum coincides with the approximate res...
Guo, Juan-Juan; Zhang, Jing-Fei; Li, Yun-He; He, Dong-Ze; Zhang, Xin
2018-03-01
We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b( a) = b 0 a+ b e(1- a), where at the early-time the coupling is given by a constant b e and today the coupling is described by another constant b 0. We explore six specific models with (i) Q = b( a) H 0 ρ 0, (ii) Q = b( a) H 0 ρ de, (iii) Q = b( a) H 0 ρ c, (iv) Q = b( a) Hρ 0, (v) Q = b( a) H ρ de, and (vi) Q = b( a) Hρ c. The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the Hubble constant direct measurement. We find that, for all the models, we have b 0 0 at around the 1 σ level, and b 0 and b e are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1 σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.
Induced gravity and the attractor dynamics of dark energy/dark matter
International Nuclear Information System (INIS)
Cervantes-Cota, Jorge L.; Putter, Roland de; Linder, Eric V.
2010-01-01
Attractor solutions that give dynamical reasons for dark energy to act like the cosmological constant, or behavior close to it, are interesting possibilities to explain cosmic acceleration. Coupling the scalar field to matter or to gravity enlarges the dynamical behavior; we consider both couplings together, which can ameliorate some problems for each individually. Such theories have also been proposed in a Higgs-like fashion to induce gravity and unify dark energy and dark matter origins. We explore restrictions on such theories due to their dynamical behavior compared to observations of the cosmic expansion. Quartic potentials in particular have viable stability properties and asymptotically approach general relativity
Energy Technology Data Exchange (ETDEWEB)
Cahn, Robert N.; de Putter, Roland; Linder, Eric V.
2008-07-08
Scalar field dark energy evolving from a long radiation- or matter-dominated epoch has characteristic dynamics. While slow-roll approximations are invalid, a well defined field expansion captures the key aspects of the dark energy evolution during much of the matter-dominated epoch. Since this behavior is determined, it is not faithfully represented if priors for dynamical quantities are chosen at random. We demonstrate these features for both thawing and freezing fields, and for some modified gravity models, and unify several special cases in the literature.
Embrace the Dark Side: Advancing the Dark Energy Survey
Suchyta, Eric
The Dark Energy Survey (DES) is an ongoing cosmological survey intended to study the properties of the accelerated expansion of the Universe. In this dissertation, I present work of mine that has advanced the progress of DES. First is an introduction, which explores the physics of the cosmos, as well as how DES intends to probe it. Attention is given to developing the theoretical framework cosmologists use to describe the Universe, and to explaining observational evidence which has furnished our current conception of the cosmos. Emphasis is placed on the dark sector - dark matter and dark energy - the content of the Universe not explained by the Standard Model of particle physics. As its name suggests, the Dark Energy Survey has been specially designed to measure the properties of dark energy. DES will use a combination of galaxy cluster, weak gravitational lensing, angular clustering, and supernovae measurements to derive its state of the art constraints, each of which is discussed in the text. The work described in this dissertation includes science measurements directly related to the first three of these probes. The dissertation presents my contributions to the readout and control system of the Dark Energy Camera (DECam); the name of this software is SISPI. SISPI uses client-server and publish-subscribe communication patterns to coordinate and command actions among the many hardware components of DECam - the survey instrument for DES, a 570 megapixel CCD camera, mounted at prime focus of the Blanco 4-m Telescope. The SISPI work I discuss includes coding applications for DECam's filter changer mechanism and hexapod, as well as developing the Scripts Editor, a GUI application for DECam users to edit and export observing sequence SISPI can load and execute. Next, the dissertation describes the processing of early DES data, which I contributed. This furnished the data products used in the first-completed DES science analysis, and contributed to improving the
Interacting holographic dark energy models: a general approach
Som, S.; Sil, A.
2014-08-01
Dark energy models inspired by the cosmological holographic principle are studied in homogeneous isotropic spacetime with a general choice for the dark energy density . Special choices of the parameters enable us to obtain three different holographic models, including the holographic Ricci dark energy (RDE) model. Effect of interaction between dark matter and dark energy on the dynamics of those models are investigated for different popular forms of interaction. It is found that crossing of phantom divide can be avoided in RDE models for β>0.5 irrespective of the presence of interaction. A choice of α=1 and β=2/3 leads to a varying Λ-like model introducing an IR cutoff length Λ -1/2. It is concluded that among the popular choices an interaction of the form Q∝ Hρ m suits the best in avoiding the coincidence problem in this model.
Observational constraints on dark matter-dark energy scattering cross section
Energy Technology Data Exchange (ETDEWEB)
Kumar, Suresh [BITS Pilani, Department of Mathematics, Rajasthan (India); Nunes, Rafael C. [Universidade Federal de Juiz de Fora, Departamento de Fisica, Juiz de Fora, MG (Brazil)
2017-11-15
In this letter, we report precise and robust observational constraints on the dark matter-dark energy scattering cross section, using the latest data from cosmic microwave background (CMB) Planck temperature and polarization, baryon acoustic oscillations (BAO) measurements and weak gravitational lensing data from Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). The scattering scenario consists of a pure momentum exchange between the dark components, and we find σ{sub d} < 10{sup -29} cm{sup 2} (m{sub dm}c{sup 2}/GeV) at 95% CL from the joint analysis (CMB + BAO + CFHTLenS), where m{sub dm} is a typical dark matter particle mass. We notice that the scattering among the dark components may influence the growth of large scale structure in the Universe, leaving the background cosmology unaltered. (orig.)
Geodesics of black holes with dark energy
Ghaderi, K.
2017-12-01
Dark energy is the most popular hypothesis to explain recent observations suggesting that the world will increasingly expand. One of the models of dark energy is quintessence which is highly plausible. In this paper, we investigate the effect of dark energy on the null geodesics of Schwarzschild, Reissner-Nordström, Schwarzschild-de Sitter and Bardeen black holes. Using the definition of effective potential, the radius of the circular orbits, the period, the instability of the circular orbits, the force exerted on the photons and the deviation angle of light in quintessence field are calculated and the results are analyzed and discussed.
2012-01-01
Particle Physics Foundations of Dark Matter, Dark Energy, and Inflation (1/3), by Dr. Edward (Rocky) Kolb (University of Chicago). Wednesday, May 9, 2012 from 11:00 to 12:00 (Europe/Zurich) at CERN ( 500-1-001 - Main Auditorium ) Ninety-five percent of the present mass-energy density of the Universe is dark. Twenty-five percent is in the form of dark matter holding together galaxies and other large scale structures, and 70% is in the form of dark energy driving an accelerated expansion of the universe. Dark matter and dark energy cannot be explained within the standard model of particle physics. In the first lecture I will review the evidence for dark matter and the observations that point to an explanation in the form of cold dark matter. I will then describe the expected properties of a hypothetical Weakly-Interacting Massive Particle, or WIMP, and review experimental and observational approaches to test the hypothesis. Finally, I will discus...
Holographic dark energy and f(R) gravity
Energy Technology Data Exchange (ETDEWEB)
Aghamohammadi, A [Faculty of Science, Islamic Azad University of Sanandaj, Sanandaj (Iran, Islamic Republic of); Saaidi, Kh, E-mail: ksaaidi@uok.ac.ir, E-mail: agha35484@yahoo.com [Department of Physics, Faculty of Science, University of Kurdistan, Sanandaj (Iran, Islamic Republic of)
2011-02-15
We investigate the corresponding relation between f(R) gravity and holographic dark energy. We introduce a type of energy density from f(R) that has the same role as holographic dark energy. We obtain the differential equation that specifies the evolution of the introduced energy density parameter based on a varying gravitational constant. We discover the relation for the equation of state parameter for low redshifts that contains varying G correction.
Dark energy from quantum matter
International Nuclear Information System (INIS)
Dappiaggi, Claudio; Hack, Thomas-Paul; Moeller, Jan; Pinamonti, Nicola
2010-07-01
We study the backreaction of free quantum fields on a flat Robertson-Walker spacetime. Apart from renormalization freedom, the vacuum energy receives contributions from both the trace anomaly and the thermal nature of the quantum state. The former represents a dynamical realisation of dark energy, while the latter mimics an effective dark matter component. The semiclassical dynamics yield two classes of asymptotically stable solutions. The first reproduces the CDM model in a suitable regime. The second lacks a classical counterpart, but is in excellent agreement with recent observations. (orig.)
Dark energy from quantum matter
Energy Technology Data Exchange (ETDEWEB)
Dappiaggi, Claudio; Hack, Thomas-Paul [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Moeller, Jan [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany). Gruppe Theorie; Pinamonti, Nicola [Rome-2 Univ. (Italy). Dipt. di Matematica
2010-07-15
We study the backreaction of free quantum fields on a flat Robertson-Walker spacetime. Apart from renormalization freedom, the vacuum energy receives contributions from both the trace anomaly and the thermal nature of the quantum state. The former represents a dynamical realisation of dark energy, while the latter mimics an effective dark matter component. The semiclassical dynamics yield two classes of asymptotically stable solutions. The first reproduces the CDM model in a suitable regime. The second lacks a classical counterpart, but is in excellent agreement with recent observations. (orig.)
A Unified Model of Phantom Energy and Dark Matter
Chaves, Max; Singleton, Douglas
2008-01-01
To explain the acceleration of the cosmological expansion researchers have considered an unusual form of mass-energy generically called dark energy. Dark energy has a ratio of pressure over mass density which obeys w = p/ρ theories based on graded Lie algebras naturally have such a negative kinetic energy and thus give a model for phantom energy in a less ad hoc manner. We find that the model also contains ordinary scalar fields and anti-commuting (Grassmann) vector fields which act as a form of two component dark matter. Thus from a gauge theory based o! n a graded algebra we naturally obtained both phantom energy and dark matter.
Evolution of holographic dark energy with interaction term Q∝ Hρde ...
Indian Academy of Sciences (India)
A flat FLRW Universe with dark matter and dark energy, which are interacting witheach other, is considered. The dark energy is represented by the holographic dark energy model and the interaction term is taken as proportional to the dark energy density. We have studied the cosmological evolution and analysed the ...
Testing the Cosmic Coincidence Problem and the Nature of Dark Energy
International Nuclear Information System (INIS)
Dalal, Neal; Abazajian, Kevork; Jenkins, Elizabeth; Manohar, Aneesh V.
2001-01-01
Dark energy models which alter the relative scaling behavior of dark energy and matter could provide a natural solution to the cosmic coincidence problem -- why the densities of dark energy and dark matter are comparable today. A generalized class of dark energy models is introduced which allows noncanonical scaling of the ratio of dark matter and dark energy with the Robertson-Walker scale factor a(t) . We show that determining whether there is a coincidence problem, and the extent of cosmic coincidence, can be addressed by several forthcoming experiments
A Unified Model of Phantom Energy and Dark Matter
Directory of Open Access Journals (Sweden)
Douglas Singleton
2008-01-01
Full Text Available To explain the acceleration of the cosmological expansion researchers have considered an unusual form of mass-energy generically called dark energy. Dark energy has a ratio of pressure over mass density which obeys $w=p/ ho <-1/3$. This form of mass-energy leads to accelerated expansion. An extreme form of dark energy, called phantom energy, has been proposed which has $w=p/ ho <-1$. This possibility is favored by the observational data. The simplest model for phantom energy involves the introduction of a scalar field with a negative kinetic energy term. Here we show that theories based on graded Lie algebras naturally have such a negative kinetic energy and thus give a model for phantom energy in a less ad hoc manner. We find that the model also contains ordinary scalar fields and anti-commuting (Grassmann vector fields which act as a form of two component dark matter. Thus from a gauge theory based on a graded algebra we naturally obtained both phantom energy and dark matter.
The DarkSide-50 Experiment: Electron Recoil Calibrations and A Global Energy Variable
Energy Technology Data Exchange (ETDEWEB)
Hackett, Brianne Rae [Hawaii U.
2017-01-01
Over the course of decades, there has been mounting astronomical evidence for non-baryonic dark matter, yet its precise nature remains elusive. A favored candidate for dark matter is the Weakly Interacting Massive Particle (WIMP) which arises naturally out of extensions to the Standard Model. WIMPs are expected to occasionally interact with particles of normal matter through nuclear recoils. DarkSide-50 aims to detect this type of particle through the use of a two-phase liquid argon time projection chamber. To make a claim of discovery, an accurate understanding of the background and WIMP search region is imperative. Knowledge of the backgrounds is done through extensive studies of DarkSide-50's response to electron and nuclear recoils. The CALibration Insertion System (CALIS) was designed and built for the purpose of introduc- ing radioactive sources into or near the detector in a joint eort between Fermi National Laboratory (FNAL) and the University of Hawai'i at Manoa. This work describes the testing, installation, and commissioning of CALIS at the Laboratori Nazionali del Gran Sasso. CALIS has been used in mul- tiple calibration campaigns with both neutron and sources. In this work, DarkSide-50's response to electron recoils, which are important for background estimations, was studied through the use of calibration sources by constructing a global energy variable which takes into account the anti- correlation between scintillation and ionization signals produced by interactions in the liquid argon. Accurately reconstructing the event energy correlates directly with quantitatively understanding the WIMP sensitivity in DarkSide-50. This work also validates the theoretically predicted decay spectrum of 39Ar against 39Ar decay data collected in the early days of DarkSide-50 while it was lled with atmospheric argon; a validation of this type is not readily found in the literature. Finally, we show how well the constructed energy variable can predict
Entanglement in holographic dark energy models
Energy Technology Data Exchange (ETDEWEB)
Horvat, R., E-mail: horvat@lei3.irb.h [Rudjer Boskovic Institute, P.O. Box 180, 10002 Zagreb (Croatia)
2010-10-18
We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the dark-energy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantum-mechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoid virtually any application in other cosmological epochs or particle-physics phenomena. The problem of negative entropies for the non-phantom stuff is also discussed.
Entanglement in holographic dark energy models
International Nuclear Information System (INIS)
Horvat, R.
2010-01-01
We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the dark-energy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantum-mechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoid virtually any application in other cosmological epochs or particle-physics phenomena. The problem of negative entropies for the non-phantom stuff is also discussed.
Coupled dark matter-dark energy in light of near universe observations
International Nuclear Information System (INIS)
Honorez, Laura Lopez; Reid, Beth A.; Verde, Licia; Jimenez, Raul; Mena, Olga
2010-01-01
Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified — and thus can be probed by a combination of tests for the expansion history and the growth of structure —, there is a class of dark coupling models where gravity is still GR, but the growth of perturbations is, in principle modified. While this effect is small in the specific models we have considered, one should bear in mind that an inconsistency between reconstructed expansion history and growth may not uniquely indicate deviations from GR. Our low redshift constraints arise from cosmic velocities, redshift space distortions and dark matter abundance in galaxy voids. We find that current data constrain the dimensionless coupling to be |ξ| < 0.2, but prospects from forthcoming data are for a significant improvement. Future, precise measurements of the Hubble constant, combined with high-precision constraints on the growth of structure, could provide the key to rule out dark coupling models which survive other tests. We shall exploit as well weak equivalence principle violation arguments, which have the potential to highly disfavour a broad family of coupled models
Condensate cosmology: Dark energy from dark matter
International Nuclear Information System (INIS)
Bassett, Bruce A.; Parkinson, David; Kunz, Martin; Ungarelli, Carlo
2003-01-01
Imagine a scenario in which the dark energy forms via the condensation of dark matter at some low redshift. The Compton wavelength therefore changes from small to very large at the transition, unlike quintessence or metamorphosis. We study cosmic microwave background (CMB), large scale structure, supernova and radio galaxy constraints on condensation by performing a four parameter likelihood analysis over the Hubble constant and the three parameters associated with Q, the condensate field: Ω Q , w f and z t (energy density and equation of state today, and redshift of transition). Condensation roughly interpolates between ΛCDM (for large z t ) and SCDM (low z t ) and provides a slightly better fit to the data than ΛCDM. We confirm that there is no degeneracy in the CMB between H and z t and discuss the implications of late-time transitions for the Lyman-α forest. Finally we discuss the nonlinear phase of both condensation and metamorphosis, which is much more interesting than in standard quintessence models
Observational constraints on dark energy and cosmic curvature
International Nuclear Information System (INIS)
Wang Yun; Mukherjee, Pia
2007-01-01
Current observational bounds on dark energy depend on our assumptions about the curvature of the universe. We present a simple and efficient method for incorporating constraints from cosmic microwave background (CMB) anisotropy data and use it to derive constraints on cosmic curvature and dark energy density as a free function of cosmic time using current CMB, Type Ia supernova (SN Ia), and baryon acoustic oscillation data. We show that there are two CMB shift parameters, R≡√(Ω m H 0 2 )r(z CMB ) (the scaled distance to recombination) and l a ≡πr(z CMB )/r s (z CMB ) (the angular scale of the sound horizon at recombination), with measured values that are nearly uncorrelated with each other. Allowing nonzero cosmic curvature, the three-year WMAP (Wilkinson Microwave Anisotropy Probe) data give R=1.71±0.03, l a =302.5±1.2, and Ω b h 2 =0.02173±0.00082, independent of the dark energy model. The corresponding bounds for a flat universe are R=1.70±0.03, l a =302.2±1.2, and Ω b h 2 =0.022±0.00082. We give the covariance matrix of (R,l a ,Ω b h 2 ) from the three-year WMAP data. We find that (R,l a ,Ω b h 2 ) provide an efficient and intuitive summary of CMB data as far as dark energy constraints are concerned. Assuming the Hubble Space Telescope (HST) prior of H 0 =72±8 (km/s) Mpc -1 , using 182 SNe Ia (from the HST/GOODS program, the first year Supernova Legacy Survey, and nearby SN Ia surveys), (R,l a ,Ω b h 2 ) from WMAP three-year data, and SDSS (Sloan Digital Sky Survey) measurement of the baryon acoustic oscillation scale, we find that dark energy density is consistent with a constant in cosmic time, with marginal deviations from a cosmological constant that may reflect current systematic uncertainties or true evolution in dark energy. A flat universe is allowed by current data: Ω k =-0.006 -0.012-0.025 +0.013+0.025 for assuming that the dark energy equation of state w X (z) is constant, and Ω k =-0.002 -0.018-0.032 +0.018+0.041 for w X (z
Interacting ghost dark energy in Brans-Dicke theory
International Nuclear Information System (INIS)
Ebrahimi, Esmaeil; Sheykhi, Ahmad
2011-01-01
We investigate the QCD ghost model of dark energy in the framework of Brans-Dicke cosmology. First, we study the non-interacting ghost dark energy in a flat Brans-Dicke theory. In this case we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of ghost energy density. Interestingly enough, we find that the equation of state parameter of the non-interacting ghost dark energy can cross the phantom line (w D =-1) provided the parameters of the model are chosen suitably. Then, we generalize the study to the interacting ghost dark energy in both flat and non-flat Brans-Dicke framework and find out that the transition of w D to phantom regime can be more easily achieved for than when resort to the Einstein field equations is made.
Energy Technology Data Exchange (ETDEWEB)
Wechsler, Risa
2007-10-30
What is the Universe made of? This question has been asked as long as humans have been questioning, and astronomers and physicists are finally converging on an answer. The picture which has emerged from numerous complementary observations over the past decade is a surprising one: most of the matter in the Universe isn't visible, and most of the Universe isn't even made of matter. In this talk, I will explain what the rest of this stuff, known as 'Dark Energy' is, how it is related to the so-called 'Dark Matter', how it impacts the evolution of the Universe, and how we can study the dark universe using observations of light from current and future telescopes.
Fingerprinting dark energy. II. Weak lensing and galaxy clustering tests
International Nuclear Information System (INIS)
Sapone, Domenico; Kunz, Martin; Amendola, Luca
2010-01-01
The characterization of dark energy is a central task of cosmology. To go beyond a cosmological constant, we need to introduce at least an equation of state and a sound speed and consider observational tests that involve perturbations. If dark energy is not completely homogeneous on observable scales, then the Poisson equation is modified and dark matter clustering is directly affected. One can then search for observational effects of dark energy clustering using dark matter as a probe. In this paper we exploit an analytical approximate solution of the perturbation equations in a general dark energy cosmology to analyze the performance of next-decade large-scale surveys in constraining equation of state and sound speed. We find that tomographic weak lensing and galaxy redshift surveys can constrain the sound speed of the dark energy only if the latter is small, of the order of c s < or approx. 0.01 (in units of c). For larger sound speeds the error grows to 100% and more. We conclude that large-scale structure observations contain very little information about the perturbations in canonical scalar field models with a sound speed of unity. Nevertheless, they are able to detect the presence of cold dark energy, i.e. a dark energy with nonrelativistic speed of sound.
Metamaterial Model of Tachyonic Dark Energy
Directory of Open Access Journals (Sweden)
Igor I. Smolyaninov
2014-02-01
Full Text Available Dark energy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of dark energy are based on tachyonic fields interacting with itself and normal (bradyonic matter. Here, we propose an experimental model of tachyonic dark energy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2 + 1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated tachyonic and bradyonic sectors in the long wavelength infrared range. This system may be used as a laboratory model of inflation and late time acceleration of the universe.
Dark energy and dark matter from hidden symmetry of gravity model with a non-Riemannian volume form
Energy Technology Data Exchange (ETDEWEB)
Guendelman, Eduardo [Ben-Gurion University of the Negev, Department of Physics, Beersheba (Israel); Nissimov, Emil; Pacheva, Svetlana [Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy, Sofia (Bulgaria)
2015-10-15
We show that dark energy and dark matter can be described simultaneously by ordinary Einstein gravity interacting with a single scalar field provided the scalar field Lagrangian couples in a symmetric fashion to two different spacetime volume forms (covariant integration measure densities) on the spacetime manifold - one standard Riemannian given by √(-g) (square root of the determinant of the pertinent Riemannian metric) and another non-Riemannian volume form independent of the Riemannian metric, defined in terms of an auxiliary antisymmetric tensor gauge field of maximal rank. Integration of the equations of motion of the latter auxiliary gauge field produce an a priori arbitrary integration constant that plays the role of a dynamically generated cosmological constant or dark energy. Moreover, the above modified scalar field action turns out to possess a hidden Noether symmetry whose associated conserved current describes a pressureless ''dust'' fluid which we can identify with the dark matter completely decoupled from the dark energy. The form of both the dark energy and dark matter that results from the above class of models is insensitive to the specific form of the scalar field Lagrangian. By adding an appropriate perturbation, which breaks the above hidden symmetry and along with this couples dark matter and dark energy, we also suggest a way to obtain growing dark energy in the present universe's epoch without evolution pathologies. (orig.)
International Nuclear Information System (INIS)
Neves, Rui; Vaz, Cenalo
2006-01-01
In the Randall-Sundrum scenario, we analyse the dynamics of an AdS 5 braneworld when conformal matter fields propagate in five dimensions. We show that conformal fields of weight -4 are associated with stable geometries which describe the dynamics of inhomogeneous dust, generalized dark radiation and homogeneous polytropic dark energy on a spherically symmetric 3-brane embedded in the compact AdS 5 orbifold. We discuss aspects of the radion stability conditions and of the localization of gravity in the vicinity of the brane
Dark Energy, Dark Matter and Science with Constellation-X
Cardiff, Ann Hornschemeier
2005-01-01
Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the dark energy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as "cosmic feedback" whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of Dark Energy.
Dark energy and the quietness of the local Hubble flow
International Nuclear Information System (INIS)
Axenides, M.; Perivolaropoulos, L.
2002-01-01
The linearity and quietness of the local ( X (t 0 ) of dark energy obeying the time independent equation of state p X =wρ X . We find that dark energy can indeed cool the LHF. However the dark energy parameter values required to make the predicted velocity dispersion consistent with the observed value v rms ≅40 km/s have been ruled out by other observational tests constraining the dark energy parameters w and Ω X . Therefore despite the claims of recent qualitative studies, dark energy with time independent equation of state cannot by itself explain the quietness and linearity of the local Hubble flow
Dark energy interacting with dark matter and a third fluid: Possible EoS for this component
International Nuclear Information System (INIS)
Cruz, Norman; Lepe, Samuel; Pena, Francisco
2011-01-01
A cosmological model of dark energy interacting with dark matter and another general component of the universe is considered. The equations for the coincidence parameters r and s, which represent the ratios between dark energy and dark matter and the other cosmic fluid respectively, are analyzed in terms of the stability of stationary solutions. The obtained general results allow to shed some light on the equations of state of the three interacting fluids, due to the constraints imposed by the stability of the solutions. We found that for an interaction proportional to the sum of the dark energy density and the third fluid density, the hypothetical fluid must have positive pressure, which leads naturally to a cosmological scenario with radiation, unparticle or even some form of warm dark matter as the third interacting fluid.
Dark energy interacting with dark matter and a third fluid: Possible EoS for this component
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman, E-mail: ncruz@lauca.usach.c [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile); Lepe, Samuel, E-mail: slepe@ucv.c [Instituto de Fisica, Facultad de Ciencias, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Pena, Francisco, E-mail: fcampos@ufro.c [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de La Frontera, Avda. Francisco Salazar 01145, Casilla 54-D, Temuco (Chile)
2011-05-09
A cosmological model of dark energy interacting with dark matter and another general component of the universe is considered. The equations for the coincidence parameters r and s, which represent the ratios between dark energy and dark matter and the other cosmic fluid respectively, are analyzed in terms of the stability of stationary solutions. The obtained general results allow to shed some light on the equations of state of the three interacting fluids, due to the constraints imposed by the stability of the solutions. We found that for an interaction proportional to the sum of the dark energy density and the third fluid density, the hypothetical fluid must have positive pressure, which leads naturally to a cosmological scenario with radiation, unparticle or even some form of warm dark matter as the third interacting fluid.
Classifying the future of universes with dark energy
International Nuclear Information System (INIS)
Chiba, Takeshi; Takahashi, Ryuichi; Sugiyama, Naoshi
2005-01-01
We classify the future of the universe for general cosmological models including matter and dark energy. If the equation of state of dark energy is less then -1, the age of the universe becomes finite. We compute the rest of the age of the universe for such universe models. The behaviour of the future growth of matter density perturbation is also studied. We find that the collapse of the spherical overdensity region is greatly changed if the equation of state of dark energy is less than -1
The Dark Energy Survey: more than dark energy – an overview
Energy Technology Data Exchange (ETDEWEB)
Vikram, Vinu; Abbott, T; Abdalla, F. B.; Allam, S.; Aleksic, J.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Levy, A.
2016-03-21
This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from ‘Science Verification’, and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).
Spherical collapse of dark energy with an arbitrary sound speed
International Nuclear Information System (INIS)
Basse, Tobias; Bjælde, Ole Eggers; Wong, Yvonne Y.Y.
2011-01-01
We consider a generic type of dark energy fluid, characterised by a constant equation of state parameter w and sound speed c s , and investigate the impact of dark energy clustering on cosmic structure formation using the spherical collapse model. Along the way, we also discuss in detail the evolution of dark energy perturbations in the linear regime. We find that the introduction of a finite sound speed into the picture necessarily induces a scale-dependence in the dark energy clustering, which in turn affects the dynamics of the spherical collapse in a scale-dependent way. As with other, more conventional fluids, we can define a Jeans scale for the dark energy clustering, and hence a Jeans mass M J for the dark matter which feels the effect of dark energy clustering via gravitational interactions. For bound objects (halos) with masses M >> M J , the effect of dark energy clustering is maximal. For those with M J , the dark energy component is effectively homogeneous, and its role in the formation of these structures is reduced to its effects on the Hubble expansion rate. To compute quantitatively the virial density and the linearly extrapolated threshold density, we use a quasi-linear approach which is expected to be valid up to around the Jeans mass. We find an interesting dependence of these quantities on the halo mass M, given some w and c s . The dependence is the strongest for masses lying in the vicinity of M ∼ M J . Observing this M-dependence will be a tell-tale sign that dark energy is dynamic, and a great leap towards pinning down its clustering properties
Interacting dark energy and the expansion of the universe
Silbergleit, Alexander S
2017-01-01
This book presents a high-level study of cosmology with interacting dark energy and no additional fields. It is known that dark energy is not necessarily uniform when other sources of gravity are present: interaction with matter leads to its variation in space and time. The present text studies the cosmological implications of this circumstance by analyzing cosmological models in which the dark energy density interacts with matter and thus changes with the time. The book also includes a translation of a seminal article about the remarkable life and work of E.B. Gliner, the first person to suggest the concept of dark energy in 1965.
Hessence: a new view of quintom dark energy
International Nuclear Information System (INIS)
Wei Hao; Cai Ronggen; Zeng Dingfang
2005-01-01
Recently a lot of attention has been given to building a dark energy model in which the equation-of-state parameter w can cross the phantom divide w = -1. One of the models to realize crossing the phantom divide is called the quintom model, in which two real scalar fields appear, one is a normal scalar field and the other is a phantom-type scalar field. In this paper we propose a non-canonical complex scalar field as the dark energy, which we dub 'hessence', to implement crossing the phantom divide, in a similar sense as the quintom dark energy model. In the hessence model, the dark energy is described by a single field with an internal degree of freedom rather than two independent real scalar fields. However, the hessence is different from an ordinary complex scalar field, we show that the hessence can avoid the difficulty of the Q-ball formation which gives trouble to the spintessence model (an ordinary complex scalar field acts as the dark energy). Furthermore, we find that, by choosing a proper potential, the hessence could correspond to a Chaplygin gas at late times
Imprints of dark energy on the structuring of the universe
International Nuclear Information System (INIS)
Bouillot, V.
2012-01-01
. Finally, we demonstrate that the spatial arrangement of the environments presenting such an anomalous cosmic flow in the Universe is correlated with the density peak distribution. This correlation indicates in a local way the structures distribution responsible for the anomalously high cosmic flow. An another way to understand Dark Energy is to use density field instead of velocity fields. In particular, we characterize the density field in terms of correlation function. In this thesis, we present many promising results to understand the role of Dark Energy in halo and galaxy clustering from correlation function measurements issued from the Dark Energy Universe Simulation Series (DEUSS). On the one hand, this is achieved by introducing a mass segregation for correlation functions. On the other hand, this is reached by considering the difference between comoving space and redshifts space. The emphasize is laid on two particular sides of this problematic. First, we underline the impact of correlation measures on the bias in cosmology: it give many results on the dependence of this bias on the cosmological model and the redshift. Then, those measurements prove that the imprint of Dark Energy on the non-linear regime of structures formation in the Universe, already shown on the continuous matter field, remains on dark matter halo correlation function. Finally, this thesis presents a lot of improvements done in numerical cosmology. In particular, the realization of the DEUSS: Full Universe Runs simulations, first numerical modeling of the whole observable Universe from Big Bang to nowadays, triggers the optimization of all cosmological codes used. This set of simulations has already given striking results, using an unprecedented statistics. The numerical methods used to follow the gravitational collapse of a density field and detect structures and their various optimizations are presented in a numerical part at the end of the thesis. (author)
Studies of dark energy with X-ray observatories.
Vikhlinin, Alexey
2010-04-20
I review the contribution of Chandra X-ray Observatory to studies of dark energy. There are two broad classes of observable effects of dark energy: evolution of the expansion rate of the Universe, and slow down in the rate of growth of cosmic structures. Chandra has detected and measured both of these effects through observations of galaxy clusters. A combination of the Chandra results with other cosmological datasets leads to 5% constraints on the dark energy equation-of-state parameter, and limits possible deviations of gravity on large scales from general relativity.
New limit on logotropic unified dark energy models
Directory of Open Access Journals (Sweden)
V.M.C. Ferreira
2017-07-01
Full Text Available A unification of dark matter and dark energy in terms of a logotropic perfect dark fluid has recently been proposed, where deviations with respect to the standard ΛCDM model are dependent on a single parameter B. In this paper we show that the requirement that the linear growth of cosmic structures on comoving scales larger than 8h−1Mpc is not significantly affected with respect to the standard ΛCDM result provides the strongest limit to date on the model (B<6×10−7, an improvement of more than three orders of magnitude over previous upper limits on the value of B. We further show that this limit rules out the logotropic Unified Dark Energy model as a possible solution to the small scale problems of the ΛCDM model, including the cusp problem of Dark Matter halos or the missing satellite problem, as well as the original version of the model where the Planck energy density was taken as one of the two parameters characterizing the logotropic dark fluid.
Large-scale stability and astronomical constraints for coupled dark-energy models
Yang, W; Pan, S; Barrow, John David
2018-01-01
The physics of the dark energy and the dark matter is still an open issue in cosmology. The dark energy occupies about 68.5% of the total energy density of the universe today [1], and is believed to accelerate its observed expansion, but the physical nature, origin, and time evolution of this dark energy remain unknown. On the other hand, the dark matter sector (occupying almost 27.5% of the total energy density of the present-day universe) appears to be the principal gravitationa...
Probing interaction and spatial curvature in the holographic dark energy model
International Nuclear Information System (INIS)
Li, Miao; Li, Xiao-Dong; Wang, Shuang; Wang, Yi; Zhang, Xin
2009-01-01
In this paper we place observational constraints on the interaction and spatial curvature in the holographic dark energy model. We consider three kinds of phenomenological interactions between holographic dark energy and matter, i.e., the interaction term Q is proportional to the energy densities of dark energy (ρ Λ ), matter (ρ m ), and matter plus dark energy (ρ m +ρ Λ ). For probing the interaction and spatial curvature in the holographic dark energy model, we use the latest observational data including the type Ia supernovae (SNIa) Constitution data, the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). Our results show that the interaction and spatial curvature in the holographic dark energy model are both rather small. Besides, it is interesting to find that there exists significant degeneracy between the phenomenological interaction and the spatial curvature in the holographic dark energy model
Direct probe of dark energy through gravitational lensing effect
Energy Technology Data Exchange (ETDEWEB)
He, Hong-Jian [T. D. Lee Institute, and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Zhen, E-mail: hjhe@tsinghua.edu.cn, E-mail: zh.zhang@pku.edu.cn [Center for High Energy Physics, Peking University, Beijing 100871 (China)
2017-08-01
We show that gravitational lensing can provide a direct method to probe the nature of dark energy at astrophysical scales. For lensing system as an isolated astrophysical object, we derive the dark energy contribution to gravitational potential as a repulsive power-law term, containing a generic equation of state parameter w . We find that it generates w -dependent and position-dependent modification to the conventional light orbital equation of w =−1. With post-Newtonian approximation, we compute its direct effect for an isolated lensing system at astrophysical scales and find that the dark energy force can deflect the path of incident light rays. We demonstrate that the dark-energy-induced deflection angle Δα{sub DE}∝ M {sup (1+1/3} {sup w} {sup )} (with 1+1/3 w > 0), which increases with the lensing mass M and consistently approaches zero in the limit M → 0. This effect is distinctive because dark energy tends to diffuse the rays and generates concave lensing effect . This is in contrast to the conventional convex lensing effect caused by both visible and dark matter. Measuring such concave lensing effect can directly probe the existence and nature of dark energy. We estimate this effect and show that the current gravitational lensing experiments are sensitive to the direct probe of dark energy at astrophysical scales. For the special case w =−1, our independent study favors the previous works that the cosmological constant can affect light bending, but our prediction qualitatively and quantitatively differ from the literature, including our consistent realization of Δα{sub DE} → 0 (under 0 M → ) at the leading order.
Energy weighted x-ray dark-field imaging.
Pelzer, Georg; Zang, Andrea; Anton, Gisela; Bayer, Florian; Horn, Florian; Kraus, Manuel; Rieger, Jens; Ritter, Andre; Wandner, Johannes; Weber, Thomas; Fauler, Alex; Fiederle, Michael; Wong, Winnie S; Campbell, Michael; Meiser, Jan; Meyer, Pascal; Mohr, Jürgen; Michel, Thilo
2014-10-06
The dark-field image obtained in grating-based x-ray phase-contrast imaging can provide information about the objects' microstructures on a scale smaller than the pixel size even with low geometric magnification. In this publication we demonstrate that the dark-field image quality can be enhanced with an energy-resolving pixel detector. Energy-resolved x-ray dark-field images were acquired with a 16-energy-channel photon-counting pixel detector with a 1 mm thick CdTe sensor in a Talbot-Lau x-ray interferometer. A method for contrast-noise-ratio (CNR) enhancement is proposed and validated experimentally. In measurements, a CNR improvement by a factor of 1.14 was obtained. This is equivalent to a possible radiation dose reduction of 23%.
Entropy of holographic dark energy and the generalized second law
International Nuclear Information System (INIS)
Praseetha, P; Mathew, Titus K
2014-01-01
In this paper we have considered holographic dark energy and studied its cosmology and thermodynamics. We have analyzed the generalized second law (GSL) of thermodynamics in a flat universe consisting of interacting dark energy and dark matter. We performed the analysis under both thermal equilibrium and nonequilibrium conditions. If the apparent horizon is taken as the boundary of the universe, we have shown that the rate of change of the total entropy of the universe is proportional to (1+q) 2 , which in fact shows that the GSL is valid at the apparent horizon, irrespective of the sign of the deceleration parameter, q. Hence, for any form of dark energy, the apparent horizon can be considered as a perfect thermodynamic boundary of the universe. We confirmed this conclusion by using the holographic dark energy model. When the event horizon is taken as the boundary, we found that the GSL is only partially satisfied. The analysis under nonequilibrium conditions revealed that the GSL is satisfied if the temperature of the dark energy is greater than the temperature of the dark matter. (paper)
Dark energy exponential potential models as curvature quintessence
International Nuclear Information System (INIS)
Capozziello, S; Cardone, V F; Piedipalumbo, E; Rubano, C
2006-01-01
It has been recently shown that, under some general conditions, it is always possible to find a fourth-order gravity theory capable of reproducing the same dynamics as a given dark energy model. Here, we discuss this approach for a dark energy model with a scalar field evolving under the action of an exponential potential. In the absence of matter, such a potential can be recovered from a fourth-order theory via a conformal transformation. Including the matter term, the function f(R) entering the generalized gravity Lagrangian can be reconstructed according to the dark energy model
Anisotropic perturbations due to dark energy
International Nuclear Information System (INIS)
Battye, Richard A.; Moss, Adam
2006-01-01
A variety of observational tests seem to suggest that the Universe is anisotropic. This is incompatible with the standard dogma based on adiabatic, rotationally invariant perturbations. We point out that this is a consequence of the standard decomposition of the stress-energy tensor for the cosmological fluids, and that rotational invariance need not be assumed, if there is elastic rigidity in the dark energy. The dark energy required to achieve this might be provided by point symmetric domain wall network with P/ρ=-2/3, although the concept is more general. We illustrate this with reference to a model with cubic symmetry and discuss various aspects of the model
Early-matter-like dark energy and the cosmic microwave background
International Nuclear Information System (INIS)
Aurich, R.; Lustig, S.
2016-01-01
Early-matter-like dark energy is defined as a dark energy component whose equation of state approaches that of cold dark matter (CDM) at early times. Such a component is an ingredient of unified dark matter (UDM) models, which unify the cold dark matter and the cosmological constant of the ΛCDM concordance model into a single dark fluid. Power series expansions in conformal time of the perturbations of the various components for a model with early-matter-like dark energy are provided. They allow the calculation of the cosmic microwave background (CMB) anisotropy from the primordial initial values of the perturbations. For a phenomenological UDM model, which agrees with the observations of the local Universe, the CMB anisotropy is computed and compared with the CMB data. It is found that a match to the CMB observations is possible if the so-called effective velocity of sound c eff of the early-matter-like dark energy component is very close to zero. The modifications on the CMB temperature and polarization power spectra caused by varying the effective velocity of sound are studied
Acceleration of the universe dark energy or modified
International Nuclear Information System (INIS)
Cardenas, Rolando; Leyva, Yoelsy
2007-01-01
We present a composite model of dark energy, motivated in string and quantum field theory considerations. Then we speak on gravity theories in which the gravity Lagrangian is modified, resulting in a modification of General Relativity. We outline a methodology allowing a mapping between these two theories, i. e., both dark energy models and modified gravity can give the same cosmological dynamics. We apply aforementioned methodology to obtain the mapping composite dark energy-modified gravity for a particular case. Cosmic expansion history takes into account very large scales, the homogeneous Universe, and can not discriminate between above two theories. However, cosmic growth history takes into consideration intermediate cluster and galactic scales, the inhomogeneous Universe, and there might be the clue to discriminate whether the current acceleration of the Universe is because it is filled with a new fluid having repulsive gravity (dark energy) or it is just that gravity gets weaker and long scales (modified gravity). (Author)
Low CMB quadrupole from dark energy isocurvature perturbations
International Nuclear Information System (INIS)
Gordon, Christopher; Hu, Wayne
2004-01-01
We explicate the origin of the temperature quadrupole in the adiabatic dark energy model and explore the mechanism by which scale invariant isocurvature dark energy perturbations can lead to its sharp suppression. The model requires anticorrelated curvature and isocurvature fluctuations and is favored by the Wilkinson Microwave Anisotropy Probe data at about the 95% confidence level in a flat scale invariant model. In an inflationary context, the anticorrelation may be established if the curvature fluctuations originate from a variable decay rate of the inflaton; such models however tend to overpredict gravitational waves. This isocurvature model can in the future be distinguished from alternatives involving a reduction in large scale power or modifications to the sound speed of the dark energy through the polarization and its cross correlation with the temperature. The isocurvature model retains the same polarization fluctuations as its adiabatic counterpart but reduces the correlated temperature fluctuations. We present a pedagogical discussion of dark energy fluctuations in a quintessence and k-essence context in the Appendix
New agegraphic dark energy in Hořava-Lifshitz cosmology
International Nuclear Information System (INIS)
Jamil, Mubasher; Saridakis, Emmanuel N.
2010-01-01
We investigate the new agegraphic dark energy scenario in a universe governed by Hořava-Lifshitz gravity. We consider both the detailed and non-detailed balanced version of the theory, we impose an arbitrary curvature, and we allow for an interaction between the matter and dark energy sectors. Extracting the differential equation for the evolution of the dark energy density parameter and performing an expansion of the dark energy equation-of-state parameter, we calculate its present and its low-redshift value as functions of the dark energy and curvature density parameters at present, of the Hořava-Lifshitz running parameter λ, of the new agegraphic dark energy parameter n, and of the interaction coupling b. We find that w 0 = −0.82 +0.08 −0.08 and w 1 = 0.08 +0.09 −0.07 . Although this analysis indicates that the scenario can be compatible with observations, it does not enlighten the discussion about the possible conceptual and theoretical problems of Hořava-Lifshitz gravity
DESTINY, The Dark Energy Space Telescope
Pasquale, Bert A.; Woodruff, Robert A.; Benford, Dominic J.; Lauer, Tod
2007-01-01
We have proposed the development of a low-cost space telescope, Destiny, as a concept for the NASA/DOE Joint Dark Energy Mission. Destiny is a 1.65m space telescope, featuring a near-infrared (0.85-1.7m) survey camera/spectrometer with a moderate flat-field field of view (FOV). Destiny will probe the properties of dark energy by obtaining a Hubble diagram based on Type Ia supernovae and a large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift.
International Nuclear Information System (INIS)
Lim, Eugene A.; Sawicki, Ignacy; Vikman, Alexander
2010-01-01
We introduce a novel class of field theories where energy always flows along timelike geodesics, mimicking in that respect dust, yet which possess non-zero pressure. This theory comprises two scalar fields, one of which is a Lagrange multiplier enforcing a constraint between the other's field value and derivative. We show that this system possesses no wave-like modes but retains a single dynamical degree of freedom. Thus, the sound speed is always identically zero on all backgrounds. In particular, cosmological perturbations reproduce the standard behaviour for hydrodynamics in the limit of vanishing sound speed. Using all these properties we propose a model unifying Dark Matter and Dark Energy in a single degree of freedom. In a certain limit this model exactly reproduces the evolution history of ΛCDM, while deviations away from the standard expansion history produce a potentially measurable difference in the evolution of structure
An effective description of dark matter and dark energy in the mildly non-linear regime
Energy Technology Data Exchange (ETDEWEB)
Lewandowski, Matthew; Senatore, Leonardo [Stanford Institute for Theoretical Physics, Stanford University, Stanford, CA 94306 (United States); Maleknejad, Azadeh, E-mail: matthew.lewandowski@cea.fr, E-mail: azade@ipm.ir, E-mail: senatore@stanford.edu [School of Physics, Institute for Research in Fundamental Sciences (IPM), P. Code. 19538-33511, Tehran (Iran, Islamic Republic of)
2017-05-01
In the next few years, we are going to probe the low-redshift universe with unprecedented accuracy. Among the various fruits that this will bear, it will greatly improve our knowledge of the dynamics of dark energy, though for this there is a strong theoretical preference for a cosmological constant. We assume that dark energy is described by the so-called Effective Field Theory of Dark Energy, which assumes that dark energy is the Goldstone boson of time translations. Such a formalism makes it easy to ensure that our signatures are consistent with well-established principles of physics. Since most of the information resides at high wavenumbers, it is important to be able to make predictions at the highest wavenumber that is possible. The Effective Field Theory of Large-Scale Structure (EFTofLSS) is a theoretical framework that has allowed us to make accurate predictions in the mildly non-linear regime. In this paper, we derive the non-linear equations that extend the EFTofLSS to include the effect of dark energy both on the matter fields and on the biased tracers. For the specific case of clustering quintessence, we then perturbatively solve to cubic order the resulting non-linear equations and construct the one-loop power spectrum of the total density contrast.
Ricci dark energy in Chern-Simons modified gravity
Energy Technology Data Exchange (ETDEWEB)
Silva, J.G.; Santos, A.F. [Universidade Federal de Mato Grosso (UFMT), Campo Grande, MT (Brazil)
2013-07-01
Full text: Currently the accelerated expansion of the universe has been strongly confirmed by some independent experiments such as the Cosmic Microwave Background Radiation (CMBR) and Sloan Digital Sky Survey (SDSS). In an attempt to explain this phenomenon there are two possible paths; first option - propose corrections to general relativity, second option - assuming that there is a dominant component of the universe, a kind of antigravity called dark energy. Any way that we intend to follow, there are numerous models that attempt to explain this effect. One of the models of modified gravity that has stood out in recent years is the Chern-Simons modified gravity. This modification consists in the addition of the Pontryagin density, which displays violation of parity symmetry in Einstein-Hilbert action. From among the various models proposed for dark energy there are some that are based on the holographic principle, known as holographic dark energy. Such models are based on the idea that the energy density of a given system is proportional to the inverse square of some characteristic length of the system. From these studies, here we consider the model proposed by Gao et. al., a model of dark energy where the characteristic length is given by the average radius of the Ricci scalar. Thus, the dark energy density is proportional to the Ricci scalar, i.e., ρ{sub x} ∝ R. It is a phenomenologically viable model and displays results similar to that presented by the cosmological model ACDM. In this work, we have considered the Ricci dark energy model in the dynamic Chern-Simons modified gravity. We show that in this context the evolution of the scale factor is similar to that displayed by the modified Chaplygin gas. (author)
Ricci dark energy in Chern-Simons modified gravity
International Nuclear Information System (INIS)
Silva, J.G.; Santos, A.F.
2013-01-01
Full text: Currently the accelerated expansion of the universe has been strongly confirmed by some independent experiments such as the Cosmic Microwave Background Radiation (CMBR) and Sloan Digital Sky Survey (SDSS). In an attempt to explain this phenomenon there are two possible paths; first option - propose corrections to general relativity, second option - assuming that there is a dominant component of the universe, a kind of antigravity called dark energy. Any way that we intend to follow, there are numerous models that attempt to explain this effect. One of the models of modified gravity that has stood out in recent years is the Chern-Simons modified gravity. This modification consists in the addition of the Pontryagin density, which displays violation of parity symmetry in Einstein-Hilbert action. From among the various models proposed for dark energy there are some that are based on the holographic principle, known as holographic dark energy. Such models are based on the idea that the energy density of a given system is proportional to the inverse square of some characteristic length of the system. From these studies, here we consider the model proposed by Gao et. al., a model of dark energy where the characteristic length is given by the average radius of the Ricci scalar. Thus, the dark energy density is proportional to the Ricci scalar, i.e., ρ x ∝ R. It is a phenomenologically viable model and displays results similar to that presented by the cosmological model ACDM. In this work, we have considered the Ricci dark energy model in the dynamic Chern-Simons modified gravity. We show that in this context the evolution of the scale factor is similar to that displayed by the modified Chaplygin gas. (author)
New limits on coupled dark energy model after Planck 2015
Li, Hang; Yang, Weiqiang; Wu, Yabo; Jiang, Ying
2018-06-01
We used the Planck 2015 cosmic microwave background anisotropy, baryon acoustic oscillation, type-Ia supernovae, redshift-space distortions, and weak gravitational lensing to test the model parameter space of coupled dark energy. We assumed the constant and time-varying equation of state parameter for dark energy, and treated dark matter and dark energy as the fluids whose energy transfer was proportional to the combined term of the energy densities and equation of state, such as Q = 3 Hξ(1 +wx) ρx and Q = 3 Hξ [ 1 +w0 +w1(1 - a) ] ρx, the full space of equation of state could be measured when we considered the term (1 +wx) in the energy exchange. According to the joint observational constraint, the results showed that wx = - 1.006-0.027+0.047 and ξ = 0.098-0.098>+0.026 for coupled dark energy with a constant equation of state, w0 = -1.076-0.076+0.085, w1 = - 0.069-0.319+0.361, and ξ = 0.210-0.210+0.048 for a variable equation of state. We did not get any clear evidence for the coupling in the dark fluids at 1 σ region.
High-Energy Neutron Backgrounds for Underground Dark Matter Experiments
Energy Technology Data Exchange (ETDEWEB)
Chen, Yu [Syracuse Univ., NY (United States)
2016-01-01
Direct dark matter detection experiments usually have excellent capability to distinguish nuclear recoils, expected interactions with Weakly Interacting Massive Particle (WIMP) dark matter, and electronic recoils, so that they can efficiently reject background events such as gamma-rays and charged particles. However, both WIMPs and neutrons can induce nuclear recoils. Neutrons are then the most crucial background for direct dark matter detection. It is important to understand and account for all sources of neutron backgrounds when claiming a discovery of dark matter detection or reporting limits on the WIMP-nucleon cross section. One type of neutron background that is not well understood is the cosmogenic neutrons from muons interacting with the underground cavern rock and materials surrounding a dark matter detector. The Neutron Multiplicity Meter (NMM) is a water Cherenkov detector capable of measuring the cosmogenic neutron flux at the Soudan Underground Laboratory, which has an overburden of 2090 meters water equivalent. The NMM consists of two 2.2-tonne gadolinium-doped water tanks situated atop a 20-tonne lead target. It detects a high-energy (>~ 50 MeV) neutron via moderation and capture of the multiple secondary neutrons released when the former interacts in the lead target. The multiplicity of secondary neutrons for the high-energy neutron provides a benchmark for comparison to the current Monte Carlo predictions. Combining with the Monte Carlo simulation, the muon-induced high-energy neutron flux above 50 MeV is measured to be (1.3 ± 0.2) ~ 10-9 cm-2s-1, in reasonable agreement with the model prediction. The measured multiplicity spectrum agrees well with that of Monte Carlo simulation for multiplicity below 10, but shows an excess of approximately a factor of three over Monte Carlo prediction for multiplicities ~ 10 - 20. In an effort to reduce neutron backgrounds for the dark matter experiment SuperCDMS SNO- LAB, an active neutron veto was developed
On Dark Energy and Matter of the Expanding Universe
Directory of Open Access Journals (Sweden)
Lehnert B.
2009-04-01
Full Text Available At present the expanding universe is observed to be dominated by the not fully under- stood concepts of dark energy and matter, in a conceived almost flat Euclidian geometry. As one of the possible efforts to understand the global behaviour of the expanding uni- verse, the present paper attempts to explain these concepts in terms of the pressure force and gravity of a spherical photon gas cloud of zero point energy, in a flat geometry. A difficult point of the conventional theory concerns the frequency distribution of the zero point energy oscillations which leads to the unacceptable result of an infinite total en- ergy per unit volume. A modification of this distribution is therefore proposed which results in finite energy density. A corresponding equilibrium state is investigated, as well as small dynamic deviations from it, to form a basis for a model of the expanding universe. Provided that the crucial points of the present approach hold true, the model satisfies the requirements of cosmic linear dimensions, results in an estimated accelera- tion of the expansion being of the order of the observed one, presents a possible solution of the coincidence problem of dark energy and matter, and provides one of the possible explanations of the observed excess of high-energy electrons and positrons in recent balloon and satellite experiments.
International Nuclear Information System (INIS)
Robles-Perez, Salvador; Martin-Moruno, Prado; Rozas-Fernandez, Alberto; Gonzalez-Diaz, Pedro F
2007-01-01
We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunches or big rips singularities. Classically these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe. (fast track communication)
Energy Technology Data Exchange (ETDEWEB)
Robles-Perez, Salvador; Martin-Moruno, Prado; Rozas-Fernandez, Alberto; Gonzalez-Diaz, Pedro F [Colina de los Chopos, Instituto de Matematicas y Fisica Fundamental, Consejo Superior de Investigaciones CientIficas, Serrano 121, 28006 Madrid (Spain)
2007-05-21
We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunches or big rips singularities. Classically these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe. (fast track communication)
Constraints on holographic dark energy from type Ia supernova observations
International Nuclear Information System (INIS)
Zhang Xin; Wu Fengquan
2005-01-01
In this paper, we use the type Ia supernovae data to constrain the holographic dark energy model proposed by Li. We also apply a cosmic age test to this analysis. We consider in this paper a spatially flat Friedmann-Robertson-Walker universe with a matter component and a holographic dark energy component. The fit result shows that the case c m 0 =0.28, and h=0.65, which lead to the present equation of state of dark energy w 0 =-1.03 and the deceleration/acceleration transition redshift z T =0.63. Finally, an expected supernova/acceleration probe simulation using ΛCDM as a fiducial model is performed on this model, and the result shows that the holographic dark energy model takes on c<1 (c=0.92) even though the dark energy is indeed a cosmological constant
Dynamical analysis for a vector-like dark energy
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Landim, Ricardo C.G. [Instituto de Fisica, Universidade de Sao Paulo, Departamento de Fisica-Matematica, Sao Paulo, SP (Brazil)
2016-09-15
In this paper we perform a dynamical analysis for a vector field as a candidate for the dark energy, in the presence of a barotropic fluid. The vector is one component of the so-called cosmic triad, which is a set of three identical copies of an abelian field pointing mutually in orthogonal directions. In order to generalize the analysis, we also assumed the interaction between dark energy and the barotropic fluid, with a phenomenological coupling. Both matter and dark energy eras can be successfully described by the critical points, indicating that the dynamical system theory is a viable tool to analyze asymptotic states of such cosmological models. (orig.)
Symmetron dark energy in laboratory experiments.
Upadhye, Amol
2013-01-18
The symmetron scalar field is a matter-coupled dark energy candidate which effectively decouples from matter in high-density regions through a symmetry restoration. We consider a previously unexplored regime, in which the vacuum mass μ~2.4×10(-3) eV of the symmetron is near the dark energy scale, and the matter coupling parameter M~1 TeV is just beyond standard model energies. Such a field will give rise to a fifth force at submillimeter distances which can be probed by short-range gravity experiments. We show that a torsion pendulum experiment such as Eöt-Wash can exclude symmetrons in this regime for all self-couplings λ is < or approximately equal to 7.5.
Searching for sterile neutrinos in dynamical dark energy cosmologies
Feng, Lu; Zhang, Jing-Fei; Zhang, Xin
2018-05-01
We investigate how the dark energy properties change the cosmological limits on sterile neutrino parameters by using recent cosmological observations. We consider the simplest dynamical dark energy models, the wCDM model and the holographic dark energy (HDE) model, to make an analysis. The cosmological observations used in this work include the Planck 2015 CMB temperature and polarization data, the baryon acoustic oscillation data, the type Ia supernova data, the Hubble constant direct measurement data, and the Planck CMB lensing data. We find that, m v,terile ff energy properties could significantly influence the constraint limits of sterile neutrino parameters.
A more general interacting model of holographic dark energy
International Nuclear Information System (INIS)
Yu Fei; Zhang Jingfei; Lu Jianbo; Wang Wei; Gui Yuanxing
2010-01-01
So far, there have been no theories or observational data that deny the presence of interaction between dark energy and dark matter. We extend naturally the holographic dark energy (HDE) model, proposed by Granda and Oliveros, in which the dark energy density includes not only the square of the Hubble scale, but also the time derivative of the Hubble scale to the case with interaction and the analytic forms for the cosmic parameters are obtained under the specific boundary conditions. The various behaviors concerning the cosmic expansion depend on the introduced numerical parameters which are also constrained. The more general interacting model inherits the features of the previous ones of HDE, keeping the consistency of the theory.
Simulations of structure formation in interacting dark energy cosmologies
International Nuclear Information System (INIS)
Baldi, M.
2009-01-01
The evidence in favor of a dark energy component dominating the Universe, and driving its presently accelerated expansion, has progressively grown during the last decade of cosmological observations. If this dark energy is given by a dynamic scalar field, it may also have a direct interaction with other matter fields in the Universe, in particular with cold dark matter. Such interaction would imprint new features on the cosmological background evolution as well as on the growth of cosmic structure, like an additional long-range fifth-force between massive particles, or a variation in time of the dark matter particle mass. We present here the implementation of these new physical effects in the N-body code GADGET-2, and we discuss the outcomes of a series of high-resolution N-body simulations for a selected family of interacting dark energy models. We interestingly find, in contrast with previous claims, that the inner overdensity of dark matter halos decreases in these models with respect to ΛCDM, and consistently halo concentrations show a progressive reduction for increasing couplings. Furthermore, the coupling induces a bias in the overdensities of cold dark matter and baryons that determines a decrease of the halo baryon fraction below its cosmological value. These results go in the direction of alleviating tensions between astrophysical observations and the predictions of the ΛCDM model on small scales, thereby opening new room for coupled dark energy models as an alternative to the cosmological constant.
Dark energy from discrete spacetime.
Directory of Open Access Journals (Sweden)
Aaron D Trout
Full Text Available Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.
Dark energy from discrete spacetime.
Trout, Aaron D
2013-01-01
Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.
Radiative inflation and dark energy
International Nuclear Information System (INIS)
Di Bari, Pasquale; King, Stephen F.; Luhn, Christoph; Merle, Alexander; Schmidt-May, Angnis
2011-01-01
We propose a model based on radiative symmetry breaking that combines inflation with dark energy and is consistent with the Wilkinson Microwave Anisotropy Probe 7-year regions. The radiative inflationary potential leads to the prediction of a spectral index 0.955 S < or approx. 0.967 and a tensor to scalar ratio 0.142 < or approx. r < or approx. 0.186, both consistent with current data but testable by the Planck experiment. The radiative symmetry breaking close to the Planck scale gives rise to a pseudo Nambu-Goldstone boson with a gravitationally suppressed mass which can naturally play the role of a quintessence field responsible for dark energy. Finally, we present a possible extra dimensional scenario in which our model could be realized.
The traces of anisotropic dark energy in light of Planck
Energy Technology Data Exchange (ETDEWEB)
Cardona, Wilmar; Kunz, Martin [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, 24 Quai Ernest Ansermet, 1211 Genève 4 (Switzerland); Hollenstein, Lukas, E-mail: wilmar.cardona@unige.ch, E-mail: lukas.hollenstein@zhaw.ch, E-mail: martin.kunz@unige.ch [IAS Institute of Applied Simulation, ZHAW Zurich University of Applied Sciences, Grüental, PO Box, 8820 Wädenswil (Switzerland)
2014-07-01
We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.
DGP cosmological model with generalized Ricci dark energy
Energy Technology Data Exchange (ETDEWEB)
Aguilera, Yeremy [Universidad de Santiago, Departamento de Matematicas y Ciencia de la Computacion, Santiago (Chile); Avelino, Arturo [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Cruz, Norman [Universidad de Santiago, Departamento de Fisica, Facultad de Ciencia, Santiago (Chile); Lepe, Samuel [Pontificia Universidad Catolica de Valparaiso, Facultad de Ciencias, Instituto de Fisica, Valparaiso (Chile); Pena, Francisco [Universidad de La Frontera, Departamento de Ciencias Fisicas, Facultad de Ingenieria y Ciencias, Temuco (Chile)
2014-11-15
The brane-world model proposed by Dvali, Gabadadze and Porrati (DGP) leads to an accelerated universe without cosmological constant or other form of dark energy for the positive branch (element of = +1). For the negative branch (element of = -1) we have investigated the behavior of a model with an holographic Ricci-like dark energy and dark matter, where the IR cutoff takes the form αH{sup 2} + βH, H being the Hubble parameter and α, β positive constants of the model. We perform an analytical study of the model in the late-time dark energy dominated epoch, where we obtain a solution for r{sub c}H(z), where r{sub c} is the leakage scale of gravity into the bulk, and conditions for the negative branch on the holographic parameters α and β, in order to hold the conditions of weak energy and accelerated universe. On the other hand, we compare the model versus the late-time cosmological data using the latest type Ia supernova sample of the Joint Light-curve Analysis (JLA), in order to constrain the holographic parameters in the negative branch, as well as r{sub c}H{sub 0} in the positive branch, where H{sub 0} is the Hubble constant. We find that the model has a good fit to the data and that the most likely values for (r{sub c}H{sub 0}, α, β) lie in the permitted region found from an analytical solution in a dark energy dominated universe. We give a justification to use a holographic cutoff in 4D for the dark energy in the 5-dimensional DGP model. Finally, using the Bayesian Information Criterion we find that this model is disfavored compared with the flat ΛCDM model. (orig.)
Constraints on early dark energy from CMB lensing and weak lensing tomography
International Nuclear Information System (INIS)
Hollenstein, Lukas; Crittenden, Robert; Sapone, Domenico; Schäfer, Björn Malte
2009-01-01
Dark energy can be studied by its influence on the expansion of the Universe as well as on the growth history of the large-scale structure. In this paper, we follow the growth of the cosmic density field in early dark energy cosmologies by combining observations of the primary CMB temperature and polarisation power spectra at high redshift, of the CMB lensing deflection field at intermediate redshift and of weak cosmic shear at low redshifts for constraining the allowed amount of early dark energy. We present these forecasts using the Fisher matrix formalism and consider the combination of Planck data with the weak lensing survey of Euclid. We find that combining these data sets gives powerful constraints on early dark energy and is able to break degeneracies in the parameter set inherent to the various observational channels. The derived statistical 1σ-bound on the early dark energy density parameter is σ(Ω e d ) = 0.0022 which suggests that early dark energy models can be well examined in our approach. In addition, we derive the dark energy figure of merit for the considered dark energy parameterisation and comment on the applicability of the growth index to early dark energy cosmologies
Nonparametric reconstruction of the dark energy equation of state
Energy Technology Data Exchange (ETDEWEB)
Heitmann, Katrin [Los Alamos National Laboratory; Holsclaw, Tracy [Los Alamos National Laboratory; Alam, Ujjaini [Los Alamos National Laboratory; Habib, Salman [Los Alamos National Laboratory; Higdon, David [Los Alamos National Laboratory; Sanso, Bruno [UC SANTA CRUZ; Lee, Herbie [UC SANTA CRUZ
2009-01-01
The major aim of ongoing and upcoming cosmological surveys is to unravel the nature of dark energy. In the absence of a compelling theory to test, a natural approach is to first attempt to characterize the nature of dark energy in detail, the hope being that this will lead to clues about the underlying fundamental theory. A major target in this characterization is the determination of the dynamical properties of the dark energy equation of state w. The discovery of a time variation in w(z) could then lead to insights about the dynamical origin of dark energy. This approach requires a robust and bias-free method for reconstructing w(z) from data, which does not rely on restrictive expansion schemes or assumed functional forms for w(z). We present a new non parametric reconstruction method for the dark energy equation of state based on Gaussian Process models. This method reliably captures nontrivial behavior of w(z) and provides controlled error bounds. We demollstrate the power of the method on different sets of simulated supernova data. The GP model approach is very easily extended to include diverse cosmological probes.
Cosmological viability conditions for f(T) dark energy models
Energy Technology Data Exchange (ETDEWEB)
Setare, M.R.; Mohammadipour, N., E-mail: rezakord@ipm.ir, E-mail: N.Mohammadipour@uok.ac.ir [Department of Science, University of Kurdistan, Sanandaj (Iran, Islamic Republic of)
2012-11-01
Recently f(T) modified teleparallel gravity where T is the torsion scalar has been proposed as the natural gravitational alternative for dark energy. We perform a detailed dynamical analysis of these models and find conditions for the cosmological viability of f(T) dark energy models as geometrical constraints on the derivatives of these models. We show that in the phase space exists two cosmologically viable trajectory which (i) The universe would start from an unstable radiation point, then pass a saddle standard matter point which is followed by accelerated expansion de sitter point. (ii) The universe starts from a saddle radiation epoch, then falls onto the stable matter era and the system can not evolve to the dark energy dominated epoch. Finally, for a number of f(T) dark energy models were proposed in the more literature, the viability conditions are investigated.
Dark energy and the accelerating universe: progress, problems and prospects
Energy Technology Data Exchange (ETDEWEB)
Lima, J.A.S. [Universidade de Sao Paulo (IAG/USP), SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas
2012-07-01
Full text: A large number of recent observational data strongly suggest that we live in a flat, accelerating Universe composed by nearly 1/3 of matter (baryonic + dark) and 2/3 of an exotic component with large negative pressure, usually named Dark Energy. The basic set of experiments includes: observations from SNe Ia, CMB anisotropies, baryon acoustic oscillations (BAO) and X-ray data from galaxy clusters. Within the general relativity, the simplest explanation for dark energy is the cosmological constant associated with the zero-point energy density of all quantum fields present in the Universe. However, all estimates for its value are many orders-of-magnitude too large. Many alternative ideas include more exotic candidates for dark energy among them an extremely light scalar field. However, some possible explanations for the present accelerating stage also invokes gravitational physics beyond general relativity. In this way, several observations using satellites and ground-based telescopes are in operation or being planned to test whether dark energy is the cosmological constant or something more exotic, as well as to decide whether or not the standard general relativity can explain cosmic acceleration. In the current view, dark energy is an interesting example of new physics, and, certainly, its possible existence is one of the most profound mysteries of modern physics. In this talk we present a simplified picture of the main results and discuss briefly the difficulties underlying the dark energy paradigm and some of its possible alternatives. (author)
Bianchi-V string cosmological model with dark energy anisotropy
Mishra, B.; Tripathy, S. K.; Ray, Pratik P.
2018-05-01
The role of anisotropic components on the dark energy and the dynamics of the universe is investigated. An anisotropic dark energy fluid with different pressures along different spatial directions is assumed to incorporate the effect of anisotropy. One dimensional cosmic strings aligned along x-direction supplement some kind of anisotropy. Anisotropy in the dark energy pressure is found to evolve with cosmic expansion at least at late times. At an early phase, the anisotropic effect due to the cosmic strings substantially affect the dynamics of the accelerating universe.
International Nuclear Information System (INIS)
De-Santiago, Josue; Cervantes-Cota, Jorge L.
2011-01-01
We study a unification model for dark energy, dark matter, and inflation with a single scalar field with noncanonical kinetic term. In this model, the kinetic term of the Lagrangian accounts for the dark matter and dark energy, and at early epochs, a quadratic potential accounts for slow roll inflation. The present work is an extension to the work by Bose and Majumdar [Phys. Rev. D 79, 103517 (2009).] with a more general kinetic term that was proposed by Chimento in Phys. Rev. D 69, 123517 (2004). We demonstrate that the model is viable at the background and linear perturbation levels.
Cosmological models with Gurzadyan-Xue dark energy
International Nuclear Information System (INIS)
Vereshchagin, G V; Yegorian, G
2006-01-01
The formula for dark energy density derived by Gurzadyan and Xue is the only formula which provides (without a free parameter) a value for dark energy density in remarkable agreement with current cosmological datasets, unlike numerous phenomenological scenarios where the corresponding value is postulated. This formula suggests the possibility of variation of physical constants such as the speed of light and the gravitational constant. Considering several cosmological models based on that formula and deriving the cosmological equations for each case, we show that in all models source terms appear in the continuity equation. So, on one hand, GX models make up a rich set covering a lot of currently proposed models of dark energy; on the other hand, they reveal hidden symmetries, with a particular role of the separatrix Ω m = 2/3, and link with the issue of the content of physical constants
Directory of Open Access Journals (Sweden)
Suresh Kumar
2014-10-01
Full Text Available In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann–Robertson–Walker space–time filled with ordinary matter (baryonic, radiation, dark matter and dark energy, where the latter two components are described by Chevallier–Polarski–Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.
International Nuclear Information System (INIS)
Kumar, Suresh; Xu, Lixin
2014-01-01
In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann–Robertson–Walker space–time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier–Polarski–Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch
Dark energy fingerprints in the nonminimal Wu-Yang wormhole structure
Balakin, Alexander B.; Zayats, Alexei E.
2014-08-01
We discuss new exact solutions to nonminimally extended Einstein-Yang-Mills equations describing spherically symmetric static wormholes supported by the gauge field of the Wu-Yang type in a dark energy environment. We focus on the analysis of three types of exact solutions to the gravitational field equations. Solutions of the first type relate to the model, in which the dark energy is anisotropic; i.e., the radial and tangential pressures do not coincide. Solutions of the second type correspond to the isotropic pressure tensor; in particular, we discuss the exact solution, for which the dark energy is characterized by the equation of state for a string gas. Solutions of the third type describe the dark energy model with constant pressure and energy density. For the solutions of the third type, we consider in detail the problem of horizons and find constraints for the parameters of nonminimal coupling and for the constitutive parameters of the dark energy equation of state, which guarantee that the nonminimal wormholes are traversable.
Dutta, Jibitesh; Khyllep, Wompherdeiki; Tamanini, Nicola
2018-01-01
We consider scalar field models of dark energy interacting with dark matter through a coupling proportional to the contraction of the four-derivative of the scalar field with the four-velocity of the dark matter fluid. The coupling is realized at the Lagrangian level employing the formalism of Scalar-Fluid theories, which use a consistent Lagrangian approach for relativistic fluid to describe dark matter. This framework produces fully covariant field equations, from which we can derive unequivocal cosmological equations at both background and linear perturbations levels. The background evolution is analyzed in detail applying dynamical systems techniques, which allow us to find the complete asymptotic behavior of the universe given any set of model parameters and initial conditions. Furthermore we study linear cosmological perturbations investigating the growth of cosmic structures within the quasi-static approximation. We find that these interacting dark energy models give rise to interesting phenomenological dynamics, including late-time transitions from dark matter to dark energy domination, matter and accelerated scaling solutions and dynamical crossing of the phantom barrier. Moreover we obtain possible deviations from standard ΛCDM behavior at the linear perturbations level, which have an impact on the dynamics of structure formation and might provide characteristic observational signatures.
Energy Technology Data Exchange (ETDEWEB)
Chimento, Luis P.; Richarte, Martin G. [Universidad de Buenos Aires, IFIBA, CONICET, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina); Forte, Monica [Universidad de Buenos Aires, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina)
2013-01-15
We examine a Friedmann-Robertson-Walker universe filled with interacting dark matter, modified holographic Ricci dark energy (MHRDE), and a decoupled baryonic component. The estimations of the cosmic parameters with Hubble data lead to an age of the universe of 13.17 Gyr and show that the MHRDE is free from the cosmic-age problem at low redshift (0{<=}z{<=}2) in contrast to holographic Ricci dark energy (HRDE) case. We constrain the parameters with the Union2 data set and contrast with the Hubble data. We also study the behavior of dark energy at early times by taking into account the severe bounds found at recombination era and/or at big bang nucleosynthesis. The inclusion of a non-interacting baryonic matter forces that the amount of dark energy at z{sub t} {proportional_to} O(1) changes abruptly implying that {Omega} {sub x} (z {approx_equal}1100)=0.03, so the bounds reported by the forecast of Planck and CMBPol experiments are more favored for the MHRDE model than in the case of HRDE cutoff. For the former model, we also find that at high redshift the fraction of dark energy varies from 0.006 to 0.002, then the amount of {Omega} {sub x} at the big bang nucleosynthesis era does not disturb the observed helium abundance in the universe provided that the bound {Omega} {sub x} (z {approx_equal}10 {sup 10}) <0.21 is hold. (orig.)
DARK ENERGY AND KEY PHYSICAL PARAMETERS OF CLUSTERS OF GALAXIES
Directory of Open Access Journals (Sweden)
Gennady S. Bisnovatyi-Kogan
2013-12-01
Full Text Available We study physics of clusters of galaxies embedded in the cosmic dark energy background. The equilibrium and stability of polytropic spheres with equation of state of the matter P = Kpγ, γ = 1 + 1/n, in presence of a non-zero cosmological constant is investigated. The equilibrium state exists only for central densities p0 larger than the critical value pc and there are no static solutions at p0
Dark energy constraints from the cosmic age and supernova
International Nuclear Information System (INIS)
Feng Bo; Wang Xiulian; Zhang Xinmin
2005-01-01
Using the low limit of cosmic ages from globular cluster and the white dwarfs: t 0 >12Gyr, together with recent new high redshift supernova observations from the HST/GOODS program and previous supernova data, we give a considerable estimation of the equation of state for dark energy, with uniform priors as weak as 0.2 m m h 2 <0.16. We find cosmic age limit plays a significant role in lowering the upper bound on the variation amplitude of dark energy equation of state. We propose in this Letter a new scenario of dark energy dubbed quintom, which gives rise to the equation of state larger than -1 in the past and less than -1 today, satisfying current observations. In addition we have also considered the implications of recent X-ray gas mass fraction data on dark energy, which favors a negative running of the equation of state
Importance of supernovae at z>1.5 to probe dark energy
International Nuclear Information System (INIS)
Linder, Eric V.; Huterer, Dragan
2003-01-01
The accelerating expansion of the universe suggests that an unknown component with strongly negative pressure, called dark energy, currently dominates the dynamics of the universe. Such a component makes up ∼70% of the energy density of the universe yet has not been predicted by the standard model of particle physics. The best method for exploring the nature of this dark energy is to map the recent expansion history, at which type Ia supernovae have proved adept. We examine here the depth of survey necessary to provide a precise and qualitatively complete description of dark energy. A realistic analysis of parameter degeneracies, allowance for natural time variation of the dark energy equation of state, and systematic errors in astrophysical observations all demonstrate the importance of a survey covering the full range 0< z < or approx. 2 for revealing the nature of dark energy
Could dark energy be measured in the lab?
International Nuclear Information System (INIS)
Beck, Christian; Mackey, Michael C.
2005-01-01
The experimentally measured spectral density of current noise in Josephson junctions provides direct evidence for the existence of zero-point fluctuations. Assuming that the total vacuum energy associated with these fluctuations cannot exceed the presently measured dark energy of the universe, we predict an upper cutoff frequency of ν c =(1.69+/-0.05)x10 12 Hz for the measured frequency spectrum of zero-point fluctuations in the Josephson junction. The largest frequencies that have been reached in the experiments are of the same order of magnitude as ν c and provide a lower bound on the dark energy density of the universe. It is shown that suppressed zero-point fluctuations above a given cutoff frequency can lead to 1/f noise. We propose an experiment which may help to measure some of the properties of dark energy in the lab
Holographic dark energy with cosmological constant
Hu, Yazhou; Li, Miao; Li, Nan; Zhang, Zhenhui
2015-08-01
Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the ΛHDE model. By studying the ΛHDE model theoretically, we find that the parameters d and Ωhde are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the ΛHDE model by using the recent observational data. We find the model yields χ2min=426.27 when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant ΛCDM model (431.35). At 68.3% CL, we obtain -0.07<ΩΛ0<0.68 and correspondingly 0.04<Ωhde0<0.79, implying at present there is considerable degeneracy between the holographic dark energy and cosmological constant components in the ΛHDE model.
Holographic dark energy with cosmological constant
Energy Technology Data Exchange (ETDEWEB)
Hu, Yazhou; Li, Nan; Zhang, Zhenhui [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190 (China); Li, Miao, E-mail: asiahu@itp.ac.cn, E-mail: mli@itp.ac.cn, E-mail: linan@itp.ac.cn, E-mail: zhangzhh@mail.ustc.edu.cn [School of Astronomy and Space Science, Sun Yat-Sen University, Guangzhou 510275 (China)
2015-08-01
Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the ΛHDE model. By studying the ΛHDE model theoretically, we find that the parameters d and Ω{sub hde} are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the ΛHDE model by using the recent observational data. We find the model yields χ{sup 2}{sub min}=426.27 when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant ΛCDM model (431.35). At 68.3% CL, we obtain −0.07<Ω{sub Λ0}<0.68 and correspondingly 0.04<Ω{sub hde0}<0.79, implying at present there is considerable degeneracy between the holographic dark energy and cosmological constant components in the ΛHDE model.
Holographic dark energy with cosmological constant
International Nuclear Information System (INIS)
Hu, Yazhou; Li, Nan; Zhang, Zhenhui; Li, Miao
2015-01-01
Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the ΛHDE model. By studying the ΛHDE model theoretically, we find that the parameters d and Ω hde are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the ΛHDE model by using the recent observational data. We find the model yields χ 2 min =426.27 when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant ΛCDM model (431.35). At 68.3% CL, we obtain −0.07<Ω Λ0 <0.68 and correspondingly 0.04<Ω hde0 <0.79, implying at present there is considerable degeneracy between the holographic dark energy and cosmological constant components in the ΛHDE model
Dark energy and the fifth force problem
International Nuclear Information System (INIS)
Guendelman, E I; Kaganovich, A B
2008-01-01
Generally accepted explanation of the observed accelerated expansion of the present day universe is based on the idea of the existence of a new entity called dark energy. Resolution of the 'cosmic coincidence' problem implies that dark energy and dark matter follow the same scaling solution during a significant period of evolution. This becomes possible only if there exists a coupling of the dark energy (modeled by a light scalar field) to dark matter. This conclusion following from the observed cosmological data serves for an additional evidence of well-known theoretical predictions of a light scalar coupled to matter. However, according to the results of the fifth force experiments, a similar coupling of the light scalar field to visible (baryonic) matter is strongly suppressed. After a brief review of some models intended for resolution of this 'fifth force problem', we present a model with spontaneously broken scale invariance where the strength of the dilaton-to-matter coupling appears to be dependent on the matter density. This is realized without any special assumptions in the underlying action intended for obtaining such a dependence. As a result the dilaton-to-matter coupling constant measured under conditions of all known fifth force experiments turns out automatically (without any sort of fine tuning) to be so small that, at least in the near future, experiments will not be able to reveal it. On the other hand, if the matter is very diluted (such as galaxy halo dark matter) then its coupling to the dilaton may not be weak. However, the latter situation is realized under conditions not compatible with the design of the fifth force experiments
Einstein's Gravity and Dark Energy/Matter
Sarfatti, J
2003-01-01
Should Einstein's general relativity be quantized in the usual way even though it is not renormalizable the way the spin 1/2 lepto-quark - spin 1 gauge force boson local field theories are? Condensed matter theorists using P.W. Anderson's "More is different" approach, consistent with Andrei Sakharov's idea of "metric elasticity" with gravity emergent out of quantum electrodynamic zero point vacuum fluctuations, is the approach I take in this paper. The QED vacuum in globally-flat Minkowski space-time is unstable due to exchange of virtual photons between virtual electrons and positron "holes" near the -mc2 Fermi surface well inside the 2mc2 energy gap. This results in a non-perturbative emergence of both Einstein's gravity and a unified dark energy/dark matter w = -1 exotic vacuum zero point fluctuation field controlled by the local macro-quantum vacuum coherent field. The latter is a Bose-Einstein condensate of virtual off-mass-shell bound electron-positron pairs. The dark matter exotic vacuum phase with pos...
Dark energy with fine redshift sampling
Linder, Eric V.
2007-03-01
The cosmological constant and many other possible origins for acceleration of the cosmic expansion possess variations in the dark energy properties slow on the Hubble time scale. Given that models with more rapid variation, or even phase transitions, are possible though, we examine the fineness in redshift with which cosmological probes can realistically be employed, and what constraints this could impose on dark energy behavior. In particular, we discuss various aspects of baryon acoustic oscillations, and their use to measure the Hubble parameter H(z). We find that currently considered cosmological probes have an innate resolution no finer than Δz≈0.2 0.3.
Dark energy with fine redshift sampling
International Nuclear Information System (INIS)
Linder, Eric V.
2007-01-01
The cosmological constant and many other possible origins for acceleration of the cosmic expansion possess variations in the dark energy properties slow on the Hubble time scale. Given that models with more rapid variation, or even phase transitions, are possible though, we examine the fineness in redshift with which cosmological probes can realistically be employed, and what constraints this could impose on dark energy behavior. In particular, we discuss various aspects of baryon acoustic oscillations, and their use to measure the Hubble parameter H(z). We find that currently considered cosmological probes have an innate resolution no finer than Δz≅0.2-0.3
Studying dark energy with galaxy cluster surveys
International Nuclear Information System (INIS)
Mohr, Joseph J.; O'Shea, Brian; Evrard, August E.; Bialek, John; Haiman, Zoltan
2003-01-01
Galaxy cluster surveys provide a powerful means of studying the density and nature of the dark energy. The redshift distribution of detected clusters in a deep, large solid angle SZE or X-ray survey is highly sensitive to the dark energy equation of state. Accurate constraints at the 5% level on the dark energy equation of state require that systematic biases in the mass estimators must be controlled at better than the ∼10% level. Observed regularity in the cluster population and the availability of multiple, independent mass estimators suggests these precise measurements are possible. Using hydrodynamical simulations that include preheating, we show that the level of preheating required to explain local galaxy cluster structure has a dramatic effect on X-ray cluster surveys, but only a mild effect on SZE surveys. This suggests that SZE surveys may be optimal for cosmology while X-ray surveys are well suited for studies of the thermal history of the intracluster medium
Reconstruction of the interaction term between dark matter and dark energy using SNe Ia
Energy Technology Data Exchange (ETDEWEB)
Solano, Freddy Cueva; Nucamendi, Ulises, E-mail: freddy@ifm.umich.mx, E-mail: ulises@ifm.umich.mx [Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio C-3, Ciudad Universitaria, CP. 58040, Morelia, Michoacán (Mexico)
2012-04-01
We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of dark energy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM)\\@. The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. This interaction term describes an exchange of energy flow between the DE and DM within dark sector. To show how the method works we do the reconstruction of the interaction function expanding it in terms of only the first six Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming three models: (a) a DE equation of the state parameter w = −1 (an interacting cosmological Λ), (b) a DE equation of the state parameter w = constant with a dark matter density parameter fixed, (c) a DE equation of the state parameter w = constant with a free constant dark matter density parameter to be estimated, and using the Union2 SNe Ia data set from ''The Supernova Cosmology Project'' (SCP) composed by 557 type Ia supernovae. In both cases, the preliminary reconstruction shows that in the best scenario there exist the possibility of a crossing of the noninteracting line Q = 0 in the recent past within the 1σ and 2σ errors from positive values at early times to negative values at late times. This means that, in this reconstruction, there is an energy transfer from DE to DM at early times and an energy transfer from DM to DE at late times. We conclude that this fact is an indication of the possible existence of a crossing behavior in a general interaction coupling between dark components.
Distance measurements from supernovae and dark energy constraints
International Nuclear Information System (INIS)
Wang Yun
2009-01-01
Constraints on dark energy from current observational data are sensitive to how distances are measured from Type Ia supernova (SN Ia) data. We find that flux averaging of SNe Ia can be used to test the presence of unknown systematic uncertainties, and yield more robust distance measurements from SNe Ia. We have applied this approach to the nearby+SDSS+ESSENCE+SNLS+HST set of 288 SNe Ia, and the 'Constitution' set of 397 SNe Ia. Combining the SN Ia data with cosmic microwave background anisotropy data from Wilkinson Microwave Anisotropy Probe 5 yr observations, the Sloan Digital Sky Survey baryon acoustic oscillation measurements, the data of 69 gamma-ray bursts (GRBs) , and the Hubble constant measurement from the Hubble Space Telescope project SHOES, we measure the dark energy density function X(z)≡ρ X (z)/ρ X (0) as a free function of redshift (assumed to be a constant at z>1 or z>1.5). Without the flux averaging of SNe Ia, the combined data using the Constitution set of SNe Ia seem to indicate a deviation from a cosmological constant at ∼95% confidence level at 0 98% confidence level for z≤0.75 using the combined data with 288 SNe Ia from nearby+SDSS+ESSENCE+SNLS+HST, independent of the assumptions about X(z≥1). We quantify dark energy constraints without assuming a flat Universe using the dark energy figure of merit for both X(z) and a dark energy equation-of-state linear in the cosmic scale factor.
James Webb Space Telescope Studies of Dark Energy
Gardner, Jonathan P.; Stiavelli, Massimo; Mather, John C.
2010-01-01
The Hubble Space Telescope (HST) has contributed significantly to studies of dark energy. It was used to find the first evidence of deceleration at z=1.8 (Riess et al. 2001) through the serendipitous discovery of a type 1a supernova (SN1a) in the Hubble Deep Field. The discovery of deceleration at z greater than 1 was confirmation that the apparent acceleration at low redshift (Riess et al. 1998; Perlmutter et al. 1999) was due to dark energy rather than observational or astrophysical effects such as systematic errors, evolution in the SN1a population or intergalactic dust. The GOODS project and associated follow-up discovered 21 SN1a, expanding on this result (Riess et al. 2007). HST has also been used to constrain cosmological parameters and dark energy through weak lensing measurements in the COSMOS survey (Massey et al 2007; Schrabback et al 2009) and strong gravitational lensing with measured time delays (Suyu et al 2010). Constraints on dark energy are often parameterized as the equation of state, w = P/p. For the cosmological constant model, w = -1 at all times; other models predict a change with time, sometimes parameterized generally as w(a) or approximated as w(sub 0)+(1-a)w(sub a), where a = (1+z)(sup -1) is the scale factor of the universe relative to its current scale. Dark energy can be constrained through several measurements. Standard candles, such as SN1a, provide a direct measurement of the luminosity distance as a function of redshift, which can be converted to H(z), the change in the Hubble constant with redshift. An analysis of weak lensing in a galaxy field can be used to derive the angular-diameter distance from the weak-lensing equation and to measure the power spectrum of dark-matter halos, which constrains the growth of structure in the Universe. Baryonic acoustic oscillations (BAO), imprinted on the distribution of matter at recombination, provide a standard rod for measuring the cosmological geometry. Strong gravitational lensing of a
Dynamics of quintessence models of dark energy with exponential coupling to dark matter
International Nuclear Information System (INIS)
Gonzalez, Tame; Leon, Genly; Quiros, Israel
2006-01-01
We explore quintessence models of dark energy which exhibit non-minimal coupling between the dark matter and dark energy components of the cosmic fluid. The kind of coupling chosen is inspired by scalar-tensor theories of gravity. We impose a suitable dynamics of the expansion allowing us to derive exact Friedmann-Robertson-Walker solutions once the coupling function is given as input. Self-interaction potentials of single and double exponential types emerge as a result of our choice of the coupling function. The stability and existence of the solutions are discussed in some detail. Although, in general, models with appropriate interaction between the components of the cosmic mixture are useful for handling the coincidence problem, in the present study this problem cannot be avoided due to the choice of solution generating ansatz
Local dark matter and dark energy as estimated on a scale of ~1 Mpc in a self-consistent way
Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.
2009-12-01
Context: Dark energy was first detected from large distances on gigaparsec scales. If it is vacuum energy (or Einstein's Λ), it should also exist in very local space. Here we discuss its measurement on megaparsec scales of the Local Group. Aims: We combine the modified Kahn-Woltjer method for the Milky Way-M 31 binary and the HST observations of the expansion flow around the Local Group in order to study in a self-consistent way and simultaneously the local density of dark energy and the dark matter mass contained within the Local Group. Methods: A theoretical model is used that accounts for the dynamical effects of dark energy on a scale of ~1 Mpc. Results: The local dark energy density is put into the range 0.8-3.7ρv (ρv is the globally measured density), and the Local Group mass lies within 3.1-5.8×1012 M⊙. The lower limit of the local dark energy density, about 4/5× the global value, is determined by the natural binding condition for the group binary and the maximal zero-gravity radius. The near coincidence of two values measured with independent methods on scales differing by ~1000 times is remarkable. The mass ~4×1012 M⊙ and the local dark energy density ~ρv are also consistent with the expansion flow close to the Local Group, within the standard cosmological model. Conclusions: One should take into account the dark energy in dynamical mass estimation methods for galaxy groups, including the virial theorem. Our analysis gives new strong evidence in favor of Einstein's idea of the universal antigravity described by the cosmological constant.
Interacting cosmic fluids and phase transitions under a holographic modeling for dark energy
Energy Technology Data Exchange (ETDEWEB)
Lepe, Samuel [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Facultad de Ciencias, Valparaiso (Chile); Pena, Francisco [Universidad de La Frontera, Departamento de Ciencias Fisicas, Facultad de Ingenieria y Ciencias, Temuco (Chile)
2016-09-15
We discuss the consequences of possible sign changes of the Q-function which measures the transfer of energy between dark energy and dark matter. We investigate this scenario from a holographic perspective by modeling dark energy by a linear parametrization and CPL-parametrization of the equation of state (ω). By imposing the strong constraint of the second law of thermodynamics, we show that the change of sign for Q, due to the cosmic evolution, imply changes in the temperatures of dark energy and dark matter. We also discuss the phase transitions, in the past and future, experienced by dark energy and dark matter (or, equivalently, the sign changes of their heat capacities). (orig.)
Interacting cosmic fluids and phase transitions under a holographic modeling for dark energy
International Nuclear Information System (INIS)
Lepe, Samuel; Pena, Francisco
2016-01-01
We discuss the consequences of possible sign changes of the Q-function which measures the transfer of energy between dark energy and dark matter. We investigate this scenario from a holographic perspective by modeling dark energy by a linear parametrization and CPL-parametrization of the equation of state (ω). By imposing the strong constraint of the second law of thermodynamics, we show that the change of sign for Q, due to the cosmic evolution, imply changes in the temperatures of dark energy and dark matter. We also discuss the phase transitions, in the past and future, experienced by dark energy and dark matter (or, equivalently, the sign changes of their heat capacities). (orig.)
Probing neutrino dark energy with extremely high-energy cosmic neutrinos
International Nuclear Information System (INIS)
Ringwald, A.; Schrempp, L.
2006-06-01
Recently, a new non-Standard Model neutrino interaction mediated by a light scalar field was proposed, which renders the big-bang relic neutrinos of the cosmic neutrino background a natural dark energy candidate, the so-called Neutrino Dark Energy. As a further consequence of this interaction, the neutrino masses become functions of the neutrino energy densities and are thus promoted to dynamical, time/redshift dependent quantities. Such a possible neutrino mass variation introduces a redshift dependence into the resonance energies associated with the annihilation of extremely high-energy cosmic neutrinos on relic anti-neutrinos and vice versa into Z-bosons. In general, this annihilation process is expected to lead to sizeable absorption dips in the spectra to be observed on earth by neutrino observatories operating in the relevant energy region above 10 13 GeV. In our analysis, we contrast the characteristic absorption features produced by constant and varying neutrino masses, including all thermal background effects caused by the relic neutrino motion. We firstly consider neutrinos from astrophysical sources and secondly neutrinos originating from the decomposition of topological defects using the appropriate fragmentation functions. On the one hand, independent of the nature of neutrino masses, our results illustrate the discovery potential for the cosmic neutrino background by means of relic neutrino absorption spectroscopy. On the other hand, they allow to estimate the prospects for testing its possible interpretation as source of Neutrino Dark Energy within the next decade by the neutrino observatories ANITA and LOFAR. (Orig.)
Exacerbating the Cosmological Constant Problem with Interacting Dark Energy Models.
Marsh, M C David
2017-01-06
Future cosmological surveys will probe the expansion history of the Universe and constrain phenomenological models of dark energy. Such models do not address the fine-tuning problem of the vacuum energy, i.e., the cosmological constant problem (CCP), but can make it spectacularly worse. We show that this is the case for "interacting dark energy" models in which the masses of the dark matter states depend on the dark energy sector. If realized in nature, these models have far-reaching implications for proposed solutions to the CCP that require the number of vacua to exceed the fine-tuning of the vacuum energy density. We show that current estimates of the number of flux vacua in string theory, N_{vac}∼O(10^{272 000}), are far too small to realize certain simple models of interacting dark energy and solve the cosmological constant problem anthropically. These models admit distinctive observational signatures that can be targeted by future gamma-ray observatories, hence making it possible to observationally rule out the anthropic solution to the cosmological constant problem in theories with a finite number of vacua.
International Nuclear Information System (INIS)
Sussman, Roberto A.
2009-01-01
A numerical approach is considered for spherically symmetric spacetimes that generalize Lemaitre-Tolman-Bondi dust solutions to nonzero pressure ('LTB spacetimes'). We introduce quasilocal (QL) variables that are covariant LTB objects satisfying evolution equations of Friedman-Lemaitre-Robertson-Walker (FLRW) cosmologies. We prove rigorously that relative deviations of the local covariant scalars from the QL scalars are nonlinear, gauge invariant and covariant perturbations on a FLRW formal background given by the QL scalars. The dynamics of LTB spacetimes is completely determined by the QL scalars and these exact perturbations. Since LTB spacetimes are compatible with a wide variety of ''equations of state,'' either single fluids or mixtures, a large number of known solutions with dark matter and dark energy sources in a FLRW framework (or with linear perturbations) can be readily examined under idealized but nontrivial inhomogeneous conditions. Coordinate choices and initial conditions are derived for a numerical treatment of the perturbation equations, allowing us to study nonlinear effects in a variety of phenomena, such as gravitational collapse, nonlocal effects, void formation, dark matter and dark energy couplings, and particle creation. In particular, the embedding of inhomogeneous regions can be performed by a smooth matching with a suitable FLRW solution, thus generalizing the Newtonian 'top hat' models that are widely used in astrophysical literature. As examples of the application of the formalism, we examine numerically the formation of a black hole in an expanding Chaplygin gas FLRW universe, as well as the evolution of density clumps and voids in an interactive mixture of cold dark matter and dark energy.
A Note on Equivalence Among Various Scalar Field Models of Dark Energies
Mandal, Jyotirmay Das; Debnath, Ujjal
2017-08-01
In this work, we have tried to find out similarities between various available models of scalar field dark energies (e.g., quintessence, k-essence, tachyon, phantom, quintom, dilatonic dark energy, etc). We have defined an equivalence relation from elementary set theory between scalar field models of dark energies and used fundamental ideas from linear algebra to set up our model. Consequently, we have obtained mutually disjoint subsets of scalar field dark energies with similar properties and discussed our observation.
Analysis of Generalized Ghost Dark Energy in LQC and Galileon Gravity
International Nuclear Information System (INIS)
Biswas, Mahasweta; Debnath, Ujjal
2016-01-01
A so-called ghost dark energy was recently proposed to explain the present acceleration of the universe. The energy density of ghost dark energy, which originates from Veneziano ghost of Quantum Chromodynamics (QCD), in a time dependent background, can be written in the form, ρ_D = (αH + βH"2) where H is the Hubble parameter. We investigate the generalized ghost dark energy (GGDE) model in the setup of loop quantum Cosmology (LQC) and Galileon Cosmology. We study the cosmological implications of the models. We also obtain the equation of state and the deceleration parameters and differential equations governing the evolution of this dark energy model for LQC and Galileon Cosmology. (paper)
Modelling non-linear effects of dark energy
Bose, Benjamin; Baldi, Marco; Pourtsidou, Alkistis
2018-04-01
We investigate the capabilities of perturbation theory in capturing non-linear effects of dark energy. We test constant and evolving w models, as well as models involving momentum exchange between dark energy and dark matter. Specifically, we compare perturbative predictions at 1-loop level against N-body results for four non-standard equations of state as well as varying degrees of momentum exchange between dark energy and dark matter. The interaction is modelled phenomenologically using a time dependent drag term in the Euler equation. We make comparisons at the level of the matter power spectrum and the redshift space monopole and quadrupole. The multipoles are modelled using the Taruya, Nishimichi and Saito (TNS) redshift space spectrum. We find perturbation theory does very well in capturing non-linear effects coming from dark sector interaction. We isolate and quantify the 1-loop contribution coming from the interaction and from the non-standard equation of state. We find the interaction parameter ξ amplifies scale dependent signatures in the range of scales considered. Non-standard equations of state also give scale dependent signatures within this same regime. In redshift space the match with N-body is improved at smaller scales by the addition of the TNS free parameter σv. To quantify the importance of modelling the interaction, we create mock data sets for varying values of ξ using perturbation theory. This data is given errors typical of Stage IV surveys. We then perform a likelihood analysis using the first two multipoles on these sets and a ξ=0 modelling, ignoring the interaction. We find the fiducial growth parameter f is generally recovered even for very large values of ξ both at z=0.5 and z=1. The ξ=0 modelling is most biased in its estimation of f for the phantom w=‑1.1 case.
Inflation via logarithmic entropy-corrected holographic dark energy model
Energy Technology Data Exchange (ETDEWEB)
Darabi, F.; Felegary, F. [Azarbaijan Shahid Madani University, Department of Physics, Tabriz (Iran, Islamic Republic of); Setare, M.R. [University of Kurdistan, Department of Science, Bijar (Iran, Islamic Republic of)
2016-12-15
We study the inflation in terms of the logarithmic entropy-corrected holographic dark energy (LECHDE) model with future event horizon, particle horizon, and Hubble horizon cut-offs, and we compare the results with those obtained in the study of inflation by the holographic dark energy HDE model. In comparison, the spectrum of primordial scalar power spectrum in the LECHDE model becomes redder than the spectrum in the HDE model. Moreover, the consistency with the observational data in the LECHDE model of inflation constrains the reheating temperature and Hubble parameter by one parameter of holographic dark energy and two new parameters of logarithmic corrections. (orig.)
Inflation via logarithmic entropy-corrected holographic dark energy model
International Nuclear Information System (INIS)
Darabi, F.; Felegary, F.; Setare, M.R.
2016-01-01
We study the inflation in terms of the logarithmic entropy-corrected holographic dark energy (LECHDE) model with future event horizon, particle horizon, and Hubble horizon cut-offs, and we compare the results with those obtained in the study of inflation by the holographic dark energy HDE model. In comparison, the spectrum of primordial scalar power spectrum in the LECHDE model becomes redder than the spectrum in the HDE model. Moreover, the consistency with the observational data in the LECHDE model of inflation constrains the reheating temperature and Hubble parameter by one parameter of holographic dark energy and two new parameters of logarithmic corrections. (orig.)
Constraints on interacting dark energy models from Planck 2015 and redshift-space distortion data
Energy Technology Data Exchange (ETDEWEB)
Costa, André A.; Abdalla, E. [Instituto de Física, Universidade de São Paulo, C.P. 66318, 05315-970, São Paulo, SP (Brazil); Xu, Xiao-Dong [Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town (South Africa); Wang, Bin, E-mail: alencar@if.usp.br, E-mail: xiaodong.xu@uct.ac.za, E-mail: wang_b@sjtu.edu.cn, E-mail: eabdalla@usp.br [Department of Physics and Astronomy, Shanghai Jiao Tong University, 200240 Shanghai (China)
2017-01-01
We investigate phenomenological interactions between dark matter and dark energy and constrain these models by employing the most recent cosmological data including the cosmic microwave background radiation anisotropies from Planck 2015, Type Ia supernovae, baryon acoustic oscillations, the Hubble constant and redshift-space distortions. We find that the interaction in the dark sector parameterized as an energy transfer from dark matter to dark energy is strongly suppressed by the whole updated cosmological data. On the other hand, an interaction between dark sectors with the energy flow from dark energy to dark matter is proved in better agreement with the available cosmological observations. This coupling between dark sectors is needed to alleviate the coincidence problem.
Dark energy equation of state parameter and its evolution at low redshift
Energy Technology Data Exchange (ETDEWEB)
Tripathi, Ashutosh; Sangwan, Archana; Jassal, H.K., E-mail: ashutosh_tripathi@fudan.edu.cn, E-mail: archanakumari@iisermohali.ac.in, E-mail: hkjassal@iisermohali.ac.in [Indian Institute of Science Education and Research Mohali, SAS Nagar, Mohali 140306, Punjab (India)
2017-06-01
In this paper, we constrain dark energy models using a compendium of observations at low redshifts. We consider the dark energy as a barotropic fluid, with the equation of state a constant as well the case where dark energy equation of state is a function of time. The observations considered here are Supernova Type Ia data, Baryon Acoustic Oscillation data and Hubble parameter measurements. We compare constraints obtained from these data and also do a combined analysis. The combined observational constraints put strong limits on variation of dark energy density with redshift. For varying dark energy models, the range of parameters preferred by the supernova type Ia data is in tension with the other low redshift distance measurements.
Confronting the sound speed of dark energy with future cluster surveys
DEFF Research Database (Denmark)
Basse, Tobias; Eggers Bjaelde, Ole; Hannestad, Steen
2012-01-01
Future cluster surveys will observe galaxy clusters numbering in the hundred thousands. We consider this work how these surveys can be used to constrain dark energy parameters: in particular, the equation of state parameter w and the non-adiabatic sound speed c_s^2. We demonstrate that, in combin......Future cluster surveys will observe galaxy clusters numbering in the hundred thousands. We consider this work how these surveys can be used to constrain dark energy parameters: in particular, the equation of state parameter w and the non-adiabatic sound speed c_s^2. We demonstrate that......, in combination with Cosmic Microwave Background (CMB) observations from Planck, cluster surveys such as that in the ESA Euclid project will be able to determine a time-independent w with subpercent precision. Likewise, if the dark energy sound horizon falls within the length scales probed by the cluster survey......, then c_s^2 can be pinned down to within an order of magnitude. In the course of this work, we also investigate the process of dark energy virialisation in the presence of an arbitrary sound speed. We find that dark energy clustering and virialisation can lead to dark energy contributing to the total...
Dark energy and neutrino constraints from a future EUCLID-like survey
DEFF Research Database (Denmark)
Basse, Tobias; Eggers Bjaelde, Ole; Hamann, Jan
2013-01-01
We perform a detailed forecast on how well a Euclid-like survey will be able to constrain dark energy and neutrino parameters from a combination of its cosmic shear power spectrum, galaxy power spectrum, and cluster mass function measurements. We find that the combination of these three probes...... vastly improves the survey's potential to measure the time evolution of dark energy. In terms of a dark energy figure-of-merit defined as (sigma(w_0) sigma(w_a))^-1, we find a value of 454 for Euclid-like data combined with Planck-like measurements of the cosmic microwave background (CMB) anisotropies...... alone. We consider also the survey's potential to measure dark energy perturbations in models wherein the dark energy is parameterised as a fluid with a nonstandard non-adiabatic sound speed, and find that in an optimistic scenario in which w_0 deviates by as much as is currently observationally allowed...
Inflation and dark energy arising from geometrical tachyons
International Nuclear Information System (INIS)
Panda, Sudhakar; Sami, M.; Tsujikawa, Shinji
2006-01-01
We study the motion of a Bogomol'nyi-Prasad-Sommerfield D3-brane in the NS5-brane ring background. The radion field becomes tachyonic in this geometrical setup. We investigate the potential of this geometrical tachyon in the cosmological scenario for inflation as well as dark energy. We evaluate the spectra of scalar and tensor perturbations generated during tachyon inflation and show that this model is compatible with recent observations of cosmic microwave background due to an extra freedom of the number of NS5-branes. It is not possible to explain the origin of both inflation and dark energy by using a single tachyon field, since the energy density at the potential minimum is not negligibly small because of the amplitude of scalar perturbations set by cosmic microwave background anisotropies. However, the geometrical tachyon can account for dark energy when the number of NS5-branes is large, provided that inflation is realized by another scalar field
Figure of merit for dark energy constraints from current observational data
International Nuclear Information System (INIS)
Wang Yun
2008-01-01
In order to make useful comparisons of different dark energy experiments, it is important to choose the appropriate figure of merit (FoM) for dark energy constraints. Here we show that for a set of dark energy parameters (f i ), it is most intuitive to define FoM=1/√(detCov(f 1 ,f 2 ,f 3 ,...)), where Cov(f 1 ,f 2 ,f 3 ,...) is the covariance matrix of (f i ). In order for this FoM to represent the dark energy constraints in an optimal manner, the dark energy parameters (f i ) should have clear physical meaning and be minimally correlated. We demonstrate two useful choices of (f i ) using 182 SNe Ia (from the HST/GOODS program, the first year Supernova Legacy Survey, and nearby SN Ia surveys), [R(z * ),l a (z * ),Ω b h 2 ] from the five year Wilkinson Microwave Anisotropy Probe observations, and Sloan Digital Sky Survey measurement of the baryon acoustic oscillation scale, assuming the Hubble Space Telescope prior of H 0 =72±8 (km/s) Mpc -1 , and without assuming spatial flatness. We find that for a dark energy equation of state linear in the cosmic scale factor a, the correlation of (w 0 ,w 0.5 ) [w 0 =w X (z=0), w 0.5 =w X (z=0.5), with w X (a)=3w 0.5 -2w 0 +3(w 0 -w 0.5 )a] is significantly smaller than that of (w 0 ,w a ) [with w X (a)=w 0 +(1-a)w a ]. In order to obtain model-independent constraints on dark energy, we parametrize the dark energy density function X(z)=ρ X (z)/ρ X (0) as a free function with X 0.5 , X 1.0 , and X 1.5 [values of X(z) at z=0.5, 1.0, and 1.5] as free parameters estimated from data. If one assumes a linear dark energy equation of state, current observational data are consistent with a cosmological constant at 68% C.L. If one assumes X(z) to be a free function parametrized by (X 0.5 ,X 1.0 ,X 1.5 ), current data deviate from a cosmological constant at z=1 at 68% C.L., but are consistent with a cosmological constant at 95% C.L. Future dark energy experiments will allow us to dramatically increase the FoM of constraints on (w 0
Novel Probes of Gravity and Dark Energy
Energy Technology Data Exchange (ETDEWEB)
Jain, Bhuvnesh; et al.
2013-09-20
The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and spectroscopy and radio observations. In the coming decade, searches for these effects have the potential for discovering fundamental new physics. We discuss how the searches can be carried out using experiments that are already under way or with modest adaptations of existing telescopes or planned experiments. The accompanying paper on the Growth of Cosmic Structure describes complementary tests of gravity with observations of large-scale structure.
Collider constraints on interactions of dark energy with the standard model
Energy Technology Data Exchange (ETDEWEB)
Brax, P. [CEA, IPhT, CNRS, Gif-sur-Yvette (France). Inst. de Physique Theorique; Burrage, C. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Davis, A.C.; Seery, D. [Cambridge Univ. (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics; Weltman, A. (eds.) [Cambridge Univ. (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics; Cape Town Univ. (South Africa). Dept. of Mathematics and Applied Mathematics
2009-04-15
We study models in which a light scalar dark energy particle couples to the gauge fields of the electroweak force, the photon, Z, and W{sup {+-}} bosons. Our analysis applies to a large class of interacting dark energy models, including those in which the dark energy mass can be adjusted to evade fifth-force bounds by the so-called ''chameleon'' mechanism. We conclude that - with the usual choice of Higgs sector - electroweak precision observables are screened from the indirect effects of dark energy, making such corrections effectively unobservable at present-day colliders, and limiting the dark energy discovery potential of any future International Linear Collider. We show that a similar screening effect applies to processes mediated by flavour-changing neutral currents, which can be traced to the Glashow-Iliopoulos-Maiani mechanism. However, Higgs boson production at the Large Hadron Collider via weak boson fusion may receive observable corrections. (orig.)
Higgs production as a probe of dark energy interactions
Brax, Philippe; Davis, Anne-Christine; Seery, David; Weltman, Amanda
2010-01-01
We study Higgs production under the influence of a light, scalar dark energy field with chameleon-like couplings to matter. Our analysis is relevant for hadron colliders, such as the Large Hadron Collider, which are expected to manufacture Higgs particles through weak boson fusion, or associated production with a Z or W. We show that the corrections arising in these models are too small to be observed. This result can be attributed to the gauge invariance of the low energy Lagrangian. As a by-product of our analysis, we provide the first microphysical realization of a dark energy model coupled to the electromagnetic field strength. In models where dark energy couples to all matter species in a uniform manner we are able to give a new, stringent bound on its coupling strength.
Higgs production as a probe of dark energy interactions
International Nuclear Information System (INIS)
Brax, Philippe; Davis, Anne-Christine; Seery, David
2009-11-01
We study Higgs production under the influence of a light, scalar dark energy field with chameleon-like couplings to matter. Our analysis is relevant for hadron colliders, such as the Large Hadron Collider, which are expected to manufacture Higgs particles through weak boson fusion, or associated production with a Z or W ± . We show that the corrections arising in these models are too small to be observed. This result can be attributed to the gauge invariance of the low energy Lagrangian. As a by-product of our analysis, we provide the first microphysical realization of a dark energy model coupled to the electromagnetic field strength. In models where dark energy couples to all matter species in a uniform manner we are able to give a new, stringent bound on its coupling strength. (orig.)
Higgs production as a probe of dark energy interactions
Energy Technology Data Exchange (ETDEWEB)
Brax, Philippe [CEA, IPhT, CNRS, URA2306, Gif-sur-Yvette (France). Inst. de Physique Theorique; Burrage, Clare [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Davis, Anne-Christine; Seery, David [Cambridge Univ. (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences; Weltmann, Amanda [Cambridge Univ. (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences; Cape Town Univ. (South Africa). Dept. of Mathematics and Applied Mathematics; Centre for Theoretical Cosmology Fellow, Cambridge (United Kingdom)
2009-11-15
We study Higgs production under the influence of a light, scalar dark energy field with chameleon-like couplings to matter. Our analysis is relevant for hadron colliders, such as the Large Hadron Collider, which are expected to manufacture Higgs particles through weak boson fusion, or associated production with a Z or W{sup {+-}}. We show that the corrections arising in these models are too small to be observed. This result can be attributed to the gauge invariance of the low energy Lagrangian. As a by-product of our analysis, we provide the first microphysical realization of a dark energy model coupled to the electromagnetic field strength. In models where dark energy couples to all matter species in a uniform manner we are able to give a new, stringent bound on its coupling strength. (orig.)
Constraining the interacting dark energy models from weak gravity conjecture and recent observations
International Nuclear Information System (INIS)
Chen Ximing; Wang Bin; Pan Nana; Gong Yungui
2011-01-01
We examine the effectiveness of the weak gravity conjecture in constraining the dark energy by comparing with observations. For general dark energy models with plausible phenomenological interactions between dark sectors, we find that although the weak gravity conjecture can constrain the dark energy, the constraint is looser than that from the observations.
Dynamical dark energy: Current constraints and forecasts
Upadhye, Amol; Ishak, Mustapha; Steinhardt, Paul J.
2005-09-01
We consider how well the dark energy equation of state w as a function of redshift z will be measured using current and anticipated experiments. We use a procedure which takes fair account of the uncertainties in the functional dependence of w on z, as well as the parameter degeneracies, and avoids the use of strong prior constraints. We apply the procedure to current data from the Wilkinson Microwave Anisotropy Probe, Sloan Digital Sky Survey, and the supernova searches, and obtain results that are consistent with other analyses using different combinations of data sets. The effects of systematic experimental errors and variations in the analysis technique are discussed. Next, we use the same procedure to forecast the dark energy constraints achievable by the end of the decade, assuming 8 years of Wilkinson Microwave Anisotropy Probe data and realistic projections for ground-based measurements of supernovae and weak lensing. We find the 2σ constraints on the current value of w to be Δw0(2σ)=0.20, and on dw/dz (between z=0 and z=1) to be Δw1(2σ)=0.37. Finally, we compare these limits to other projections in the literature. Most show only a modest improvement; others show a more substantial improvement, but there are serious concerns about systematics. The remaining uncertainty still allows a significant span of competing dark energy models. Most likely, new kinds of measurements, or experiments more sophisticated than those currently planned, are needed to reveal the true nature of dark energy.
The Dark Energy Survey and Operations: Years 1 to 3
Energy Technology Data Exchange (ETDEWEB)
Diehl, H. T. [Fermilab
2016-01-01
The Dark Energy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 1” (Y1) to “Year 3” (Y3), the strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of the first three season's data, and describes how we are adjusting the survey strategy in the face of the El Niño Southern Oscillation
Modeling and Testing Dark Energy and Gravity with Galaxy Cluster Data
Rapetti, David; Cataneo, Matteo; Heneka, Caroline; Mantz, Adam; Allen, Steven W.; Von Der Linden, Anja; Schmidt, Fabian; Lombriser, Lucas; Li, Baojiu; Applegate, Douglas; Kelly, Patrick; Morris, Glenn
2018-06-01
The abundance of galaxy clusters is a powerful probe to constrain the properties of dark energy and gravity at large scales. We employed a self-consistent analysis that includes survey, observable-mass scaling relations and weak gravitational lensing data to obtain constraints on f(R) gravity, which are an order of magnitude tighter than the best previously achieved, as well as on cold dark energy of negligible sound speed. The latter implies clustering of the dark energy fluid at all scales, allowing us to measure the effects of dark energy perturbations at cluster scales. For this study, we recalibrated the halo mass function using the following non-linear characteristic quantities: the spherical collapse threshold, the virial overdensity and an additional mass contribution for cold dark energy. We also presented a new modeling of the f(R) gravity halo mass function that incorporates novel corrections to capture key non-linear effects of the Chameleon screening mechanism, as found in high resolution N-body simulations. All these results permit us to predict, as I will also exemplify, and eventually obtain the next generation of cluster constraints on such models, and provide us with frameworks that can also be applied to other proposed dark energy and modified gravity models using cluster abundance observations.
Has ESA's XMM-Newton cast doubt over dark energy?
2003-12-01
-Newton Omega Project present results showing that clusters of galaxies in the distant Universe are not like those of today. They seem to give out more X-rays than today. So clearly, clusters of galaxies have changed their appearance with time. In an accompanying paper, Alain Blanchard of the Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées and his team use the results to calculate how the abundance of galaxy clusters changes with time. Blanchard says, "There were fewer galaxy clusters in the past." Such a result indicates that the Universe must be a high-density environment, in clear contradiction to the 'concordance model,' which postulates a Universe with up to 70% dark energy and a very low density of matter. Blanchard knows that this conclusion will be highly controversial, saying, "To account for these results you have to have a lot of matter in the Universe and that leaves little room for dark energy." To reconcile the new XMM-Newton observations with the concordance models, astronomers would have to admit a fundamental gap in their knowledge about the behaviour of the clusters and, possibly, of the galaxies within them. For instance, galaxies in the faraway clusters would have to be injecting more energy into their surrounding gas than is currently understood. That process should then gradually taper off as the cluster and the galaxies within it grow older. No matter which way the results are interpreted, XMM-Newton has given astronomers a new insight into the Universe and a new mystery to puzzle over. As for the possibility that the XMM-Newton results are simply wrong, they are in the process of being confirmed by other X-ray observations. Should these return the same answer, we might have to rethink our understanding of the Universe. Notes for editors The two papers, The XMM-Newton Omega Project: I. The X-ray Luminosity-Temperature Relationship at z>0.4 by D.H. Lumb et al. and The XMM-Newton Omega Project: II. Cosmological implications from the high
Modified holographic dark energy in DGP brane world
International Nuclear Information System (INIS)
Liu, Dao-Jun; Wang, Hua; Yang, Bin
2010-01-01
In this Letter, the cosmological dynamics of a modified holographic dark energy which is derived from the UV/IR duality by considering the black hole mass in higher dimensions as UV cutoff, is investigated in Dvali-Gabadadze-Porrati (DGP) brane world model. We choose Hubble horizon and future event horizon as IR cutoff respectively. And the two branches of the DGP model are both taken into account. When Hubble horizon is considered as IR cutoff, the modified holographic dark energy (HDE) behaves like an effect dark energy that modification of gravity in pure DGP brane world model acts and it can drive the expansion of the universe speed up at late time in ε=-1 branch which in pure DGP model cannot undergo an accelerating phase. When future event horizon acts as IR cutoff, the equation of state parameter of the modified HDE can cross the phantom divide.
Higgs seesaw mechanism as a source for dark energy.
Krauss, Lawrence M; Dent, James B
2013-08-09
Motivated by the seesaw mechanism for neutrinos which naturally generates small neutrino masses, we explore how a small grand-unified-theory-scale mixing between the standard model Higgs boson and an otherwise massless hidden sector scalar can naturally generate a small mass and vacuum expectation value for the new scalar which produces a false vacuum energy density contribution comparable to that of the observed dark energy dominating the current expansion of the Universe. This provides a simple and natural mechanism for producing the correct scale for dark energy, even if it does not address the long-standing question of why much larger dark energy contributions are not produced from the visible sector. The new scalar produces no discernible signatures in existing terrestrial experiments so that one may have to rely on other cosmological tests of this idea.
Gravity resonance spectroscopy constrains dark energy and dark matter scenarios.
Jenke, T; Cronenberg, G; Burgdörfer, J; Chizhova, L A; Geltenbort, P; Ivanov, A N; Lauer, T; Lins, T; Rotter, S; Saul, H; Schmidt, U; Abele, H
2014-04-18
We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14 eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant β>5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of λ=20 μm (95% C.L.).
Status of the Dark Energy Survey Camera (DECam) Project
Energy Technology Data Exchange (ETDEWEB)
Flaugher, Brenna L.; Abbott, Timothy M.C.; Angstadt, Robert; Annis, Jim; Antonik, Michelle, L.; Bailey, Jim; Ballester, Otger.; Bernstein, Joseph P.; Bernstein, Rebbeca; Bonati, Marco; Bremer, Gale; /Fermilab /Cerro-Tololo InterAmerican Obs. /ANL /Texas A-M /Michigan U. /Illinois U., Urbana /Ohio State U. /University Coll. London /LBNL /SLAC /IFAE
2012-06-29
The Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the remainder of the time, and after the survey, DECam will be available as a community instrument. All components of DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and commissioning will be presented.
Status of the Dark Energy Survey Camera (DECam) project
Energy Technology Data Exchange (ETDEWEB)
Flaugher, Brenna L.; McLean, Ian S.; Ramsay, Suzanne K.; Abbott, Timothy M. C.; Angstadt, Robert; Takami, Hideki; Annis, Jim; Antonik, Michelle L.; Bailey, Jim; Ballester, Otger; Bernstein, Joseph P.; Bernstein, Rebecca A.; Bonati, Marco; Bremer, Gale; Briones, Jorge; Brooks, David; Buckley-Geer, Elizabeth J.; Campa, Juila; Cardiel-Sas, Laia; Castander, Francisco; Castilla, Javier; Cease, Herman; Chappa, Steve; Chi, Edward C.; da Costa, Luis; DePoy, Darren L.; Derylo, Gregory; de Vincente, Juan; Diehl, H. Thomas; Doel, Peter; Estrada, Juan; Eiting, Jacob; Elliott, Anne E.; Finley, David A.; Flores, Rolando; Frieman, Josh; Gaztanaga, Enrique; Gerdes, David; Gladders, Mike; Guarino, V.; Gutierrez, G.; Grudzinski, Jim; Hanlon, Bill; Hao, Jiangang; Holland, Steve; Honscheid, Klaus; Huffman, Dave; Jackson, Cheryl; Jonas, Michelle; Karliner, Inga; Kau, Daekwang; Kent, Steve; Kozlovsky, Mark; Krempetz, Kurt; Krider, John; Kubik, Donna; Kuehn, Kyler; Kuhlmann, Steve E.; Kuk, Kevin; Lahav, Ofer; Langellier, Nick; Lathrop, Andrew; Lewis, Peter M.; Lin, Huan; Lorenzon, Wolfgang; Martinez, Gustavo; McKay, Timothy; Merritt, Wyatt; Meyer, Mark; Miquel, Ramon; Morgan, Jim; Moore, Peter; Moore, Todd; Neilsen, Eric; Nord, Brian; Ogando, Ricardo; Olson, Jamieson; Patton, Kenneth; Peoples, John; Plazas, Andres; Qian, Tao; Roe, Natalie; Roodman, Aaron; Rossetto, B.; Sanchez, E.; Soares-Santos, Marcelle; Scarpine, Vic; Schalk, Terry; Schindler, Rafe; Schmidt, Ricardo; Schmitt, Richard; Schubnell, Mike; Schultz, Kenneth; Selen, M.; Serrano, Santiago; Shaw, Terri; Simaitis, Vaidas; Slaughter, Jean; Smith, R. Christopher; Spinka, Hal; Stefanik, Andy; Stuermer, Walter; Sypniewski, Adam; Talaga, R.; Tarle, Greg; Thaler, Jon; Tucker, Doug; Walker, Alistair R.; Weaverdyck, Curtis; Wester, William; Woods, Robert J.; Worswick, Sue; Zhao, Allen
2012-09-24
The Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the remainder of the time, and after the survey, DECam will be available as a community instrument. All components of DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and commissioning will be presented.
The effect of anisotropy on the thermodynamics of the interacting holographic dark energy model
Hossienkhani, H.; Jafari, A.; Fayaz, V.; Ramezani, A. H.
2018-02-01
By considering a holographic model for the dark energy in an anisotropic universe, the thermodynamics of a scheme of dark matter and dark energy interaction has been investigated. The results suggest that when holographic dark energy and dark matter evolve separately, each of them remains in thermodynamic equilibrium, therefore the interaction between them may be viewed as a stable thermal fluctuation that brings a logarithmic correction to the equilibrium entropy. Also the relation between the interaction term of the dark components and this thermal fluctuation has been obtained. Additionally, for a cosmological interaction as a free function, the anisotropy effects on the generalized second law of thermodynamics have been studied. By using the latest observational data on the holographic dark energy models as the unification of dark matter and dark energy, the observational constraints have been probed. To do this, we focus on observational determinations of the Hubble expansion rate H( z). Finally, we evaluate the anisotropy effects (although low) on various topics, such as the evolution of the statefinder diagnostic, the distance modulus and the spherical collapse from the holographic dark energy model and compare them with the results of the holographic dark energy of the Friedmann-Robertson-Walker and Λ CDM models.
Dark energy and the BOOMERANG data.
Amendola, L
2001-01-08
The recent high-quality BOOMERANG data allow the testing of many competing cosmological models. Here I present a seven-parameter likelihood analysis of dark energy models with exponential potential and explicit coupling to dark matter. The BOOMERANG data constrain the dimensionless coupling beta to be smaller than 0.1, an order of magnitude better than previous limits. In terms of the constant xi of nonminimally coupled theories, this amounts to xiBOOMERANG does not have enough sensitivity to put constraints on the potential slope.
A Possible Interpretation of Dark Energy and Matter of the Expanding Universe
International Nuclear Information System (INIS)
Lehnert, B.
2009-01-01
At present the expanding universe is observed to be dominated by the not fully understood concepts of dark energy and matter, in a conceived almost flat Euclidian geometry. As one of the possible efforts to understand its global behaviour, the present paper attempts to explain these concepts in terms of the pressure force and gravity of a spherical photon gas cloud of zero point energy, in flat geometry. A difficult point concerns the frequency distribution of the zero point energy oscillations which leads to the unacceptable result of an infinite total energy. A modification of this distribution is therefore proposed which results in finite energy density. A corresponding equilibrium is investigated, as well as small dynamic deviations from it, to form a basis for a model of the expanding universe. Provided that the crucial points of the present approach hold true, the model satisfies the requirements of cosmic linear dimensions, results in an estimated acceleration of the expansion being of the order of the observed one, presents a possible solution of the coincidence problem of dark energy and matter, and provides one of the possible explanations of the observed excess of high-energy electrons and positrons in recent balloon and satellite experiments.
Ultraviolet complete dark energy model
Narain, Gaurav; Li, Tianjun
2018-04-01
We consider a local phenomenological model to explain a nonlocal gravity scenario which has been proposed to address dark energy issues. This nonlocal gravity action has been seen to fit the data as well as Λ -CDM and therefore demands a more fundamental local treatment. The induced gravity model coupled with higher-derivative gravity is exploited for this proposal, as this perturbatively renormalizable model has a well-defined ultraviolet (UV) description where ghosts are evaded. We consider a generalized version of this model where we consider two coupled scalar fields and their nonminimal coupling with gravity. In this simple model, one of the scalar field acquires a vacuum expectation value (VEV), thereby inducing a mass for one of the scalar fields and generating Newton's constant. The induced mass however is seen to be always above the running energy scale thereby leading to its decoupling. The residual theory after decoupling becomes a platform for driving the accelerated expansion under certain conditions. Integrating out the residual scalar generates a nonlocal gravity action. The leading term of which is the nonlocal gravity action used to fit the data of dark energy.
Directory of Open Access Journals (Sweden)
Weiqiang Yang
2017-07-01
Full Text Available The coupling between dark energy and dark matter provides a possible approach to mitigate the coincidence problem of the cosmological standard model. In this paper, we assumed the interacting term was related to the Hubble parameter, energy density of dark energy, and equation of state of dark energy. The interaction rate between dark energy and dark matter was a constant parameter, which was, Q = 3 H ξ ( 1 + w x ρ x . Based on the Markov chain Monte Carlo method, we made a global fitting on the interacting dark energy model from Planck 2015 cosmic microwave background anisotropy and observational Hubble data. We found that the observational data sets slightly favored a small interaction rate between dark energy and dark matter; however, there was not obvious evidence of interaction at the 1 σ level.
What do we really know about dark energy?
Durrer, Ruth
2011-12-28
In this paper, we discuss what we truly know about dark energy. I shall argue that, to date, our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, cosmic microwave background anisotropies and observations of baryon acoustic oscillations simply tell us that the observed distance to a given redshift z is larger than the one expected from a Friedmann-Lemaître universe with matter only and the locally measured Hubble parameter.
Dark energy and the hierarchy problem
International Nuclear Information System (INIS)
Chen, Pisin
2007-01-01
The well-known hierarchy between the Planck scale (∼10 19 GeV) and the TeV scale, namely a ratio of ∼10 16 between the two, is coincidentally repeated in a inverted order between the TeV scale and the dark energy scale at ∼10 -3 eV implied by the observations. We argue that this is not a numerical coincidence. The same brane-world setups to address the first hierarchy problem may also in principle address this second hierarchy issue. Specifically, we consider supersymmetry in the bulk and its breaking on the brane and resort to the Casimir energy induced by the bulk graviton-gravitino mass-shift on the brane as the dark energy. For the ADD model we found that our notion is sensible only if the number of extra dimension n=2. We extend our study to the Randall-Sundrum model. Invoking the chirality-flip on the boundaries for SUSY-breaking, the zero-mode gravitino contribution to the Casimir energy does give rise to the double hierarchy. Unfortunately since the higher Kaluza-Klein modes acquire relative mass-shifts at the TeV level, the zero-mode contribution to Casimir energy is overshadowed
Physical Alternative to the Dark Energy Paradigm
Directory of Open Access Journals (Sweden)
Sapar A.
2013-12-01
Full Text Available The physical nature of the presently dominating enigmatic dark energy in the expanding universe is demonstrated to be explainable as an excess of the kinetic energy with respect to its potential energy. According to traditional Friedman cosmology, any non-zero value of the total energy integral is ascribed to the space curvature. However, as we show, in the flat universe the total energy also can be different from zero. Initially, a very small excess of kinetic energy originates from the early universe. The present observational data show that our universe has probably a flat space with an excess of kinetic energy. The evolutionary scenario shows that the universe presently is in the transitional stage where its radial coordinate expansion approaches the velocity of light. A possibility of the closed Bubble universe with the local Big Bang and everlasting expansion is demonstrated. Dark matter can be essentially contributed by the non-relativistic massive neutrinos, which have cooled to very low temperatures and velocities thus favoring the formation of the observed broad equipotential wells in galaxies.
Crossing the phantom divide: Dark energy internal degrees of freedom
International Nuclear Information System (INIS)
Hu, Wayne
2005-01-01
Dark energy constraints have forced viable alternatives that differ substantially from a cosmological constant Λ to have an equation of state w that evolves across the phantom divide set by Λ. Naively, crossing this divide makes the dark energy gravitationally unstable, a problem that is typically finessed by unphysically ignoring the perturbations. While this procedure does not affect constraints near the favored cosmological constant model it can artificially enhance the confidence with which alternative models are rejected. Similar to the general problem of stability for w<0, the solution lies in the internal degrees of freedom in the dark energy sector. We explicitly show how to construct a two scalar field model that crosses the phantom divide and mimics the single field behavior on either side to substantially better than 1% in all observables. It is representative of models where the internal degrees of freedom keep the dark energy smooth out to the horizon scale independently of the equation of state
Dark energy in scalar-tensor theories
International Nuclear Information System (INIS)
Moeller, J.
2007-12-01
We investigate several aspects of dynamical dark energy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the dark energy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of σ-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)
Dark energy in scalar-tensor theories
Energy Technology Data Exchange (ETDEWEB)
Moeller, J.
2007-12-15
We investigate several aspects of dynamical dark energy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the dark energy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of {sigma}-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)
Cosmic structure sizes in generic dark energy models
Energy Technology Data Exchange (ETDEWEB)
Bhattacharya, Sourav [Indian Institute of Technology Ropar, Department of Physics, Rupnagar, Punjab (India); Tomaras, Theodore N. [ITCP and Department of Physics, University of Crete, Heraklion (Greece)
2017-08-15
The maximum allowable size of a spherical cosmic structure as a function of its mass is determined by the maximum turn around radius R{sub TA,max}, the distance from its center where the attraction on a radial test particle due to the spherical mass is balanced with the repulsion due to the ambient dark energy. In this work, we extend the existing results in several directions. (a) We first show that, for w ≠ -1, the expression for R{sub TA,max} found earlier, using the cosmological perturbation theory, can be derived using a static geometry as well. (b) In the generic dark energy model with arbitrary time dependent state parameter w(t), taking into account the effect of inhomogeneities upon the dark energy as well, it is shown that the data constrain w(t = today) > -2.3. (c) We address the quintessence and the generalized Chaplygin gas models, both of which are shown to predict structure sizes consistent with observations. (orig.)
Gravastars and black holes of anisotropic dark energy
International Nuclear Information System (INIS)
Chan, Roberto; Silva, Maria de Fatima Alves da; Rocha, Pedro Senna
2011-01-01
Full text: Dynamical models of prototype gravastars made of anisotropic dark energy are constructed, in which an infinitely thin spherical shell of a perfect fluid with the equation of state p = (1 - γ)σ divides the whole spacetime into two regions, the internal region filled with a dark energy fluid, and the external Schwarzschild region. The models represent 'bounded excursion' stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes. Here we show, for the first time in the literature, a model of gravastar and formation of black hole with both interior and thin shell constituted exclusively of dark energy. Besides, the sign of the parameter of anisotropy (Pt - Pr ) seems to be relevant to the gravastar formation. The formation is favored when the tangential pressure is greater than the radial pressure, at least in the neighborhood of the isotropic case (ω = -1). (author)
Gravastars and black holes of anisotropic dark energy
Energy Technology Data Exchange (ETDEWEB)
Chan, Roberto [Observatorio Nacional (ON), Rio de Janeiro, RJ (Brazil); Silva, Maria de Fatima Alves da; Rocha, Pedro Senna [Universidade do Estado do Rio de Janeiro (UERJ), RJ (Brazil)
2011-07-01
Full text: Dynamical models of prototype gravastars made of anisotropic dark energy are constructed, in which an infinitely thin spherical shell of a perfect fluid with the equation of state p = (1 - {gamma}){sigma} divides the whole spacetime into two regions, the internal region filled with a dark energy fluid, and the external Schwarzschild region. The models represent 'bounded excursion' stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes. Here we show, for the first time in the literature, a model of gravastar and formation of black hole with both interior and thin shell constituted exclusively of dark energy. Besides, the sign of the parameter of anisotropy (Pt - Pr ) seems to be relevant to the gravastar formation. The formation is favored when the tangential pressure is greater than the radial pressure, at least in the neighborhood of the isotropic case ({omega} = -1). (author)
Scale Dependence of Dark Energy Antigravity
Perivolaropoulos, L.
2002-09-01
We investigate the effects of negative pressure induced by dark energy (cosmological constant or quintessence) on the dynamics at various astrophysical scales. Negative pressure induces a repulsive term (antigravity) in Newton's law which dominates on large scales. Assuming a value of the cosmological constant consistent with the recent SnIa data we determine the critical scale $r_c$ beyond which antigravity dominates the dynamics ($r_c \\sim 1Mpc $) and discuss some of the dynamical effects implied. We show that dynamically induced mass estimates on the scale of the Local Group and beyond are significantly modified due to negative pressure. We also briefly discuss possible dynamical tests (eg effects on local Hubble flow) that can be applied on relatively small scales (a few $Mpc$) to determine the density and equation of state of dark energy.
First SN Discoveries from the Dark Energy Survey
Abbott, T.; Abdalla, F.; Achitouv, I.; Ahn, E.; Aldering, G.; Allam, S.; Alonso, D.; Amara, A.; Annis, J.; Antonik, M.; Aragon-Salamanca, A.; Armstrong, R.; Ashall, C.; Asorey, J.; Bacon, D.; Balbinot, E.; Banerji, M.; Barbary, K.; Barkhouse, W.; Baruah, L.; Bauer, A.; Bechtol, K.; Becker, M.; Bender, R.; Benoist, C.; Benoit-Levy, A.; Bernardi, M.; Bernstein, G.; Bernstein, J. P.; Bernstein, R.; Bertin, E.; Beynon, E.; Bhattacharya, S.; Biesiadzinski, T.; Biswas, R.; Blake, C.; Bloom, J. S.; Bocquet, S.; Brandt, C.; Bridle, S.; Brooks, D.; Brown, P. J.; Brunner, R.; Buckley-Geer, E.; Burke, D.; Burkert, A.; Busha, M.; Campa, J.; Campbell, H.; Cane, R.; Capozzi, D.; Carlstrom, J.; Carnero Rosell, A.; Carollo, M.; Carrasco-Kind, M.; Carretero, J.; Carter, M.; Casas, R.; Castander, F. J.; Chen, Y.; Chiu, I.; Chue, C.; Clampitt, J.; Clerkin, L.; Cohn, J.; Colless, M.; Copeland, E.; Covarrubias, R. A.; Crittenden, R.; Crocce, M.; Cunha, C.; da Costa, L.; d'Andrea, C.; Das, S.; Das, R.; Davis, T. M.; Deb, S.; DePoy, D.; Derylo, G.; Desai, S.; de Simoni, F.; Devlin, M.; Diehl, H. T.; Dietrich, J.; Dodelson, S.; Doel, P.; Dolag, K.; Efstathiou, G.; Eifler, T.; Erickson, B.; Eriksen, M.; Estrada, J.; Etherington, J.; Evrard, A.; Farrens, S.; Fausti Neto, A.; Fernandez, E.; Ferreira, P. C.; Finley, D.; Fischer, J. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; Furlanetto, C.; Garcia-Bellido, J.; Gaztanaga, E.; Gelman, M.; Gerdes, D.; Giannantonio, T.; Gilhool, S.; Gill, M.; Gladders, M.; Gladney, L.; Glazebrook, K.; Gray, M.; Gruen, D.; Gruendl, R.; Gupta, R.; Gutierrez, G.; Habib, S.; Hall, E.; Hansen, S.; Hao, J.; Heitmann, K.; Helsby, J.; Henderson, R.; Hennig, C.; High, W.; Hirsch, M.; Hoffmann, K.; Holhjem, K.; Honscheid, K.; Host, O.; Hoyle, B.; Hu, W.; Huff, E.; Huterer, D.; Jain, B.; James, D.; Jarvis, M.; Jarvis, M. J.; Jeltema, T.; Johnson, M.; Jouvel, S.; Kacprzak, T.; Karliner, I.; Katsaros, J.; Kent, S.; Kessler, R.; Kim, A.; Kim-Vy, T.; King, L.; Kirk, D.; Kochanek, C.; Kopp, M.; Koppenhoefer, J.; Kovacs, E.; Krause, E.; Kravtsov, A.; Kron, R.; Kuehn, K.; Kuemmel, M.; Kuhlmann, S.; Kunder, A.; Kuropatkin, N.; Kwan, J.; Lahav, O.; Leistedt, B.; Levi, M.; Lewis, P.; Liddle, A.; Lidman, C.; Lilly, S.; Lin, H.; Liu, J.; Lopez-Arenillas, C.; Lorenzon, W.; LoVerde, M.; Ma, Z.; Maartens, R.; Maccrann, N.; Macri, L.; Maia, M.; Makler, M.; Manera, M.; Maraston, C.; March, M.; Markovic, K.; Marriner, J.; Marshall, J.; Marshall, S.; Martini, P.; Marti Sanahuja, P.; Mayers, J.; McKay, T.; McMahon, R.; Melchior, P.; Merritt, K. W.; Merson, A.; Miller, C.; Miquel, R.; Mohr, J.; Moore, T.; Mortonson, M.; Mosher, J.; Mould, J.; Mukherjee, P.; Neilsen, E.; Ngeow, C.; Nichol, R.; Nidever, D.; Nord, B.; Nugent, P.; Ogando, R.; Old, L.; Olsen, J.; Ostrovski, F.; Paech, K.; Papadopoulos, A.; Papovich, C.; Patton, K.; Peacock, J.; Pellegrini, P. S. S.; Peoples, J.; Percival, W.; Perlmutter, S.; Petravick, D.; Plazas, A.; Ponce, R.; Poole, G.; Pope, A.; Refregier, A.; Reyes, R.; Ricker, P.; Roe, N.; Romer, K.; Roodman, A.; Rooney, P.; Ross, A.; Rowe, B.; Rozo, E.; Rykoff, E.; Sabiu, C.; Saglia, R.; Sako, M.; Sanchez, A.; Sanchez, C.; Sanchez, E.; Sanchez, J.; Santiago, B.; Saro, A.; Scarpine, V.; Schindler, R.; Schmidt, B. P.; Schmitt, R. L.; Schubnell, M.; Seitz, S.; Senger, R.; Sevilla, I.; Sharp, R.; Sheldon, E.; Sheth, R.; Smith, R. C.; Smith, M.; Snigula, J.; Soares-Santos, M.; Sobreira, F.; Song, J.; Soumagnac, M.; Spinka, H.; Stebbins, A.; Stoughton, C.; Suchyta, E.; Suhada, R.; Sullivan, M.; Sun, F.; Suntzeff, N.; Sutherland, W.; Swanson, M. E. C.; Sypniewski, A. J.; Szepietowski, R.; Talaga, R.; Tarle, G.; Tarrant, E.; Balan, S. Thaithara; Thaler, J.; Thomas, D.; Thomas, R. C.; Tucker, D.; Uddin, S. A.; Ural, S.; Vikram, V.; Voigt, L.; Walker, A. R.; Walker, T.; Wechsler, R.; Weinberg, D.; Weller, J.; Wester, W.; Wetzstein, M.; White, M.; Wilcox, H.; Wilman, D.; Yanny, B.; Young, J.; Zablocki, A.; Zenteno, A.; Zhang, Y.; Zuntz, J.
2012-12-01
The Dark Energy Survey (DES) report the discovery of the first set of supernovae (SN) from the project. Images were observed as part of the DES Science Verification phase using the newly-installed 570-Megapixel Dark Energy Camera on the CTIO Blanco 4-m telescope by observers J. Annis, E. Buckley-Geer, and H. Lin. SN observations are planned throughout the observing campaign on a regular cadence of 4-6 days in each of the ten 3-deg2 fields in the DES griz filters.
Weakly dynamic dark energy via metric-scalar couplings with torsion
Energy Technology Data Exchange (ETDEWEB)
Sur, Sourav; Bhatia, Arshdeep Singh, E-mail: sourav.sur@gmail.com, E-mail: arshdeepsb@gmail.com [Department of Physics and Astrophysics, University of Delhi, New Delhi, 110 007 (India)
2017-07-01
We study the dynamical aspects of dark energy in the context of a non-minimally coupled scalar field with curvature and torsion. Whereas the scalar field acts as the source of the trace mode of torsion, a suitable constraint on the torsion pseudo-trace provides a mass term for the scalar field in the effective action. In the equivalent scalar-tensor framework, we find explicit cosmological solutions representing dark energy in both Einstein and Jordan frames. We demand the dynamical evolution of the dark energy to be weak enough, so that the present-day values of the cosmological parameters could be estimated keeping them within the confidence limits set for the standard LCDM model from recent observations. For such estimates, we examine the variations of the effective matter density and the dark energy equation of state parameters over different redshift ranges. In spite of being weakly dynamic, the dark energy component differs significantly from the cosmological constant, both in characteristics and features, for e.g. it interacts with the cosmological (dust) fluid in the Einstein frame, and crosses the phantom barrier in the Jordan frame. We also obtain the upper bounds on the torsion mode parameters and the lower bound on the effective Brans-Dicke parameter. The latter turns out to be fairly large, and in agreement with the local gravity constraints, which therefore come in support of our analysis.
Constraints on the dark matter and dark energy interactions from weak lensing bispectrum tomography
Energy Technology Data Exchange (ETDEWEB)
An, Rui [School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Feng, Chang [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Wang, Bin, E-mail: an_rui@sjtu.edu.cn, E-mail: chang.feng@uci.edu, E-mail: wang_b@sjtu.edu.cn [Center for Gravitation and Cosmology, College of Physical Science and Technology, Yangzhou University, Yangzhou 225009 (China)
2017-10-01
We estimate uncertainties of cosmological parameters for phenomenological interacting dark energy models using weak lensing convergence power spectrum and bispectrum. We focus on the bispectrum tomography and examine how well the weak lensing bispectrum with tomography can constrain the interactions between dark sectors, as well as other cosmological parameters. Employing the Fisher matrix analysis, we forecast parameter uncertainties derived from weak lensing bispectra with a two-bin tomography and place upper bounds on strength of the interactions between the dark sectors. The cosmic shear will be measured from upcoming weak lensing surveys with high sensitivity, thus it enables us to use the higher order correlation functions of weak lensing to constrain the interaction between dark sectors and will potentially provide more stringent results with other observations combined.
Time arrow is influenced by the dark energy.
Allahverdyan, A E; Gurzadyan, V G
2016-05-01
The arrow of time and the accelerated expansion are two fundamental empirical facts of the universe. We advance the viewpoint that the dark energy (positive cosmological constant) accelerating the expansion of the universe also supports the time asymmetry. It is related to the decay of metastable states under generic perturbations, as we show on example of a microcanonical ensemble. These states will not be metastable without dark energy. The latter also ensures a hyperbolic motion leading to dynamic entropy production with the rate determined by the cosmological constant.
Effects of Low Anisotropy on Generalized Ghost Dark Energy in Galileon Gravity
Hossienkhani, H.; Fayaz, V.; Jafari, A.; Yousefi, H.
2018-04-01
The definition of the Galileon gravity form is extended to the Brans-Dicke theory. Given, the framework of the Galileon theory, the generalized ghost dark energy model in an anisotropic universe is investigated. We study the cosmological implications of this model. In particular, we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy in Bianchi type I model. We also probe observational constraints by using the latest observational data on the generalized ghost dark energy models as the unification of dark matter and dark energy. In order to do so, we focus on observational determinations of the Hubble expansion rate (namely, the expansion history) H(z). As a result, we show the influence of the anisotropy (although low) on the evolution of the universe in the statefinder diagrams for Galileon gravity.
Fundamentalist physics: why Dark Energy is bad for astronomy
International Nuclear Information System (INIS)
White, Simon D M
2007-01-01
Astronomers carry out observations to explore the diverse processes and objects which populate our Universe. High-energy physicists carry out experiments to approach the Fundamental Theory underlying space, time and matter. Dark Energy is a unique link between them, reflecting deep aspects of the Fundamental Theory, yet apparently accessible only through astronomical observation. Large sections of the two communities have therefore converged in support of astronomical projects to constrain Dark Energy. In this essay I argue that this convergence can be damaging for astronomy. The two communities have different methodologies and different scientific cultures. By uncritically adopting the values of an alien system, astronomers risk undermining the foundations of their own current success and endangering the future vitality of their field. Dark Energy is undeniably an interesting problem to tackle through astronomical observation, but it is one of many and not necessarily the one where significant progress is most likely to follow a major investment of resources
Dark energy cosmology with generalized linear equation of state
International Nuclear Information System (INIS)
Babichev, E; Dokuchaev, V; Eroshenko, Yu
2005-01-01
Dark energy with the usually used equation of state p = wρ, where w const 0 ), where the constants α and ρ 0 are free parameters. This non-homogeneous linear equation of state provides the description of both hydrodynamically stable (α > 0) and unstable (α < 0) fluids. In particular, the considered cosmological model describes the hydrodynamically stable dark (and phantom) energy. The possible types of cosmological scenarios in this model are determined and classified in terms of attractors and unstable points by using phase trajectories analysis. For the dark energy case, some distinctive types of cosmological scenarios are possible: (i) the universe with the de Sitter attractor at late times, (ii) the bouncing universe, (iii) the universe with the big rip and with the anti-big rip. In the framework of a linear equation of state the universe filled with a phantom energy, w < -1, may have either the de Sitter attractor or the big rip
Dark energy and the structure of the Coma cluster of galaxies
Chernin, A. D.; Bisnovatyi-Kogan, G. S.; Teerikorpi, P.; Valtonen, M. J.; Byrd, G. G.; Merafina, M.
2013-05-01
Context. We consider the Coma cluster of galaxies as a gravitationally bound physical system embedded in the perfectly uniform static dark energy background as implied by ΛCDM cosmology. Aims: We ask if the density of dark energy is high enough to affect the structure of a large and rich cluster of galaxies. Methods: We base our work on recent observational data on the Coma cluster, and apply our theory of local dynamical effects of dark energy, including the zero-gravity radius RZG of the local force field as the key parameter. Results: 1) Three masses are defined that characterize the structure of a regular cluster: the matter mass MM, the dark-energy effective mass MDE (antigravity affects the structure of the Coma cluster strongly at large radii R ≳ 14 Mpc and should be considered when its total mass is derived.
Dark energy and neutrino constraints from a future EUCLID-like survey
Basse, Tobias; Hamann, Jan; Hannestad, Steen; Wong, Yvonne Y.Y.
2014-01-01
We perform a detailed forecast on how well a Euclid-like survey will be able to constrain dark energy and neutrino parameters from a combination of its cosmic shear power spectrum, galaxy power spectrum, and cluster mass function measurements. We find that the combination of these three probes vastly improves the survey's potential to measure the time evolution of dark energy. In terms of a dark energy figure-of-merit defined as (sigma(w_0) sigma(w_a))^-1, we find a value of 454 for Euclid-like data combined with Planck-like measurements of the cosmic microwave background (CMB) anisotropies in a fiducial LambdaCDM cosmology, a number that is quite conservative compared with existing estimates because of our choice of model parameter space and analysis method, but still represents a factor of 3 to 8 improvement over using either CMB+galaxy clustering+cosmic shear data, or CMB+cluster mass function alone. We consider also the survey's potential to measure dark energy perturbations in models wherein the dark ene...
Dark energy from pNGB mediated Dirac neutrino condensate
Directory of Open Access Journals (Sweden)
Ujjal Kumar Dey
2018-03-01
Full Text Available We consider an extension of the Standard Model that provide an unified description of eV scale neutrino mass and dark energy. An explicit model is presented by augmenting the Standard Model with an SU(2L doublet scalar, a singlet scalar and right handed neutrinos where all of them are assumed to be charged under a global U(1X symmetry. A light pseudo-Nambu–Goldstone Boson, associated with the spontaneously broken U(1X symmetry, acts as a mediator of an attractive force leading to a Dirac neutrino condensate, with large correlation length, and a non-zero gap in the right range providing a cosmologically feasible dark energy scenario. The neutrino mass is generated through the usual Dirac seesaw mechanism. Parameter space, reproducing viable dark energy scenario while having neutrino mass in the right ballpark, is presented.
Inflation and dark energy from three-forms
International Nuclear Information System (INIS)
Koivisto, Tomi S.; Nunes, Nelson J.
2009-01-01
Three-forms can give rise to viable cosmological scenarios of inflation and dark energy with potentially observable signatures distinct from standard single scalar field models. In this study, the background dynamics and linear perturbations of self-interacting three-form cosmology are investigated. The phase space of cosmological solutions possesses (super)-inflating attractors and saddle points, which can describe three-form driven inflation or dark energy. The quantum generation and the classical evolution of perturbations is considered. The scalar and tensor spectra from a three-form inflation and the impact from the presence of a three-form on matter perturbations are computed. Stability properties and equivalence of the model with alternative formulations are discussed.
Neutrino dark energy. Revisiting the stability issue
Energy Technology Data Exchange (ETDEWEB)
Eggers Bjaelde, O.; Hannestad, S. [Aarhus Univ. (Denmark). Dept. of Physics and Astronomy; Brookfield, A.W. [Sheffield Univ. (United Kingdom). Dept. of Applied Mathematics and Dept. of Physics, Astro-Particle Theory and Cosmology Group; Van de Bruck, C. [Sheffield Univ. (United Kingdom). Dept. of Applied Mathematics, Astro-Particle Theory and Cosmology Group; Mota, D.F. [Heidelberg Univ. (Germany). Inst. fuer Theoretische Physik]|[Institute of Theoretical Astrophysics, Oslo (Norway); Schrempp, L. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Tocchini-Valentini, D. [Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Physics and Astronomy
2007-05-15
A coupling between a light scalar field and neutrinos has been widely discussed as a mechanism for linking (time varying) neutrino masses and the present energy density and equation of state of dark energy. However, it has been pointed out that the viability of this scenario in the non-relativistic neutrino regime is threatened by the strong growth of hydrodynamic perturbations associated with a negative adiabatic sound speed squared. In this paper we revisit the stability issue in the framework of linear perturbation theory in a model independent way. The criterion for the stability of a model is translated into a constraint on the scalar-neutrino coupling, which depends on the ratio of the energy densities in neutrinos and cold dark matter. We illustrate our results by providing meaningful examples both for stable and unstable models. (orig.)
Do stochastic inhomogeneities affect dark-energy precision measurements?
Ben-Dayan, I; Gasperini, M; Marozzi, G; Nugier, F; Veneziano, G
2013-01-11
The effect of a stochastic background of cosmological perturbations on the luminosity-redshift relation is computed to second order through a recently proposed covariant and gauge-invariant light-cone averaging procedure. The resulting expressions are free from both ultraviolet and infrared divergences, implying that such perturbations cannot mimic a sizable fraction of dark energy. Different averages are estimated and depend on the particular function of the luminosity distance being averaged. The energy flux being minimally affected by perturbations at large z is proposed as the best choice for precision estimates of dark-energy parameters. Nonetheless, its irreducible (stochastic) variance induces statistical errors on Ω(Λ)(z) typically lying in the few-percent range.
Do stochastic inhomogeneities affect dark-energy precision measurements?
Ben-Dayan, Ido; Marozzi, Giovanni; Nugier, Fabien; Veneziano, Gabriele
2013-01-01
The effect of a stochastic background of cosmological perturbations on the luminosity-redshift relation is computed to second order through a recently proposed covariant and gauge-invariant light-cone averaging procedure. The resulting expressions are free from both ultraviolet and infrared divergences, implying that such perturbations cannot mimic a sizable fraction of dark energy. Different averages are estimated and depend on the particular function of the luminosity distance being averaged. The energy flux, being minimally affected by perturbations at large z, is proposed as the best choice for precision estimates of dark-energy parameters. Nonetheless, its irreducible (stochastic) variance induces statistical errors on \\Omega_{\\Lambda}(z) typically lying in the few-percent range.
Cosmological implications of a dark matter self-interaction energy density
International Nuclear Information System (INIS)
Stiele, Rainer; Boeckel, Tillmann; Schaffner-Bielich, Juergen
2010-01-01
We investigate cosmological constraints on an energy density contribution of elastic dark matter self-interactions characterized by the mass of the exchange particle m SI and coupling constant α SI . Because of the expansion behavior in a Robertson-Walker metric we investigate self-interacting dark matter that is warm in the case of thermal relics. The scaling behavior of dark matter self-interaction energy density (ρ SI ∝a -6 ) shows that it can be the dominant contribution (only) in the very early universe. Thus its impact on primordial nucleosynthesis is used to restrict the interaction strength m SI /√(α SI ), which we find to be at least as strong as the strong interaction. Furthermore we explore dark matter decoupling in a self-interaction dominated universe, which is done for the self-interacting warm dark matter as well as for collisionless cold dark matter in a two component scenario. We find that strong dark matter self-interactions do not contradict superweak inelastic interactions between self-interacting dark matter and baryonic matter (σ A SIDM weak ) and that the natural scale of collisionless cold dark matter decoupling exceeds the weak scale (σ A CDM >σ weak ) and depends linearly on the particle mass. Finally structure formation analysis reveals a linear growing solution during self-interaction domination (δ∝a); however, only noncosmological scales are enhanced.
International Nuclear Information System (INIS)
Gupta, R.C.; Pradhan, Anirudh; Gupta, Sushant
2012-01-01
Comparatively recent observations on Type-Ia supernovae and low density (Um = 0.3) measurement of matter including dark matter suggest that the present day universe consists mainly of repulsive-gravity type 'exotic matter' with negative-pressure often said 'dark energy' (Ux = O7). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, are intriguing. In the present paper the authors attempt to answer these questions while making an effort to reveal the genesis of dark energy, and suggest that the cosmological nuclear binding energy liberated during primordial nucleo-synthesis remains trapped dormant for a long time and then is released free which manifests itself as dark energy in the universe. It is also explained why for dark energy the parameter w = -2/3. Noting that w = 1 for stiff matter and w = 1/3 for radiation; w = -2/3 is for dark energy because '- 1' is due to 'deficiency of stiff- nuclear-matter' and that this binding energy is ultimately released as 'radiation' contributing '+ 1/3', making w = -1+ 1/3 = -2/3. When dark energy is released free at Z = 80, w = -2/3. But as on present day at Z = 0 when radiation strength has diminished to ä ? 0, the parameter w = -1 + ä 1/3 = -1. This, thus almost solves the dark- energy mystery of negative pressure and repulsive-gravity. The proposed theory makes several estimates/predictions which agree reasonably well with the astrophysical constraints and observations. Though there are many candidate-theories, the proposed model of this paper presents an entirely new approach (cosmological nuclear energy) as a possible candidate for dark energy. The secret of acceleration of big-universe is hidden in the small-nucleus. (author)
Probing the stability of superheavy dark matter particles with high-energy neutrinos
International Nuclear Information System (INIS)
Esmaili, Arman; Peres, O.L.G.
2012-01-01
Full text: There is currently mounting evidence for the existence of dark matter in our Universe from various astrophysical and cosmological observations, but the two of the most fundamental properties of the dark matter particle, the mass and the lifetime, are only weakly constrained by the astronomical and cosmological evidence of dark matter. We derive lower limits on the lifetime of dark matter particles with masses in the range 10 TeV - 10 18 GeV from the non-observation of ultrahigh energy neutrinos in the AMANDA, IceCube, Auger and ANITA experiments. All these experiments probe different energy windows and perfectly complement each other. For dark matter particles which produce neutrinos in a two body or a three body decay, we find that the dark matter lifetime must be longer than ∼ 10 26 s for masses between 10 TeV and the Grand Unification scale. We will consider various scenarios where the decay of the dark matter particle produces high energy neutrinos. Neutrinos travel in the Universe without suffering an appreciable attenuation, even for EeV neutrinos, in contrast to photons which rapidly lose their energy via pair production. This remarkable property makes neutrinos a very suitable messenger to constrain the lifetime of superheavy dark matter particles. Finally, we also calculate, for concrete particle physics scenarios, the limits on the strength of the interactions that induce the dark matter decay. (author)
Fitting and forecasting coupled dark energy in the non-linear regime
Energy Technology Data Exchange (ETDEWEB)
Casas, Santiago; Amendola, Luca; Pettorino, Valeria; Vollmer, Adrian [Institut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 16, Heidelberg, 69120 Germany (Germany); Baldi, Marco, E-mail: casas@thphys.uni-heidelberg.de, E-mail: l.amendola@thphys.uni-heidelberg.de, E-mail: mail@marcobaldi.it, E-mail: v.pettorino@thphys.uni-heidelberg.de, E-mail: vollmer@thphys.uni-heidelberg.de [Dipartimento di Fisica e Astronomia, Alma Mater Studiorum Università di Bologna, viale Berti Pichat, 6/2, Bologna, I-40127 Italy (Italy)
2016-01-01
We consider cosmological models in which dark matter feels a fifth force mediated by the dark energy scalar field, also known as coupled dark energy. Our interest resides in estimating forecasts for future surveys like Euclid when we take into account non-linear effects, relying on new fitting functions that reproduce the non-linear matter power spectrum obtained from N-body simulations. We obtain fitting functions for models in which the dark matter-dark energy coupling is constant. Their validity is demonstrated for all available simulations in the redshift range 0z=–1.6 and wave modes below 0k=1 h/Mpc. These fitting formulas can be used to test the predictions of the model in the non-linear regime without the need for additional computing-intensive N-body simulations. We then use these fitting functions to perform forecasts on the constraining power that future galaxy-redshift surveys like Euclid will have on the coupling parameter, using the Fisher matrix method for galaxy clustering (GC) and weak lensing (WL). We find that by using information in the non-linear power spectrum, and combining the GC and WL probes, we can constrain the dark matter-dark energy coupling constant squared, β{sup 2}, with precision smaller than 4% and all other cosmological parameters better than 1%, which is a considerable improvement of more than an order of magnitude compared to corresponding linear power spectrum forecasts with the same survey specifications.
Fitting and forecasting coupled dark energy in the non-linear regime
International Nuclear Information System (INIS)
Casas, Santiago; Amendola, Luca; Pettorino, Valeria; Vollmer, Adrian; Baldi, Marco
2016-01-01
We consider cosmological models in which dark matter feels a fifth force mediated by the dark energy scalar field, also known as coupled dark energy. Our interest resides in estimating forecasts for future surveys like Euclid when we take into account non-linear effects, relying on new fitting functions that reproduce the non-linear matter power spectrum obtained from N-body simulations. We obtain fitting functions for models in which the dark matter-dark energy coupling is constant. Their validity is demonstrated for all available simulations in the redshift range 0z=–1.6 and wave modes below 0k=1 h/Mpc. These fitting formulas can be used to test the predictions of the model in the non-linear regime without the need for additional computing-intensive N-body simulations. We then use these fitting functions to perform forecasts on the constraining power that future galaxy-redshift surveys like Euclid will have on the coupling parameter, using the Fisher matrix method for galaxy clustering (GC) and weak lensing (WL). We find that by using information in the non-linear power spectrum, and combining the GC and WL probes, we can constrain the dark matter-dark energy coupling constant squared, β 2 , with precision smaller than 4% and all other cosmological parameters better than 1%, which is a considerable improvement of more than an order of magnitude compared to corresponding linear power spectrum forecasts with the same survey specifications
An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos
Energy Technology Data Exchange (ETDEWEB)
Zhao HongSheng [Scottish University Physics Alliance, University of St Andrews, KY16 8SB (United Kingdom); Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden (Netherlands)], E-mail: hz4@st-andrews.ac.uk
2008-11-01
Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as antagnising frameworks, e.g. in the muddled debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It is timely to consider an interdisciplinary approach across all semantic boundaries of dark sectors, treating the dark stress as one identity, hence accounts for several 'coincidences' naturally.
Is w≠-1 evidence for a dynamical dark energy equation of state?
International Nuclear Information System (INIS)
Avelino, P. P.; Trindade, A. M. M.; Viana, P. T. P.
2009-01-01
Current constraints on the dark energy equation of state parameter, w, are expected to be improved by more than 1 order of magnitude in the next decade. If |w-1| > or approx. 0.01 around the present time, but the dark energy dynamics is sufficiently slow, it is possible that future constraints will rule out a cosmological constant while being consistent with a time-independent equation of state parameter. In this paper, we show that although models with such behavior can be constructed, they do require significant fine-tuning. Therefore, if the observed acceleration of the Universe is induced by a dark energy component, then finding w≠-1 would, on its own, constitute very strong evidence for a dynamical dark energy equation of state.
Dark energy from the string axiverse.
Kamionkowski, Marc; Pradler, Josef; Walker, Devin G E
2014-12-19
String theories suggest the existence of a plethora of axionlike fields with masses spread over a huge number of decades. Here, we show that these ideas lend themselves to a model of quintessence with no super-Planckian field excursions and in which all dimensionless numbers are order unity. The scenario addresses the "Why now?" problem-i.e., Why has accelerated expansion begun only recently?-by suggesting that the onset of dark-energy domination occurs randomly with a slowly decreasing probability per unit logarithmic interval in cosmic time. The standard axion potential requires us to postulate a rapid decay of most of the axion fields that do not become dark energy. The need for these decays is averted, though, with the introduction of a slightly modified axion potential. In either case, a universe like ours arises in roughly 1 in 100 universes. The scenario may have a host of observable consequences.
Non-Abelian S-term dark energy and inflation
Rodríguez, Yeinzon; Navarro, Andrés A.
2018-03-01
We study the role that a cosmic triad in the generalized SU(2) Proca theory, specifically in one of the pieces of the Lagrangian that involves the symmetric version Sμν of the gauge field strength tensor Fμν, has on dark energy and primordial inflation. Regarding dark energy, the triad behaves asymptotically as a couple of radiation perfect fluids whose energy densities are negative for the S term but positive for the Yang-Mills term. This leads to an interesting dynamical fine-tuning mechanism that gives rise to a combined equation of state parameter ω ≃ - 1 and, therefore, to an eternal period of accelerated isotropic expansion for an ample spectrum of initial conditions. Regarding primordial inflation, one of the critical points of the associated dynamical system can describe a prolonged period of isotropic slow-roll inflation sustained by the S term. This period ends up when the Yang-Mills term dominates the energy density leading to the radiation dominated epoch. Unfortunately, in contrast to the dark energy case, the primordial inflation scenario is strongly sensitive to the coupling constants and initial conditions. The whole model, including the other pieces of the Lagrangian that involve Sμν, might evade the recent strong constraints coming from the gravitational wave signal GW170817 and its electromagnetic counterpart GRB 170817A.
Simple implementation of general dark energy models
International Nuclear Information System (INIS)
Bloomfield, Jolyon K.; Pearson, Jonathan A.
2014-01-01
We present a formalism for the numerical implementation of general theories of dark energy, combining the computational simplicity of the equation of state for perturbations approach with the generality of the effective field theory approach. An effective fluid description is employed, based on a general action describing single-scalar field models. The formalism is developed from first principles, and constructed keeping the goal of a simple implementation into CAMB in mind. Benefits of this approach include its straightforward implementation, the generality of the underlying theory, the fact that the evolved variables are physical quantities, and that model-independent phenomenological descriptions may be straightforwardly investigated. We hope this formulation will provide a powerful tool for the comparison of theoretical models of dark energy with observational data
A direct probe of dark energy interactions with a solar System laboratory
National Aeronautics and Space Administration — We propose a mission concept for direct detection of dark energy interactions with normal matter in a Solar System laboratory. Dark energy is the leading proposal to...
Static Universe model existing due to the matter-dark energy coupling
International Nuclear Information System (INIS)
Cabo Bizet, A.; Cabo Montes de Oca, A.
2007-08-01
The work investigates a static, isotropic and almost homogeneous Universe containing a real scalar field modeling the Dark-Energy (quintaessence) interacting with pressureless matter. It is argued that the interaction between matter and the Dark Energy, is essential for the very existence of the considered solution. Assuming the possibility that Dark-Energy can be furnished by the Dilaton (a scalar field reflecting the condensation of string states with zero angular momentum) we fix the value of scalar field at the origin to the Planck scale. It became possible to fix the ratio of the amount of Dark Energy to matter energy, in the currently estimated value (0.7)/0.3 and also the observed magnitude of the Hubble constant. The small value of the mass for the scalar field chosen for fixing the above ratio and Hubble effect strength, results to be of the order of 10 -29 cm -1 , a small value which seems to be compatible with the zero mass of the Dilaton in the lowest approximations. (author)
Wormhole supported by dark energy admitting conformal motion
Energy Technology Data Exchange (ETDEWEB)
Bhar, Piyali [Government General Degree College, Singur, Department of Mathematics, Hooghly, West Bengal (India); Rahaman, Farook; Banerjee, Ayan [Jadavpur University, Department of Mathematics, Kolkata, West Bengal (India); Manna, Tuhina [St. Xavier' s College, Department of Mathematics and Statistics (Commerce Evening), Kolkata, West Bengal (India)
2016-12-15
In this article, we study the possibility of sustaining static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of the detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. Studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also performed. (orig.)
On the internal consistency of holographic dark energy models
International Nuclear Information System (INIS)
Horvat, R
2008-01-01
Holographic dark energy (HDE) models, underpinned by an effective quantum field theory (QFT) with a manifest UV/IR connection, have become convincing candidates for providing an explanation of the dark energy in the universe. On the other hand, the maximum number of quantum states that a conventional QFT for a box of size L is capable of describing relates to those boxes which are on the brink of experiencing a sudden collapse to a black hole. Another restriction on the underlying QFT is that the UV cut-off, which cannot be chosen independently of the IR cut-off and therefore becomes a function of time in a cosmological setting, should stay the largest energy scale even in the standard cosmological epochs preceding a dark energy dominated one. We show that, irrespective of whether one deals with the saturated form of HDE or takes a certain degree of non-saturation in the past, the above restrictions cannot be met in a radiation dominated universe, an epoch in the history of the universe which is expected to be perfectly describable within conventional QFT
Energy Technology Data Exchange (ETDEWEB)
Khosravi, Shahram; Mollazadeh, Amir [Department of Astronomy and High Energy Physics, Faculty of Physics, Kharazmi University, Mofateh Ave., Tehran (Iran, Islamic Republic of); Baghram, Shant, E-mail: khosravi_sh@khu.ac.ir, E-mail: amirmollazadeh@khu.ac.ir, E-mail: baghram@sharif.edu [Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran (Iran, Islamic Republic of)
2016-09-01
Cross correlation of the Integrated Sachs-Wolfe signal (ISW) with the galaxy distribution in late time is a promising tool for constraining the dark energy properties. Here, we study the effect of dark energy clustering on the ISW-galaxy cross correlation and demonstrate the fact that the bias parameter between the distribution of the galaxies and the underlying dark matter introduces a degeneracy and complications. We argue that as the galaxy's host halo formation time is different from the observation time, we have to consider the evolution of the halo bias parameter. It will be shown that any deviation from ΛCDM model will change the evolution of the bias as well. Therefore, it is deduced that the halo bias depends strongly on the sub-sample of galaxies which is chosen for cross correlation and that the joint kernel of ISW effect and the galaxy distribution has a dominant effect on the observed signal. In this work, comparison is made specifically between the clustered dark energy models using two samples of galaxies. The first one is a sub-sample of galaxies from Sloan Digital Sky Survey, chosen with the r-band magnitude 18 < r < 21 and the dark matter halo host of mass M ∼10{sup 12} M {sub ⊙} and formation redshift of z {sub f} ∼ 2.5. The second one is the sub-sample of Luminous Red galaxies with the dark matter halo hosts of mass M ∼ 10{sup 13} M {sub ⊙} and formation redshift of z {sub f} ∼ 2.0. Using the evolved bias we improve the χ{sup 2} for the ΛCDM which reconciles the ∼1σ-2σ tension of the ISW-galaxy signal with ΛCDM prediction. Finally, we study the parameter estimation of a dark energy model with free parameters w {sub 0} and w {sub a} in the equation of state w {sub de} = w {sub 0} + w {sub az} /(1+ z ) with the constant bias parameter and also with an evolved bias model with free parameters of galaxy's host halo mass and the halo formation redshift.
New Views on Dark Matter from Emergent Gravity
Directory of Open Access Journals (Sweden)
Sun Sichun
2018-01-01
Full Text Available We discuss a scenario that apparent dark matter comes from the induced gravity in the (3+1- dimensional spacetime, which can be embedded into one higher dimensional flat spacetime. The stress tensor of dark energy and dark matter is identified with the Brown-York stress tensor on the hypersurface, and we find an interesting constraint relation between the dark matter and dark energy density parameter and baryonic density parameter. Our approach may show a new understanding for Verlinde’s emergent gravity from higher dimensions. We also comment on some phenomenological implications, including gravitational wave solutions and MOND limit.
Radiation-tolerant, red-sensitive CCDs for dark energy investigations
International Nuclear Information System (INIS)
Roe, N.A.; Bebek, C.J.; Dawson, K.S.; Emes, J.H.; Fabricius, M.H.; Fairfield, J.A.; Groom, D.E.; Holland, S.E.; Karcher, A.; Kolbe, W.F.; Palaio, N.P.; Wang, G.
2007-01-01
We describe the development of thick (200-300 μm), fully depleted p-channel, charge-coupled devices (CCDs). The advantages of these CCDs relative to conventional thin, n-channel CCDs include: high quantum efficiency over a wide range of wavelengths, extending into the near-infrared; negligible fringing at long (∼900-1000 nm) wavelengths; improved radiation tolerance; and a small point-spread function controlled through the application of the bias voltage. These visible-to-near-infrared light detectors are good candidates for the next generation of large focal-plane mosaics under development for dark energy measurements. The Dark Energy Survey has selected these CCDs for the focal plane of a new camera being designed for the Blanco 4 m telescope at CTIO in Chile. They also meet all the requirements for the visible-light detectors for the SuperNova/Acceleration Probe, a satellite-based experiment designed to make precision measurements of dark energy
3D map of Universe bolsters case for dark energy and dark matter
2003-01-01
"Astronomers from the Sloan Digital Sky Survey (SDSS) have made the most precise measurement to date of the cosmic clustering of galaxies and dark matter, refining our understanding of the structure and evolution of the Universe" (1 page).
Holographic dark energy in Brans-Dicke cosmology with chameleon scalar field
Energy Technology Data Exchange (ETDEWEB)
Setare, M.R., E-mail: rezakord@ipm.i [Department of Science of Bijar, University of Kurdistan, Bijar (Iran, Islamic Republic of); Jamil, Mubasher, E-mail: mjamil@camp.edu.p [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi 46000 (Pakistan)
2010-06-07
We study a cosmological implication of holographic dark energy in the Brans-Dicke gravity. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named L. Our analysis shows that one can obtain the phantom crossing scenario if the model parameter {alpha} (of order unity) is tuned accordingly. Moreover, this behavior is achieved by treating the Brans-Dicke scalar field as a Chameleon scalar field and taking a non-minimal coupling of the scalar field with matter. Hence one can generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans-Dicke cosmology framework.
Holographic dark energy in Brans-Dicke cosmology with chameleon scalar field
International Nuclear Information System (INIS)
Setare, M.R.; Jamil, Mubasher
2010-01-01
We study a cosmological implication of holographic dark energy in the Brans-Dicke gravity. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named L. Our analysis shows that one can obtain the phantom crossing scenario if the model parameter α (of order unity) is tuned accordingly. Moreover, this behavior is achieved by treating the Brans-Dicke scalar field as a Chameleon scalar field and taking a non-minimal coupling of the scalar field with matter. Hence one can generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans-Dicke cosmology framework.
Instability in interacting dark sector: an appropriate holographic Ricci dark energy model
Energy Technology Data Exchange (ETDEWEB)
Herrera, Ramón [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Avenida Brasil 2950, Casilla 4059, Valparaíso (Chile); Hipólito-Ricaldi, W.S. [Departamento de Ciências Naturais, Universidade Federal do Espírito Santo, Rodovia BR 101 Norte, km. 60, São Mateus, Espírito Santo (Brazil); Videla, Nelson, E-mail: ramon.herrera@pucv.cl, E-mail: wiliam.ricaldi@ufes.br, E-mail: nelson.videla@ing.uchile.cl [Departamento de Física, Universidad de Chile, FCFM, Blanco Encalada 2008, Santiago (Chile)
2016-08-01
In this paper we investigate the consequences of phantom crossing considering the perturbative dynamics in models with interaction in their dark sector. By mean of a general study of gauge-invariant variables in comoving gauge, we relate the sources of instabilities in the structure formation process with the phantom crossing. In order to illustrate these relations and its consequences in more detail, we consider a specific case of an holographic dark energy interacting with dark matter. We find that in spite of the model is in excellent agreement with observational data at background level, however it is plagued of instabilities in its perturbative dynamics. We reconstruct the model in order to avoid these undesirable instabilities, and we show that this implies a modification of the concordance model at background. Also we find drastic changes on the parameters space in our model when instabilities are avoided.
Fermion field as inflaton, dark energy and dark matter
International Nuclear Information System (INIS)
Grams, Guilherme; Souza, Rudinei C de; Kremer, Gilberto M
2014-01-01
The search for constituents that can explain the periods of accelerating expansion of the Universe is a fundamental topic in cosmology. In this context, we investigate how fermionic fields minimally and non-minimally coupled with the gravitational field may be responsible for accelerated regimes during the evolution of the Universe. The forms of the potential and coupling of the model are determined through the technique of the Noether symmetry for two cases. The first case comprises a Universe filled only with the fermion field. Cosmological solutions are straightforwardly obtained for this case and an exponential inflation mediated by the fermion field is possible with a non-minimal coupling. The second case takes account of the contributions of radiation and baryonic matter in the presence of the fermion field. In this case the fermion field plays the role of dark energy and dark matter, and when a non-minimal coupling is allowed, it mediates a power-law inflation. (paper)
Quantisation of the holographic Ricci dark energy model
Energy Technology Data Exchange (ETDEWEB)
Albarran, Imanol; Bouhmadi-López, Mariam, E-mail: imanol@ubi.pt, E-mail: mbl@ubi.pt [Departamento de Física, Universidade da Beira Interior, 6200 Covilhã (Portugal)
2015-08-01
While general relativity is an extremely robust theory to describe the gravitational interaction in our Universe, it is expected to fail close to singularities like the cosmological ones. On the other hand, it is well known that some dark energy models might induce future singularities; this can be the case for example within the setup of the Holographic Ricci Dark Energy model (HRDE). On this work, we perform a cosmological quantisation of the HRDE model and obtain under which conditions a cosmic doomsday can be avoided within the quantum realm. We show as well that this quantum model not only avoid future singularities but also the past Big Bang.
Holographic dark energy with varying gravitational constant in Hořava-Lifshitz cosmology
Energy Technology Data Exchange (ETDEWEB)
Setare, M.R. [Department of Physics, University of Kurdistan, Pasdaran Ave., Sanandaj (Iran, Islamic Republic of); Jamil, Mubasher, E-mail: rezakord@ipm.ir, E-mail: mjamil@camp.nust.edu.pk [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi, 46000 (Pakistan)
2010-02-01
We investigate the holographic dark energy scenario with a varying gravitational constant in a flat background in the context of Hořava-Lifshitz gravity. We extract the exact differential equation determining the evolution of the dark energy density parameter, which includes G variation term. Also we discuss a cosmological implication of our work by evaluating the dark energy equation of state for low redshifts containing varying G corrections.
Pilgrim dark energy with apparent and event horizons in non-flat universe
International Nuclear Information System (INIS)
Sharif, M.; Jawad, Abdul
2013-01-01
Pilgrim dark energy is an interesting proposal which is based on the conjecture that phantom-like dark energy with strong enough repulsive force can prevent the formation of a black hole. We investigate this conjecture by assuming the apparent and event horizons in non-flat universe and we develop different cosmological parameters. We construct the corresponding equation of state parameter, which indicates that its present values lie in the phantom era of the universe for different ranges of μ (pilgrim dark energy parameter) as well as ξ 2 (interacting parameter). It is interesting to mention here that the pilgrim dark energy with event horizon yields a phantom region for all cases of ξ 2 with μ Λ - ω' Λ plane and explore the thawing as well as freezing region and ΛCDM limit for these models. The statefinders plane is also constructed, which shows the correspondence with different models such as quintessence and phantom dark energy, ΛCDM and Chaplygin gas. Finally, we investigate the validity of the generalized second law of thermodynamics with event horizon in a flat as well as non-flat universe. (orig.)
Cosmological effects of scalar-photon couplings: dark energy and varying-α Models
Energy Technology Data Exchange (ETDEWEB)
Avgoustidis, A. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Martins, C.J.A.P.; Monteiro, A.M.R.V.L.; Vielzeuf, P.E. [Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Luzzi, G., E-mail: tavgoust@gmail.com, E-mail: Carlos.Martins@astro.up.pt, E-mail: mmonteiro@fc.up.pt, E-mail: up110370652@alunos.fc.up.pt, E-mail: gluzzi@lal.in2p3.fr [Laboratoire de l' Accélérateur Linéaire, Université de Paris-Sud, CNRS/IN2P3, Bâtiment 200, BP 34, 91898 Orsay Cedex (France)
2014-06-01
We study cosmological models involving scalar fields coupled to radiation and discuss their effect on the redshift evolution of the cosmic microwave background temperature, focusing on links with varying fundamental constants and dynamical dark energy. We quantify how allowing for the coupling of scalar fields to photons, and its important effect on luminosity distances, weakens current and future constraints on cosmological parameters. In particular, for evolving dark energy models, joint constraints on the dark energy equation of state combining BAO radial distance and SN luminosity distance determinations, will be strongly dominated by BAO. Thus, to fully exploit future SN data one must also independently constrain photon number non-conservation arising from the possible coupling of SN photons to the dark energy scalar field. We discuss how observational determinations of the background temperature at different redshifts can, in combination with distance measures data, set tight constraints on interactions between scalar fields and photons, thus breaking this degeneracy. We also discuss prospects for future improvements, particularly in the context of Euclid and the E-ELT and show that Euclid can, even on its own, provide useful dark energy constraints while allowing for photon number non-conservation.
Stochastic dark energy from inflationary quantum fluctuations
Glavan, Dražen; Prokopec, Tomislav; Starobinsky, Alexei A.
2018-05-01
We study the quantum backreaction from inflationary fluctuations of a very light, non-minimally coupled spectator scalar and show that it is a viable candidate for dark energy. The problem is solved by suitably adapting the formalism of stochastic inflation. This allows us to self-consistently account for the backreaction on the background expansion rate of the Universe where its effects are large. This framework is equivalent to that of semiclassical gravity in which matter vacuum fluctuations are included at the one loop level, but purely quantum gravitational fluctuations are neglected. Our results show that dark energy in our model can be characterized by a distinct effective equation of state parameter (as a function of redshift) which allows for testing of the model at the level of the background.
ASTROPHYSICS. Atom-interferometry constraints on dark energy.
Hamilton, P; Jaffe, M; Haslinger, P; Simmons, Q; Müller, H; Khoury, J
2015-08-21
If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms, however, can evade these tests by suppressing the forces in regions of high density, such as the laboratory. Using a cesium matter-wave interferometer near a spherical mass in an ultrahigh-vacuum chamber, we reduced the screening mechanism by probing the field with individual atoms rather than with bulk matter. We thereby constrained a wide class of dark energy theories, including a range of chameleon and other theories that reproduce the observed cosmic acceleration. Copyright © 2015, American Association for the Advancement of Science.
CMB bounds on dark matter annihilation: Nucleon energy losses after recombination
Weniger, C.; Serpico, P.D.; Iocco, F.; Bertone, G.
2013-01-01
We consider the propagation and energy losses of protons and antiprotons produced by dark matter annihilation at redshifts 100
Linder, Eric V.
2010-01-01
Cosmologists are just beginning to probe the properties of the cosmic vacuum and its role in reversing the attractive pull of gravity to cause an acceleration in the expansion of the cosmos. The cause of this acceleration is given the generic name of dark energy, whether it is due to a true vacuum, a false, temporary vacuum, or a new relation between the vacuum and the force of gravity. Despite the common name, the distinction between these origins is of utmost interest and physicists are act...
Plane Symmetric Dark Energy Models in the Form of Wet Dark Fluid in f ( R, T) Gravity
Chirde, V. R.; Shekh, S. H.
2016-06-01
In this paper, we have investigated the plane symmetric space-time with wet dark fluid (WDF), which is a candidate for dark energy, in the framework of f ( R, T) gravity Harko et al. 2011, Phys. Rev. D, 84, 024020), where R and T denote the Ricci scalar and the trace of the energy-momentum tensor respectively. We have used the equation of state in the form of WDF for the dark energy component of the Universe. It is modeled on the equation of state p = ω( ρ - ρ ∗). The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied. Also, we have discussed the well-known astrophysical phenomena, namely the look-back time, proper distance, the luminosity distance and angular diameter distance with red shift.
DOE and NASA joint Dark Energy mission
2003-01-01
"DOE and NASA announced their plan for a Joint Dark Energy Mission (JDEM) on October 23, 2003, at the NASA Office of Space Science Structure and Evolution of the Universe Subcommittee (SEUS) meeting" (1 paragraph).
Modified dark matter: Relating dark energy, dark matter and baryonic matter
Edmonds, Douglas; Farrah, Duncan; Minic, Djordje; Ng, Y. Jack; Takeuchi, Tatsu
Modified dark matter (MDM) is a phenomenological model of dark matter, inspired by gravitational thermodynamics. For an accelerating universe with positive cosmological constant (Λ), such phenomenological considerations lead to the emergence of a critical acceleration parameter related to Λ. Such a critical acceleration is an effective phenomenological manifestation of MDM, and it is found in correlations between dark matter and baryonic matter in galaxy rotation curves. The resulting MDM mass profiles, which are sensitive to Λ, are consistent with observational data at both the galactic and cluster scales. In particular, the same critical acceleration appears both in the galactic and cluster data fits based on MDM. Furthermore, using some robust qualitative arguments, MDM appears to work well on cosmological scales, even though quantitative studies are still lacking. Finally, we comment on certain nonlocal aspects of the quanta of modified dark matter, which may lead to novel nonparticle phenomenology and which may explain why, so far, dark matter detection experiments have failed to detect dark matter particles.
Dark matter, dark energy, gravitational lensing and the formation of structure in the universe
International Nuclear Information System (INIS)
Bernardeau, Francis
2003-01-01
The large-scale structure of the universe and its statistical properties can reveal many aspects of the physics of the early universe as well as of its matter content during the cosmic history. Numerous observations, based to a large extent on large-scale structure data, have given us a concordant picture of the energy and matter content in the universe. In view of these results the existence of dark matter has been firmly established although it still evades attempts at direct detection. An even more challenging puzzle is, however, yet to be explained. Indeed the model suggested by the observations is only viable with the presence of a 'dark energy', an ethereal energy associated with the cosmological vacuum, that would represent about two-thirds of the total energy density of the universe. Although strongly indicated by observations, the existence of this component is nonetheless very uncomfortable from a high-energy physics point of view. Its interpretation is a matter of far reaching debates. Indeed, the phenomenological manifestation of this component can be viewed as a geometrical property of large-scale gravity, or as the energy associated with the quantum field vacuum, or else as the manifestation of a new sort of cosmic fluid that would fill space and remain unclustered. Low redshift detailed examinations of the geometrical or clustering properties of the universe should in all cases help clarify the true nature of the dark energy. We present methods that can be used in the future for exploring the low redshift physical properties of the universe. Particular emphasis will be placed on the use of large-scale structure surveys and more specifically on weak lensing surveys that promise to be extremely powerful in exploring the large-scale mass distribution in the universe
Dark Energy Studies with LSST Image Simulations, Final Report
International Nuclear Information System (INIS)
Peterson, John Russell
2016-01-01
This grant funded the development and dissemination of the Photon Simulator (PhoSim) for the purpose of studying dark energy at high precision with the upcoming Large Synoptic Survey Telescope (LSST) astronomical survey. The work was in collaboration with the LSST Dark Energy Science Collaboration (DESC). Several detailed physics improvements were made in the optics, atmosphere, and sensor, a number of validation studies were performed, and a significant number of usability features were implemented. Future work in DESC will use PhoSim as the image simulation tool for data challenges used by the analysis groups.
Search for dark sectors in missing energy events
Enik, T; Rubbia, A; Depero, E; Krasnikov, N; Petukhov, O; Kuleshov, S; Volkov, P; Trifonov, A; Radics, B; Toropin, A; Dermenev, A; Ahmed, N; Peshekhonov, D; Peshekhonov, V; Kekelidze, G; Dusaev, R; Vasilishin, B; Crivelli, P; Tlisov, D; Karjavine, V; Donskov, S; Lyubovitsky, V; Zhukov, K; Kirsanov, M; Karneyeu, A; Matveev, V; Lysan, V; Samoylenko, V
The NA64 experiment (known as P348 at the proposal stage) is a fixed-target experiment at the CERN SPS combining the active beam dump and missing energy techniques to search for rare events. The experiment will build and operate a fully hermetic detector placed on the H4 beam line with the primary goal to search for light dark bosons (Z') from dark sector that are coupled to photons, e.g. dark photons (A'), or sub-GeV Z' coupled only to quarks. In some cases the Z' is coupled only to µ or tau, so we call the Z′ the dark leptonic gauge boson. The experiment is also capable to search for K_L -> invisible decay, which is complementary to K+ -> π+ + ν ν, and invisible decays of π0, η, η′, K_S mesons.
Debnath, Ujjal
2010-01-01
We have considered a cosmological model of holographic dark energy interacting with dark matter and another unknown component of dark energy of the universe. We have assumed two interaction terms $Q$ and $Q'$ in order to include the scenario in which the mutual interaction between the two principal components (i.e., holographic dark energy and dark matter) of the universe leads to some loss in other forms of cosmic constituents. Our model is valid for any sign of $Q$ and $Q'$. If $Q
International Nuclear Information System (INIS)
Wang, Y. T.; Xu, L. X.; Gui, Y. X.
2010-01-01
In this paper, we investigate the integrated Sachs-Wolfe effect in the quintessence cold dark matter model with constant equation of state and constant speed of sound in dark energy rest frame, including dark energy perturbation and its anisotropic stress. Comparing with the ΛCDM model, we find that the integrated Sachs-Wolfe (ISW)-power spectrums are affected by different background evolutions and dark energy perturbation. As we change the speed of sound from 1 to 0 in the quintessence cold dark matter model with given state parameters, it is found that the inclusion of dark energy anisotropic stress makes the variation of magnitude of the ISW source uncertain due to the anticorrelation between the speed of sound and the ratio of dark energy density perturbation contrast to dark matter density perturbation contrast in the ISW-source term. Thus, the magnitude of the ISW-source term is governed by the competition between the alterant multiple of (1+3/2xc-circumflex s 2 ) and that of δ de /δ m with the variation of c-circumflex s 2 .
Neutrino mixing, flavor states and dark energy
International Nuclear Information System (INIS)
Blasone, M.; Capolupo, A.; Capozziello, S.; Vitiello, G.
2008-01-01
We shortly summarize the quantum field theory formalism for the neutrino mixing and report on recent results showing that the vacuum condensate induced by neutrino mixing can be interpreted as a dark energy component of the Universe
Energy-exchange collisions of dark-bright-bright vector solitons.
Radhakrishnan, R; Manikandan, N; Aravinthan, K
2015-12-01
We find a dark component guiding the practically interesting bright-bright vector one-soliton to two different parametric domains giving rise to different physical situations by constructing a more general form of three-component dark-bright-bright mixed vector one-soliton solution of the generalized Manakov model with nine free real parameters. Moreover our main investigation of the collision dynamics of such mixed vector solitons by constructing the multisoliton solution of the generalized Manakov model with the help of Hirota technique reveals that the dark-bright-bright vector two-soliton supports energy-exchange collision dynamics. In particular the dark component preserves its initial form and the energy-exchange collision property of the bright-bright vector two-soliton solution of the Manakov model during collision. In addition the interactions between bound state dark-bright-bright vector solitons reveal oscillations in their amplitudes. A similar kind of breathing effect was also experimentally observed in the Bose-Einstein condensates. Some possible ways are theoretically suggested not only to control this breathing effect but also to manage the beating, bouncing, jumping, and attraction effects in the collision dynamics of dark-bright-bright vector solitons. The role of multiple free parameters in our solution is examined to define polarization vector, envelope speed, envelope width, envelope amplitude, grayness, and complex modulation of our solution. It is interesting to note that the polarization vector of our mixed vector one-soliton evolves in sphere or hyperboloid depending upon the initial parametric choices.
Interacting polytropic gas model of phantom dark energy in non-flat universe
International Nuclear Information System (INIS)
Karami, K.; Ghaffari, S.; Fehri, J.
2009-01-01
By introducing the polytropic gas model of interacting dark energy, we obtain the equation of state for the polytropic gas energy density in a non-flat universe. We show that for an even polytropic index by choosing K>Ba (3)/(n) , one can obtain ω Λ eff <-1, which corresponds to a universe dominated by phantom dark energy. (orig.)
Cosmological effects of a class of fluid dark energy models
International Nuclear Information System (INIS)
Carturan, Daniela; Finelli, Fabio
2003-01-01
We study the impact of a generalized Chaplygin gas as a candidate for dark energy on density perturbations and on cosmic microwave background (CMB) anisotropies. The generalized Chaplygin gas is a fluid component with an exotic equation of state p=-A/ρ α (a polytropic gas with negative constant and exponent). Such a component interpolates in time between dust and a cosmological constant, with an intermediate behavior as p=A 1/(1+α) +αρ. Perturbations of this fluid are stable on small scales but behave in a very different way with respect to standard quintessence. Moreover, a generalized Chaplygin gas could also represent an archetypal example of the phenomenological unified models of dark energy and dark matter. The results presented here show how CMB anisotropies and density perturbations in this class of models differ from those of a cold dark matter model with a cosmological constant
Evolution of perturbations in distinct classes of canonical scalar field models of dark energy
International Nuclear Information System (INIS)
Jassal, H. K.
2010-01-01
Dark energy must cluster in order to be consistent with the equivalence principle. The background evolution can be effectively modeled by either a scalar field or by a barotropic fluid. The fluid model can be used to emulate perturbations in a scalar field model of dark energy, though this model breaks down at large scales. In this paper we study evolution of dark energy perturbations in canonical scalar field models: the classes of thawing and freezing models. The dark energy equation of state evolves differently in these classes. In freezing models, the equation of state deviates from that of a cosmological constant at early times. For thawing models, the dark energy equation of state remains near that of the cosmological constant at early times and begins to deviate from it only at late times. Since the dark energy equation of state evolves differently in these classes, the dark energy perturbations too evolve differently. In freezing models, since the equation of state deviates from that of a cosmological constant at early times, there is a significant difference in evolution of matter perturbations from those in the cosmological constant model. In comparison, matter perturbations in thawing models differ from the cosmological constant only at late times. This difference provides an additional handle to distinguish between these classes of models and this difference should manifest itself in the integrated Sachs-Wolfe effect.
International Nuclear Information System (INIS)
Guo, Rui-Yun; Zhang, Xin
2016-01-01
The nature of dark energy affects the Hubble expansion rate (namely, the expansion history) H(z) by an integral over w(z). However, the usual observables are the luminosity distances or the angular diameter distances, which measure the distance.redshift relation. Actually, the property of dark energy affects the distances (and the growth factor) by a further integration over functions of H(z). Thus, the direct measurements of the Hubble parameter H(z) at different redshifts are of great importance for constraining the properties of dark energy. In this paper, we show how the typical dark energy models, for example, the ΛCDM, wCDM, CPL, and holographic dark energy models, can be constrained by the current direct measurements of H(z) (31 data used in total in this paper, covering the redshift range of z @ element of [0.07, 2.34]). In fact, the future redshift-drift observations (also referred to as the Sandage-Loeb test) can also directly measure H(z) at higher redshifts, covering the range of z @ element of [2, 5]. We thus discuss what role the redshift-drift observations can play in constraining dark energy with the Hubble parameter measurements. We show that the constraints on dark energy can be improved greatly with the H(z) data from only a 10-year observation of redshift drift. (orig.)
Another two dark energy models motivated from Karolyhazy uncertainty relation
Energy Technology Data Exchange (ETDEWEB)
Sun, Cheng-Yi; Yang, Wen-Li; Song, Yu. [Northwest University, Institute of Modern Physics, Xian (China); Yue, Rui-Hong [Ningbo University, Faculty of Science, Ningbo (China)
2012-03-15
The Karolyhazy uncertainty relation indicates that there exists a minimal detectable cell {delta}t{sup 3} over the region t{sup 3} in Minkowski space-time. Due to the energy-time uncertainty relation, the energy of the cell {delta}t {sup 3} cannot be less {delta}t{sup -1}. Then we get a new energy density of metric fluctuations of Minkowski spacetime as {delta}t{sup -4}. Motivated by the energy density, we propose two new dark-energy models. One model is characterized by the age of the universe and the other is characterized by the conformal age of the universe. We find that in the two models, the dark energy mimics a cosmological constant in the late time. (orig.)
Dissipative generalized Chaplygin gas as phantom dark energy
International Nuclear Information System (INIS)
Cruz, Norman; Lepe, Samuel; Pena, Francisco
2007-01-01
The generalized Chaplygin gas, characterized by the equation of state p=-A/ρ α , has been considered as a model for dark energy due to its dark-energy-like evolution at late times. When dissipative processes are taken into account, within the framework of the standard Eckart theory of relativistic irreversible thermodynamics, cosmological analytical solutions are found. Using the truncated causal version of the Israel-Stewart formalism, a suitable model was constructed which crosses the w=-1 barrier. The future-singularities encountered in both approaches are of a new type, and not included in the classification presented by Nojiri and Odintsov [S. Nojiri, S.D. Odintsov, Phys. Rev. D 72 (2005) 023003
Dissipative generalized Chaplygin gas as phantom dark energy
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile)]. E-mail: ncruz@lauca.usach.cl; Lepe, Samuel [Instituto de Fisica, Facultad de Ciencias Basicas y Matematicas, Pontificia Universidad Catolica de Valparaiso, Avenida Brasil 2950, Valparaiso (Chile)]. E-mail: slepe@ucv.cl; Pena, Francisco [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de la Frontera, Avda. Francisco Salazar 01145, Casilla 54-D, Temuco (Chile)]. E-mail: fcampos@ufro.cl
2007-03-15
The generalized Chaplygin gas, characterized by the equation of state p=-A/{rho}{sup {alpha}}, has been considered as a model for dark energy due to its dark-energy-like evolution at late times. When dissipative processes are taken into account, within the framework of the standard Eckart theory of relativistic irreversible thermodynamics, cosmological analytical solutions are found. Using the truncated causal version of the Israel-Stewart formalism, a suitable model was constructed which crosses the w=-1 barrier. The future-singularities encountered in both approaches are of a new type, and not included in the classification presented by Nojiri and Odintsov [S. Nojiri, S.D. Odintsov, Phys. Rev. D 72 (2005) 023003].
Ten scenarios from early radiation to late time acceleration with a minimally coupled dark energy
Energy Technology Data Exchange (ETDEWEB)
Fay, Stéphane, E-mail: steph.fay@gmail.com [Palais de la Découverte, Astronomy Department, Avenue Franklin Roosevelt, 75008 Paris (France)
2013-09-01
We consider General Relativity with matter, radiation and a minimally coupled dark energy defined by an equation of state w. Using dynamical system method, we find the equilibrium points of such a theory assuming an expanding Universe and a positive dark energy density. Two of these points correspond to classical radiation and matter dominated epochs for the Universe. For the other points, dark energy mimics matter, radiation or accelerates Universe expansion. We then look for possible sequences of epochs describing a Universe starting with some radiation dominated epoch(s) (mimicked or not by dark energy), then matter dominated epoch(s) (mimicked or not by dark energy) and ending with an accelerated expansion. We find ten sequences able to follow this Universe history without singular behaviour of w at some saddle points. Most of them are new in dark energy literature. To get more than these ten sequences, w has to be singular at some specific saddle equilibrium points. This is an unusual mathematical property of the equation of state in dark energy literature, whose physical consequences tend to be discarded by observations. This thus distinguishes the ten above sequences from an infinity of ways to describe Universe expansion.
Ten scenarios from early radiation to late time acceleration with a minimally coupled dark energy
International Nuclear Information System (INIS)
Fay, Stéphane
2013-01-01
We consider General Relativity with matter, radiation and a minimally coupled dark energy defined by an equation of state w. Using dynamical system method, we find the equilibrium points of such a theory assuming an expanding Universe and a positive dark energy density. Two of these points correspond to classical radiation and matter dominated epochs for the Universe. For the other points, dark energy mimics matter, radiation or accelerates Universe expansion. We then look for possible sequences of epochs describing a Universe starting with some radiation dominated epoch(s) (mimicked or not by dark energy), then matter dominated epoch(s) (mimicked or not by dark energy) and ending with an accelerated expansion. We find ten sequences able to follow this Universe history without singular behaviour of w at some saddle points. Most of them are new in dark energy literature. To get more than these ten sequences, w has to be singular at some specific saddle equilibrium points. This is an unusual mathematical property of the equation of state in dark energy literature, whose physical consequences tend to be discarded by observations. This thus distinguishes the ten above sequences from an infinity of ways to describe Universe expansion
Dark interactions and cosmological fine-tuning
Energy Technology Data Exchange (ETDEWEB)
Quartin, Miguel; Calvao, Mauricio O; Joras, Sergio E; Reis, Ribamar R R; Waga, Ioav, E-mail: mquartin@if.ufrj.br, E-mail: orca@if.ufrj.br, E-mail: joras@if.ufrj.br, E-mail: ribamar@if.ufrj.br, E-mail: ioav@if.ufrj.br [Instituto de Fisica, Universidade Federal do Rio de Janeiro, CEP 21941-972, Rio de Janeiro, RJ (Brazil)
2008-05-15
Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the {Lambda}CDM (CDM: cold dark matter) model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme, this paper aims to unite these different approaches and shed some light on whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way.
Quantum mechanical look at the radioactive-like decay of metastable dark energy
Energy Technology Data Exchange (ETDEWEB)
Szydlowski, Marek [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Jagiellonian University, Mark Kac Complex Systems Research Centre, Krakow (Poland); Stachowski, Aleksander [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Urbanowski, Krzysztof [University of Zielona Gora, Institute of Physics, Zielona Gora (Poland)
2017-12-15
We derive the Shafieloo, Hazra, Sahni and Starobinsky (SHSS) phenomenological formula for the radioactive-like decay of metastable dark energy directly from the principles of quantum mechanics. To this aim we use the Fock-Krylov theory of quantum unstable states. We obtain deeper insight on the decay process as having three basic phases: the phase of radioactive decay, the next phase of damping oscillations, and finally the phase of power-law decay. We consider the cosmological model with matter and dark energy in the form of decaying metastable dark energy and study its dynamics in the framework of non-conservative cosmology with an interacting term determined by the running cosmological parameter. We study the cosmological implications of metastable dark energy and estimate the characteristic time of ending of the radioactive-like decay epoch to be 2.2 x 10{sup 4} of the present age of the Universe. We also confront the model with astronomical data which show that the model is in good agreement with the observations. Our general conclusion is that we are living in the epoch of the radioactive-like decay of metastable dark energy which is a relict of the quantum age of the Universe. (orig.)
Probing the dynamics of dark energy with novel parametrizations
International Nuclear Information System (INIS)
Ma Jingzhe; Zhang Xin
2011-01-01
We point out that the CPL parametrization has a problem that the equation of state w(z) diverges in the far future, so that this model can only properly describe the past evolution but cannot depict the future evolution. To overcome such a difficulty, in this Letter we propose two novel parametrizations for dark energy, the logarithm form w(z)=w 0 +w 1 ((ln(2+z))/(1+z) -ln2) and the oscillating form w(z)=w 0 +w 1 ((sin(1+z))/(1+z) -sin(1)), successfully avoiding the future divergency problem in the CPL parametrization, and use them to probe the dynamics of dark energy in the whole evolutionary history. Our divergency-free parametrizations are proven to be very successful in exploring the dynamical evolution of dark energy and have powerful prediction capability for the ultimate fate of the universe. Constraining the CPL model and the new models with the current observational data, we show that the new models are more favored. The features and the predictions for the future evolution in the new models are discussed in detail.
Constraining Dark Energy with X-ray Clusters, SNe Ia and the CMB
International Nuclear Information System (INIS)
Rapetti, D
2005-01-01
In [1] we present new constraints on the evolution of dark energy from an analysis of Cosmic Microwave Background, supernova and X-ray galaxy cluster data. From a combined analysis of all three data sets and assuming that the Universe is at, we examine a series of dark energy models with up to three free parameters: the current dark energy equation of state w 0 , the early time equation of state w et and the scale factor at transition, a t . Allowing the transition scale factor to vary over the range 0.5 t 0 = -1.27 -0.39 +0.33 and w et = -0.66 -0.62 +0.44 . They find no significant evidence for evolution in the dark energy equation of state parameter with redshift. The complementary nature of the data sets leads to a tight constraint on the mean matter density, (Omega) m , alleviates a number of other parameter degeneracies, including that between the scalar spectral index n s , the physical baryon density (Omega) b h 2 and the optical depth τ and also allows us to examine models dropping the flatness prior. As required for the energy-momentum conservation our analysis includes spatial perturbations in the dark energy component. We show that not including them leads to spuriously tighter constraints on w 0 and especially on wet
Revisiting a model-independent dark energy reconstruction method
Energy Technology Data Exchange (ETDEWEB)
Lazkoz, Ruth; Salzano, Vincenzo; Sendra, Irene [Euskal Herriko Unibertsitatea, Fisika Teorikoaren eta Zientziaren Historia Saila, Zientzia eta Teknologia Fakultatea, Bilbao (Spain)
2012-09-15
In this work we offer new insights into the model-independent dark energy reconstruction method developed by Daly and Djorgovski (Astrophys. J. 597:9, 2003; Astrophys. J. 612:652, 2004; Astrophys. J. 677:1, 2008). Our results, using updated SNeIa and GRBs, allow to highlight some of the intrinsic weaknesses of the method. Conclusions on the main dark energy features as drawn from this method are intimately related to the features of the samples themselves, particularly for GRBs, which are poor performers in this context and cannot be used for cosmological purposes, that is, the state of the art does not allow to regard them on the same quality basis as SNeIa. We find there is a considerable sensitivity to some parameters (window width, overlap, selection criteria) affecting the results. Then, we try to establish what the current redshift range is for which one can make solid predictions on dark energy evolution. Finally, we strengthen the former view that this model is modest in the sense it provides only a picture of the global trend and has to be managed very carefully. But, on the other hand, we believe it offers an interesting complement to other approaches, given that it works on minimal assumptions. (orig.)
Finding structure in the dark: Coupled dark energy, weak lensing, and the mildly nonlinear regime
Miranda, Vinicius; González, Mariana Carrillo; Krause, Elisabeth; Trodden, Mark
2018-03-01
We reexamine interactions between the dark sectors of cosmology, with a focus on robust constraints that can be obtained using only mildly nonlinear scales. While it is well known that couplings between dark matter and dark energy can be constrained to the percent level when including the full range of scales probed by future optical surveys, calibrating matter power spectrum emulators to all possible choices of potentials and couplings requires many computationally expensive n-body simulations. Here we show that lensing and clustering of galaxies in combination with the cosmic microwave background (CMB) are capable of probing the dark sector coupling to the few percent level for a given class of models, using only linear and quasilinear Fourier modes. These scales can, in principle, be described by semianalytical techniques such as the effective field theory of large-scale structure.
Characterizing Dark Energy Through Supernovae
Davis, Tamara M.; Parkinson, David
Type Ia supernovae are a powerful cosmological probe that gave the first strong evidence that the expansion of the universe is accelerating. Here we provide an overview of how supernovae can go further to reveal information about what is causing the acceleration, be it dark energy or some modification to our laws of gravity. We first review the methods of statistical inference that are commonly used, making a point of separating parameter estimation from model selection. We then summarize the many different approaches used to explain or test the acceleration, including parametric models (like the standard model, ΛCDM), nonparametric models, dark fluid models such as quintessence, and extensions to standard gravity. Finally, we also show how supernova data can be used beyond the Hubble diagram, to give information on gravitational lensing and peculiar velocities that can be used to distinguish between models that predict the same expansion history.
Holographic Dark Energy with Generalized Chaplygin Gas in Higher Dimensions
Ghose, S.; Saha, A.; Paul, B. C.
2014-11-01
We investigate holographic dark energy (HDE) correspondence of interacting Generalized Chaplygin Gas (GCG) in the framework of compact Kaluza-Klein (KK) cosmology. The evolution of the modified HDE with corresponding equation of state is obtained here. Considering the present value of the density parameter a stable configuration is found which accommodates Dark Energy (DE). We note a connection between DE and Phantom fields. It reveals that the DE might have evolved from a Phantom state in the past.
International Nuclear Information System (INIS)
Arun, K G; Mishra, Chandra Kant; Iyer, B R; Sinha, Siddhartha; Van Den Broeck, Chris; Sathyaprakash, B S
2009-01-01
Recently, it has been shown that the inclusion of higher signal harmonics in the inspiral signals of binary supermassive black holes (SMBH) leads to dramatic improvements in the parameter estimation with Laser Interferometer Space Antenna (LISA). In particular, the angular resolution becomes good enough to identify the host galaxy or galaxy cluster, in which case the redshift can be determined by electromagnetic means. The gravitational wave signal also provides the luminosity distance with high accuracy, and the relationship between this and the redshift depends sensitively on the cosmological parameters, such as the equation-of-state parameter w = p DE /ρ DE of dark energy. Using binary SMBH events at z < 1 with appropriate masses and orientations, one would be able to constrain w to within a few per cent. We show that, if the measured sky location is folded into the error analysis, the uncertainty on w goes down by an additional factor of 2-3, leaving weak lensing as the only limiting factor in using LISA as a dark energy probe.
Quadratic interaction effect on the dark energy density in the universe
International Nuclear Information System (INIS)
Deveci, Derya G; Aydiner, Ekrem
2017-01-01
In this study, we deal with the holographic model of interacting dark components of dark energy and dark matter quadratic case of the equation of state parameter (EoS). The effective equations of states for the interacting holographic energy density are derived and the results are analyzed and compared with the solution of the linear form in the literature. The result of our work shows that the value of interaction term between dark components affects the fixed points at far future in the DE-dominated universe in the case of quadratic EoS parameter; it is a different result from the linear case in the theoretical results in the literature, and as the Quintom scenario the equations of state had coincidence at the cosmological constant boundary of –1 from above to below. (paper)
The Matrix Reloaded - on the Dark Energy Seesaw
DEFF Research Database (Denmark)
Enqvist, Kari; Hannestad, Steen; Sloth, Martin Snoager
2007-01-01
We propose a novel mechanism for dark energy, based on an extended seesaw for scalar fields, which does not require any new physics at energies below the TeV scale. A very light quintessence mass is usually considered to be technically unnatural, unless it is protected by some symmetry broken...
The year in ideas; dark energy
Burdick, A
2002-01-01
Gravity should halt the expansion of the universe but a few years ago a study of supernovae showed that in fact cosmic expansion is speeding up. To explain this, cosmologists have postulated that a strange, repulsive force, which they call dark energy, is at work, counteracting gravity and pushing galaxies apart at an accelerating rate (1/2 page).
Dark energy and the anthropic principle
Czech Academy of Sciences Publication Activity Database
Křížek, Michal
2012-01-01
Roč. 17, č. 1 (2012), s. 1-7 ISSN 1384-1076 R&D Projects: GA AV ČR(CZ) IAA100190803 Institutional research plan: CEZ:AV0Z10190503 Keywords : Hubble constant * dark energy * Mars * gravitational aberration Subject RIV: BA - General Mathematics Impact factor: 1.850, year: 2012 http://www.sciencedirect.com/science/article/pii/S1384107611000558
Unified dark energy and dust dark matter dual to quadratic purely kinetic K-essence
International Nuclear Information System (INIS)
Guendelman, Eduardo; Nissimov, Emil; Pacheva, Svetlana
2016-01-01
We consider a modified gravity plus single scalar-field model, where the scalar Lagrangian couples symmetrically both to the standard Riemannian volume-form (spacetime integration measure density) given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume-form in terms of an auxiliary maximal-rank antisymmetric tensor gauge field. As shown in a previous paper, the pertinent scalar-field dynamics provides an exact unified description of both dark energy via dynamical generation of a cosmological constant, and dark matter as a ''dust'' fluid with geodesic flow as a result of a hidden Noether symmetry. Here we extend the discussion by considering a non-trivial modification of the purely gravitational action in the form of f(R) = R -αR 2 generalized gravity. Upon deriving the corresponding ''Einstein-frame'' effective action of the latter modified gravity-scalar-field theory we find explicit duality (in the sense of weak versus strong coupling) between the original model of unified dynamical dark energy and dust fluid dark matter, on one hand, and a specific quadratic purely kinetic ''k-essence'' gravity-matter model with special dependence of its coupling constants on only two independent parameters, on the other hand. The canonical Hamiltonian treatment and Wheeler-DeWitt quantization of the dual purely kinetic ''k-essence'' gravity-matter model is also briefly discussed. (orig.)
First Light for BOSS - A New Kind of Search for Dark Energy | Berkeley
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Dark energy and modified gravity in the Effective Field Theory of Large-Scale Structure
Cusin, Giulia; Lewandowski, Matthew; Vernizzi, Filippo
2018-04-01
We develop an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models. We do so by combining the Effective Field Theory of Dark Energy and Effective Field Theory of Large-Scale Structure approaches. In particular, we parametrize the linear and nonlinear effects of dark energy on dark matter clustering in terms of the Lagrangian terms introduced in a companion paper [1], focusing on Horndeski theories and assuming the quasi-static approximation. The Euler equation for dark matter is sourced, via the Newtonian potential, by new nonlinear vertices due to modified gravity and, as in the pure dark matter case, by the effects of short-scale physics in the form of the divergence of an effective stress tensor. The effective fluid introduces a counterterm in the solution to the matter continuity and Euler equations, which allows a controlled expansion of clustering statistics on mildly nonlinear scales. We use this setup to compute the one-loop dark-matter power spectrum.
International Nuclear Information System (INIS)
Feng Chaojun; Li Xinzhou
2009-01-01
We investigate the viscous Ricci dark energy (RDE) model by assuming that there is bulk viscosity in the linear barotropic fluid and the RDE. In the RDE model without bulk viscosity, the universe is younger than some old objects at certain redshifts. Since the age of the universe should be longer than any objects living in the universe, the RDE model suffers the age problem, especially when we consider the object APM 08279+5255 at z=3.91 with age t=2.1 Gyr. In this Letter, we find that once the viscosity is taken into account, this age problem is alleviated.
Exploring parameter constraints on quintessential dark energy: The exponential model
International Nuclear Information System (INIS)
Bozek, Brandon; Abrahamse, Augusta; Albrecht, Andreas; Barnard, Michael
2008-01-01
We present an analysis of a scalar field model of dark energy with an exponential potential using the Dark Energy Task Force (DETF) simulated data models. Using Markov Chain Monte Carlo sampling techniques we examine the ability of each simulated data set to constrain the parameter space of the exponential potential for data sets based on a cosmological constant and a specific exponential scalar field model. We compare our results with the constraining power calculated by the DETF using their 'w 0 -w a ' parametrization of the dark energy. We find that respective increases in constraining power from one stage to the next produced by our analysis give results consistent with DETF results. To further investigate the potential impact of future experiments, we also generate simulated data for an exponential model background cosmology which cannot be distinguished from a cosmological constant at DETF 'Stage 2', and show that for this cosmology good DETF Stage 4 data would exclude a cosmological constant by better than 3σ
Interacting viscous ghost tachyon, K-essence and dilaton scalar field models of dark energy
International Nuclear Information System (INIS)
Karami, K; Fahimi, K
2013-01-01
We study the correspondence between the interacting viscous ghost dark energy model with the tachyon, K-essence and dilaton scalar field models in the framework of Einstein gravity. We consider a spatially non-flat FRW universe filled with interacting viscous ghost dark energy and dark matter. We reconstruct both the dynamics and potential of these scalar field models according to the evolutionary behavior of the interacting viscous ghost dark energy model, which can describe the accelerated expansion of the universe. Our numerical results show that the interaction and viscosity have opposite effects on the evolutionary properties of the ghost scalar field models. (paper)
Constraining Dark Energy with X-ray Galaxy Clusters, Supernovae and the Cosmic Microwave Background
International Nuclear Information System (INIS)
Rapetti, D
2005-01-01
We present new constraints on the evolution of dark energy from an analysis of Cosmic Microwave Background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state w 0 , the early time equation of state w et and the scale factor at transition, a t . From a combined analysis of all three data sets, assuming a constant equation of state and that the Universe is flat, we measure w 0 = 1.05 -0.12 +0.10 . Including w et as a free parameter and allowing the transition scale factor to vary over the range 0.5 t 0 = -1.27 -0.39 +0.33 and w et = -0.66 -0.62 +0.44 . We find no significant evidence for evolution in the dark energy equation of state parameter with redshift. Marginal hints of evolution in the supernovae data become less significant when the cluster constraints are also included in the analysis. The complementary nature of the data sets leads to a tight constraint on the mean matter density, (Omega) m and alleviates a number of other parameter degeneracies, including that between the scalar spectral index n s , the physical baryon density (Omega) b h 2 and the optical depth τ. This complementary nature also allows us to examine models in which we drop the prior on the curvature. For non-flat models with a constant equation of state, we measure w 0 = -1.09 -0.15 +0.12 and obtain a tight constraint on the current dark energy density, (Omega) de = 0.70 ± 0.03. For dark energy models other than a cosmological constant, energy-momentum conservation requires the inclusion of spatial perturbations in the dark energy component. Our analysis includes such perturbations, assuming a sound speed c s 2 = 1 in the dark energy fluid as expected for Quintessence scenarios. For our most general dark energy model, not including such perturbations would lead to spurious constraints
Ordinary matter, dark matter, and dark energy on normal Zeeman space-times
Imre Szabó, Zoltán
2017-01-01
Zeeman space-times are new, relativistic, and operator based Hamiltonian models representing multi-particle systems. They are established on Lorentzian pseudo Riemannian manifolds whose Laplacian immediately appears in the form of original quantum physical wave operators. In classical quantum theory they emerge, differently, from the Hamilton formalism and the correspondence principle. Nonetheless, this new model does not just reiterate the well known conceptions but holds the key to solving open problems of quantum theory. Most remarkably, it represents the dark matter, dark energy, and ordinary matter by the same ratios how they show up in experiments. Another remarkable agreement with reality is that the ordinary matter appears to be non-expanding and is described in consent with observations. The theory also explains gravitation, moreover, the Hamilton operators of all energy and matter formations, together with their physical properties, are solely derived from the Laplacian of the Zeeman space-time. By this reason, it is called Monistic Wave Laplacian which symbolizes an all-comprehensive unification of all matter and energy formations. This paper only outlines the normal case where the particles do not have proper spin but just angular momentum. The complete anomalous theory is detailed in [Sz2, Sz3, Sz4, Sz5, Sz6, Sz7].
The weight of the vacuum a scientific history of dark energy
Kragh, Helge S
2014-01-01
The 2011 Nobel Prize in Physics was awarded for the discovery of cosmic acceleration due to dark energy, a discovery that is all the more perplexing as nobody knows what dark energy actually is. We put the modern concept of cosmological vacuum energy into historical context and show how it grew out of disparate roots in quantum mechanics (zero-point energy) and relativity theory (the cosmological constant, Einstein's “greatest blunder”). These two influences have remained strangely aloof and still co-exist in an uneasy alliance that is at the heart of the greatest crisis in theoretical physics, the cosmological-constant problem.
Dark matter particle production in b→s transitions with missing energy
International Nuclear Information System (INIS)
Bird, Chris; Jackson, Paul; Kowalewski, Robert; Pospelov, Maxim
2004-01-01
Dedicated underground experiments searching for dark matter have little sensitivity to GeV and sub-GeV masses of dark matter particles. We show that the decay of B mesons to K(K * ) and missing energy in the final state can be an efficient probe of dark matter models in this mass range. We analyze the minimal scalar dark matter model to show that the width of the decay mode with two dark matter scalars B→KSS may exceed the decay width in the standard model channel, B→Kνν-bar, by up to 2 orders of magnitude. Existing data from B physics experiments almost entirely exclude dark matter scalars with masses less than 1 GeV. Expected data from B factories probe the range of dark matter masses up to 2 GeV
Thermodynamics of interacting holographic dark energy with the apparent horizon as an IR cutoff
International Nuclear Information System (INIS)
Sheykhi, Ahmad
2010-01-01
As soon as an interaction between holographic dark energy and dark matter is taken into account, the identification of an IR cutoff with the Hubble radius H -1 , in a flat universe, can simultaneously drive accelerated expansion and solve the coincidence problem. Based on this, we demonstrate that in a non-flat universe the natural choice for the IR cutoff could be the apparent horizon radius, r-tilde A =1/√(H 2 +k/a 2 ). We show that any interaction of dark matter with holographic dark energy, whose infrared cutoff is set by the apparent horizon radius, implies an accelerated expansion and a constant ratio of the energy densities of both components thus solving the coincidence problem. We also verify that for a universe filled with dark energy and dark matter, the Friedmann equation can be written in the form of the modified first law of thermodynamics, dE = T h dS h + WdV, at the apparent horizon. In addition, the generalized second law of thermodynamics is fulfilled in a region enclosed by the apparent horizon. These results hold regardless of the specific form of dark energy and interaction term. Our study might reveal that in an accelerating universe with spatial curvature, the apparent horizon is a physical boundary from the thermodynamical point of view.
The Dark Energy Survey Image Processing Pipeline
Energy Technology Data Exchange (ETDEWEB)
Morganson, E.; et al.
2018-01-09
The Dark Energy Survey (DES) is a five-year optical imaging campaign with the goal of understanding the origin of cosmic acceleration. DES performs a 5000 square degree survey of the southern sky in five optical bands (g,r,i,z,Y) to a depth of ~24th magnitude. Contemporaneously, DES performs a deep, time-domain survey in four optical bands (g,r,i,z) over 27 square degrees. DES exposures are processed nightly with an evolving data reduction pipeline and evaluated for image quality to determine if they need to be retaken. Difference imaging and transient source detection are also performed in the time domain component nightly. On a bi-annual basis, DES exposures are reprocessed with a refined pipeline and coadded to maximize imaging depth. Here we describe the DES image processing pipeline in support of DES science, as a reference for users of archival DES data, and as a guide for future astronomical surveys.
Dark energy in hybrid inflation
International Nuclear Information System (INIS)
Gong, Jinn-Ouk; Kim, Seongcheol
2007-01-01
The situation that a scalar field provides the source of the accelerated expansion of the Universe while rolling down its potential is common in both the simple models of the primordial inflation and the quintessence-based dark energy models. Motivated by this point, we address the possibility of causing the current acceleration via the primordial inflation using a simple model based on hybrid inflation. We trigger the onset of the motion of the quintessence field via the waterfall field, and find that the fate of the Universe depends on the true vacuum energy determined by choosing the parameters. We also briefly discuss the variation of the equation of state and the possible implementation of our scenario in supersymmetric theories
Bayesian evidences for dark energy models in light of current observational data
Lonappan, Anto. I.; Kumar, Sumit; Ruchika; Dinda, Bikash R.; Sen, Anjan A.
2018-02-01
We do a comprehensive study of the Bayesian evidences for a large number of dark energy models using a combination of latest cosmological data from SNIa, CMB, BAO, strong lensing time delay, growth measurements, measurements of Hubble parameter at different redshifts and measurements of angular diameter distance by Megamaser Cosmology Project. We consider a variety of scalar field models with different potentials as well as different parametrizations for the dark energy equation of state. Among 21 models that we consider in our study, we do not find strong evidences in favor of any evolving dark energy model compared to Λ CDM . For the evolving dark energy models, we show that purely nonphantom models have much better evidences compared to those models that allow both phantom and nonphantom behaviors. Canonical scalar field with exponential and tachyon field with square potential have highest evidences among all the models considered in this work. We also show that a combination of low redshift measurements decisively favors an accelerating Λ CDM model compared to a nonaccelerating power law model.
On the Origin of the Dark Matter/Energy in the Universe and the Pioneer Anomaly
Directory of Open Access Journals (Sweden)
Abraham A. Ungar
2008-07-01
Full Text Available Einstein's special relativity is a theory rich of paradoxes, one of which is the recently discovered Relativistic Invariant Mass Paradox. According to this Paradox, the relativistic invariant mass of a galaxy of moving stars exceeds the sum of the relativistic invariant masses of the constituent stars owing to their motion relative to each other. This excess of mass is the mass of virtual matter that has no physical properties other than positive relativistic invariant mass and, hence, that reveals its presence by no means other than gravity. As such, this virtual matter is the dark matter that cosmologists believe is necessary in order to supply the missing gravity that keeps galaxies stable. Based on the Relativistic Invariant Mass Paradox we offer in this article a model which quantifies the anomalous acceleration of Pioneer 10 and 11 spacecrafts and other deep space missions, and explains the presence of dark matter and dark energy in the universe. It turns out that the origin of dark matter and dark energy in the Universe lies in the Paradox, and that the origin of the Pioneer anomaly results from neglecting the Paradox. In order to appreciate the physical significance of the Paradox within the frame of Einstein's special theory of relativity, following the presentation of the Paradox we demonstrate that the Paradox is responsible for the extension of the kinetic energy theorem and of the additivity of energy and momentum from classical to relativistic mechanics. Clearly, the claim that the acceleration of Pioneer 10 and 11 spacecrafts is anomalous is incomplete, within the frame of Einstein's special relativity, since those who made the claim did not take into account the presence of the Relativistic Invariant Mass Paradox (which is understandable since the Paradox, published in the author's 2008 book, was discovered by the author only recently. It remains to test how well the Paradox accords with observations.
Strongly coupled dark energy with warm dark matter vs. LCDM
Energy Technology Data Exchange (ETDEWEB)
Bonometto, S.A.; Mezzetti, M. [INAF, Osservatorio di Trieste and Trieste University, Physics Department, Astronomy Unit, Via Tiepolo 11, 34143 Trieste (Italy); Mainini, R., E-mail: bonometto@oats.inaf.it, E-mail: mezzetti@oats.inaf.it, E-mail: roberto.mainini@mib.infn.it [Physics Department G. Occhialini, Milano-Bicocca University, Piazza della Scienza 3, 20126 Milano (Italy)
2017-10-01
Cosmologies including strongly Coupled (SC) Dark Energy (DE) and Warm dark matter (SCDEW) are based on a conformally invariant (CI) attractor solution modifying the early radiative expansion. Then, aside of radiation, a kinetic field Φ and a DM component account for a stationary fraction, ∼ 1 %, of the total energy. Most SCDEW predictions are hardly distinguishable from LCDM, while SCDEW alleviates quite a few LCDM conceptual problems, as well as its difficulties to meet data below the average galaxy scale. The CI expansion begins at the end of inflation, when Φ (future DE) possibly plays a role in reheating, and ends at the Higgs scale. Afterwards, a number of viable options is open, allowing for the transition from the CI expansion to the present Universe. In this paper: (i) We show how the attractor is recovered when the spin degrees of freedom decreases. (ii) We perform a detailed comparison of CMB anisotropy and polarization spectra for SCDEW and LCDM, including tensor components, finding negligible discrepancies. (iii) Linear spectra exhibit a greater parameter dependence at large k 's, but are still consistent with data for suitable parameter choices. (iv) We also compare previous simulation results with fresh data on galaxy concentration. Finally, (v) we outline numerical difficulties at high k . This motivates a second related paper [1], where such problems are treated in a quantitative way.
Examining the evidence for dynamical dark energy.
Zhao, Gong-Bo; Crittenden, Robert G; Pogosian, Levon; Zhang, Xinmin
2012-10-26
We apply a new nonparametric Bayesian method for reconstructing the evolution history of the equation of state w of dark energy, based on applying a correlated prior for w(z), to a collection of cosmological data. We combine the latest supernova (SNLS 3 year or Union 2.1), cosmic microwave background, redshift space distortion, and the baryonic acoustic oscillation measurements (including BOSS, WiggleZ, and 6dF) and find that the cosmological constant appears consistent with current data, but that a dynamical dark energy model which evolves from w-1 at higher redshift is mildly favored. Estimates of the Bayesian evidence show little preference between the cosmological constant model and the dynamical model for a range of correlated prior choices. Looking towards future data, we find that the best fit models for current data could be well distinguished from the ΛCDM model by observations such as Planck and Euclid-like surveys.
Holographic dark energy models: a comparison from the latest observational data
International Nuclear Information System (INIS)
Li, Miao; Li, Xiao-Dong; Wang, Shuang; Zhang, Xin
2009-01-01
The holographic principle of quantum gravity theory has been applied to the dark energy (DE) problem, and so far three holographic DE models have been proposed: the original holographic dark energy (HDE) model, the agegraphic dark energy (ADE) model, and the holographic Ricci dark energy (RDE) model. In this work, we perform the best-fit analysis on these three models, by using the latest observational data including the Union+CFA3 sample of 397 Type Ia supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). The analysis shows that for HDE, χ min 2 = 465.912; for RDE, χ min 2 = 483.130; for ADE, χ min 2 = 481.694. Among these models, HDE model can give the smallest χ 2 min . Besides, we also use the Bayesian evidence (BE) as a model selection criterion to make a comparison. It is found that for HDE, ADE, and RDE, Δln BE = −0.86, −5.17, and −8.14, respectively. So, it seems that the HDE model is more favored by the observational data
Dark energy equation of state and anthropic selection
International Nuclear Information System (INIS)
Garriga, Jaume; Linde, Andrei; Vilenkin, Alexander
2004-01-01
We explore the possibility that the dark energy is due to a potential of a scalar field and that the magnitude and the slope of this potential in our part of the Universe are largely determined by anthropic selection effects. We find that, in some models, the most probable values of the slope are very small, implying that the dark energy density stays constant to very high accuracy throughout cosmological evolution. In other models, however, the most probable values of the slope are such that the slow roll condition is only marginally satisfied, leading to a recollapse of the local universe on a time scale comparable to the lifetime of the Sun. In the latter case, the effective equation of state varies appreciably with the redshift, leading to a number of testable predictions
The Dark Energy Survey instrument design
International Nuclear Information System (INIS)
Flaugher, B.; Fermilab
2006-01-01
We describe a new project, the Dark Energy Survey (DES), aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of ∼5%, with four complementary techniques. The survey will use a new 3 sq. deg. mosaic camera (DECam) mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic camera, a five element optical corrector, four filters (g,r,i,z), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of 62 2K x 4K CCD modules (0.27''/pixel) arranged in a hexagon inscribed within the 2.2 deg. diameter field of view. We plan to use the 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). At Fermilab, we will establish a packaging factory to produce four-side buttable modules for the LBNL devices, as well as to test and grade the CCDs. R and D is underway and delivery of DECam to CTIO is scheduled for 2009
International Nuclear Information System (INIS)
Silk, Joseph
2010-01-01
One of the greatest mysteries in the cosmos is that it is mostly dark. That is, not only is the night sky dark, but also most of the matter and the energy in the universe is dark. For every atom visible in planets, stars and galaxies today there exists at least five or six times as much 'Dark Matter' in the universe. Astronomers and particle physicists today are seeking to unravel the nature of this mysterious but pervasive dark matter, which has profoundly influenced the formation of structure in the universe. Dark energy remains even more elusive, as we lack candidate fields that emerge from well established physics. I will describe various attempts to measure dark matter by direct and indirect means, and discuss the prospects for progress in unravelling dark energy.
Crossing the phantom divide with Ricci-like holographic dark energy
Energy Technology Data Exchange (ETDEWEB)
Lepe, S. [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Facultad de Ciencias, Casilla, Valparaiso (Chile); Pena, F. [Universidad de La Frontera, Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Temuco (Chile)
2010-10-15
In this work we study the dark energy problem by adopting an holographic model proposed recently in the literature. In this model there has been postulated an energy density {rho}{proportional_to}R, where R is the Ricci scalar curvature. Under this consideration, we have obtained a cosmological scenario which arises from considering two non-interacting fluids along the lines of a reasonable Ansatz for the cosmic coincidence parameter. We have adjusted the involved parameters in the model according to the observational data, showing that the equation of state for the dark energy exhibits a cross through the -1 barrier. Additionally, we have found a disagreement of these parameters in comparison with a scalar field theory approach. (orig.)
Entropy in the Present and Early Universe: New Small Parameters and Dark Energy Problem
Directory of Open Access Journals (Sweden)
Alexander Shalyt-Margolin
2010-04-01
Full Text Available It is demonstrated that entropy and its density play a significant role in solving the problem of the vacuum energy density (cosmological constant of the Universe and hence the dark energy problem. Taking this in mind, two most popular models for dark energy—Holographic Dark Energy Model and Agegraphic Dark Energy Model—are analysed. It is shown that the fundamental quantities in the first of these models may be expressed in terms of a new small dimensionless parameter that is naturally occurring in High Energy Gravitational Thermodynamics and Gravitational Holography (UV-limit. On this basis, the possibility of a new approach to the problem of Quantum Gravity is discussed. Besides, the results obtained on the uncertainty relation of the pair “cosmological constant–volume of space-time”, where the cosmological constant is a dynamic quantity, are reconsidered and generalized up to the Generalized Uncertainty Relation.
Interacting vacuum energy in the dark sector
Energy Technology Data Exchange (ETDEWEB)
Chimento, L. P. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Cuidad Universitaria, Buenos Aires 1428 (Argentina); Carneiro, S. [Instituto de Física, Uníversídade Federal da Bahia, 40210-340, Salvador, BA (Brazil)
2015-03-26
We analyse three cosmological scenarios with interaction in the dark sector, which are particular cases of a general expression for the energy flux from vacuum to matter. In the first case the interaction leads to a transition from an unstable de Sitter phase to a radiation dominated universe, avoiding in this way the initial singularity. In the second case the interaction gives rise to a slow-roll power-law inflation. Finally, the third scenario is a concordance model for the late-time universe, with the vacuum term decaying into cold dark matter. We identify the physics behind these forms of interaction and show that they can be described as particular types of the modified Chaplygin gas.
Dark-Energy Equation-of-State parameter for high redshifts
International Nuclear Information System (INIS)
Montiel, Ariadna; Breton, Nora
2011-01-01
Since the elucidation of the nature of dark energy depends strongly on redshift observations, it is desirable to measure them over a wider range, but supernovae cannot be detected out past redshift 1.7. Gamma-ray-bursts (GRBs) offer means to extend the analysis to at least redshifts of > 6. The reason is that GRBs are visible across much larger distances than supernovae. GRBs are now known to have several light-curve and spectral properties from which the luminosity of the burst can be calculated, and it might GRBs become into standard candles. We have used data of 69 GRB to study the behavior of the parameter of the dark energy equation of state as a function of redshift.
White Dwarfs in the HET Dark Energy Experiment
Castanheira, B. G.; Winget, D. E.; Williams, K.; Montgomery, M. H.; Falcon, R. E.; Hermes, J. J.
2010-11-01
In the past decades, large scale surveys have discovered a large number of white dwarfs. For example, the Sloan Digital Sky Survey (SDSS) Data Release 7 [5] lists about 20 000 spectroscopically confirmed new white dwarfs. More than just a number, the new discoveries revealed different flavors of white dwarfs, including a new class of pulsators [7] and a larger percentage of stars with a magnetic field [4]. The HET Dark Energy Experiment (HETDEX) will use the 9.2 m Hobby-Eberly Telescope at McDonald Observatory and a set of 150 spectrographs to map the three-dimensional positions of one million galaxies. The main goal of the survey is to probe dark energy by observing the recent universe (2products. We expect to obtain spectra for about 10 000 white dwarfs in the next 3 to 4 years.
Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion
International Nuclear Information System (INIS)
Huterer, Dragan; Kirkby, David; Bean, Rachel; Connolly, Andrew; Dawson, Kyle; Dodelson, Scott; Evrard, August; Jain, Bhuvnesh; Jarvis, Michael; Linder, Eric; Mandelbaum, Rachel; May, Morgan; Raccanelli, Alvise; Reid, Beth; Rozo, Eduardo; Schmidt, Fabian; Sehgal, Neelima; Slosar, Anze; Van Engelen, Alex; Wu, Hao-Yi; Zhao, Gongbo
2014-01-01
The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansion such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe
Illuminating dark photons with high-energy colliders
Energy Technology Data Exchange (ETDEWEB)
Curtin, David [Maryland Center for Fundamental Physics, University of Maryland,College Park, MD 20742 (United States); Essig, Rouven [C.N. Yang Institute for Theoretical Physics, Stony Brook University,Stony Brook, NY 11794 (United States); Gori, Stefania [Perimeter Institute for Theoretical Physics,31 Caroline St. N, Waterloo, Ontario (Canada); Shelton, Jessie [Dept. of Physics, University of Illinois at Urbana-Champaign,1110 West Green Street, Urbana, IL 61801 (United States)
2015-02-24
High-energy colliders offer a unique sensitivity to dark photons, the mediators of a broken dark U(1) gauge theory that kinetically mixes with the Standard Model (SM) hypercharge. Dark photons can be detected in the exotic decay of the 125 GeV Higgs boson, h→ZZ{sub D}→4ℓ, and in Drell-Yan events, pp→Z{sub D}→ℓℓ. If the dark U(1) is broken by a hidden-sector Higgs mechanism, then mixing between the dark and SM Higgs bosons also allows the exotic decay h→Z{sub D}Z{sub D}→4ℓ. We show that the 14 TeV LHC and a 100 TeV proton-proton collider provide powerful probes of both exotic Higgs decay channels. In the case of kinetic mixing alone, direct Drell-Yan production offers the best sensitivity to Z{sub D}, and can probe ϵ≳9×10{sup −4} (4×10{sup −4}) at the HL-LHC (100 TeV pp collider). The exotic Higgs decay h→ZZ{sub D} offers slightly weaker sensitivity, but both measurements are necessary to distinguish the kinetically mixed dark photon from other scenarios. If Higgs mixing is also present, then the decay h→Z{sub D}Z{sub D} can allow sensitivity to the Z{sub D} for ϵ≳10{sup −9}−10{sup −6} (10{sup −10}−10{sup −7}) for the mass range 2m{sub μ}
Dynamics of Mixed Dark Energy Domination in Teleparallel Gravity and Phase-Space Analysis
Directory of Open Access Journals (Sweden)
Emre Dil
2015-01-01
Full Text Available We consider a novel dark energy model to investigate whether it will provide an expanding universe phase. Here we propose a mixed dark energy domination which is constituted by tachyon, quintessence, and phantom scalar fields nonminimally coupled to gravity, in the absence of background dark matter and baryonic matter, in the framework of teleparallel gravity. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions implying the acceleration phase of universe.
Bose-Einstein condensate haloes embedded in dark energy
Membrado, M.; Pacheco, A. F.
2018-04-01
Context. We have studied clusters of self-gravitating collisionless Newtonian bosons in their ground state and in the presence of the cosmological constant to model dark haloes of dwarf spheroidal (dSph) galaxies. Aim. We aim to analyse the influence of the cosmological constant on the structure of these systems. Observational data of Milky Way dSph galaxies allow us to estimate the boson mass. Methods: We obtained the energy of the ground state of the cluster in the Hartree approximation by solving a variational problem in the particle density. We have also developed and applied the virial theorem. Dark halo models were tested in a sample of 19 galaxies. Galaxy radii, 3D deprojected half-light radii, mass enclosed within them, and luminosity-weighted averages of the square of line-of-sight velocity dispersions are used to estimate the particle mass. Results: Cosmological constant repulsive effects are embedded in one parameter ξ. They are appreciable for ξ > 10-5. Bound structures appear for ξ ≤ ξc = 1.65 × 10-4, what imposes a lower bound for cluster masses as a function of the particle mass. In principle, these systems present tunnelling through a potential barrier; however, after estimating their mean lifes, we realize that their existence is not affected by the age of the Universe. When Milky Way dSph galaxies are used to test the model, we obtain 3.5-1.0+1.3 × 10-22 eV for the particle mass and a lower limit of 5.1-2.8+2.2 × 106 M⊙ for bound haloes. Conclusions: Our estimation for the boson mass is in agreement with other recent results which use different methods. From our particle mass estimation, the treated dSph galaxies would present dark halo masses 5-11 ×107 M⊙. With these values, they would not be affected by the cosmological constant (ξ 10-5) would already feel their effects. Our model that includes dark energy allows us to deal with these dark haloes. Assuming quantities averaged in the sample of galaxies, 10-5 < ξ ≤ ξc dark
Non-minimal derivative coupling scalar field and bulk viscous dark energy
Energy Technology Data Exchange (ETDEWEB)
Mostaghel, Behrang [Shahid Beheshti University, Department of Physics, Tehran (Iran, Islamic Republic of); Moshafi, Hossein [Institute for Advanced Studies in Basic Sciences, Department of Physics, Zanjan (Iran, Islamic Republic of); Movahed, S.M.S. [Shahid Beheshti University, Department of Physics, Tehran (Iran, Islamic Republic of); Institute for Research in Fundamental Sciences (IPM), School of Physics, Tehran (Iran, Islamic Republic of)
2017-08-15
Inspired by thermodynamical dissipative phenomena, we consider bulk viscosity for dark fluid in a spatially flat two-component Universe. Our viscous dark energy model represents phantom-crossing which avoids big-rip singularity. We propose a non-minimal derivative coupling scalar field with zero potential leading to accelerated expansion of the Universe in the framework of bulk viscous dark energy model. In this approach, the coupling constant, κ, is related to viscosity coefficient, γ, and the present dark energy density, Ω{sub DE}{sup 0}. This coupling is bounded as κ element of [-1/9H{sub 0}{sup 2}(1 - Ω{sub DE}{sup 0}), 0]. We implement recent observational data sets including a joint light-curve analysis (JLA) for SNIa, gamma ray bursts (GRBs) for most luminous astrophysical objects at high redshifts, baryon acoustic oscillations (BAO) from different surveys, Hubble parameter from HST project, Planck CMB power spectrum and lensing to constrain model free parameters. The joint analysis of JLA + GRBs + BAO + HST shows that Ω{sub DE}{sup 0} = 0.696 ± 0.010, γ = 0.1404 ± 0.0014 and H{sub 0} = 68.1 ± 1.3. Planck TT observation provides γ = 0.32{sup +0.31}{sub -0.26} in the 68% confidence limit for the viscosity coefficient. The cosmographic distance ratio indicates that current observed data prefer to increase bulk viscosity. The competition between phantom and quintessence behavior of the viscous dark energy model can accommodate cosmological old objects reported as a sign of age crisis in the ΛCDM model. Finally, tension in the Hubble parameter is alleviated in this model. (orig.)
Curvature force and dark energy
International Nuclear Information System (INIS)
Balakin, Alexander B; Pavon, Diego; Schwarz, Dominik J; Zimdahl, Winfried
2003-01-01
A curvature self-interaction of the cosmic gas is shown to mimic a cosmological constant or other forms of dark energy, such as a rolling tachyon condensate or a Chaplygin gas. Any given Hubble rate and deceleration parameter can be traced back to the action of an effective curvature force on the gas particles. This force self-consistently reacts back on the cosmological dynamics. The links between an imperfect fluid description, a kinetic description with effective antifriction forces and curvature forces, which represent a non-minimal coupling of gravity to matter, are established
Dark Energy, Newton's Law and the LHC Vacuum Energy: the Dog that Didn’t Bark
Burgess, C P
2014-01-01
This note briefly summarizes two things. First, it states why I believe progress understand- ing Dark Energy hinges crucially on finding a solution to the ‘old’ Cosmological Constant Problem, and more generally reviews why technical naturalness provides such an important clue to solving problems in cosmology. A set of criteria are formulated for judging success when discussing prospective solutions to the problem with their proponents, with a goal to helping properly hold everyone’s feet to the fire. Second, I summarize what I see as the most promising approach (so far), which is possibly the only known technically natural solution yet proposed. Its consistency tests and observational predictions are summarized, as well as a list of outstanding problems.
Testing the cosmological constant as a candidate for dark energy
International Nuclear Information System (INIS)
Kratochvil, Jan; Linde, Andrei; Linder, Eric V.; Shmakova, Marina
2004-01-01
It may be difficult to single out the best model of dark energy on the basis of the existing and planned cosmological observations, because many different models can lead to similar observational consequences. However, each particular model can be studied and either found consistent with observations or ruled out. In this paper, we concentrate on the possibility to test and rule out the simplest and by far the most popular of the models of dark energy, the theory described by general relativity with positive vacuum energy (the cosmological constant). We evaluate the conditions under which this model could be ruled out by the future observations made by the Supernova/Acceleration Probe SNAP (both for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave background satellite
Late time phase transition as dark energy
Indian Academy of Sciences (India)
Abstract. We show that the dark energy field can naturally be described by the scalar condensates of a non-abelian gauge group. This gauge group is unified with the standard model gauge groups and it has a late time phase transition. The small phase transition explains why the positive acceleration of the universe is ...
Deep Rapid Optical Follow-Up of Gravitational Wave Sources with the Dark Energy Camera
Cowperthwaite, Philip
2018-01-01
The detection of an electromagnetic counterpart associated with a gravitational wave detection by the Advanced LIGO and VIRGO interferometers is one of the great observational challenges of our time. The large localization regions and potentially faint counterparts require the use of wide-field, large aperture telescopes. As a result, the Dark Energy Camera, a 3.3 sq deg CCD imager on the 4-m Blanco telescope at CTIO in Chile is the most powerful instrument for this task in the Southern Hemisphere. I will report on the results from our joint program between the community and members of the dark energy survey to conduct rapid and efficient follow-up of gravitational wave sources. This includes systematic searches for optical counterparts, as well as developing an understanding of contaminating sources on timescales not normally probed by traditional untargeted supernova surveys. I will additionally comment on the immense science gains to be made by a joint detection and discuss future prospects from the standpoint of both next generation wide-field telescopes and next generation gravitational wave detectors.
Unification of inflation, dark energy, and dark matter within the Salam-Sezgin cosmological model
International Nuclear Information System (INIS)
Henriques, Alfredo B.; Potting, Robertus; Sa, Paulo M.
2009-01-01
We investigate a cosmological model, based on the Salam-Sezgin six-dimensional supergravity theory and on previous work by Anchordoqui, Goldberg, Nawata, and Nunez. Assuming a period of warm inflation, we show that it is possible to extend the evolution of the model back in time, to include the inflationary period, thus unifying inflation, dark matter, and dark energy within a single framework. Like the previous authors, we were not able to obtain the full dark matter content of the universe from the Salam-Sezgin scalar fields. However, even if only partially successful, this work shows that present-day theories, based on superstrings and supergravity, may eventually lead to a comprehensive modeling of the evolution of the universe. We find that the gravitational-wave spectrum of the model has a nonconstant negative slope in the frequency range (10 -15 -10 6 ) rad/s, and that, unlike standard (cold) inflation models, it shows no structure in the MHz/GHz range of frequencies.
Imperfect dark energy from kinetic gravity braiding
Energy Technology Data Exchange (ETDEWEB)
Deffayet, Cédric [AstroParticule and Cosmologie, UMR7164-CNRS, Université Denis Diderot-Paris 7, CEA, Observatoire de Paris, 10 rue Alice Domon et Léonie Duquet, F-75205 Paris Cedex 13 (France); Pujolàs, Oriol [CERN, Theory Division, CH-1211 Geneva 23 (Switzerland); Sawicki, Ignacy; Vikman, Alexander, E-mail: deffayet@iap.fr, E-mail: oriol.pujolas@cern.ch, E-mail: ignacy.sawicki@nyu.edu, E-mail: alexander.vikman@nyu.edu [Center for Cosmology and Particle Physics, New York University, New York, NY 10003 (United States)
2010-10-01
We introduce a large class of scalar-tensor models with interactions containing the second derivatives of the scalar field but not leading to additional degrees of freedom. These models exhibit peculiar features, such as an essential mixing of scalar and tensor kinetic terms, which we have named kinetic braiding. This braiding causes the scalar stress tensor to deviate from the perfect-fluid form. Cosmology in these models possesses a rich phenomenology, even in the limit where the scalar is an exact Goldstone boson. Generically, there are attractor solutions where the scalar monitors the behaviour of external matter. Because of the kinetic braiding, the position of the attractor depends both on the form of the Lagrangian and on the external energy density. The late-time asymptotic of these cosmologies is a de Sitter state. The scalar can exhibit phantom behaviour and is able to cross the phantom divide with neither ghosts nor gradient instabilities. These features provide a new class of models for Dark Energy. As an example, we study in detail a simple one-parameter model. The possible observational signatures of this model include a sizeable Early Dark Energy and a specific equation of state evolving into the final de-Sitter state from a healthy phantom regime.
Imperfect dark energy from kinetic gravity braiding
International Nuclear Information System (INIS)
Deffayet, Cédric; Pujolàs, Oriol; Sawicki, Ignacy; Vikman, Alexander
2010-01-01
We introduce a large class of scalar-tensor models with interactions containing the second derivatives of the scalar field but not leading to additional degrees of freedom. These models exhibit peculiar features, such as an essential mixing of scalar and tensor kinetic terms, which we have named kinetic braiding. This braiding causes the scalar stress tensor to deviate from the perfect-fluid form. Cosmology in these models possesses a rich phenomenology, even in the limit where the scalar is an exact Goldstone boson. Generically, there are attractor solutions where the scalar monitors the behaviour of external matter. Because of the kinetic braiding, the position of the attractor depends both on the form of the Lagrangian and on the external energy density. The late-time asymptotic of these cosmologies is a de Sitter state. The scalar can exhibit phantom behaviour and is able to cross the phantom divide with neither ghosts nor gradient instabilities. These features provide a new class of models for Dark Energy. As an example, we study in detail a simple one-parameter model. The possible observational signatures of this model include a sizeable Early Dark Energy and a specific equation of state evolving into the final de-Sitter state from a healthy phantom regime
Debiasing the Dark Energy Survey's Search for Trans-Neptunian Objects
Napier, Kevin; Gerdes, David
2018-01-01
The Dark Energy Survey (DES) is rich in transient detections of trans-Neptunian objects (TNOs). This has resulted in many newly detected TNOs. It is important to be mindful that astronomical surveys are intrinsically biased in their detections. Understanding a survey’s bias is necessary to understand the significance of any clustering in the orbital parameters of our detections. To quantify this bias, we examine the DES’s selection function for the detection of TNOs. To do so, we developed a survey simulator in Python. We generate clones of known TNOs with uniformly varied argument of perihelion, longitude of ascending node, and mean anomaly. We test the detectability of each clone based on the pointing location and limiting magnitude of each exposure in DES. Our preliminary results show that our simulator is functional. However, we do not yet have any conclusions about the DES’s bias, as we have not yet run the simulator on the entirety of DES for all of our TNOs.
No-Go Theorem for k-Essence Dark Energy
International Nuclear Information System (INIS)
Bonvin, Camille; Caprini, Chiara; Durrer, Ruth
2006-01-01
We demonstrate that if k-essence can solve the coincidence problem and play the role of dark energy in the Universe, the fluctuations of the field have to propagate superluminally at some stage. We argue that this implies that successful k-essence models violate causality. It is not possible to define a time ordered succession of events in a Lorentz invariant way. Therefore, k-essence cannot arise as a low energy effective field theory of a causal, consistent high energy theory
An introduction to the dark energy problem
Dobado, Antonio; Maroto, Antonio L.
2009-04-01
In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the dark energy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require an urgent solution for the sake of the internal consistency of theoretical physics.
The DarkLight Experiment: A Precision Search for New Physics at Low Energies
Balewski, J.; Bernauer, J.; Bessuille, J.; Corliss, R.; Cowan, R.; Epstein, C.; Fisher, P.; Hasell, D.; Ihloff, E.; Kahn, Y.; Kelsey, J.; Milner, R.; Steadman, S.; Thaler, J.; Tschalaer, C.
2014-01-01
We describe the current status of the DarkLight experiment at Jefferson Laboratory. DarkLight is motivated by the possibility that a dark photon in the mass range 10 to 100 MeV/c$^2$ could couple the dark sector to the Standard Model. DarkLight will precisely measure electron proton scattering using the 100 MeV electron beam of intensity 5 mA at the Jefferson Laboratory energy recovering linac incident on a windowless gas target of molecular hydrogen. The complete final state including scatte...
Dark Energy and Dark Matter Phenomena and the Universe with Variable Gravitational Mass
Gorkavyi, N.
2005-12-01
Generation of high-frequency gravitational waves near the singularity is a crucial factor for understanding the origin and dynamics of the Universe. Emission of gravitational waves increases with a decreasing radius of collapsed object much faster than a gravitational force itself. Gravitationally unstable matter of the Universe will be completely converted into gravitational radiation during the Big Crunch. According to Misner, Thorne & Wheeler (Gravitation, 1977, p.959) plane gravitational waves have not gravitational mass or spacetime is flat everywhere outside the pulse. We can propose that the gravitational mass of the Universe is vanished after converting matter into gravitational waves. This hypothesis in the framework of Einstein's theory of gravitation can solve the problem of singularity without contradiction with theorems by Penrose-Hawking; explain the acceleration of our Universe as the effect of a retarded gravitational potential (Gorkavyi, BAAS, 2003, 35, #3) and the low quadrupole in fluctuations in CMB as result of blue-shift effect in a gravitational field. Proposed solution of dark energy problem free from coincidence problems. The hypothesis keeps best parts of Big Bang theory and inflation model without any unknown physical fields or new dimensions. According to this hypothesis a relic sea of high-frequency gravitational radiation in our Universe can be very dense. Interaction of relic gravitational waves with gravitational fields of galaxies and stars can create an additional dynamical effects like pressure of relic radiation that proportional to gravitational potential GM/(Rc2). This effect can be responsible for dark matter phenomena in galaxies and the Pioneer acceleration in the solar system (Gorkavyi, BAAS, 2005, 37, #2).
ΛGR Centennial: Cosmic Web in Dark Energy Background
Chernin, A. D.
The basic building blocks of the Cosmic Web are groups and clusters of galaxies, super-clusters (pancakes) and filaments embedded in the universal dark energy background. The background produces antigravity, and the antigravity effect is strong in groups, clusters and superclusters. Antigravity is very weak in filaments where matter (dark matter and baryons) produces gravity dominating in the filament internal dynamics. Gravity-antigravity interplay on the large scales is a grandiose phenomenon predicted by ΛGR theory and seen in modern observations of the Cosmic Web.
On the Origin of Gravity, Dark Energy and Matter.
CERN. Geneva
2011-01-01
Insights from black hole physics and developments in string theory strongly indicate that the gravity is derived from an underlying microscopic description in which it has no a priori meaning. Starting from first principles we argue that inertia and gravity are caused by the fact that phase space volume (or entropy) associated with the underlying microscopic system is influenced by the positions of material objects. Application of these ideas to cosmology leads to surprising new insights into the nature of dark energy and dark matter.
Tales from the dark side: Privacy dark strategies and privacy dark patterns
DEFF Research Database (Denmark)
Bösch, Christoph; Erb, Benjamin; Kargl, Frank
2016-01-01
Privacy strategies and privacy patterns are fundamental concepts of the privacy-by-design engineering approach. While they support a privacy-aware development process for IT systems, the concepts used by malicious, privacy-threatening parties are generally less understood and known. We argue...... that understanding the “dark side”, namely how personal data is abused, is of equal importance. In this paper, we introduce the concept of privacy dark strategies and privacy dark patterns and present a framework that collects, documents, and analyzes such malicious concepts. In addition, we investigate from...... a psychological perspective why privacy dark strategies are effective. The resulting framework allows for a better understanding of these dark concepts, fosters awareness, and supports the development of countermeasures. We aim to contribute to an easier detection and successive removal of such approaches from...
Tkachev, Igor
2017-01-01
This lecture course covers cosmology from the particle physicist perspective. Therefore, the emphasis will be on the evidence for the new physics in cosmological and astrophysical data together with minimal theoretical frameworks needed to understand and appreciate the evidence. I review the case for non-baryonic dark matter and describe popular models which incorporate it. In parallel, the story of dark energy will be developed, which includes accelerated expansion of the Universe today, the Universe origin in the Big Bang, and support for the Inflationary theory in CMBR data.
β-Glucan and Dark Chocolate: A Randomized Crossover Study on Short-Term Satiety and Energy Intake
Directory of Open Access Journals (Sweden)
Asli Akyol
2014-09-01
Full Text Available Aim: The aims of this study were to adapt a traditional recipe into a healthier form by adding 3 g of oat β-glucan, substituting milk chocolate to dark chocolate with 70% cocoa, and to examine the effect of these alterations on short-term satiety and energy intake. Materials and Methods: Study subjects (n = 25 were tested in a randomized, crossover design with four products closely matched for energy content. Four different versions of a traditional recipe including milk chocolate-control (CON, oat β-glucan (B-GLU, dark chocolate (DARK or oat β-glucan and dark chocolate (B-GLU + DARK were given to subjects on different test days. After subjects were asked to report visual analog scale (VAS scores on sensory outcomes and related satiety for four hours ad libitum, lunch was served and energy intake of individuals was measured. Results: VAS scores indicated that none of the test foods exerted an improved effect on satiety feelings. However, energy intake of individuals during ad libitum lunch was significantly lower in dark chocolate groups (CON: 849.46 ± 47.45 kcal versus DARK: 677.69 ± 48.45 kcal and B-GLU + DARK: 691.08 ± 47.45 kcal, p = 0.014. Conclusion: The study demonstrated that substituting dark chocolate for milk chocolate is more effective in inducing satiety during subsequent food intake in healthy subjects.
β-Glucan and dark chocolate: a randomized crossover study on short-term satiety and energy intake.
Akyol, Asli; Dasgin, Halil; Ayaz, Aylin; Buyuktuncer, Zehra; Besler, H Tanju
2014-09-23
The aims of this study were to adapt a traditional recipe into a healthier form by adding 3 g of oat β-glucan, substituting milk chocolate to dark chocolate with 70% cocoa, and to examine the effect of these alterations on short-term satiety and energy intake. Study subjects (n = 25) were tested in a randomized, crossover design with four products closely matched for energy content. Four different versions of a traditional recipe including milk chocolate-control (CON), oat β-glucan (B-GLU), dark chocolate (DARK) or oat β-glucan and dark chocolate (B-GLU + DARK) were given to subjects on different test days. After subjects were asked to report visual analog scale (VAS) scores on sensory outcomes and related satiety for four hours ad libitum, lunch was served and energy intake of individuals was measured. VAS scores indicated that none of the test foods exerted an improved effect on satiety feelings. However, energy intake of individuals during ad libitum lunch was significantly lower in dark chocolate groups (CON: 849.46 ± 47.45 kcal versus DARK: 677.69 ± 48.45 kcal and B-GLU + DARK: 691.08 ± 47.45 kcal, p = 0.014). The study demonstrated that substituting dark chocolate for milk chocolate is more effective in inducing satiety during subsequent food intake in healthy subjects.
Magnetized Anisotropic Dark Energy Models in Barber’s Second Self-Creation Theory
Directory of Open Access Journals (Sweden)
D. D. Pawar
2014-01-01
Full Text Available The present paper deals with Bianchi type IX cosmological model with magnetized anisotropic dark energy by using Barber’s self-creation theory. The energy momentum tensor consists of anisotropic fluid with EoS parameter ω and a uniform magnetic field of energy density ρB. In order to obtain the exact solution we have assumed that dark energy components and the components of magnetic field interact minimally and obey the law of conservation of energy momentum tensors. We have also used the special law of variation for the mean generalized Hubble parameter and power law relation between scalar field and scale factor. Some physical and kinematical properties of the models have been discussed.
Higgs production as a probe of chameleon dark energy
International Nuclear Information System (INIS)
Brax, Philippe; Burrage, Clare; Davis, Anne-Christine; Seery, David; Weltman, Amanda
2010-01-01
In this paper we study various particle physics effects of a light, scalar dark energy field with chameleonlike couplings to matter. We show that a chameleon model with only matter couplings will induce a coupling to photons. In doing so, we derive the first microphysical realization of a chameleonic dark energy model coupled to the electromagnetic field strength. This analysis provides additional motivation for current and near-future tests of axionlike and chameleon particles. We find a new bound on the coupling strength of chameleons in uniformly coupled models. We also study the effect of chameleon fields on Higgs production, which is relevant for hadron colliders. These are expected to manufacture Higgs particles through weak boson fusion, or associated production with a Z or W ± . We show that, like the Tevatron, the LHC will not be able to rule out or observe chameleons through this mechanism, because gauge invariance of the low energy Lagrangian suppresses the corrections that may arise.
Vector dark energy and high-z massive clusters
Carlesi, Edoardo; Knebe, Alexander; Yepes, Gustavo; Gottlöber, Stefan; Jiménez, Jose Beltrán.; Maroto, Antonio L.
2011-12-01
The detection of extremely massive clusters at z > 1 such as SPT-CL J0546-5345, SPT-CL J2106-5844 and XMMU J2235.3-2557 has been considered by some authors as a challenge to the standard Λ cold dark matter cosmology. In fact, assuming Gaussian initial conditions, the theoretical expectation of detecting such objects is as low as ≤1 per cent. In this paper we discuss the probability of the existence of such objects in the light of the vector dark energy paradigm, showing by means of a series of N-body simulations that chances of detection are substantially enhanced in this non-standard framework.
Topology and dark energy: testing gravity in voids.
Spolyar, Douglas; Sahlén, Martin; Silk, Joe
2013-12-13
Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field--here with a Galileon-type symmetry. The field can lead to a nontrivial equation of state of DE which is density and scale dependent. Tension between type Ia supernovae and Planck could be reduced. In voids, the scalar field dramatically alters the equation of state of DE, induces a soon-observable gravitational slip between the two metric potentials, and develops a topological defect (domain wall) due to a nontrivial vacuum structure for the field.
Determination of the cosmological parameters and the nature of dark energy
International Nuclear Information System (INIS)
Linden, S.
2010-04-01
The measured properties of the dark energy component being consistent with a Cosmological Constant, Λ, this cosmological standard model is referred to as the Λ-Cold-Dark-Matter (ΛCDM) model. Despite its overall success, this model suffers from various problems. The existence of a Cosmological Constant raises fundamental questions. Attempts to describe it as the energy contribution from the vacuum as following from Quantum Field Theory failed quantitatively. In consequence, a large number of alternative models have been developed to describe the dark energy component: modified gravity, additional dimensions, Quintessence models. Also, astrophysical effects have been considered to mimic an accelerated expansion. The basics of the ΛCDM model and the various attempts of explaining dark energy are outlined in this thesis. Another major problem of the model comes from the dependencies of the fit results on a number of a priori assumptions and parameterization effects. Today, combined analyses of the various cosmological probes are performed to extract the parameters of the model. Due to a wrong model assumption or a bad parameterization of the real physics, one might end up measuring with high precision something which is not there. We show, that indeed due to the high precision of modern cosmological measurements, purely kinematic approaches to distance measurements no longer yield valid fit results except for accidental special cases, and that a fit of the exact (integral) redshift-distance relation is necessary. The main results of this work concern the use of the CPL parameterization of dark energy when coping with the dynamics of tracker solutions of Quintessence models, and the risk of introducing biases on the parameters due to the possibly prohibited extrapolation to arbitrary high redshifts of the SN type Ia magnitude calibration relation, which is obtained in the low-redshift regime. Whereas the risks of applying CPL shows up to be small for a wide range of
Traversable geometric dark energy wormholes constrained by astrophysical observations
Energy Technology Data Exchange (ETDEWEB)
Wang, Deng [Nankai University, Theoretical Physics Division, Chern Institute of Mathematics, Tianjin (China); Meng, Xin-he [Nankai University, Department of Physics, Tianjin (China); Institute of Theoretical Physics, CAS, State Key Lab of Theoretical Physics, Beijing (China)
2016-09-15
In this paper, we introduce the astrophysical observations into the wormhole research. We investigate the evolution behavior of the dark energy equation of state parameter ω by constraining the dark energy model, so that we can determine in which stage of the universe wormholes can exist by using the condition ω < -1. As a concrete instance, we study the Ricci dark energy (RDE) traversable wormholes constrained by astrophysical observations. Particularly, we find from Fig. 5 of this work, when the effective equation of state parameter ω{sub X} < -1 (or z < 0.109), i.e., the null energy condition (NEC) is violated clearly, the wormholes will exist (open). Subsequently, six specific solutions of statically and spherically symmetric traversable wormhole supported by the RDE fluids are obtained. Except for the case of a constant redshift function, where the solution is not only asymptotically flat but also traversable, the five remaining solutions are all non-asymptotically flat, therefore, the exotic matter from the RDE fluids is spatially distributed in the vicinity of the throat. Furthermore, we analyze the physical characteristics and properties of the RDE traversable wormholes. It is worth noting that, using the astrophysical observations, we obtain the constraints on the parameters of the RDE model, explore the types of exotic RDE fluids in different stages of the universe, limit the number of available models for wormhole research, reduce theoretically the number of the wormholes corresponding to different parameters for the RDE model, and provide a clearer picture for wormhole investigations from the new perspective of observational cosmology. (orig.)
Traversable geometric dark energy wormholes constrained by astrophysical observations
International Nuclear Information System (INIS)
Wang, Deng; Meng, Xin-he
2016-01-01
In this paper, we introduce the astrophysical observations into the wormhole research. We investigate the evolution behavior of the dark energy equation of state parameter ω by constraining the dark energy model, so that we can determine in which stage of the universe wormholes can exist by using the condition ω < -1. As a concrete instance, we study the Ricci dark energy (RDE) traversable wormholes constrained by astrophysical observations. Particularly, we find from Fig. 5 of this work, when the effective equation of state parameter ω X < -1 (or z < 0.109), i.e., the null energy condition (NEC) is violated clearly, the wormholes will exist (open). Subsequently, six specific solutions of statically and spherically symmetric traversable wormhole supported by the RDE fluids are obtained. Except for the case of a constant redshift function, where the solution is not only asymptotically flat but also traversable, the five remaining solutions are all non-asymptotically flat, therefore, the exotic matter from the RDE fluids is spatially distributed in the vicinity of the throat. Furthermore, we analyze the physical characteristics and properties of the RDE traversable wormholes. It is worth noting that, using the astrophysical observations, we obtain the constraints on the parameters of the RDE model, explore the types of exotic RDE fluids in different stages of the universe, limit the number of available models for wormhole research, reduce theoretically the number of the wormholes corresponding to different parameters for the RDE model, and provide a clearer picture for wormhole investigations from the new perspective of observational cosmology. (orig.)
What measurable zero point fluctuations can(not) tell us about dark energy
International Nuclear Information System (INIS)
Doran, M.
2006-05-01
We show that laboratory experiments cannot measure the absolute value of dark energy. All known experiments rely on electromagnetic interactions. They are thus insensitive to particles and fields that interact only weakly with ordinary matter. In addition, Josephson junction experiments only measure differences in vacuum energy similar to Casimir force measurements. Gravity, however, couples to the absolute value. Finally we note that Casimir force measurements have tested zero point fluctuations up to energies of ∝ 10 eV, well above the dark energy scale of ∝ 0.01 eV. Hence, the proposed cut-off in the fluctuation spectrum is ruled out experimentally. (Orig.)
Sørensen, L B; Astrup, A
2011-12-05
To compare the effect of dark and milk chocolate on appetite sensations and energy intake at an ad libitum test meal in healthy, normal-weight men. A total of 16 young, healthy, normal-weight men participated in a randomized, crossover study. Test meals were 100 g of either milk (2285 kJ) or dark chocolate (2502 kJ). Visual-analogue scales were used to record appetite sensations before and after the test meal was consumed and subsequently every 30 min for 5 h. An ad libitum meal was served 2 h after the test meal had been consumed. The participants felt more satiated, less hungry, and had lower ratings of prospective food consumption after consumption of the dark chocolate than after the milk chocolate. Ratings of the desire to eat something sweet, fatty or savoury were all lower after consumption of the dark chocolate. Energy intake at the ad libitum meal was 17% lower after consumption of the dark chocolate than after the milk chocolate (P=0.002). If the energy provided by the chocolate is included in the calculation, the energy intake after consumption of the dark chocolate was still 8% lower than after the milk chocolate (P=0.01). The dark chocolate load resulted in an overall energy difference of -584 kJ (95% confidence interval (-1027;-141)) during the test period. In the present study, dark chocolate promotes satiety, lowers the desire to eat something sweet, and suppresses energy intake compared with milk chocolate.
How CMB and large-scale structure constrain chameleon interacting dark energy
International Nuclear Information System (INIS)
Boriero, Daniel; Das, Subinoy; Wong, Yvonne Y.Y.
2015-01-01
We explore a chameleon type of interacting dark matter-dark energy scenario in which a scalar field adiabatically traces the minimum of an effective potential sourced by the dark matter density. We discuss extensively the effect of this coupling on cosmological observables, especially the parameter degeneracies expected to arise between the model parameters and other cosmological parameters, and then test the model against observations of the cosmic microwave background (CMB) anisotropies and other cosmological probes. We find that the chameleon parameters α and β, which determine respectively the slope of the scalar field potential and the dark matter-dark energy coupling strength, can be constrained to α < 0.17 and β < 0.19 using CMB data and measurements of baryon acoustic oscillations. The latter parameter in particular is constrained only by the late Integrated Sachs-Wolfe effect. Adding measurements of the local Hubble expansion rate H 0 tightens the bound on α by a factor of two, although this apparent improvement is arguably an artefact of the tension between the local measurement and the H 0 value inferred from Planck data in the minimal ΛCDM model. The same argument also precludes chameleon models from mimicking a dark radiation component, despite a passing similarity between the two scenarios in that they both delay the epoch of matter-radiation equality. Based on the derived parameter constraints, we discuss possible signatures of the model for ongoing and future large-scale structure surveys
How CMB and large-scale structure constrain chameleon interacting dark energy
Energy Technology Data Exchange (ETDEWEB)
Boriero, Daniel [Fakultät für Physik, Universität Bielefeld, Universitätstr. 25, Bielefeld (Germany); Das, Subinoy [Indian Institute of Astrophisics, Bangalore, 560034 (India); Wong, Yvonne Y.Y., E-mail: boriero@physik.uni-bielefeld.de, E-mail: subinoy@iiap.res.in, E-mail: yvonne.y.wong@unsw.edu.au [School of Physics, The University of New South Wales, Sydney NSW 2052 (Australia)
2015-07-01
We explore a chameleon type of interacting dark matter-dark energy scenario in which a scalar field adiabatically traces the minimum of an effective potential sourced by the dark matter density. We discuss extensively the effect of this coupling on cosmological observables, especially the parameter degeneracies expected to arise between the model parameters and other cosmological parameters, and then test the model against observations of the cosmic microwave background (CMB) anisotropies and other cosmological probes. We find that the chameleon parameters α and β, which determine respectively the slope of the scalar field potential and the dark matter-dark energy coupling strength, can be constrained to α < 0.17 and β < 0.19 using CMB data and measurements of baryon acoustic oscillations. The latter parameter in particular is constrained only by the late Integrated Sachs-Wolfe effect. Adding measurements of the local Hubble expansion rate H{sub 0} tightens the bound on α by a factor of two, although this apparent improvement is arguably an artefact of the tension between the local measurement and the H{sub 0} value inferred from Planck data in the minimal ΛCDM model. The same argument also precludes chameleon models from mimicking a dark radiation component, despite a passing similarity between the two scenarios in that they both delay the epoch of matter-radiation equality. Based on the derived parameter constraints, we discuss possible signatures of the model for ongoing and future large-scale structure surveys.
Singularities and Entropy in Bulk Viscosity Dark Energy Model
International Nuclear Information System (INIS)
Meng Xinhe; Dou Xu
2011-01-01
In this paper bulk viscosity is introduced to describe the effects of cosmic non-perfect fluid on the cosmos evolution and to build the unified dark energy (DE) with (dark) matter models. Also we derive a general relation between the bulk viscosity form and Hubble parameter that can provide a procedure for the viscosity DE model building. Especially, a redshift dependent viscosity parameter ζ ∝ λ 0 + λ 1 (1 + z) n proposed in the previous work [X.H. Meng and X. Dou, Commun. Theor. Phys. 52 (2009) 377] is investigated extensively in this present work. Further more we use the recently released supernova dataset (the Constitution dataset) to constrain the model parameters. In order to differentiate the proposed concrete dark energy models from the well known ΛCDM model, statefinder diagnostic method is applied to this bulk viscosity model, as a complementary to the Om parameter diagnostic and the deceleration parameter analysis performed by us before. The DE model evolution behavior and tendency are shown in the plane of the statefinder diagnostic parameter pair {r, s} as axes where the fixed point represents the ΛCDM model. The possible singularity property in this bulk viscosity cosmology is also discussed to which we can conclude that in the different parameter regions chosen properly, this concrete viscosity DE model can have various late evolution behaviors and the late time singularity could be avoided. We also calculate the cosmic entropy in the bulk viscosity dark energy frame, and find that the total entropy in the viscosity DE model increases monotonously with respect to the scale factor evolution, thus this monotonous increasing property can indicate an arrow of time in the universe evolution, though the quantum version of the arrow of time is still very puzzling. (geophysics, astronomy, and astrophysics)
Current constraints on interacting holographic dark energy
International Nuclear Information System (INIS)
Wu Qiang; Gong Yungui; Wang Anzhong; Alcaniz, J.S.
2008-01-01
Although there is mounting observational evidence that the cosmic expansion is undergoing a late-time acceleration, the physical mechanism behind such a phenomenon is yet unknown. In this Letter, we investigate a holographic dark energy (HDE) model with interaction between the components of the dark sector in the light of current cosmological observations. We use both the new gold sample of 182 type Ia supernovae (SNe Ia) and the 192 SNe Ia ESSENCE data, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and the shift parameter from the three-year Wilkinson Microwave Anisotropy Probe data. In agreement with previous results, we show that these observations suggest a very weak coupling or even a noninteracting HDE. The phantom crossing behavior in the context of these scenarios is also briefly discussed
A Short History of the Missing Mass and Dark Energy Paradigms
Bergh, Sidney van den
2000-01-01
In 1900 it was believed that almost 100% of the mass of the Universe resided in stars. Now, in the year 2000, such stars (and cold gas) are known to account for only ~1% its mass. The remaining mass of the Universe is thought to reside in hot baryons (~3%), cold dark matter (~30%) and dark energy (~66%). The present paper traces the evolution of our thinking about the density of the Universe during the Twentieth Century, with special emphasis on the of the discovery of cold dark matter.
Dark energy and the cosmic microwave background radiation
Dodelson, S.; Knox, L.
2000-01-01
We find that current cosmic microwave background anisotropy data strongly constrain the mean spatial curvature of the Universe to be near zero, or, equivalently, the total energy density to be near critical-as predicted by inflation. This result is robust to editing of data sets, and variation of other cosmological parameters (totaling seven, including a cosmological constant). Other lines of argument indicate that the energy density of nonrelativistic matter is much less than critical. Together, these results are evidence, independent of supernovae data, for dark energy in the Universe.
Smoller, Joel; Temple, Blake; Vogler, Zeke
2017-11-01
We identify the condition for smoothness at the centre of spherically symmetric solutions of Einstein's original equations without the cosmological constant or dark energy. We use this to derive a universal phase portrait which describes general, smooth, spherically symmetric solutions near the centre of symmetry when the pressure p=0. In this phase portrait, the critical k=0 Friedmann space-time appears as a saddle rest point which is unstable to spherical perturbations. This raises the question as to whether the Friedmann space-time is observable by redshift versus luminosity measurements looking outwards from any point. The unstable manifold of the saddle rest point corresponding to Friedmann describes the evolution of local uniformly expanding space-times whose accelerations closely mimic the effects of dark energy. A unique simple wave perturbation from the radiation epoch is shown to trigger the instability, match the accelerations of dark energy up to second order and distinguish the theory from dark energy at third order. In this sense, anomalous accelerations are not only consistent with Einstein's original theory of general relativity, but are a prediction of it without the cosmological constant or dark energy.
Smoller, Joel; Temple, Blake; Vogler, Zeke
2017-11-01
We identify the condition for smoothness at the centre of spherically symmetric solutions of Einstein's original equations without the cosmological constant or dark energy. We use this to derive a universal phase portrait which describes general, smooth, spherically symmetric solutions near the centre of symmetry when the pressure p =0. In this phase portrait, the critical k =0 Friedmann space-time appears as a saddle rest point which is unstable to spherical perturbations. This raises the question as to whether the Friedmann space-time is observable by redshift versus luminosity measurements looking outwards from any point. The unstable manifold of the saddle rest point corresponding to Friedmann describes the evolution of local uniformly expanding space-times whose accelerations closely mimic the effects of dark energy. A unique simple wave perturbation from the radiation epoch is shown to trigger the instability, match the accelerations of dark energy up to second order and distinguish the theory from dark energy at third order. In this sense, anomalous accelerations are not only consistent with Einstein's original theory of general relativity, but are a prediction of it without the cosmological constant or dark energy.
The Casimir effect as a candidate of dark energy
Matsumoto, Jiro
2013-01-01
It is known that the simply evaluated value of the zero point energy of quantum fields is extremely deviated from the observed value of dark energy density. In this paper, we consider whether the Casimir energy, which is the zero point energy brought from boundary conditions, can cause the accelerating expansion of the Universe by using proper renormalization method and introducing the fermions of finite temperature living in $3+n+1$ space-time. We show that the zero temperature Casimir energ...
Zero-point quantum fluctuations and dark energy
International Nuclear Information System (INIS)
Maggiore, Michele
2011-01-01
In the Hamiltonian formulation of general relativity, the energy associated to an asymptotically flat space-time with metric g μν is related to the Hamiltonian H GR by E=H GR [g μν ]-H GR [η μν ], where the subtraction of the flat-space contribution is necessary to get rid of an otherwise divergent boundary term. This classic result indicates that the energy associated to flat space does not gravitate. We apply the same principle to study the effect of the zero-point fluctuations of quantum fields in cosmology, proposing that their contribution to cosmic expansion is obtained computing the vacuum energy of quantum fields in a Friedmann-Robertson-Walker space-time with Hubble parameter H(t) and subtracting from it the flat-space contribution. Then the term proportional to Λ c 4 (where Λ c is the UV cutoff) cancels, and the remaining (bare) value of the vacuum energy density is proportional to Λ c 2 H 2 (t). After renormalization, this produces a renormalized vacuum energy density ∼M 2 H 2 (t), where M is the scale where quantum gravity sets is, so for M of the order of the Planck mass a vacuum energy density of the order of the critical density can be obtained without any fine-tuning. The counterterms can be chosen so that the renormalized energy density and pressure satisfy p=wρ, with w a parameter that can be fixed by comparison to the observed value, so, in particular, one can choose w=-1. An energy density evolving in time as H 2 (t) is however observationally excluded as an explanation for the dominant dark energy component that is responsible for the observed acceleration of the Universe. We rather propose that zero-point vacuum fluctuations provide a new subdominant ''dark'' contribution to the cosmic expansion that, for a UV scale M slightly smaller than the Planck mass, is consistent with existing limits and potentially detectable.
Relic dark energy from the trans-Planckian regime
International Nuclear Information System (INIS)
Mersini, Laura; Bastero-Gil, Mar; Kanti, Panagiota
2001-01-01
As yet, there is no underlying fundamental theory for the trans-Planckian regime. There is a need to address the issue of how the observables in our present Universe are affected by processes that may have occurred at super-Planckian energies (referred to as the trans-Planckian regime). Specifically, we focus on the impact the trans-Planckian regime has on two observables: namely, dark energy and the cosmic microwave background radiation (CMBR) spectrum. We model the trans-Planckian regime by introducing a 1-parameter family of smooth non-linear dispersion relations which modify the frequencies at very short distances. A particular feature of the family of dispersion functions chosen is the production of ultralow frequencies at very high momenta k (for k>M P ). We name the range of the ultralow energy modes (of very short distances) that have frequencies equal to or less than the current Hubble rate H 0 as the tail modes. These modes are still frozen today due to the expansion of the Universe. We calculate their energy today and show that the tail provides a strong candidate for the dark energy of the Universe. During inflation, their energy is about 122 to 123 orders of magnitude smaller than the total energy, for any random value of the free parameter in the family of dispersion relations. For this family of dispersions, we present the exact solutions and show that the CMBR spectrum is that of a (nearly) blackbody, and that the adiabatic vacuum is the only choice for the initial conditions
System Architecture of the Dark Energy Survey Camera Readout Electronics
Energy Technology Data Exchange (ETDEWEB)
Shaw, Theresa; /FERMILAB; Ballester, Otger; Cardiel-Sas, Laia; Castilla, Javier; /Barcelona, IFAE; Chappa, Steve; /Fermilab; de Vicente, Juan; /Madrid, CIEMAT; Holm, Scott; Huffman, Dave; Kozlovsky, Mark; /Fermilab; Martinez, Gustavo; /Madrid, CIEMAT; Moore, Todd; /Madrid, CIEMAT /Fermilab /Illinois U., Urbana /Fermilab
2010-05-27
The Dark Energy Survey makes use of a new camera, the Dark Energy Camera (DECam). DECam will be installed in the Blanco 4M telescope at Cerro Tololo Inter-American Observatory (CTIO). DECam is presently under construction and is expected to be ready for observations in the fall of 2011. The focal plane will make use of 62 2Kx4K and 12 2kx2k fully depleted Charge-Coupled Devices (CCDs) for guiding, alignment and focus. This paper will describe design considerations of the system; including, the entire signal path used to read out the CCDs, the development of a custom crate and backplane, the overall grounding scheme and early results of system tests.
R2 dark energy in the laboratory
Brax, Philippe; Valageas, Patrick; Vanhove, Pierre
2018-05-01
We analyze the role, on large cosmological scales and laboratory experiments, of the leading curvature squared contributions to the low-energy effective action of gravity. We argue for a natural relationship c0λ2≃1 at low energy between the R2 coefficients c0 of the Ricci scalar squared term in this expansion and the dark energy scale Λ =(λ MPl)4 in four-dimensional Planck mass units. We show how the compatibility between the acceleration of the expansion rate of the Universe, local tests of gravity and the quantum stability of the model all converge to select such a relationship up to a coefficient which should be determined experimentally. When embedding this low-energy theory of gravity into candidates for its ultraviolet completion, we find that the proposed relationship is guaranteed in string-inspired supergravity models with modulus stabilization and supersymmetry breaking leading to de Sitter compactifications. In this case, the scalar degree of freedom of R2 gravity is associated to a volume modulus. Once written in terms of a scalar-tensor theory, the effective theory corresponds to a massive scalar field coupled with the universal strength β =1 /√{6 } to the matter stress-energy tensor. When the relationship c0λ2≃1 is realized, we find that on astrophysical scales and in cosmology the scalar field is ultralocal and therefore no effect arises on such large scales. On the other hand, the scalar field mass is tightly constrained by the nonobservation of fifth forces in torsion pendulum experiments such as Eöt-Wash. It turns out that the observation of the dark energy scale in cosmology implies that the scalar field could be detectable by fifth-force experiments in the near future.
Cosmological models described by a mixture of van der Waals fluid and dark energy
International Nuclear Information System (INIS)
Kremer, G.M.
2003-01-01
The Universe is modeled as a binary mixture whose constituents are described by a van der Waals fluid and by a dark energy density. The dark energy density is considered either as quintessence or as the Chaplygin gas. The irreversible processes concerning the energy transfer between the van der Waals fluid and the gravitational field are taken into account. This model can simulate (a) an inflationary period where the acceleration grows exponentially and the van der Waals fluid behaves like an inflaton, (b) an accelerated period where the acceleration is positive but it decreases and tends to zero whereas the energy density of the van der Waals fluid decays, (c) a decelerated period which corresponds to a matter dominated period with a non-negative pressure, and (d) a present accelerated period where the dark energy density outweighs the energy density of the van der Waals fluid
Equation of state description of the dark energy transition between quintessence and phantom regimes
International Nuclear Information System (INIS)
Stefancic, Hrvoje
2006-01-01
The dark energy crossing of the cosmological constant boundary (the transition between the quintessence and phantom regimes) is described in terms of the implicitly defined dark energy equation of state. The generalizations of the models explicitly constructed to exhibit the crossing provide the insight into the cancellation mechanism which makes the transition possible
Sørensen, L B; Astrup, A
2011-01-01
Objective: To compare the effect of dark and milk chocolate on appetite sensations and energy intake at an ad libitum test meal in healthy, normal-weight men. Subjects/methods: A total of 16 young, healthy, normal-weight men participated in a randomized, crossover study. Test meals were 100 g of either milk (2285 kJ) or dark chocolate (2502 kJ). Visual-analogue scales were used to record appetite sensations before and after the test meal was consumed and subsequently every 30 min for 5 h. An ad libitum meal was served 2 h after the test meal had been consumed. Results: The participants felt more satiated, less hungry, and had lower ratings of prospective food consumption after consumption of the dark chocolate than after the milk chocolate. Ratings of the desire to eat something sweet, fatty or savoury were all lower after consumption of the dark chocolate. Energy intake at the ad libitum meal was 17% lower after consumption of the dark chocolate than after the milk chocolate (P=0.002). If the energy provided by the chocolate is included in the calculation, the energy intake after consumption of the dark chocolate was still 8% lower than after the milk chocolate (P=0.01). The dark chocolate load resulted in an overall energy difference of −584 kJ (95% confidence interval (−1027;−141)) during the test period. Conclusion: In the present study, dark chocolate promotes satiety, lowers the desire to eat something sweet, and suppresses energy intake compared with milk chocolate. PMID:23455041
Holographic dark energy from fluid/gravity duality constraint by cosmological observations
Pourhassan, Behnam; Bonilla, Alexander; Faizal, Mir; Abreu, Everton M. C.
2018-06-01
In this paper, we obtain a holographic model of dark energy using the fluid/gravity duality. This model will be dual to a higher dimensional Schwarzschild black hole, and we would use fluid/gravity duality to relate to the parameters of this black hole to such a cosmological model. We will also analyze the thermodynamics of such a solution, and discuss the stability model. Finally, we use cosmological data to constraint the parametric space of this dark energy model. Thus, we will use observational data to perform cosmography for this holographic model based on fluid/gravity duality.
Dark Energy and the Fate of the Universe
Linde, A.
2002-12-01
The present stage of acceleration of the universe may continue forever. However, we have found a broad class of theories of dark energy that lead to a global collapse of the universe 10-30 billion years from now. I will discuss the possibility to find our destiny using cosmological observations.
Possible Measurable Effects of Dark Energy in Rotating Superconductors
Directory of Open Access Journals (Sweden)
Clovis Jacinto de Matos
2009-01-01
Full Text Available We discuss recent laboratory experiments with rotating superconductors and show that three so far unexplained experimentally observed effects (anomalous acceleration signals, anomalous gyroscope signals, Cooper pair mass excess can be physically explained in terms of a possible interaction of dark energy with Cooper pairs. Our approach is based on a Ginzburg-Landau-like model of electromagnetic dark energy, where gravitationally active photons obtain mass in the superconductor. We show that this model can account simultaneously for the anomalous acceleration and anomalous gravitomagnetic fields around rotating superconductors measured by Tajmar et al. and for the anomalous Cooper pair mass in superconductive Niobium, measured by Cabrera and Tate. It is argued that these three different physical effects are ultimately different experimental manifestations of the simultaneous spontaneous breaking of gauge invariance and of the principle of general covariance in superconductive materials.
A geometric measure of dark energy with pairs of galaxies.
Marinoni, Christian; Buzzi, Adeline
2010-11-25
Observations indicate that the expansion of the Universe is accelerating, which is attributed to a ‘dark energy’ component that opposes gravity. There is a purely geometric test of the expansion of the Universe (the Alcock–Paczynski test), which would provide an independent way of investigating the abundance (Ω(X)) and equation of state (W(X)) of dark energy. It is based on an analysis of the geometrical distortions expected from comparing the real-space and redshift-space shape of distant cosmic structures, but it has proved difficult to implement. Here we report an analysis of the symmetry properties of distant pairs of galaxies from archival data. This allows us to determine that the Universe is flat. By alternately fixing its spatial geometry at Ω(k)≡0 and the dark energy equation-of-state parameter at W(X)≡-1, and using the results of baryon acoustic oscillations, we can establish at the 68.3% confidence level that and -0.85>W(X)>-1.12 and 0.60<Ω(X)<0.80.
Manifestations of dark energy in the solar system
Czech Academy of Sciences Publication Activity Database
Křížek, Michal; Somer, L.
2015-01-01
Roč. 21, č. 1 (2015), s. 59-72 ISSN 0202-2893 R&D Projects: GA ČR GA14-02067S Institutional support: RVO:67985840 Keywords : dark energy * solar system Subject RIV: BA - General Mathematics Impact factor: 0.909, year: 2015 http://link.springer.com/article/10.1134%2FS0202289315010090
Cosmological Analysis of Dynamical Chern-Simons Modified Gravity via Dark Energy Scenario
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Abdul Jawad
2015-01-01
Full Text Available The purpose of this paper is to study the cosmological evolution of the universe in the framework of dynamical Chern-Simons modified gravity. We take pilgrim dark energy model with Hubble and event horizons in interacting scenario with cold dark matter. For this scenario, we discuss cosmological parameters such as Hubble and equation of state and cosmological plane like ωϑ-ωϑ′ and squared speed of sound. It is found that Hubble parameter approaches the ranges 75-0.5+0.5 (for u=2 and (74, 74.30 (for u=1,-1,-2 for Hubble horizon pilgrim dark energy. It implies the ranges 74.80-0.005+0.005 (for u=2 and (73.4, 74 (for u=-2 for event horizon pilgrim dark energy. The equation of state parameter provides consistent ranges with different observational schemes. Also, ωϑ-ωϑ′ planes lie in the range (ωϑ=-1.13-0.25+0.24,ωϑ′<1.32. The squared speed of sound shows stability for all present models in the present scenario. We would like to mention here that our results of various cosmological parameters show consistency with different observational data like Planck, WP, BAO, H0, SNLS, and WMAP.
Probing dark energy with atom interferometry
International Nuclear Information System (INIS)
Burrage, Clare; Copeland, Edmund J.; Hinds, E.A.
2015-01-01
Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry
Probing dark energy with atom interferometry
Energy Technology Data Exchange (ETDEWEB)
Burrage, Clare; Copeland, Edmund J. [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom); Hinds, E.A., E-mail: Clare.Burrage@nottingham.ac.uk, E-mail: Edmund.Copeland@nottingham.ac.uk, E-mail: Ed.Hinds@imperial.ac.uk [Centre for Cold Matter, Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom)
2015-03-01
Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.
Imaging Galactic Dark Matter with High-Energy Cosmic Neutrinos.
Argüelles, Carlos A; Kheirandish, Ali; Vincent, Aaron C
2017-11-17
We show that the high-energy cosmic neutrinos seen by the IceCube Neutrino Observatory can be used to probe interactions between neutrinos and the dark sector that cannot be reached by current cosmological methods. The origin of the observed neutrinos is still unknown, and their arrival directions are compatible with an isotropic distribution. This observation, together with dedicated studies of Galactic plane correlations, suggests a predominantly extragalactic origin. Interactions between this isotropic extragalactic flux and the dense dark matter (DM) bulge of the Milky Way would thus lead to an observable imprint on the distribution, which would be seen by IceCube as (i) slightly suppressed fluxes at energies below a PeV and (ii) a deficit of events in the direction of the Galactic center. We perform an extended unbinned likelihood analysis using the four-year high-energy starting event data set to constrain the strength of DM-neutrino interactions for two model classes. We find that, in spite of low statistics, IceCube can probe regions of the parameter space inaccessible to current cosmological methods.
High Energy Electron Signals from Dark Matter Annihilation in the Sun
Energy Technology Data Exchange (ETDEWEB)
Schuster, Philip; /SLAC; Toro, Natalia; /Stanford U., ITP; Weiner, Neal; Yavin, Itay; /New York U., CCPP
2012-04-09
In this paper we discuss two mechanisms by which high energy electrons resulting from dark matter annihilations in or near the Sun can arrive at the Earth. Specifically, electrons can escape the sun if DM annihilates into long-lived states, or if dark matter scatters inelastically, which would leave a halo of dark matter outside of the sun. Such a localized source of electrons may affect the spectra observed by experiments with narrower fields of view oriented towards the sun, such as ATIC, differently from those with larger fields of view such as Fermi. We suggest a simple test of these possibilities with existing Fermi data that is more sensitive than limits from final state radiation. If observed, such a signal will constitute an unequivocal signature of dark matter.
Large Scale Cosmological Anomalies and Inhomogeneous Dark Energy
Directory of Open Access Journals (Sweden)
Leandros Perivolaropoulos
2014-01-01
Full Text Available A wide range of large scale observations hint towards possible modifications on the standard cosmological model which is based on a homogeneous and isotropic universe with a small cosmological constant and matter. These observations, also known as “cosmic anomalies” include unexpected Cosmic Microwave Background perturbations on large angular scales, large dipolar peculiar velocity flows of galaxies (“bulk flows”, the measurement of inhomogenous values of the fine structure constant on cosmological scales (“alpha dipole” and other effects. The presence of the observational anomalies could either be a large statistical fluctuation in the context of ΛCDM or it could indicate a non-trivial departure from the cosmological principle on Hubble scales. Such a departure is very much constrained by cosmological observations for matter. For dark energy however there are no significant observational constraints for Hubble scale inhomogeneities. In this brief review I discuss some of the theoretical models that can naturally lead to inhomogeneous dark energy, their observational constraints and their potential to explain the large scale cosmic anomalies.
USING A PHENOMENOLOGICAL MODEL TO TEST THE COINCIDENCE PROBLEM OF DARK ENERGY
International Nuclear Information System (INIS)
Chen Yun; Zhu Zonghong; Alcaniz, J. S.; Gong Yungui
2010-01-01
By assuming a phenomenological form for the ratio of the dark energy and matter densities ρ X ∝ ρ m a ξ , we discuss the cosmic coincidence problem in light of current observational data. Here, ξ is a key parameter to denote the severity of the coincidence problem. In this scenario, ξ = 3 and ξ = 0 correspond to ΛCDM and the self-similar solution without the coincidence problem, respectively. Hence, any solution with a scaling parameter 0 X = 0, where ω X is the equation of state of the dark energy component, whereas the inequality ξ + 3ω X ≠ 0 represents non-standard cosmology. We place observational constraints on the parameters (Ω X,0 , ω X , ξ) of this model, where Ω X,0 is the present value of density parameter of dark energy Ω X , by using the Constitution Set (397 supernovae of type Ia data, hereafter SNeIa), the cosmic microwave background shift parameter from the five-year Wilkinson Microwave Anisotropy Probe and the Sloan Digital Sky Survey baryon acoustic peak. Combining the three samples, we get Ω X,0 = 0.72 ± 0.02, ω X = -0.98 ± 0.07, and ξ = 3.06 ± 0.35 at 68.3% confidence level. The result shows that the ΛCDM model still remains a good fit to the recent observational data, and the coincidence problem indeed exists and is quite severe, in the framework of this simple phenomenological model. We further constrain the model with the transition redshift (deceleration/acceleration). It shows that if the transition from deceleration to acceleration happens at the redshift z > 0.73, within the framework of this model, we can conclude that the interaction between dark energy and dark matter is necessary.
International Nuclear Information System (INIS)
Cruz, Norman; Palma, Guillermo; Zambrano, David; Avelino, Arturo
2013-01-01
We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear λρ m α ρ e β form, where ρ m and ρ e are the energy densities of the dark matter and dark energy, respectively. The parameters α and β are in principle not constrained to take any particular values, and were estimated from observations. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the phase space of the dark matter and dark energy densities. The constants (λ,α,β) as well as w m and w e of the EoS of dark matter and dark energy respectively, were estimated using the cosmological observations of the type Ia supernovae and the Hubble expansion rate H(z) data sets. We find that the best estimated values for the free parameters of the model correspond to a warm dark matter interacting with a phantom dark energy component, with a well goodness-of-fit to data. However, using the Bayesian Information Criterion (BIC) we find that this model is overcame by a warm dark matter – phantom dark energy model without interaction, as well as by the ΛCDM model. We find also a large dispersion on the best estimated values of the (λ,α,β) parameters, so even if we are not able to set strong constraints on their values, given the goodness-of-fit to data of the model, we find that a large variety of theirs values are well compatible with the observational data used
More on the holographic Ricci dark energy model: smoothing Rips through interaction effects?
Bouhmadi-López, Mariam; Errahmani, Ahmed; Ouali, Taoufik; Tavakoli, Yaser
2018-04-01
The background cosmological dynamics of the late Universe is analysed on the framework of a dark energy model described by an holographic Ricci dark energy component. Several kind of interactions between the dark energy and the dark matter components are considered herein. We solve the background cosmological dynamics for the different choices of interactions with the aim to analyse not only the current evolution of the universe but also its asymptotic behaviour and, in particular, possible future singularities removal. We show that in most of the cases, the Big Rip singularity, a finger print of this model in absence of an interaction between the dark sectors, is substituted by a de Sitter or a Minkowski state. Most importantly, we found two new future bouncing solutions leading to two possible asymptotic behaviours, we named Little Bang and Little Sibling of the Big Bang. At a Little Bang, as the size of the universe shrinks to zero in an infinite cosmic time, the Hubble rate and its cosmic time derivative blow up. In addition, at a Little sibling of the Big Bang, as the size of the universe shrinks to zero in an infinite cosmic time, the Hubble rate blows up but its cosmic time derivative is finite. These two abrupt events can happen as well in the past.
More on the holographic Ricci dark energy model: smoothing Rips through interaction effects?
Bouhmadi-López, Mariam; Errahmani, Ahmed; Ouali, Taoufik; Tavakoli, Yaser
2018-01-01
The background cosmological dynamics of the late Universe is analysed on the framework of a dark energy model described by an holographic Ricci dark energy component. Several kind of interactions between the dark energy and the dark matter components are considered herein. We solve the background cosmological dynamics for the different choices of interactions with the aim to analyse not only the current evolution of the universe but also its asymptotic behaviour and, in particular, possible future singularities removal. We show that in most of the cases, the Big Rip singularity, a finger print of this model in absence of an interaction between the dark sectors, is substituted by a de Sitter or a Minkowski state. Most importantly, we found two new future bouncing solutions leading to two possible asymptotic behaviours, we named Little Bang and Little Sibling of the Big Bang. At a Little Bang, as the size of the universe shrinks to zero in an infinite cosmic time, the Hubble rate and its cosmic time derivative blow up. In addition, at a Little sibling of the Big Bang, as the size of the universe shrinks to zero in an infinite cosmic time, the Hubble rate blows up but its cosmic time derivative is finite. These two abrupt events can happen as well in the past.
Precision cosmological measurements: Independent evidence for dark energy
International Nuclear Information System (INIS)
Bothun, Greg; Hsu, Stephen D.H.; Murray, Brian
2008-01-01
Using recent precision measurements of cosmological parameters, we re-examine whether these observations alone, independent of type Ia supernova surveys, are sufficient to imply the existence of dark energy. We find that best measurements of the age of the Universe t 0 , the Hubble parameter H 0 and the matter fraction Ω m strongly favor an equation of state defined by (w<-1/3). This result is consistent with the existence of a repulsive, acceleration-causing component of energy if the Universe is nearly flat
Inflation and dark energy from f(R) gravity
Energy Technology Data Exchange (ETDEWEB)
Artymowski, Michał [Department of Physics, Beijing Normal University, Beijing 100875 (China); Lalak, Zygmunt, E-mail: artymowski@bnu.edu.cn, E-mail: Zygmunt.Lalak@fuw.edu.pl [Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, ul. Hoża 69, 00-681 Warszawa (Poland)
2014-09-01
The standard Starobinsky inflation has been extended to the R + α R{sup n} - β R{sup 2-n} model to obtain a stable minimum of the Einstein frame scalar potential of the auxiliary field. As a result we have obtained obtain a scalar potential with non-zero value of residual vacuum energy, which may be a source of Dark Energy. Our results can be easily consistent with PLANCK or BICEP2 data for appropriate choices of the value of n.
Holographic Dark Energy in Brans-Dicke Theory with Logarithmic Form of Scalar Field
Singh, C. P.; Kumar, Pankaj
2017-10-01
In this paper, an interacting holographic dark energy model with Hubble horizon as an infra-red cut-off is considered in the framework of Brans-Dicke theory. We assume the Brans-Dicke scalar field as a logarithmic form ϕ = ϕ 0 l n( α + β a), where a is the scale factor, α and β are arbitrary constants, to interpret the physical phenomena of the Universe. The equation of state parameter w h and deceleration parameter q are obtained to discuss the dynamics of the evolution of the Universe. We present a unified model of holographic dark energy which explains the early time acceleration (inflation), medieval time deceleration and late time acceleration. It is also observed that w h may cross the phantom divide line in the late time evolution. We also discuss the cosmic coincidence problem. We obtain a time-varying density ratio of holographic dark energy to dark matter which is a constant of order one (r˜ O(1)) during early and late time evolution, and may evolve sufficiently slow at present time. Thus, the model successfully resolves the cosmic coincidence problem.
A sensitive search for dark energy through chameleon scalar fields using neutron interferometry
International Nuclear Information System (INIS)
Snow, W M; Li, K; Skavysh, V; Arif, M; Huber, M; Heacock, B; Young, A R; Pushin, D
2015-01-01
The physical origin of the dark energy, which is postulated to cause the accelerated expansion rate of the universe, is one of the major open questions of cosmology. A large subset of theories postulate the existence of a scalar field with a nonlinear coupling to matter chosen so that the effective range and/or strength of the field is greatly suppressed unless the source is placed in vacuum. We describe a measurement using neutron interferometry which can place a stringent upper bound on chameleon fields proposed as a solution to the problem of the origin of dark energy of the universe in the regime with a strongly-nolinear coupling term. In combination with other experiments searching for exotic short-range forces and laser-based measurements, slow neutron experiments are capable of eliminating this and many similar types of scalar-field-based dark energy models by laboratory experiments
Generalized entropy formalism and a new holographic dark energy model
Sayahian Jahromi, A.; Moosavi, S. A.; Moradpour, H.; Morais Graça, J. P.; Lobo, I. P.; Salako, I. G.; Jawad, A.
2018-05-01
Recently, the Rényi and Tsallis generalized entropies have extensively been used in order to study various cosmological and gravitational setups. Here, using a special type of generalized entropy, a generalization of both the Rényi and Tsallis entropy, together with holographic principle, we build a new model for holographic dark energy. Thereinafter, considering a flat FRW universe, filled by a pressureless component and the new obtained dark energy model, the evolution of cosmos has been investigated showing satisfactory results and behavior. In our model, the Hubble horizon plays the role of IR cutoff, and there is no mutual interaction between the cosmos components. Our results indicate that the generalized entropy formalism may open a new window to become more familiar with the nature of spacetime and its properties.
Dark energy: Vacuum fluctuations, the effective phantom phase, and holography
International Nuclear Information System (INIS)
Elizalde, E.; Nojiri, S.; Odintsov, S. D.; Wang Peng
2005-01-01
We aim at the construction of dark energy models without exotic matter but with a phantomlike equation of state (an effective phantom phase). The first model we consider is decaying vacuum cosmology where the fluctuations of the vacuum are taken into account. In this case, the phantom cosmology (with an effective, observational ω being less than -1 ) emerges even for the case of a real dark energy with a physical equation of state parameter ω larger than -1. The second proposal is a generalized holographic model, which is produced by the presence of an infrared cutoff. It also leads to an effective phantom phase, which is not a transient one as in the first model. However, we show that quantum effects are able to prevent its evolution towards a big rip singularity
International Nuclear Information System (INIS)
Caprini, Chiara; Tamanini, Nicola
2016-01-01
We perform a forecast analysis of the capability of the eLISA space-based interferometer to constrain models of early and interacting dark energy using gravitational wave standard sirens. We employ simulated catalogues of standard sirens given by merging massive black hole binaries visible by eLISA, with an electromagnetic counterpart detectable by future telescopes. We consider three-arms mission designs with arm length of 1, 2 and 5 million km, 5 years of mission duration and the best-level low frequency noise as recently tested by the LISA Pathfinder. Standard sirens with eLISA give access to an intermediate range of redshift 1 ∼< z ∼< 8, and can therefore provide competitive constraints on models where the onset of the deviation from ΛCDM (i.e. the epoch when early dark energy starts to be non-negligible, or when the interaction with dark matter begins) occurs relatively late, at z ∼< 6. If instead early or interacting dark energy is relevant already in the pre-recombination era, current cosmological probes (especially the cosmic microwave background) are more efficient than eLISA in constraining these models, except possibly in the interacting dark energy model if the energy exchange is proportional to the energy density of dark energy.
Cosmological evolution of interacting dark energy in Lorentz violation
International Nuclear Information System (INIS)
Zen, Freddy P.; Gunara, Bobby E.; Triyanta; Arianto; Purwanto, A.
2009-01-01
The cosmological evolution of an interacting scalar-field model in which the scalar field interacts with dark matter, radiation, and baryons via Lorentz violation is investigated. We propose a model of interaction through the effective coupling, anti β. Using dynamical system analysis, we study the linear dynamics of an interacting model and show that the dynamics of critical points are completely controlled by two parameters. Some results can be mentioned as follows. Firstly, the sequence of radiation, the dark matter, and the scalar-field dark energy exist and baryons are subdominant. Secondly, the model also allows for the possibility of having a universe in the phantom phase with constant potential. Thirdly, the effective gravitational constant varies with respect to time through anti β. In particular, we consider the simple case where anti β has a quadratic form and has a good agreement with the modified ΛCDM and quintessence models. Finally, we also calculate the first post-Newtonian parameters for our model. (orig.)
On dark degeneracy and interacting models
International Nuclear Information System (INIS)
Carneiro, S.; Borges, H.A.
2014-01-01
Cosmological background observations cannot fix the dark energy equation of state, which is related to a degeneracy in the definition of the dark sector components. Here we show that this degeneracy can be broken at perturbation level by imposing two observational properties on dark matter. First, dark matter is defined as the clustering component we observe in large scale structures. This definition is meaningful only if dark energy is unperturbed, which is achieved if we additionally assume, as a second condition, that dark matter is cold, i.e. non-relativistic. As a consequence, dark energy models with equation-of-state parameter −1 ≤ ω < 0 are reduced to two observationally distinguishable classes with ω = −1, equally competitive when tested against observations. The first comprises the ΛCDM model with constant dark energy density. The second consists of interacting models with an energy flux from dark energy to dark matter
Vacuum fluctuations in an ancestor vacuum: A possible dark energy candidate
Aoki, Hajime; Iso, Satoshi; Lee, Da-Shin; Sekino, Yasuhiro; Yeh, Chen-Pin
2018-02-01
We consider an open universe created by bubble nucleation, and study possible effects of our "ancestor vacuum," a de Sitter space in which bubble nucleation occurred, on the present universe. We compute vacuum expectation values of the energy-momentum tensor for a minimally coupled scalar field, carefully taking into account the effect of the ancestor vacuum by the Euclidean prescription. We pay particular attention to the so-called supercurvature mode, a non-normalizable mode on a spatial slice of the open universe, which has been known to exist for sufficiently light fields. This mode decays in time most slowly, and may leave residual effects of the ancestor vacuum, potentially observable in the present universe. We point out that the vacuum energy of the quantum field can be regarded as dark energy if mass of the field is of order the present Hubble parameter or smaller. We obtain preliminary results for the dark energy equation of state w (z ) as a function of the redshift.
Constraints on deflation from the equation of state of dark energy
International Nuclear Information System (INIS)
Baum, Lauris; Frampton, Paul H; Matsuzaki, Shinya
2008-01-01
In cyclic cosmology based on phantom dark energy the requirement that our universe satisfy a CBE condition (comes back empty) imposes a lower bound on the number N cp of causal patches which separate just prior to turnaround. This bound depends on the dark energy equation of state w = p/ρ = −1−φ with φ>0. More accurate measurement of φ will constrain N cp . The critical density ρ c in the model has a lower bound ρ c ≥(10 9 GeV) 4 or ρ c ≥(10 18 GeV) 4 when the smallest bound state has size 10 −15 m, or 10 −35 m, respectively
Chameleon dark energy models with characteristic signatures
International Nuclear Information System (INIS)
Gannouji, Radouane; Moraes, Bruno; Polarski, David; Mota, David F.; Winther, Hans A.; Tsujikawa, Shinji
2010-01-01
In chameleon dark energy models, local gravity constraints tend to rule out parameters in which observable cosmological signatures can be found. We study viable chameleon potentials consistent with a number of recent observational and experimental bounds. A novel chameleon field potential, motivated by f(R) gravity, is constructed where observable cosmological signatures are present both at the background evolution and in the growth rate of the perturbations. We study the evolution of matter density perturbations on low redshifts for this potential and show that the growth index today γ 0 can have significant dispersion on scales relevant for large scale structures. The values of γ 0 can be even smaller than 0.2 with large variations of γ on very low redshifts for the model parameters constrained by local gravity tests. This gives a possibility to clearly distinguish these chameleon models from the Λ-cold-dark-matter (ΛCDM) model in future high-precision observations.