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1

Unified Field Equations Coupling Four Forces and Theory of Dark Matter and Dark Energy

Unified Field Equations Coupling Four Forces and Theory of Dark Matter and Dark Energy Tian Ma. Electroweak Theory VI. Unified Theory of Dark Energy and Dark Matter VII. Concluding Remarks 2 #12;References: 1. Tian Ma & Shouhong Wang, Gravitational Field Equations and Theory of Dark Matter and Dark Energy

Wang, Shouhong

2

A Nonuniform Dark Energy Fluid: Perturbation Equations

NASA Astrophysics Data System (ADS)

We propose that galactic dark matter can be described by a nonuniform dark energy fluid. The underlying field is a decaying vector field, which might corresponds to a photon-like but massive particle of 4 degrees of dynamical freedom. We propose a very general Lagrangian for this vector field. The model includes a continuous spectrum of plausible gravity theories, for example, quintessence, f(R), Einstein-Aether, MOND, TeVeS, BSTV, V-? theories, and the inflaton scalar field as special cases. We study in detail a special class of models with a fixed norm of the timelike vector field in the physical metric, which includes a nonlinear K4 term and a Ricci scalar term. We derive the Einstein equations in the perturbed form, which are needed for simulating structure growth in an FRW universe to test such theories. A special case of the model V-? shows promise of resembling the ?CDM cosmology. We show that the vector field has the effect of a nonuniform dark fluid, which resembles dark matter in galaxies and dark energy in the late universe.

Halle, Anaelle; Zhao, HongSheng; Li, Baojiu

2008-07-01

3

Effective dark energy equation of state in interacting dark energy models

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 paper 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.

P. P. Avelino; H. M. R. da Silva

2012-01-02

4

CONSTRAINING THE DARK ENERGY EQUATION OF STATE WITH COSMIC VOIDS

Our universe is observed to be accelerating due to the dominant dark energy with negative pressure. The dark energy equation of state (w) holds a key to understanding the ultimate fate of the universe. The cosmic voids behave like bubbles in the universe so that its shapes must be quite sensitive to the background cosmology. Assuming a flat universe and using the priors on the matter density parameter ({omega} {sub m}) and the dimensionless Hubble parameter (h), we demonstrate analytically that the ellipticity evolution of cosmic voids may be a sensitive probe of the dark energy equation of state. We also discuss the parameter degeneracy between w and {omega} {sub m}.

Lee, Jounghun; Park, Daeseong [Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-747 (Korea, Republic of)

2009-05-01

5

Linear Dark Energy Equation of State Revealed by Supernovae?

NASA Astrophysics Data System (ADS)

In this paper, we propose a test to detect the linearity of the dark energy equation of state, and apply it to the SNLS3 Type Ia Supernova (SN Ia) data set. We find that: (a) current SN Ia data are well described by a dark energy equation of state linear in the cosmic scale factor a, at least up to a redshift z = 1, independent of the pivot points chosen for the linear relation; (b) there is no significant evidence of any deviation from linearity. This apparent linearity may reflect the limit of dark energy information extractable from current SN Ia data.

Salzano, Vincenzo; Wang, Yun; Sendra, Irene; Lazkoz, Ruth

2014-01-01

6

Scaling cosmology with variable dark-energy equation of state

Interactions between dark matter and dark energy which result in a power-law behavior (with respect to the cosmic scale factor) of the ratio between the energy densities of the dark components (thus generalizing the ?CDM model) have been considered as an attempt to alleviate the cosmic coincidence problem phenomenologically. We generalize this approach by allowing for a variable equation of state for the dark energy within the CPL-parametrization. Based on analytic solutions for the Hubble rate and using the Constitution and Union2 SNIa sets, we present a statistical analysis and classify different interacting and non-interacting models according to the Akaike (AIC) and the Bayesian (BIC) information criteria. We do not find noticeable evidence for an alleviation of the coincidence problem with the mentioned type of interaction.

Castro, David R.; Velten, Hermano; Zimdahl, Winfried, E-mail: drodriguez-ufes@hotmail.com, E-mail: velten@physik.uni-bielefeld.de, E-mail: winfried.zimdahl@pq.cnpq.br [Universidade Federal do Espírito Santo, Departamento de Física, Av. Fernando Ferrari, 514, Campus de Goiabeiras, CEP 29075-910, Vitória, Espírito Santo (Brazil)

2012-06-01

7

NASA Astrophysics Data System (ADS)

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.

Kumar, Suresh; Xu, Lixin

2014-10-01

8

Nonparametric reconstruction of the dark energy equation of state

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.

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

9

The state of the dark energy equation of state

By combining data from seven cosmic microwave background experiments (including the latest WMAP results) with the Hubble parameter measurement from the Hubble space telescope and luminosity measurements of type Ia supernovae, we demonstrate the bounds on the dark energy equation of state wQ to be -1.45

Alessandro Melchiorri; Laura Mersini; Carolina J. Ödman; Mark Trodden

2003-01-01

10

A new equation of state for dark energy model

A new parameterization for the dark energy equation of state(EoS) is proposed and some of its cosmological consequences are also investigated. This new parameterization is the modification of Efstathiou' dark energy EoS parameterization. w(z) is a well behaved function for z >> 1 and has same behavior in z at low redshifts with Efstathiou' parameterization. In this parameterization there are two free parameter w{sub 0} and w{sub a}. We discuss the constraints on this model's parameters from current observational data. The best fit values of the cosmological parameters with 1? confidence-level regions are: ?{sub m} = 0.2735{sup +0.0171}{sub ?0.0163}, w{sub 0} = ?1.0537{sup +0.1432}{sub ?0.1511} and w{sub a} = 0.2738{sup +0.8018}{sub ?0.8288}.

Feng, Lei [Department of Physics, Nanjing University, Nanjing 210093 (China); Lu, Tan, E-mail: fenglei@chenwang.nju.edu.cn, E-mail: t.lu@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2011-11-01

11

Nonparametric reconstruction of the dark energy equation of state

A basic aim of ongoing and upcoming cosmological surveys is to unravel the mystery of dark energy. In the absence of a compelling theory to test, a natural approach is to better characterize the properties of dark energy in search of clues that can lead to a more fundamental understanding. One way to view this characterization is the improved determination of the redshift-dependence of the dark energy equation of state parameter, w(z). To do this requires a robust and bias-free method for reconstructing w(z) from data that does not rely on restrictive expansion schemes or assumed functional forms for w(z). We present a new nonparametric reconstruction method that solves for w(z) as a statistical inverse problem, based on a Gaussian process representation. This method reliably captures nontrivial behavior of w(z) and provides controlled error bounds. We demonstrate the power of the method on different sets of simulated supernova data; the approach can be easily extended to include diverse cosmological probes.

Holsclaw, Tracy; Sanso, Bruno; Lee, Herbert [Department of Applied Mathematics and Statistics, University of California, Santa Cruz, California 95064 (United States); Alam, Ujjaini; Heitmann, Katrin [ISR-1, Mailstop D466, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Habib, Salman [T-2, Mailstop B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Higdon, David [CCS-6, Mailstop F600, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2010-11-15

12

Dark energy as a modification of the Friedmann equation

Dark energy could actually be the manifestation of a modification to the Friendmann equation arising from new physics (e.g., extra dimensions). Writing the correction as (1 - {Omega}{sub M})H{sup {alpha}}/H{sub 0}{sup {alpha}-2}, they explore the phenomenology and detectability of such. They show that: (1) {alpha} must be {approx}< 1; (2) such a correction behaves like dark energy with equation-of-state w{sub eff} = -1 + {alpha}/2 in the recent past (10{sup 4} > z >> 1) and w = -1 in the distant future and can mimic w < -1 without violating the weak-energy condition; (3) w{sub eff} changes, dz/dw|{sub z {approx} 0.5} {approx} {Omicron}(0.2), which is likely detectable; and (4) a future supernova experiment like SNAP that can determine w with precision {sigma}{sub w}, could determine {alpha} to precision {sigma}{sub {alpha}} {approx} 2{sigma}{sub w}.

Dvali, Gia; /New York U.; Turner, Michael S.; /Chicago U., Astron. Astrophys. Ctr. /KICP, Chicago /Chicago U., EFI /Fermilab

2003-01-01

13

Reconstruction of the dark energy equation of state

One of the main challenges of modern cosmology is to investigate the nature of dark energy in our Universe. The properties of such a component are normally summarised as a perfect fluid with a (potentially) time-dependent equation-of-state parameter w(z). We investigate the evolution of this parameter with redshift by performing a Bayesian analysis of current cosmological observations. We model the temporal evolution as piecewise linear in redshift between 'nodes', whose w-values and redshifts are allowed to vary. The optimal number of nodes is chosen by the Bayesian evidence. In this way, we can both determine the complexity supported by current data and locate any features present in w(z). We compare this node-based reconstruction with some previously well-studied parameterisations: the Chevallier-Polarski-Linder (CPL), the Jassal-Bagla-Padmanabhan (JBP) and the Felice-Nesseris-Tsujikawa (FNT). By comparing the Bayesian evidence for all of these models we find an indication towards possible time-dependence in the dark energy equation-of-state. It is also worth noting that the CPL and JBP models are strongly disfavoured, whilst the FNT is just significantly disfavoured, when compared to a simple cosmological constant w = ?1. We find that our node-based reconstruction model is slightly disfavoured with respect to the ?CDM model.

Vázquez, J. Alberto; Bridges, M.; Lasenby, A.N. [Kavli Institute for Cosmology, Madingley Road, Cambridge CB3 0HA (United Kingdom); Hobson, M.P., E-mail: jv292@cam.ac.uk, E-mail: mb435@mrao.cam.ac.uk, E-mail: mph@mrao.cam.ac.uk, E-mail: a.n.lasenby@mrao.cam.ac.uk [Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2012-09-01

14

Reconstructing the dark energy equation of state with varying couplings

We revisit the idea of using varying couplings to probe the nature of dark energy, in particular, by reconstructing its equation of state. We show that for the class of models studied this method can be far superior to the standard methods (using type Ia supernovae or weak lensing). We also show that the simultaneous use of measurements of the fine-structure constant {alpha} and the electron-to-proton mass ratio {mu} allows a direct probe of grand unification scenarios. We present forecasts for the sensitivity of this method, both for the near future and for the next generation of spectrographs--for the latter we focus on the planned CODEX instrument for ESO's Extremely Large Telescope (formerly known as OWL). A high-accuracy reconstruction of the equation of state may be possible all the way up to redshift z{approx}4.

Avelino, P. P. [Centro de Fisica do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Departamento de Fisica da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Martins, C. J. A. P. [Centro de Fisica do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Nunes, N. J.; Olive, K. A. [School of Physics and Astronomy, University of Minnesota, 116 Church Street S.E., Minneapolis, Minnesota 55455 (United States)

2006-10-15

15

From Generalized Dirac Equations to a Candidate for Dark Energy

We consider extensions of the Dirac equation with mass terms m1+i*gamma5*m2 and i*m_1+gamma*m2. The corresponding Hamiltonians are Hermitian and pseudo-Hermitian ("gamma5 Hermitian"), respectively. The fundamental spinor solutions for all generalized Dirac equations are found in the helicity basis and brought into concise analytic form. We postulate that the time-ordered product of field operators should yield the Feynman propagator (i*epsilon prescription), and we also postulate that the tardyonic as well as tachyonic Dirac equations should have a smooth massless limit. These postulates lead to sum rules that connect the form of the fundamental field anticommutators with the tensor sums of the fundamental plane-wave eigenspinors and the projectors over positive-energy and negative-energy states. In the massless case, the sum rules are fulfilled by two egregiously simple, distinguished functional forms. The first sum rule remains valid in the case of a tardyonic theory and leads to the canonical massive Dirac field. The second sum rule is valid for a tachyonic mass term and leads to a natural suppression of the right-handed helicity states for tachyonic particles, and left-handed helicity states for tachyonic spin-1/2 antiparticles. When applied to neutrinos, the theory contains a free tachyonic mass parameter. Tachyons are known to be repulsed by gravity. We discuss a possible role of a tachyonic neutrino as a contribution to the accelerated expansion of the Universe ("dark energy").

U. D. Jentschura; B. J. Wundt

2012-05-02

16

Time variation of the equation of state for dark energy

NASA Astrophysics Data System (ADS)

The time variation of the equation of state (w_Q) for the dark energy is analyzed by the current values of the parameters ? _Q, w_Q and their time derivatives. In the future, detailed features of the dark energy could be observed, so we have considered the second derivative of w_Q for two types of potential: One is an inverse power-law type (V=M^{4+ ? }/Q^{? }) and the other is an exponential one (V=M^4exp {(? M/Q)}). The first derivative dw_Q/da and the second derivative d^2 w_Q/da^2 for both potentials are derived. The first derivative is estimated by the observed two parameters ? =w_Q+1 and ? _Q, with the tracker approximation for Q. In the limit ? rArr 0, the first derivative is null and, under the tracker approximation, the second derivative also becomes null. The evolution of forward and/or backward time variation could be analyzed from some fixed time point. If the potential is known, the evolution will be estimated from values Q and dot {Q} at this point, because the equation for the scalar field is the second derivative equation. For the inverse power potential, if we do not adopt the tracker approximations, the observed first and second derivatives with ? and ? _Q must be utilized to determine the two parameters of the potential, M and ?. For the exponential potential, the second derivative is estimated by the observed parameters ?, ? _Q, and dw_Q/da, because the parameter for this potential is essentially one, ? . If the parameter number is n for the potential form, it will be necessary for n+2 independent observations to determine the potential, Q and dot {Q}, for the evolution of the scalar field.

Hara, Tetsuya; Sakata, Ryohei; Muromachi, Yusuke; Itoh, Yutaka

2014-11-01

17

Transition of the dark energy equation of state in an interacting holographic dark energy model

A model of holographic dark energy with an interaction with matter fields has been investigated. Choosing the future event horizon as an IR cutoff, we have shown that the ratio of energy densities can vary with time. With the interaction between the two different constituents of the universe, we observed the evolution of the universe, from early deceleration to late

Bin Wang; Yungui Gong; Elcio Abdalla

2005-01-01

18

Equation of state of the trans-Planckian dark energy and the coincidence problem

NASA Astrophysics Data System (ADS)

Observational evidence suggests that our Universe is presently dominated by a dark energy component and is undergoing accelerated expansion. We recently introduced a model, motivated by string theory for short-distance physics, for explaining dark energy without appealing to any fine tuning. The idea of trans-Planckian dark energy (TDE) was based on the freeze-out mechanism of the ultralow frequency modes, ?(k), of very short distances, by the expansion of the background universe, ?(k)?H. In this paper we address the issue of the stress-energy tensor for nonlinear short-distance physics and explain the need to modify Einstein equations in this regime. From the modified Einstein equations we then derive the equation of state for the TDE model, which has the distinctive feature of being continually time dependent. The explanation of the coincidence puzzle relies entirely on the intrinsic time evolution of the TDE equation of state.

Bastero-Gil, Mar; Mersini, Laura

2003-05-01

19

Perceiving the equation of state of Dark Energy while living in a Cold Spot

The Cold Spot could be an adiabatic perturbation on the surface of last scattering, in which case it is an over-density with comoving radius of the order of 1 Gpc. We assess the effect that living in a similar structure, without knowing it, has on our perception of the equation of state of Dark Energy. We find that structures of dimensions such that they could cause the Cold Spot on the CMB, affect the perceived equation of state of Dark Energy possibly up to ten percent.

Valkenburg, Wessel, E-mail: w.valkenburg@thphys.uni-heidelberg.de [Institut für Theoretische Teilchenphysik und Kosmologie, RWTH Aachen University, D-52056 Aachen (Germany)

2012-01-01

20

Dynamical Mutation of Dark Energy

We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.

L. R. Abramo; R. C. Batista; L. Liberato; R. Rosenfeld

2007-10-12

21

On the possibility of dark energy from corrections to the Wheeler DeWitt equation

NASA Astrophysics Data System (ADS)

We present a method for approximating the effective consequence of generic quantum gravity corrections to the Wheeler DeWitt equation. We show that in many cases these corrections can produce departures from classical physics at large scales and that this behaviour can be interpreted as additional matter components. This opens up the possibility that dark energy (and possible dark matter) could be large scale manifestations of quantum gravity corrections to classical general relativity. As a specific example we examine the first order corrections to the Wheeler DeWitt equation arising from loop quantum cosmology in the absence of lattice refinement and show how the ultimate breakdown in large scale physics occurs.

Nelson, William; Sakellariadou, Mairi

2008-03-01

22

NASA Astrophysics Data System (ADS)

Preface; Part I. Theory: 1. Dark energy, gravitation and the Copernican principle J.-P. Uzan; 2. Dark energy and modified gravity R. Maartens and R. Durrer; 3. Some views on dark energy D. Polarski; 4. Emergent gravity and dark energy T. Padmanabhan; Part II. Observations: 5. Foundations of supernova cosmology R. P. Kirshner; 6. Dark energy and supernovae P. Ruiz-Lapuente; 7. The future of supernova cosmology M. Wood-Vasey; 8. The space advantage A. Kim; 9. Baryon acoustic oscillations B. Bassett and R. Hlozek; 10. Weak gravitational lensing A. Heavens; Index.

Ruiz-Lapuente, Pilar

2010-03-01

23

NASA Astrophysics Data System (ADS)

Preface; Part I. Theory: 1. Dark energy, gravitation and the Copernican principle J.-P. Uzan; 2. Dark energy and modified gravity R. Maartens and R. Durrer; 3. Some views on dark energy D. Polarski; 4. Emergent gravity and dark energy T. Padmanabhan; Part II. Observations: 5. Foundations of supernova cosmology R. P. Kirshner; 6. Dark energy and supernovae P. Ruiz-Lapuente; 7. The future of supernova cosmology M. Wood-Vasey; 8. The space advantage A. Kim; 9. Baryon acoustic oscillations B. Bassett and R. Hlozek; 10. Weak gravitational lensing A. Heavens; Index.

Ruiz-Lapuente, Pilar

2014-02-01

24

Fables of reconstruction: controlling bias in the dark energy equation of state

We develop an efficient, non-parametric Bayesian method for reconstructing the time evolution of the dark energy equation of state w(z) from observational data. Of particular importance is the choice of prior, which must be chosen carefully to minimise variance and bias in the reconstruction. Using a principal component analysis, we show how a correlated prior can be used to create a smooth reconstruction and also avoid bias in the mean behaviour of w(z). We test our method using Wiener reconstructions based on Fisher matrix projections, and also against more realistic MCMC analyses of simulated data sets for Planck and a future space-based dark energy mission. While the accuracy of our reconstruction depends on the smoothness of the assumed w(z), the relative error for typical dark energy models is ?<10% out to redshift z = 1.5.

Crittenden, Robert G.; Zhao, Gong-Bo; Samushia, Lado [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom); Pogosian, Levon [Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6 (Canada); Zhang, Xinmin, E-mail: Robert.Crittenden@port.ac.uk, E-mail: gong-bo.zhao@port.ac.uk, E-mail: levon@sfu.ca, E-mail: lado.samushia@port.ac.uk, E-mail: xmzhang@ihep.ac.cn [Theoretical Physics Division, Institute of High Energy Physics, Chinese Academy of Science, P.O.Box 918-4, Beijing 100049 (China)

2012-02-01

25

Reconstructing equation of state of dark energy with principal component analysis

We represent a method to reconstruct the equation of state for dark energy directly from observational Hubble parameter data in a nonparametric way. We use principal component analysis (PCA) to extract the signal from data with noise. In addition, we modify Akaike information criteria (AIC) to guarantee the quality of reconstruction and avoid over-fitting simultaneously. The results show that our method is robust in reconstruction of dark energy equation of state. Although current observational Hubble parameter data alone can not give a strong constraint yet, future observations with more accurate data can help to improve the quality of reconstruction significantly, which is consistent with the results of H.-R. Yu et al.

Qin, Hao-Feng; Wan, Hao-Yi; Zhang, Tong-Jie

2015-01-01

26

Observational constraints on scalar field models of dark energy with barotropic equation of state

We constrain the parameters of dynamical dark energy in the form of a classical or tachyonic scalar field with barotropic equation of state jointly with other cosmological parameters using the following datasets: the CMB power spectra from WMAP7, the baryon acoustic oscillations in the space distribution of galaxies from SDSS DR7, the power spectrum of luminous red galaxies from SDSS DR7 and the light curves of SN Ia from 2 different compilations: Union2 (SALT2 light curve fitting) and SDSS (SALT2 and MLCS2k2 light curve fittings). It has been found that the initial value of dark energy equation of state parameter is constrained very weakly by most of the data while the other cosmological parameters are well constrained: their likelihoods and posteriors are similar, their forms are close to Gaussian (or half-Gaussian) and the confidence ranges are narrow. The most reliable determinations of the best-fit value and 1? confidence range for the initial value of the dark energy equation of state parameter are obtained from the combined datasets including SN Ia data from the full SDSS compilation with MLCS2k2 light curve fitting. In all such cases the best-fit value of this parameter is lower than the value of corresponding parameter for current epoch. Such dark energy loses its repulsive properties and in future the expansion of the Universe changes into contraction. We also perform a forecast for the Planck mock data and show that they narrow significantly the confidence ranges of cosmological parameters values, moreover, their combination with SN SDSS compilation with MLCS2k2 light curve fitting may exclude the fields with initial equation of state parameter > ?0.1 at 2? confidence level.

Sergijenko, Olga; Novosyadlyj, Bohdan [Astronomical Observatory of Ivan Franko National University of Lviv, Kyryla i Methodia str. 8, Lviv, 79005 (Ukraine); Durrer, Ruth, E-mail: olka@astro.franko.lviv.ua, E-mail: ruth.durrer@unige.ch, E-mail: novos@astro.franko.lviv.ua [Département de Physique Théorique and CAP, Université de Genčve, 24 quai Ernest-Ansermet, CH-1211 Genčve 4 (Switzerland)

2011-08-01

27

Probing Dark Energy Using Its Density Instead of Its Equation of State

The variation of dark energy density with redshift, $\\rho_X(z)$, provides a critical clue to the nature of dark energy. Since $\\rho_X(z)$ depends on the dark energy equation of state $w_X(z)$ through an integral, $\\rho_X(z)$ can be constrained more tightly than $w_X(z)$ given the same observational data. We demonstrate this explicitly using current type Ia supernova (SN Ia) data [the Tonry/Barris sample], together with the Cosmic Microwave Background (CMB) shift parameter from CMB data (WMAP, CBI, and ACBAR), and the large scale structure (LSS) growth factor from 2dF galaxy survey data. We assume a flat universe, and use Markov Chain Monte Carlo (MCMC) technique in our analysis. We find that, while $w_X(z)$ extracted from current data is consistent with a cosmological constant at 68% C.L., $\\rho_X(z)$ (which has far smaller uncertainties) is not. Our results clearly show the advantage of using $\\rho_X(z)$, instead of $w_X(z)$, to probe dark energy.

Yun Wang; Katherine Freese

2004-02-09

28

Properties and uncertainties of scalar field models of dark energy with barotropic equation of state

The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state are analyzed. It is shown that the past dynamics of expansion and future of the Universe - eternal accelerated expansion or turnaround and collapse - are completely defined by the current energy density of a scalar field and relation between its current and early equation of state parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the 'effective sound speed' of a scalar field, defined by its Lagrangian. It is concluded that such scalar fields with different values of these parameters are distinguishable in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year Wilkinson Microwave Anisotropy Probe data on cosmic microwave background anisotropies, the Union2 data set on Supernovae Ia and the seventh data release of the Sloan Digital Sky Survey data on luminous red galaxies space distribution. Using the Markov Chain Monte Carlo technique the marginalized posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper.

Novosyadlyj, Bohdan; Sergijenko, Olga; Apunevych, Stepan; Pelykh, Volodymyr [Astronomical Observatory of Ivan Franko National University of Lviv, Kyryla i Methodia str., 8, Lviv, 79005 (Ukraine); Ya. S. Pidstryhach Institute for Applied Problems of Mechanics and Mathematics, Naukova Street, 3-b, Lviv, 79060 (Ukraine)

2010-11-15

29

We study some aspects of cosmological evolution in a universe described by a viable curvature corrected exponential $F(R)$ gravity model, in the presence of matter fluids consisting of collisional matter and radiation. Particularly, we express the Friedmann-Robertson-Walker equations of motion in terms of parameters that are appropriate for describing the dark energy oscillations and compare the dark energy density and the dark energy equation of state parameter corresponding to collisional and non-collisional matter. In addition to these, and owing to the fact that the cosmological evolution of collisional and non-collisional matter universes, when quantified in terms of the Hubble parameter and the effective equation of states parameters, is very much alike, we further scrutinize the cosmological evolution study by extending the analysis to the study of matter perturbations in the matter domination era. We quantify this analysis in terms of the growth factor of matter perturbations, in which case the resulting picture of the cosmological evolution is clear, since collisional and non-collisional universes can be clearly distinguished. Interestingly enough, since it is known that the oscillations of the effective equation of state parameter around the phantom divide are undesirable and unwanted in $F(R)$ gravities, when these are considered for redshifts near the matter domination era and before, in the curvature corrected exponential model with collisional matter which we study here there exist oscillations that never cross the phantom divide. Therefore, this rather unwanted feature of the effective equation of state parameter is also absent in the collisional matter filled universe.

V. K. Oikonomou; N. Karagiannakis; Miok Park

2014-11-12

30

After some remarks about the history and the mystery of the vacuum energy I shall review the current evidence for a cosmologically significant nearly homogeneous exotic energy density with negative pressure (`Dark Energy'). Special emphasis will be put on the recent polarization measurements by WMAP and their implications. I shall conclude by addressing the question: Do the current observations really imply the existence of a dominant dark energy component?

Norbert Straumann

2003-11-26

31

High-redshift investigation on the dark energy equation of state

NASA Astrophysics Data System (ADS)

The understanding of the accelerated expansion of the Universe poses one of the most fundamental questions in physics and cosmology today. Whether or not the acceleration is driven by some form of dark energy, and in the absence of a well-based theory to interpret the observations, many models have been proposed to solve this problem, both in the context of General Relativity and alternative theories of gravity. Actually, a further possibility to investigate the nature of dark energy lies in measuring the dark energy equation of state (EOS), w, and its time (or redshift) dependence at high accuracy. However, since w(z) is not directly accessible to measurement, reconstruction methods are needed to extract it reliably from observations. Here, we investigate different models of dark energy, described through several parametrizations of the EOS. Our high-redshift analysis is based on the Union2 Type Ia supernovae data set (Suzuki et al.), the Hubble diagram constructed from some gamma-ray bursts luminosity-distance indicators, and Gaussian priors on the distance from the baryon acoustic oscillations, and the Hubble constant h (these priors have been included in order to help to break the degeneracies among model parameters). To perform our statistical analysis and to explore the probability distributions of the EOS parameters, we use the Markov Chain Monte Carlo Method. It turns out that, if exact flatness is assumed, the dark energy EOS is evolving for all the parametrizations that we considered. We finally compare our results with the ones obtained by previous cosmographic analyses performed on the same astronomical data sets, showing that the latter ones are sufficient to test and compare the new parametrizations.

Piedipalumbo, E.; Della Moglie, E.; De Laurentis, M.; Scudellaro, P.

2014-07-01

32

Dark Energy is the dominant constituent of the universe and we have little understanding of it. We describe a new project aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of ~5% with four separate techniques. The survey will image 5000 deg2 in the southern sky and collect 300 million galaxies, 30,000 galaxy clusters,

G. Aldering; J. Annis; M. Barlow; C. Bebek; B. Bigelow; C. Beldica; R. Bernstein; S. Bridle; R. Brunner; J. Carlstrom; M. Campbell; F. Castander; C. Cunha; H. T. Diehl; S. Dodelson; P. Doel; G. Efstathiou; J. Estrada; A. Evrard; E. Fernández; B. Flaugher; P. Fosalba; J. Frieman; E. Gaztańaga; D. Gerdes; M. Gladders; W. Hu; D. Huterer; B. Jain; I. Karliner; S. Kent; O. Lahav; M. Levi; M. Lima; H. Lin; P. Limon; M. Martínez; T. McKay; R. McMahon; K. W. Merritt; C. Miller; J. Miralda-Escude; J. Mohr; R. Nichol; H. Oyaizu; J. Peacock; J. Peoples; S. Perlmutter; R. Plante; P. Ricker; N. Roe; V. Scarpine; M. Schubnell; M. Selen; E. Sheldon; C. Smith; A. Stebbins; C. Stoughton; N. Suntzeff; W. Sutherland; M. Takada; G. Tarle; M. Tecchio; J. Thaler; D. Tucker; S. Viti; A. Walker; R. Wechsler; J. Weller

2005-01-01

33

Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar-field models) which is often generically called 'dark energy'. We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.

Sapone, Domenico; Kunz, Martin [Departement de Physique Theorique, Universite de Geneve, 24 quai Ernest Ansermet, CH-1211 Geneve 4 (Switzerland); Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom)

2009-10-15

34

Effective equation of state for running vacuum: "mirage" quintessence and phantom dark energy

Past analyses of the equation of state (EoS) of the Dark Energy (DE) were not incompatible with a phantom phase near our time. This has been the case in the years of WMAP observations, in combination with the remaining cosmological observables. Such situation did not completely disappear from the data collected from the Planck satellite mission. In it the EoS analysis may still be interpreted as suggesting wmirage" effect is caused by an attempt to describe them as if the DE would be caused by fundamental phantom scalar fields. Remarkably, the effective DE behavior can also appear as quintessence in transit to phantom, or vice versa.

Spyros Basilakos; Joan Sola

2013-07-17

35

Effective equation of state for running vacuum: "mirage" quintessence and phantom dark energy

The analysis of the equation of state (EoS) of the Dark Energy (DE) has been persistently suggesting a phantom phase near our time. This has been the case in the years of WMAP observations, in combination with the remaining cosmological observables. Such situation, far from fading away from the latest accurate data on the cosmic microwave anisotropies collected from the PLANCK satellite mission, remains there unscathed. Despite it is claimed there is no much evidence for dynamical DE, the bare fact is that the EoS analysis still points to wmirage" effect is caus...

Basilakos, Spyros

2013-01-01

36

dark matter dark energy inflation

theory dark matter dark energy inflation The National Science Foundation The Kavli Foundation NSF Site Review November 28-29, 2005 #12;dark matter dark energy inflation NSF Site Visit Â November 28 - 29, 2005The National Science Foundation The Kavli Foundation The Theoretical Web UHE cosmic rays B

Hu, Wayne

37

Inference for the dark energy equation of state using Type IA supernova data

The surprising discovery of an accelerating universe led cosmologists to posit the existence of dark energya mysterious energy field that permeates the universe. Understanding dark energy has become the central problem of modern cosmology. After describing the scientific background in depth, we formulate the task as a nonlinear inverse problem that expresses the comoving distance function in terms of the

Christopher R. Genovese; Peter Freeman; Larry Wasserman; Robert C. Nichol; Christopher Miller

2009-01-01

38

Dark-energy thermodynamic models

We study cosmological consequences of dark-energy thermodynamic models. The assumption that dark energy is conformed of quanta, and an extensivity argument generalize its equation of state. This implies that dark energy and another key component exchange energy. The energy densities of dark energy and the other component then tend asymptotically to a constant, thus explaining the coincidence of dark matter and dark energy today. On the other hand, a model of non-relativistic particles in a Bose-Einstein condensate, with a short-range attractive interaction, produces acceleration. It is shown that the phantom-acceleration regime, at the beginning of the universe, solves the horizon problem.

Besprosvany, Jaime [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, Mexico 01000, Distrito Federal (Mexico); Izquierdo, German [Institut de Mathematiques de Bourgogne, Universite de Bourgogne, 9 Av. Alain Savary, 21078 Dijon Cedex (France)

2010-12-07

39

A brief overview of our current understanding of abundance and properties of dark energy and dark matter is presented. A more focused discussion of supersymmetric dark matter follows. Included is a frequentist approach to the supersymmetric parameter space and consequences for the direct detection of dark matter.

Keith A. Olive

2010-01-27

40

Thermodynamical properties of dark energy with the equation of state $% ?=?_{0}+?_{1}z$

The thermodynamical properties of dark energy are usually investigated with the equation of state $\\omega =\\omega_{0}+\\omega_{1}z$. Recent observations show that our universe is accelerating, and the apparent horizon and the event horizon vary with redshift $z$. When definitions of the temperature and entropy of a black hole are used to the two horizons of the universe, we examine the thermodynamical properties of the universe which is enveloped by the apparent horizon and the event horizon respectively. We show that the first and the second laws of thermodynamics inside the apparent horizon in any redshift are satisfied, while they are broken down inside the event horizon in some redshift. Therefore, the apparent horizon for the universe may be the boundary of thermodynamical equilibrium for the universe like the event horizon for a black hole.

Yongping Zhang; Ze-Long Yi; Tong-Jie Zhang; Wenbiao Liu

2007-09-18

41

We describe the Dark Energy Survey (DES), a proposed optical-near infrared survey of 5000 sq. deg of the South Galactic Cap to ~24th magnitude in SDSS griz, that would use a new 3 sq. deg CCD camera to be mounted on the Blanco 4-m telescope at Cerro Telolo Inter-American Observatory (CTIO). The survey data will allow us to measure the dark energy and dark matter densities and the dark energy equation of state through four independent methods: galaxy clusters, weak gravitational lensing tomography, galaxy angular clustering, and supernova distances. These methods are doubly complementary: they constrain different combinations of cosmological model parameters and are subject to different systematic errors. By deriving the four sets of measurements from the same data set with a common analysis framework, we will obtain important cross checks of the systematic errors and thereby make a substantial and robust advance in the precision of dark energy measurements.

The Dark Energy Survey Collaboration

2005-10-12

42

Exploring the diversity of dark energy dynamics, we discover a calibration relation, a uniform stretching of the amplitude of the equation of state time variation with scale factor. This defines homogeneous families of dark energy physics. The calibration factor has a close relation to the standard time variation parameter w_a, and we show that the new, calibrated w_a describes observables, i.e. distance and Hubble parameter as a function of redshift, typically to an accuracy level of 10^{-3}. We discuss implications for figures of merit for dark energy science programs.

Roland de Putter; Eric V. Linder

2008-08-01

43

Cosmo-dynamics and dark energy with non-linear equation of state: a quadratic model

We investigate the general relativistic dynamics of Robertson-Walker models with a non-linear equation of state (EoS), focusing on the quadratic case P = P_0 + \\alpha \\rho + \\beta \\rho^2. This may be taken to represent the Taylor expansion of any arbitrary barotropic EoS, P(\\rho). With the right combination of P_0, \\alpha and \\beta, it serves as a simple phenomenological model for dark energy, or even unified dark matter. Indeed we show that this simple model for the EoS can produce a large variety of qualitatively different dynamical behaviors that we classify using dynamical systems theory. An almost universal feature is that accelerated expansion phases are mostly natural for these non-linear EoS's. These are often asymptotically de Sitter thanks to the appearance of an effective cosmological constant. Other interesting possibilities that arise from the quadratic EoS are closed models that can oscillate with no singularity, models that bounce between infinite contraction/expansion and models which evolve from a phantom phase, asymptotically approaching a de Sitter phase instead of evolving to a "Big Rip". In a second paper we investigate the effects of the quadratic EoS in inhomogeneous and anisotropic models, focusing in particular on singularities.

Kishore N. Ananda; Marco Bruni

2005-12-08

44

Unified Description of Dark Energy and Dark Matter

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. This yields that dark matter is one third of dark energy for all times implying an explanation of the coincidence of dark matter and dark energy. In the final state, the universe becomes dark, consisting of dark matter and dark energy.

Walter Petry

2008-11-09

45

Interacting Agegraphic Dark Energy

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 agegraphic dark energy model and holographic dark energy model. The similarity and difference between agegraphic dark energy and holographic dark energy are also discussed.

Hao Wei; Rong-Gen Cai

2007-07-27

46

Cosmic chronometers: constraining the equation of state of dark energy. I: H(z) measurements

We present new determinations of the cosmic expansion history from red-envelope galaxies. We have obtained for this purpose high-quality spectra with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with high-quality, publicly available archival spectra from the SPICES and VVDS surveys. We improve over our previous expansion history measurements in Simon et al. (2005) by providing two new determinations of the expansion history: H(z) = 97ą62 km sec{sup ?1} Mpc{sup ?1} at z ? 0.5 and H(z) = 90ą40 km sec{sup ?1} Mpc{sup ?1} at z ? 0.9. We discuss the uncertainty in the expansion history determination that arises from uncertainties in the synthetic stellar-population models. We then use these new measurements in concert with cosmic-microwave-background (CMB) measurements to constrain cosmological parameters, with a special emphasis on dark-energy parameters and constraints to the curvature. In particular, we demonstrate the usefulness of direct H(z) measurements by constraining the dark-energy equation of state parameterized by w{sub 0} and w{sub a} and allowing for arbitrary curvature. Further, we also constrain, using only CMB and H(z) data, the number of relativistic degrees of freedom to be 4ą0.5 and their total mass to be < 0.2 eV, both at 1?.

Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 169-506, Pasadena CA-91109 (United States); Jimenez, Raul; Verde, Licia [ICREA and Institute of Sciences of the Cosmos (ICC), University of Barcelona, Barcelona 08028 (Spain); Kamionkowski, Marc [California Institute of Technology, Mail Code 350-17, Pasadena, California 91125 (United States); Stanford, S. Adam, E-mail: stern@thisvi.jpl.nasa.gov, E-mail: raul@icc.ub.edu, E-mail: licia@icc.ub.edu, E-mail: kamion@tapir.caltech.edu, E-mail: stanford@physics.ucdavis.edu [University of California, Davis, CA 95616 (United States)

2010-02-01

47

Dark energy without dark energy

It is proposed that the current acceleration of the universe is not originated by the existence of a mysterious dark energy fluid nor by the action of extra terms in the gravity Lagrangian, but just from the sub-quantum potential associated with the CMB particles. The resulting cosmic scenario corresponds to a benigner phantom model which is free from the main problems of the current phantom approaches.

Pedro F. Gonzalez-Diaz

2006-08-29

48

Dark energy and dark matter from cosmological observations

The present status of our knowledge about the dark matter and dark energy is reviewed. Bounds on the content of cold and hot dark matter from cosmological observations are discussed in some detail. I also review current bounds on the physical properties of dark energy, mainly its equation of state and effective speed of sound.

Steen Hannestad

2005-09-14

49

Effective equation of state for running vacuum: `mirage' quintessence and phantom dark energy

NASA Astrophysics Data System (ADS)

Past analyses of the equation of state (EoS) of the Dark Energy (DE) were not incompatible with a phantom phase near our time. This has been the case in the years of Wilkinson Microwave Anisotropy Probe observations, in combination with the remaining cosmological observables. Such situations did not completely disappear from the data collected from the Planck satellite mission. In it the EoS analysis may still be interpreted as suggesting ?D ? -1, and so a mildly evolving DE cannot be discarded. In our opinion, the usual ansatzs made on the structure of the EoS for dynamical DE models (e.g. quintessence and the like) is too simplified. In this work, we examine in detail some of these issues and suggest that a general class of models with a dynamical vacuum energy density could explain the persistent phantom anomaly, despite this there is no trace of real phantom behaviour in them. The spurious or `mirage' effect is caused by an attempt to describe them as if the DE would be caused by fundamental phantom scalar fields. Remarkably, the effective DE behaviour can also appear as quintessence in transit to phantom, or vice versa.

Basilakos, Spyros; Solŕ, Joan

2014-02-01

50

Spherical collapse with dark energy

I discuss the work of Maor and Lahav [1], in which the inclusion of dark energy into the spherical collapse formalism is reviewed. Adopting a phenomenological approach, I consider the consequences of - a) allowing the dark energy to cluster, and, b) including the dark energy in the virialization process. Both of these issues affect the final state of the system in a fundamental way. The results suggest a potentially differentiating signature between a true cosmological constant and a dynamic form of dark energy. This signature is unique in the sense that it does not depend on a measurement of the value of the equation of state of dark energy.

Irit Maor

2006-02-20

51

We propose to use HII galaxies (HIIG) to trace the redshift-distance relation, by means of their $L(\\mathrm{H}\\beta) - \\sigma$ correlation, in an attempt to constrain the dark energy equation of state parameter solution space, as an alternative to the cosmological use of type Ia supernovae. For a sample of 128 local compact HIIG with high equivalent widths of their Balmer emission lines we obtained ionised gas velocity dispersion from high S/N, high-dispersion spectroscopy (Subaru-HDS and ESO VLT-UVES) and integrated H$\\beta$ fluxes from low dispersion wide aperture spectrophotometry. We find that the $L(\\mathrm{H}\\beta) - \\sigma$ relation is strong and stable against restrictions in the sample. The size of the starforming region is an important second parameter, while adding the emission line equivalent width or the continuum colour and metallicity, produces the solution with the smallest rms scatter. We have used the $L(\\mathrm{H}\\beta) - \\sigma$ relation from a local sample of HIIG and a local calibration ...

Chávez, Ricardo

2014-01-01

52

On dark energy isocurvature perturbation

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.

Liu, Jie; Zhang, Xinmin [Institute of High Energy Physics, Chinese Academy of Science, P.O. Box 918-4, Beijing 100049 (China); Li, Mingzhe, E-mail: liujie@ihep.ac.cn, E-mail: limz@nju.edu.cn, E-mail: xmzhang@ihep.ac.cn [Department of Physics, Nanjing University, Nanjing 210093 (China)

2011-06-01

53

Dark Energy is the dominant constituent of the universe and they have little understanding of it. They describe a new project aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of {approx} 5%, with four separate techniques. The survey will image 5000 deg{sup 2} in the southern sky and collect 300 million galaxies, 30,000 galaxy clusters, and 2000 Type Ia supernovae. The survey will be carried out using a new 3 deg{sup 2} mosaic camera mounted at the prime focus of the 4m Blanco telescope at CTIO.

Flaugher, Brenna; /Fermilab

2004-11-01

54

Dark Energy Present and Future

By studying the present cosmological data, particularly on CMB, SNeIA and LSS, we find that the future fate of the universe, for simple linear models of the dark energy equation-of-state, can vary between the extremes of (I) a divergence of the scale factor in as little as 7 Gyr; (II) an infinite lifetime of the universe with dark energy dominant for all future time; (III) a disappearing dark energy where the universe asymptotes as $t \\to \\infty$ to $a(t) \\sim t^{2/3}$ {\\it i.e.} matter domination. Precision cosmological data hint that a dark energy with equation of state $w = P/\\rho 0$ to $\\Lambda = 0$ in a first-order phase transition. The critical radius is argued to be at least of galactic size and the corresponding nucleation rate glacial, thus underwriting the dark energy's stability and rendering remote any microscopic effect.

Paul H. Frampton

2003-07-03

55

Beyond two dark energy parameters.

Our ignorance of dark energy is generally described by a two-parameter equation of state. In these approaches, a particular ad hoc functional form is assumed, and only two independent parameters are incorporated. We propose a model-independent, multiparameter approach to fitting dark energy and show that next-generation surveys will constrain the equation of state in three or more independent redshift bins to better than 10%. Future knowledge of dark energy will surpass two numbers (e.g., [w{0},w{1}] or [w{0},w{a}]), and we propose a more flexible approach to the analysis of present and future data. PMID:18643568

Sarkar, Devdeep; Sullivan, Scott; Joudaki, Shahab; Amblard, Alexandre; Holz, Daniel E; Cooray, Asantha

2008-06-20

56

Dark Energy Perturbations Revisited

In this paper we study the evolution of cosmological perturbations in the presence of dynamical dark energy, and revisit the issue of dark energy perturbations. For a generally parameterized equation of state (EoS) such as w_D(z) = w_0+w_1\\frac{z}{1+z}, (for a single fluid or a single scalar field ) the dark energy perturbation diverges when its EoS crosses the cosmological constant boundary w_D=-1. In this paper we present a method of treating the dark energy perturbations during the crossing of the $w_D=-1$ surface by imposing matching conditions which require the induced 3-metric on the hypersurface of w_D=-1 and its extrinsic curvature to be continuous. These matching conditions have been used widely in the literature to study perturbations in various models of early universe physics, such as Inflation, the Pre-Big-Bang and Ekpyrotic scenarios, and bouncing cosmologies. In all of these cases the EoS undergoes a sudden change. Through a detailed analysis of the matching conditions, we show that \\delta_D an...

Li, Mingzhe; Li, Hong; Brandenberger, Robert; Zhang, Xinmin

2010-01-01

57

Cosmological Consequences of a Dark Energy Component with Super-Negative Equation of State

It is extraordinary that a number of observations indicate that we live in a spatially flat, low matter density Universe, which is currently undergoing a period of accelerating expansion. The effort to explain this current state has focused attention on cosmological models in which the dominant component of the cosmic energy density has negative pressure, with an equation of state

R. R. Caldwell

58

Galaxy Clustering and Dark Energy

We study the evolution of galaxy clustering in various cosmological models with quintessence. We investigate how the analytical predictions vary with change of dark energy equation of state $w_X$. Comparing these predictions against available data we discuss to what extent the problems of galaxy biasing can be modelled. This will be key in constraining the dark energy equation of state with future galaxy surveys. We use a compilation of various surveys to study the number density and amplitude of galaxy clustering from observations of the local universe at $z \\sim 0$ to that of the Lyman break galaxies and Ly-$\\alpha$ emitters at $z \\sim 4.9$. We find that there is a degeneracy between the dark energy equation of state and the way galaxies populate dark matter haloes; objects are more biased in models with more negative values of dark energy equation of state $w_X$. We conclude that, while future all sky CMB observations will determine cosmological parameters with unprecedented precision, and cross correlation of weak lensing experiments and galaxy surveys will provide a cleaner and accurate picture of bias associated with collapsed objects, the rate of growth of large scale structure in such surveys can potentially constrain the equation of state of dark energy and the potential of the scalar field associated with quintessence. In particular, we show that the abundance and spatial distribution of galaxy clusters at intermediate redshifts strongly depend on the dark energy equation of state. When accurate measurement of galaxy clustering at high-redshit becomes possible, it will provide constraints on dark energy that are independent and complementary to type Ia supernova studies.

Dipak Munshi; Cristiano Porciani; Yun Wang

2003-02-25

59

Correspondence between Ricci and other dark energies

Purpose of the present paper is to view the correspondence between Ricci and other dark energies. We have considered the Ricci dark energy in presence of dark matter in non-interacting situation. Subsequently, we have derived the pressure and energy density for Ricci dark energy. The equation of state parameter has been generated from these pressure and energy density. Next, we have considered the correspondence between Ricci and other dark energy models, namely tachyonic field, DBI-essence and new agegraphic dark energy without any interaction and investigated possible cosmological consequences.

Surajit Chattopadhyay; Ujjal Debnath

2010-09-26

60

Though the concept of a dark energy driven accelerating universe was introduced by the author in 1997, to date dark energy itself, as described below has remained a paradigm. A model for the cosmological constant is suggested.

Burra G. Sidharth

2014-12-30

61

Measuring the speed of dark: Detecting dark energy perturbations

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){ne}-1], degrees of freedom distinct from quintessence (c{sub s{ne}}1), and early presence of dark energy [{Omega}{sub de}(a<<1){ne}0]. Future data may open a new window on dark energy by measuring its spatial as well as time variation.

Putter, Roland de [Berkeley Lab and University of California, Berkeley, California 94720 (United States); Huterer, Dragan [Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan, 48109 (United States); Linder, Eric V. [Berkeley Lab and University of California, Berkeley, California 94720 (United States); Institute for the Early Universe, Ewha Womans University, Seoul (Korea, Republic of)

2010-05-15

62

Weak lensing and dark energy: The impact of dark energy on nonlinear dark matter clustering

We examine the influence of percent-level dark energy corrections to the nonlinear matter power spectrum on constraints of the dark energy equation of state from future weak lensing probes. We explicitly show that a poor approximation (off by > or approx.10%) to the nonlinear corrections causes a > or approx. 1{sigma} bias on the determination of the dark energy equation of state. Future weak lensing surveys must therefore incorporate dark energy modifications to the nonlinear matter power spectrum accurate to the percent-level, to avoid introducing significant bias in their measurements. For the WMAP5 cosmology, the more accurate power spectrum is more sensitive to dark energy properties, resulting in a factor of 2 improvement in dark energy equation of state constraints. We explore the complementary constraints on dark energy from future weak lensing and supernova surveys. A space-based, Joint Dark Energy Mission-like survey measures the equation of state in five independent redshift bins to {approx}10%, while this improves to {approx}5% for a wide-field ground-based survey like the Large Synoptic Survey Telescope. These constraints are contingent upon our ability to control weak lensing systematic uncertainties to the sub-percent level.

Joudaki, Shahab; Cooray, Asantha; Holz, Daniel E. [Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2009-07-15

63

Entropy bounds and dark energy

NASA Astrophysics Data System (ADS)

Entropy bounds render quantum corrections to the cosmological constant ? finite. Under certain assumptions, the natural value of ? is of order the observed dark energy density ~10-10 eV4, thereby resolving the cosmological constant problem. We note that the dark energy equation of state in these scenarios is w?p/?=0 over cosmological distances, and is strongly disfavored by observational data. Alternatively, ? in these scenarios might account for the diffuse dark matter component of the cosmological energy density. Permanent address: Institute of Theoretical Science and Department of Physics, University of Oregon, Eugene, OR 97403.

Hsu, Stephen D. H.

2004-07-01

64

Dark Energy From Fifth Dimension

Observational evidence for the existence of dark energy is strong. Here we suggest a model which is based on a modified gravitational theory in 5D and interpret the 5th dimension as a manifestation of dark energy in the 4D observable universe. We also obtain an equation of state parameter which varies with time. Finally, we match our model with observations by choosing the free parameters of the model.

H. Alavirad; N. Riazi

2008-01-21

65

Entropy bounds and dark energy

Entropy bounds render quantum corrections to the cosmological constant ? finite. Under certain assumptions, the natural value of ? is of order the observed dark energy density ?10?10 eV4, thereby resolving the cosmological constant problem. We note that the dark energy equation of state in these scenarios is w?p\\/?=0 over cosmological distances, and is strongly disfavored by observational data. Alternatively, ?

Stephen D. H. Hsu

2004-01-01

66

In the present work, we reconsider the idea of holographic dark energy. One of its key points is the formation of the black hole. And then, we propose the so-called "pilgrim dark energy" based on the speculation that the repulsive force contributed by the phantom-like dark energy ($w<-1$) is strong enough to prevent the formation of the black hole. We also consider the cosmological constraints on pilgrim dark energy by using the latest observational data. Of course, one can instead regard pilgrim dark energy as a purely phenomenological model without any physical motivation. We also briefly discuss this issue.

Hao Wei

2012-08-30

67

We present a model in which the equation of state parameter w approaches -1 near a particular value of z, and has significant negative values in a restricted range of z. For example, one can have w ~ -1 near z = 1, and w > -0.2 from z = 0 to z = 0.3, and for z > 9. The ingredients of the model are neutral fermions (which may be neutrinos, neutralinos, etc) which are very weakly coupled to a light scalar field. This model emphasises the importance of the proposed studies of the properties of dark energy into the region z > 1.

B. H. J. McKellar; T. Goldman; G. J. Stephenson, Jr.; P. M. Alsing

2009-08-06

68

We discuss the phenomenology of the dark energy in first order perturbation theory, demonstrating that the dark energy cannot be fully constrained unless the dark matter is found, and that there are two functions that characterise the observational properties of the dark sector for cosmological probes. We argue that measuring these two functions should be an important goal for observational cosmology in the next decades.

Martin Kunz; Luca Amendola; Domenico Sapone

2008-06-08

69

Dark Energy in Global Brane Universe

We discuss the exact solutions of brane universes and the results indicate the Friedmann equations on the branes are modified with a new density term. Then, we assume the new term as the density of dark energy. Using Wetterich's parametrization equation of state (EOS) of dark energy, we obtain the new term varies with the red-shift z. Finally, the evolutions of the mass density parameter $\\Omega_2$, dark energy density parameter $\\Omega_x$ and deceleration parameter q_2 are studied.

Yongli Ping; Lixin Xu; Chengwu Zhang; Hongya Liu

2007-07-19

70

The thermodynamical properties of dark energy are usually investigated with the equation of state {omega}={omega}{sub 0}+{omega}{sub 1}z. Recent observations show that our Universe is accelerating, and the apparent horizon and the event horizon vary with redshift z. Because definitions of the temperature and entropy of a black hole are used to describe the two horizons of the Universe, we examine the thermodynamical properties of the Universe, which is enveloped by the apparent horizon and the event horizon, respectively. We show that the first and the second laws of thermodynamics inside the apparent horizon in any redshift are satisfied, while they are broken down inside the event horizon in some redshifts. Therefore, the apparent horizon for the Universe may be the boundary of thermodynamical equilibrium for the Universe like the event horizon for a black hole.

Zhang Yongping; Yi Zelong; Zhang Tongjie; Liu Wenbiao [Department of Physics, Institute of Theoretical Physics, Beijing Normal University, Beijing, 100875 (China); Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Kavli Institute for Theoretical Physics China, Institute of Theoretical Physics, Chinese Academy of Sciences (KITPC/ITP-CAS), P.O. Box 2735, Beijing, 100080 (China); Department of Physics, Institute of Theoretical Physics, Beijing Normal University, Beijing, 100875 (China)

2008-01-15

71

Matter Field, Dark Matter and Dark Energy

A model concerning particle theory and cosmology is proposed. Matter field, dark matter and dark energy are created by an energy flow from space to primordial matter fields at the phase transition in the early universe.

Masayasu Tsuge

2009-03-24

72

Dark Energy Search with Supernovae

To determine the nature of dark energy from observational data, it is important that we use model-independent and optimal methods. We should probe dark energy using its density (allowed to be a free function of cosmic time) instead of its equation of state. We should minimize gravitational lensing effect on supernovae by flux-averaging. We need to include complementary data (for example, from the Cosmic Microwave Background [CMB] and large scale structure [LSS]) in a consistent manner to help break the degeneracy between the dark energy density and the matter density fraction. We should push for ambitious future supernova surveys that can observe a large number of supernovae at the highest possible redshifts. I discuss these and other issues that will be important in our quest to unravel the mystery of the nature of dark energy. Current supernova, CMB, and LSS data already rule out dark energy models with dark energy densities that vary greatly with time; with the cosmological constant model providing an excellent fit to the data. A precise measurement of dark energy density as a free function of cosmic time will have a fundamental impact on particle physics and cosmology.

Yun Wang

2004-04-25

73

Direct reconstruction of dark energy.

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. PMID:20867085

Clarkson, Chris; Zunckel, Caroline

2010-05-28

74

Thermodynamic properties of dark energy are discussed assuming that dark energy is described in terms of a selfinteracting complex scalar. We first show that, under certain assumptions, selfinteracting complex scalar field theories are equivalent to purely kinetic k-essence models. Then we analyze the themal properties of k-essence and in particular we show that dark-energy in the phantom regime does not necessarily yield negative entropy.

Neven Bilic

2008-12-30

75

Can Dark Matter Decay in Dark Energy?

We analyze the interaction between Dark Energy and Dark Matter from a thermodynamical perspective. By assuming they have different temperatures, we study the possibility of occurring a decay from Dark Matter into Dark Energy, characterized by a negative parameter $Q$. We find that, if at least one of the fluids has non vanishing chemical potential, for instance $\\mu_x0$, the decay is possible, where $\\mu_x$ and $\\mu_{dm}$ are the chemical potentials of Dark Energy and Dark Matter, respectively. Using recent cosmological data, we find that, for a fairly simple interaction, the Dark Matter decay is favored with a probability of $\\sim 93%$ over the Dark Energy decay. This result comes from a likelihood analysis where only background evolution has been considered.

S. H. Pereira; J. F. Jesus

2009-02-26

76

I briefly review our current understanding of dark matter and dark energy. The first part of this review focusses on issues pertaining to dark matter including observational evidence for its existence, current constraints and the a...\\/a H3 = 1\\\\stackrel{...}{a}\\/a H^3 = 1 for LCDM, which is helpful for differentiating between LCDM and rival dark energy models. The review ends with

Varun Sahni

2005-01-01

77

The Fully Quantized Axion and Dark Energy

This letter reviews the exact evolution equation for the axion effective potential with the axion scale factor f and phenomenological consequences of the flat effective potential solution are discussed. It is shown that the corresponding vacuum energy can be consistent with Dark Energy, and we compare this result to other studies relating the axion and Dark Energy.

Dylan Tanner

2012-12-17

78

Scattering of dark matter and dark energy

We demonstrate how the two dominant constituents of the Universe, dark energy and dark matter, could possess a large scattering cross section without considerably impacting observations. Unlike interacting models which invoke energy exchange between the two fluids, the background cosmology remains unaltered, leaving fewer observational signatures. Following a brief review of the scattering cross sections between cosmologically significant particles, we explore the implications of an elastic interaction between dark matter and dark energy. The growth of large scale structure is suppressed, yet this effect is found to be weak due to the persistently low dark energy density. Thus we conclude that the dark matter-dark energy cross section may exceed the Thomson cross section by several orders of magnitude.

Simpson, Fergus [SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)

2010-10-15

79

The Phase Transition of Dark Energy

Considering that the universe is filled with the nonrelativistic matter and dark energy and each component is respectively satisfied with its conservation condition in the absence of their interaction, we give the change rate of the fractional density and the density of dark energy from the conservation condition. It is clear that the fractional density of dark energy will monotonously increase and gradually become the dominating contribution to the universe as the redshift becomes low. Combining the evolutional trend of the state equation of dark energy and the change rate of the density of dark energy we find that the density of dark energy will decrease up to a minimum and whereafter it will increase again as the redshift becomes low. This can be regarded as the phase transition of dark energy from the quintessence phase to the phantom phase.

Wei Wang; Yuanxing Gui; Ying Shao

2006-12-05

80

A model of holographic dark energy

A model for holographic dark energy is proposed, following the idea that the short distance cut-off is related to the infrared cut-off. We assume that the infrared cut-off relevant to the dark energy is the size of the event horizon. With the input ??=0.73, we predict the equation of state of the dark energy at the present time be characterized

Miao Li

2004-01-01

81

NASA Astrophysics Data System (ADS)

If the Universe behaves as an ordinary macroscopic system, it must approach a state of maximum entropy in the long run. Realizing that the Einstein-de Sitter model cannot but dark energy dominated universes can, provided its equation of state falls in the range -1 ? w < -2/3, we conclude that the present era of cosmic accelerated expansion could have been predicted on solid thermodynamic grounds. We apply these ideas to dark energy models also with variable w and to some popular modified gravity models. Further, we argue that the evolution of the Hubble function seems to hint that indeed the Universe evolves as an ordinary thermodynamic system.

Pavón, Diego; Radicella, Ninfa

82

Dark Energy Coupled with Dark Matter in Viscous Fluid Cosmology

We investigate cosmological models with two interacting fluids: dark energy and dark matter in flat Friedmann-Robertson-Walker universe. The interaction between dark energy and dark matter is described in terms of the parameters present in the inhomogeneous equation of state when allowance is made for bulk viscosity, for the Little Rip, the Pseudo Rip, and the bounce universes. We obtain analytic representation for characteristic properties in these cosmological models, in particular the bulk viscosity $\\zeta=\\zeta(H,t)$ as function of Hubble parameter and time. We discuss the corrections of thermodynamical parameters in the equations of state due coupling between the viscous fluid and dark matter. Some common properties of these corrections are elucidated.

I. Brevik; V. V. Obukhov; A. V. Timoshkin

2014-10-10

83

Three decades ago Heath found the integral form of the exact analytic growing mode solution of the linear density perturbation $\\delta$ on sub-horizon scales including the cosmological constant or the curvature term. Recently, we obtained the exact analytic form of this solution in our previous work \\cite{SK}. Interestingly, we are able to extend this solution for general dark energy models with the constant equation of state $\\omega_{de}$ in a flat universe. This analytic solution provides the accurate and efficient tools for probing the properties of dark energy models such as the behavior of the growth factor and the growth index. We investigate the growth index and its parameter at any epoch with this exact solution for different dark energy models and find that the growth index is quite model dependent in the redshift space, $0.25 \\leq z \\leq 1.5$, so observations of the structure growth around this epoch would be very interesting. Also one may be able to rule out some dark energy models by using the analysis from this exact solution. Thus, the analytic solution for the growth factor provides the very useful tools for future observations to constrain the exact values of observational quantities at any epoch related to the growth factor in the dark energy models.

Seokcheon Lee; Kin-Wang Ng

2010-04-01

84

General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.

Professor Sean Carroll

2006-11-13

85

We review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark

Edmund J. Copeland; M. Sami; Shinji Tsujikawa

2006-01-01

86

General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.

Professor Sean Carroll

2010-01-08

87

Dark Energy: Taking SidesDark Energy: Taking SidesDark Energy: Taking Sides Rocky Kolb Barocky The University of Chicago #12;#12; Cold Dark Matter: (CDM) 25% Dark Energy (): 70% Stars: 0.5% H & He: gas 4 For Dark EnergyEvidence For Dark EnergyEvidence For Dark Energy 3) Baryon acoustic oscillations 4) Weak

Yamamoto, Hirosuke

88

Brane-Bulk energy exchange and agegraphic dark energy

We consider the agegraphic models of dark energy in a braneworld scenario with brane-bulk energy exchange. We assume that the adiabatic equation for the dark matter is satisfied while it is violated for the agegraphic dark energy due to the energy exchange between the brane and the bulk. Our study shows that with the brane-bulk interaction, the equation of state parameter of agegraphic dark energy on the brane, $w_D$, can have a transition from normal state where $w_D >-1 $ to the phantom regime where $w_D energy always satisfies $w^{\\mathrm{eff}}_D\\geq-1$.

Ahmad Sheykhi

2009-08-09

89

Supernova Constraints on Braneworld Dark Energy

Braneworld models of dark energy are examined in the light of observations of high redshift type Ia supernovae. Braneworld models admit several novel and even exotic possibilities which include: (i) The effective equation of state of dark energy can be more negative than in LCDM: $w \\\\leq -1$; (ii) A class of braneworld models can encounter a `quiescent' future singularity

Ujjaini Alam; Varun Sahni

2002-01-01

90

1 The Quintom Model of Dark Energy

In this paper I give a brief review on the recently proposed new scenario of dark energy model dubbed Quintom. Quintom describes the dynamical dark energy models where the equation of state getting across the cosmological constant boundary during evolutions. I discuss some aspects on the quintom model buildings and the observational consequences. 1

Bo Feng A B

2006-01-01

91

Some seventy five years ago, the concept of dark matter was introduced by Zwicky to explain the anomaly of galactic rotation curves, though there is no clue to its identity or existence to date. In 1997, the author had introduced a model of the universe which went diametrically opposite to the existing paradigm which was a dark matter assisted decelarating universe. The new model introduces a dark energy driven accelarating universe though with a small cosmological constant. The very next year this new picture was confirmed by the Supernova observations of Perlmutter, Riess and Schmidt. These astronomers got the 2011 Nobel Prize for this dramatic observation. All this is discussed briefly, including the fact that dark energy may obviate the need for dark matter.

Burra G. Sidharth

2011-11-15

92

Some seventy five years ago, the concept of dark matter was introduced by Zwicky to explain the anomaly of galactic rotation curves, though there is no clue to its identity or existence to date. In 1997, the author had introduced a model of the universe which went diametrically opposite to the existing paradigm which was a dark matter assisted decelarating universe. The new model introduces a dark energy driven accelarating universe though with a small cosmological constant. The very next year this new picture was confirmed by the Supernova observations of Perlmutter, Riess and Schmidt. These astronomers got the 2011 Nobel Prize for this dramatic observation. All this is discussed briefly, including the fact that dark energy may obviate the need for dark matter.

Burra G. Sidharth

2015-01-12

93

The dark energy problem may have a simple solution in the model of cosmology based on the space-time interaction hypothesis. The hypothesis throws light on the nature of time (see Time-Transcendence-Truth, to be published).

S. C. Tiwari

2005-02-08

94

Dark energy dynamics in the recent universe is influenced by its evolution through the long, matter-dominated expansion history. A particular dynamical property, the flow variable, remains constant in several classes of scalar field models as long as matter dominates; the dark energy is only free to change this behavior at recent times. This gives natural initial conditions for Monte Carlo studies of dark energy dynamics. We propose a parametrization for the later evolution that covers a wide range of possible behaviors, is tractable in making predictions, and can be constrained by observations. We compare the approach to directly parametrizing the potential, which does not take into account the history of the dark energy dynamics.

Cortes, Marina [Berkeley Lab, Berkeley, California 94720 (United States); Linder, Eric V. [Berkeley Lab, Berkeley, California 94720 (United States); University of California, Berkeley, California 94720 (United States); Institute for the Early Universe, Ewha Womans University, Seoul (Korea, Republic of)

2010-03-15

95

We look for evidence for the evolution in dark energy density by employing Principal Component Analysis (PCA). Distance redshift data from supernovae and baryon acoustic oscillations (BAO) along with WMAP7 distance priors are used to put constraints on curvature parameter ?{sub k} and dark energy parameters. The data sets are consistent with a flat Universe. The constraints on the dark energy evolution parameters obtained from supernovae (including CMB distance priors) are consistent with a flat ?CDM Universe. On the other hand, in the parameter estimates obtained from the addition of BAO data the second principal component, which characterize a non-constant contribution from dark energy, is non-zero at 1?. This could be a systematic effect and future BAO data holds key to making more robust claims.

Nair, Remya; Jhingan, Sanjay, E-mail: remya_phy@yahoo.com, E-mail: sanjay.jhingan@gmail.com [Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi 110025 (India)

2013-02-01

96

Constraining dark energy fluctuations with supernova correlations

We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state w??1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.

Blomqvist, Michael [The Oskar Klein Centre for Cosmoparticle Physics, Department of Astronomy, Stockholm University, AlbaNova University Center, SE106 91 Stockholm (Sweden); Enander, Jonas; Mörtsell, Edvard, E-mail: michaelb@astro.su.se, E-mail: enander@fysik.su.se, E-mail: edvard@fysik.su.se [The Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, AlbaNova University Center, SE106 91 Stockholm (Sweden)

2010-10-01

97

Interacting holographic dark energy with logarithmic correction

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.

Jamil, Mubasher; Farooq, M. Umar, E-mail: mjamil@camp.nust.edu.pk, E-mail: mufarooq@yahoo.com [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi, 46000 (Pakistan)

2010-03-01

98

Statefinder Diagnostic for Dilaton Dark Energy

Statefinder diagnostic is a useful method which can differ one dark energy model from the others. The Statefinder pair $\\{r, s\\}$ is algebraically related to the equation of state of dark energy and its first time derivative. We apply in this paper this method to the dilaton dark energy model based on Weyl-Scaled induced gravitational theory. We investigate the effect of the coupling between matter and dilaton when the potential of dilaton field is taken as the Mexican hat form. We find that the evolving trajectory of our model in the $r-s$ diagram is quite different from those of other dark energy models.

Z. G. Huang; X. M. Song; H. Q. Lu; W. Fang

2008-02-16

99

Non-negligible dark energy density at high redshifts would indicate dark energy physics distinct from a cosmological constant or ``reasonable'' canonical scalar fields. Such dark energy can be constrained tightly through investigation of the growth of structure, with limits of \\la2% of total energy density at z\\gg1 for many models. Intermediate dark energy can have effects distinct from its energy density; the dark ages acceleration can be constrained to last less than 5% of a Hubble e-fold time, exacerbating the coincidence problem. Both the total linear growth, or equivalently \\sigma_8, and the shape and evolution of the nonlinear mass power spectrum for zenergy behavior over the entire range z=0-1100.

Eric V. Linder

2006-03-21

100

I review the problem of dark energy focussing on cosmological constant as the candidate and discuss what it tells us regarding\\u000a the nature of gravity. Section 1 briefly overviews the currently popular concordance cosmology and summarizes the evidence\\u000a for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as a\\u000a candidate and emphasizes

T. Padmanabhan

2008-01-01

101

Dark Energy and Dark Matter in Stars Physic

We present the basic equations and relations for the relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which is {\\em locally} equivalent to the f(R) theories of gravity and gives an alternative description of the effects of dark matter and dark energy. The results for the simplest form of the relativistic equation of state (EOS) of neutron matter are represented. Our approach overcomes the well-known difficulties of the physics of SSSS in the f(R) theories of gravity introducing two novel EOS for cosmological energy-pressure densities and dilaton energy-pressure densities, as well as proper boundary conditions.

Plamen Fiziev

2014-11-02

102

Holographic dark energy interacting with dark matter in a Closed Universe

A cosmological model of an holographic dark energy interacting with dark matter throughout a decaying term of the form $Q=3(\\lambda_1\\rho_{DE} + \\lambda_2\\rho_m) H$ is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenarios, without any reference to a specific equation of state for the dark energy. The behavior of equation of stated for dark energy is also discussed.

Norman Cruz; Samuel Lepe; Francisco Pena; Joel Saavedra

2008-07-24

103

Generalizing the cosmic energy equation

NASA Astrophysics Data System (ADS)

We generalize the cosmic energy equation to the case when massive particles interact via a modified gravitational potential of the form ?(a,r), which is allowed to explicitly depend upon the cosmological time through the expansion factor a(t). Using the nonrelativistic approximation for particle dynamics, we derive the equation for the cosmological expansion which has the form of the Friedmann equation with a renormalized gravitational constant. The generalized Layzer-Irvine cosmic energy equation and the associated cosmic virial theorem are applied to some recently proposed modifications of the Newtonian gravitational interaction between dark-matter particles. We also draw attention to the possibility that the cosmic energy equation may be used to probe the expansion history of the universe thereby throwing light on the nature of dark matter and dark energy.

Shtanov, Yuri; Sahni, Varun

2010-11-01

104

Interacting Dark Matter and Dark Energy

We discuss models for the cosmological dark sector in which the energy\\u000adensity of a scalar field approximates Einstein's cosmological constant and the\\u000ascalar field value determines the dark matter particle mass by a Yukawa\\u000acoupling. A model with one dark matter family can be adjusted so the\\u000aobservational constraints on the cosmological parameters are close to but\\u000adifferent from

Glennys R. Farrar; P. J. E. Peebles

2003-01-01

105

Kaluza-Klein Cosmology With Modified Holographic Dark Energy

We investigate the compact Kaluza-Klein cosmology in which modified holographic dark energy is interacting with dark matter. Using this scenario, we evaluate equation of state parameter as well as equation of evolution of the modified holographic dark energy. Further, it is shown that the generalized second law of thermodynamics holds without any constraint.

M. Sharif; Farida Khanum

2011-06-13

106

UNIFIED THEORY OF DARK ENERGY AND DARK SHOUHONG WANG 2

UNIFIED THEORY OF DARK ENERGY AND DARK MATTER TIAN MA, 1 SHOUHONG WANG 2 Abstract. The aim of this research report is to derive a uni- fied theory for dark matter and dark energy. Due to the presence of dark energy and dark matter, we postulate that the energy- momentum tensor of the normal matter

Wang, Shouhong

107

Thermodynamics of dark energy interacting with dark matter and radiation

We investigate the validity of the generalized second law of thermodynamics, in the cosmological scenario where dark energy interacts with both dark matter and radiation. Calculating separately the entropy variation for each fluid component and for the apparent horizon itself, we show that the generalized second law is always and generally valid, independently of the specific interaction form, of the fluids equation-of-state parameters and of the background geometry.

Jamil, Mubasher [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi, 46000 (Pakistan); Saridakis, Emmanuel N. [Department of Physics, University of Athens, GR-15771 Athens (Greece); Setare, M. R. [Department of Science, Payame Noor University, Bijar (Iran, Islamic Republic of)

2010-01-15

108

Irreversible thermodynamic description of interacting dark energy-dark matter cosmological models

NASA Astrophysics Data System (ADS)

We investigate the interaction between dark energy and dark matter in the framework of irreversible thermodynamics of open systems with matter creation/annihilation. We consider dark energy and dark matter as an interacting two-component (scalar field and ordinary dark matter) cosmological fluid in a homogeneous spatially flat and isotropic Friedmann-Robertson-Walker Universe. The thermodynamics of open systems as applied together with the gravitational field equations to the two-component cosmological fluid leads to a generalization of the elementary dark energy-dark matter interaction theory, in which the decay (creation) pressures are explicitly considered as parts of the cosmological fluid stress-energy tensor. Specific models describing coherently oscillating scalar waves, leading to a high particle production at the beginning of the oscillatory period, and models with a constant potential energy scalar field are considered. Furthermore, exact and numerical solutions of the gravitational field equations with dark energy-dark matter interactions are also obtained.

Harko, Tiberiu; Lobo, Francisco S. N.

2013-02-01

109

Interacting dark energy: the role of microscopic feedback in the dark sector

We investigate the impact on the classical dynamics of dark matter particles and dark energy of a non-minimal coupling in the dark sector, assuming that the mass of the dark matter particles is coupled to a dark energy scalar field. We show that standard results can only be recovered if the space-time variation of the dark energy scalar field is sufficiently smooth on the characteristic length scale of the dark matter particles, and we determine the associated constraint dependent on both the mass and radius of the dark matter particles and the coupling to the dark energy scalar field. We further show, using field theory numerical simulations, that a violation of such constraint results in a microscopic feedback effect strongly affecting the dynamics of dark matter particles, with a potential impact on structure formation and on the space-time evolution of the dark energy equation of state.

Avelino, P P

2015-01-01

110

Dark energy from quantum wave function collapse of dark matter

Dynamical wave function collapse models entail the continuous liberation of a specified rate of energy arising from the interaction of a fluctuating scalar field with the matter wave function. We consider the wave function collapse process for the constituents of dark matter in our universe. Beginning from a particular early era of the universe chosen from physical considerations, the rate of the associated energy liberation is integrated to yield the requisite magnitude of dark energy around the era of galaxy formation. Further, the equation of state for the liberated energy approaches $w \\to -1$ asymptotically, providing a mechanism to generate the present acceleration of the universe.

A. S. Majumdar; D. Home; S. Sinha

2009-09-03

111

Material models of dark energy

We review and develop a new class of "dark energy" models, in which the relativistic theory of solids is used to construct material models of dark energy. These are models which include the effects of a continuous medium with well defined physical properties at the level of linearized perturbations. The formalism is constructed for a medium with arbitrary symmetry, and then specialised to isotropic media (which will be the case of interest for the majority of cosmological applications). We develop the theory of relativistic isotropic viscoelastic media whilst keeping in mind that we ultimately want to observationally constrain the allowed properties of the material model. We do this by obtaining the viscoelastic equations of state for perturbations (the entropy and anisotropic stress), as well as identifying the consistent corner of the theory which has constant equation of state parameter $\\dot{w}=0$. We also connect to the non-relativistic theory of solids, by identifying the two quadratic invariants that are needed to construct the energy-momentum tensor, namely the Rayleigh dissipation function and Lagrangian for perturbations. Finally, we develop the notion that the viscoelastic behavior of the medium can be thought of as a non-minimally coupled massive gravity theory. This also provides a tool-kit for constructing consistent generalizations of coupled dark energy theories.

Jonathan A. Pearson

2014-03-05

112

Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

Lincoln, Don

2014-04-15

113

We investigate the clustering properties of a dynamical dark energy component. In a cosmic mix of a pressureless fluid and a light scalar field, we follow the linear evolution of spherical matter perturbations. We find that the scalar field tends to form underdensities in response to the gravitationally collapsing matter. We thoroughly investigate these voids for a variety of initial conditions, explain the physics behind their formation and consider possible observational implications. Detection of dark energy voids will clearly rule out the cosmological constant as the main source of the present acceleration.

Sourish Dutta; Irit Maor

2007-11-15

114

We investigate the clustering properties of a dynamical dark energy component. In a cosmic mix of a pressureless fluid and a light scalar field, we follow the linear evolution of spherical matter perturbations. We find that the scalar field tends to form underdensities in response to the gravitationally collapsing matter. We thoroughly investigate these voids for a variety of initial conditions, explain the physics behind their formation, and consider possible observational implications. Detection of dark energy voids will clearly rule out the cosmological constant as the main source of the present acceleration.

Dutta, Sourish; Maor, Irit [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States)

2007-03-15

115

Schwarzschild black hole in dark energy background

NASA Astrophysics Data System (ADS)

In this paper we present an exact solution of Einstein's field equations describing the Schwarzschild black hole in dark energy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the dark energy space producing Schwarzschild-dark energy black hole. It is found that the space-time geometry of Schwarzschild-dark energy solution is non-vacuum Petrov type D in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-dark energy solution. We also find that the energy-momentum tensor of the Schwarzschild-dark energy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity and the area of the horizons for the Schwarzschild-dark energy black hole.

Ishwarchandra, Ngangbam; Ibohal, N.; Yugindro Singh, K.

2014-10-01

116

Schwarzschild black hole in dark energy background

In this paper we present an exact solution of Einstein's field equations describing the Schwarzschild black hole in dark energy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the dark energy space producing Schwarzschild-dark energy black hole. It is found that the space-time geometry of Schwarzschild-dark energy solution is non-vacuum Petrov type $D$ in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-dark energy solution. We also find that the energy-momentum tensor of the Schwarzschild-dark energy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity and the area of the horizons for the Schwarzschild-dark energy black hole.

Ngangbam Ishwarchandra; Ng. Ibohal; K. Yugindro Singh

2014-09-27

117

NASA Astrophysics Data System (ADS)

It has recently been proposed by Bastero-Gil, Mersini and co-workers that dark energy could be attributed to the cosmological properties of a scalar field with a nonstandard dispersion relation that decreases exponentially at wave numbers larger than the Planck scale (kphys>MPl). In this scenario, the energy density stored in the modes of trans-Planckian wave numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present paper examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave numbers considered: hence, the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order M4Pl) for modes with momenta MPl, far in excess of the background energy density. We evaluate the amount of fine tuning in the initial data necessary to avoid this back-reaction problem and find it is of order H/MPl. We also argue that the equation of state of the trans-Planckian modes is not vacuumlike. Therefore this model does not provide a suitable explanation for the dark energy.

Lemoine, Martin; Martin, Jérôme; Uzan, Jean-Philippe

2003-05-01

118

Cosmic steps in modeling dark energy

Past and recent data analyses gave some hints of steps in dark energy. Considering dark energy as a dynamical scalar field, we investigate several models with various steps: a step in the scalar potential, a step in the kinetic term, a step in the energy density, and a step in the equation-of-state parameter w. These toy models provide a workable mechanism to generate steps and features of dark energy. Remarkably, a single real scalar can cross w=-1 dynamically with a step in the kinetic term.

Wang Tower [Center for High-Energy Physics, Peking University, Beijing 100871 (China)

2009-11-15

119

In the light of recent developments in Dark Energy, we consider the electron in a such a background field and show that at the Compton wavelength the electron is stable, in that the Cassini inward pressure exactly counterbalances the outward Coulomb repulsive pressure thus answering a problem of the earlier electron theory.

Burra G. Sidharth

2008-08-05

120

This review summarizes recent attempts to reconstruct the expansion history of the universe and to probe the nature of dark energy. Reconstruction methods can be broadly classified into parametric and non-parametric approaches. It is encouraging that, even with the limited observational data currently available, different approaches give consistent results for the reconstruction of the Hubble parameter H(z) and the effective

Varun Sahni; Alexei Starobinsky

2006-01-01

121

A new type of dark energy model

In this paper, we propose a general form of the equation of state (EoS) which is the function of the fractional dark energy density ?{sub d}. At least, five related models, the cosmological constant model, the holographic dark energy model, the agegraphic dark energy model, the modified holographic dark energy model and the Ricci scalar holographic dark energy model are included in this form. Furthermore, if we consider proper interactions, the interactive variants of those models can be included as well. The phase-space analysis shows that the scaling solutions may exist both in the non-interacting and interacting cases. And the stability analysis of the system could give out the attractor solution which could alleviate the coincidence problem.

Zhang, Yi [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Li, Hui, E-mail: zhangyia@cqupt.edu.cn, E-mail: lihui@ytu.edu.cn [Department of Physics, Yantai University, Yantai 264005 (China)

2010-06-01

122

CAPUT DARK ENERGY TOPICS, 2013 1. The Cosmological Constant

CAPUT DARK ENERGY TOPICS, 2013 1 #12;1. The Cosmological Constant - The acceleration as curvature term in the Einstein field equation and not a form of dark energy. Provide a critical discussion., Rovelli C., 2010 Is dark energy really a mystery ? Nature, 466, 321 (July 2010) - Padmanabhan T., 2003

Weijgaert, Rien van de

123

Dark energy from quantum fluctuations

We have derived the quantum vacuum pressure P_vac as a primary entity, removing a trivial and a gauge terms from the cosmological constant-like part (the zeroth term) of the effective action for a free matter field. The quantum vacuum energy density G_vac appears a secondary entity, but both are of expected order. Moreover P_vac and G_vac are dynamical, and therefore they can be used in the Einstein equations. In particular, they could dynamically support holographic dark energy model as well as the `thermodynamic' one.

Bogus?aw Broda; Micha? Szanecki

2009-11-12

124

Dark energy from entanglement entropy

We show that quantum decoherence, in the context of observational cosmology, can be connected to the cosmic dark energy. The decoherence signature could be characterized by the existence of quantum entanglement between cosmological eras. As a consequence, the Von Neumann entropy related to the entanglement process, can be compared to the thermodynamical entropy in a homogeneous and isotropic universe. The corresponding cosmological models are compatible with the current observational bounds being able to reproduce viable equations of state without introducing {\\it a priori} any cosmological constant. In doing so, we investigate two cases, corresponding to two suitable cosmic volumes, $V\\propto a^3$ and $V\\propto H^{-3}$, and find two models which fairly well approximate the current cosmic speed up. The existence of dark energy can be therefore reinterpreted as a quantum signature of entanglement, showing that the cosmological constant represents a limiting case of a more complicated model derived from the quantum decoherence.

Salvatore Capozziello; Orlando Luongo

2013-03-06

125

In the Randall-Sundrum scenario, we analyse the dynamics of an AdS5 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 AdS5 orbifold. We discuss aspects of the radion stability conditions and of the localization of gravity in the vicinity of the brane.

Rui Neves; Cenalo Vaz

2006-01-06

126

Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?

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. PMID:19905618

Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim

2009-10-01

127

Investigating Dark Energy with Black Hole Binaries

The accelerated expansion of the universe is ascribed to the existence of dark energy. Black holes accretion of dark energy 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 too 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. In this talk I describe how binaries can provide a useful tool in obtaining complementary information on the nature of dark energy, based on the work done with A.Kelleher.

Laura Mersini-Houghton; Adam Kelleher

2009-06-08

128

Dark energy: myths and reality

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 [4].

V. N. Lukash; V. A. Rubakov

2008-07-10

129

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.

Dragan Huterer

2002-01-01

130

Probing the time dependence of dark energy

A new method to investigate a possible time-dependence of the dark energy equation of state w is proposed. We apply this methodology to a combination of data involving one of the most recent type Ia supernova sample (SNLS3) along with the current baryon acoustic oscillation and H(z) measurements. We show that current observations cannot rule out a non-evolving dark energy component (dw/dz = 0). The approach developed here reduces considerably the so-called smearing effect on w determinations and may be useful to probe a possible evolving dark energy component when applied to upcoming observational data.

Barboza Edésio Jr, M. [Departamento de Física, Universidade do Estado do Rio Grande do Norte, Rua Professor Antônio Campos s/n, Mossoró (Brazil); Alcaniz, J.S., E-mail: edesiobarboza@uern.br, E-mail: alcaniz@on.br [Departamento de Astronomia, Observatório Nacional, Rua General José Cristino 77, Rio de Janeiro (Brazil)

2012-02-01

131

Can dark energy evolve to the phantom?

Dark energy with the equation of state w(z) rapidly evolving from the dustlike (w~=0 at z1) to the phantomlike (-1.2≲w≲-1 at z~=0) has been recently proposed as the best fit for the supernovae Ia data. Assuming that a dark energy component with an arbitrary scalar-field Lagrangian p(phi,?muphi) dominates in the flat Friedmann universe, we analyze the possibility of a dynamical

Alexander Vikman

2005-01-01

132

Universal Forces and the Dark Energy Problem

The Dark Energy problem is forcing us to re-examine our models and our understanding of relativity and space-time. Here a novel idea of Fundamental Forces is introduced. This allows us to perceive the General Theory of Relativity and Einstein's Equation from a new pesrpective. In addition to providing us with an improved understanding of space and time, it will be shown how it leads to a resolution of the Dark Energy problem.

Afsar Abbas

2007-04-01

133

We examine a dark energy model where a scalar unparticle degree of freedom plays the role of quintessence. In particular, we study a model where the unparticle degree of freedom has a standard kinetic term and a simple mass potential, the evolution is slowly rolling and the field value is of the order of the unparticle energy scale ({lambda}{sub u}). We study how the evolution of w depends on the parameters B (a function of unparticle scaling dimension d{sub u}), the initial value of the field {phi}{sub i} (or equivalently, {lambda}{sub u}) and the present matter density {omega}{sub m0}. We use observational data from type Ia supernovae, baryon acoustic oscillations and the cosmic microwave background to constrain the model parameters and find that these models are not ruled out by the observational data. From a theoretical point of view, unparticle dark energy model is very attractive, since unparticles (being bound states of fundamental fermions) are protected from radiative corrections. Further, coupling of unparticles to the standard model fields can be arbitrarily suppressed by raising the fundamental energy scale M{sub F}, making the unparticle dark energy model free of most of the problems that plague conventional scalar field quintessence models.

Dai, D.-C.; Stojkovic, Dejan [HEPCOS, Department of Physics, SUNY at Buffalo, Buffalo, New York 14260-1500 (United States); Dutta, Sourish [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States)

2009-09-15

134

Black hole and holographic dark energy

We discuss the connection between black hole and holographic dark energy. We examine the issue of the equation of state (EOS) for holographic energy density as a candidate for the dark energy carefully. This is closely related to the EOS for black hole, because the holographic dark energy comes from the black hole energy density. In order to derive the EOS of a black hole, we may use its dual (quantum) systems. Finally, a regular black hole without the singularity is introduced to describe an accelerating universe inside the cosmological horizon. Inspired by this, we show that the holographic energy density with the cosmological horizon as the IR cutoff leads to the dark energy-dominated universe with $\\omega_{\\rm \\Lambda}=-1$.

Yun Soo Myung

2007-04-11

135

Dark Matter and Dark Energy Explained

NASA Astrophysics Data System (ADS)

The standard model of the universe has many mysteries and defects requiring the use of large fudge factors such as Dark Matter and Dark Energy. We will show that Dark Matter is needed when we try to extend Newton's law of gravity (based upon observations in our solar system) to galactic distances. Dark Matter was introduced to explain the observed flat velocity rotation curves of the outer parts of spiral galaxies, as observed by Vera. Rubin. Much earlier, the (under appreciated) Fritz Zwicky introduced the need for large amounts of missing invisible matter to explain the surprising observed motion of groups of remote galaxies. In our hypothesis, the modification of Newton's laws by the addition of a linear term to the gravitational constant that increases with distance will eliminate the need for dark matter. Our hypothesis is different from the MOND theory of Milgrom, which depends upon acceleration. The Red shift observations by Hubble as a function of distance, and interpreted as ``apparent Doppler effect'' led to the unproven belief that the universe is expanding, and thus to the Big Bang. In turn the apparent acceleration of the expansion required the introduction of Dark Energy. Actually there are three additional components of the red shift that are solely due to gravity and distance and can be larger than the Doppler contribution.

Aisenberg, Sol

2006-03-01

136

NASA Astrophysics Data System (ADS)

The DES Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera which is now mounted at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory. DECam is comprised of 74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. A filter set of u,g,r,i,z, and Y, a hexapod for focus and lateral alignment as well as thermal management of the cage temperature. DECam will be used to perform the 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. An overview of the DECam design, construction and initial on-sky performance information will be presented.

Flaugher, Brenna; DES Collaboration

2013-01-01

137

Cosmological Evolution of Pilgrim Dark Energy

We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of $\\omega_\\vartheta$ and $\\omega'_\\vartheta$. We conclude that the consistent value of parameter $\\mu$ is $\\mu<0$ in accordance with the current Planck and WMAP$9$ results.

M. Sharif; M. Zubair

2014-09-26

138

Cosmological Evolution of Pilgrim Dark Energy

We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of $\\omega_\\vartheta$ and $\\omega'_\\vartheta$. We conclude that the consistent value of parameter $\\mu$ is $\\mu<0$ in accordance with the current Planck and WMAP$9$ results.

Sharif, M

2015-01-01

139

Dark Energy, Inflation and Extra Dimensions

We consider how accelerated expansion, whether due to inflation or dark energy, imposes strong constraints on fundamental theories obtained by compactification from higher dimensions. For theories that obey the null energy condition (NEC), we find that inflationary cosmology is impossible for a wide range of compactifications; and a dark energy phase consistent with observations is only possible if both Newton's gravitational constant and the dark energy equation-of-state vary with time. If the theory violates the NEC, inflation and dark energy are only possible if the NEC-violating elements are inhomogeneously distributed in thecompact dimensions and vary with time in precise synchrony with the matter and energy density in the non-compact dimensions. Although our proofs are derived assuming general relativity applies in both four and higher dimensions and certain forms of metrics, we argue that similar constraints must apply for more general compactifications.

Paul J. Steinhardt; Daniel Wesley

2008-11-11

140

Is this the end of dark energy?

In this paper we investigate the limits imposed by thermodynamics to a dark energy fluid. We obtain the heat capacities and the compressibilities for a dark energy fluid. These thermodynamical variables are easily accessible experimentally for any terrestrial fluid. The thermal and mechanical stabilities require these quantities to be positive. We show that such requirements forbid the existence of a cosmic fluid with negative constant EoS parameter which excludes vacuum energy as a candidate to explain the cosmic acceleration. We also show that the current observational data from SN Ia, BAO and $H(z)$ are in conflict with the physical constraints that a general dark energy fluid with a time-dependent EoS parameter must obey which can be interpreted as an evidence against the dark energy hypothesis. Although our result excludes the vacuum energy, a geometrical cosmological term as originally introduced by Einstein in the field equations remains untouched.

Barboza, Edésio M; Abreu, Éverton M C; Neto, Jorge Ananias

2015-01-01

141

1 construct a general description for neutrino dark energy models, that do not require exotic particles or strange couplings. With the help of the above, this class of models is reduced to a single function with several constraints. It is shown that these models lead to some concrete predictions that can be verified (or disproved) within the next decade, using results from PLANK, EUCLID and JDEM.

Gurwich, Ilya [Physics Department, Ben-Gurion University, Beer-Sheva 84105 (Israel)

2010-06-23

142

The Dark Side: from Dark Energy & Dark Matter to Washington and Science Policy

The Dark Side: from Dark Energy & Dark Matter to Washington and Science Policy Presenter: Michael: The Map Room (www.maproom.com )1949 N. Hoyne #12;The Dark Side: from Dark Energy and Dark Matter questions --- what is the dark matter that holds our galaxy and every structure in the Universe together

Collar, Juan I.

143

Dark Energy Search Using Type Ia Supernovae

NASA Astrophysics Data System (ADS)

Type Ia supernovae (SNe Ia) provide us with a unique probe into the nature of dark energy in the universe. Different dark energy models can be differentiated phenomenologically by the different time dependences of the dark energy density ? X, or, alternatively, by the dark energy equation of state wX. Wang & Garnavich (2001, ApJ, 552, 445) have shown that parametrizing the dark energy density ? X as an arbitrary function of redshift offers some useful advantages when used instead of the more familiar wX formulation. In particular, the time variation of ? X can be determined from data with smaller uncertainty than that of wX. This is because ? X is on the same footing as the matter density fraction ? m in making theoretical predications for the observables, while wX must be integrated over z to obtain ? X before comparison with data can be made. In order to determine the time dependence of the dark energy density ? X, it is important that the supernova survey be optimized for detecting large numbers of supernovae at the highest possible redshifts (Wang & Lovelace 2001, ApJ, 562, L115). A supernova pencil beam survey on a dedicated telescope (Wang 2000, ApJ, 531, 676, astro-ph/9806185) provides the most efficient method to obtain the largest possible number of supernovae at high redshifts. These can be supplemented by surveys of nearby supernovae to constrain dark energy. I will show that data from an optimized supernova pencil beam survey, such as that planned by the proposed SNAP mission, should allow us to determine the basic time dependence of the dark energy density ? X (Wang et al. 2003, astro-ph/0302064). This would allow us to differentiate among many different classes of dark energy models. The observational detection of the time variation (or invariance) of the dark energy density ? X would be an important landmark in particle physics and cosmology.

Wang, Y.

2003-05-01

144

Conformal Higgs model: predicted dark energy density

Postulated universal Weyl conformal scaling symmetry provides an alternative to the $\\Lambda$CDM paradigm for cosmology. Recent applications to galactic rotation velocities, Hubble expansion, and a model of dark galactic halos explain qualitative phenomena and fit observed data without invoking dark matter. Significant revision of theory relevant to galactic collisions and clusters is implied, but not yet tested. Dark energy is found to be a consequence of conformal symmetry for the Higgs scalar field of electroweak physics. The present paper tests this implication. The conformal Higgs model acquires a gravitational effect described by a modified Friedmann cosmic evolution equation, shown to fit cosmological data going back to the cosmic microwave background epoch. The tachyonic mass parameter of the Higgs model becomes dark energy in the Friedmann equation. A dynamical model of this parameter, analogous to the Higgs mechanism for gauge boson mass, is derived and tested here. An approximate calculation yields a result consistent with the empirical magnitude inferred from Hubble expansion.

R. K. Nesbet

2014-11-03

145

NASA Astrophysics Data System (ADS)

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.

Piattella, O. F.; Martins, D. L. A.; Casarini, L.

2014-10-01

146

Covariantizing the interaction between dark energy and dark matter

NASA Astrophysics Data System (ADS)

Coupling dark energy and dark matter through an effective fluid description is a very common procedure in cosmology; however, it always remains in comoving coordinates in the special FLRW space. We construct a consistent, general, and covariant formulation, where the interaction is a natural implication of the imperfectness of the fluids. This imperfectness makes difficult the final step towards a robust formulation of interacting fluids, namely the construction of a Lagrangian whose variation would give rise to the interacting equations. Nevertheless, we present a formal solution to this problem for a single fluid, through the introduction of an effective metric.

Faraoni, Valerio; Dent, James B.; Saridakis, Emmanuel N.

2014-09-01

147

Virialization in Dark Energy Cosmology

We discuss the issue of energy nonconservation in the virialzation process of spherical collapse model with homogeneous dark energy. We propose an approximation scheme to find the virialization radius. By comparing various schemes and estimating the parameter characterizing the ratio of dark energy to dark matter at the turn-around time, we conclude that the problem of energy nonconservation may have sizable effects in fitting models to observations.

Peng Wang

2005-11-15

148

Interacting Dark Energy: Decay into Fermions

A dark energy component is responsible for the present stage of acceleration of our universe. If no fine tuning is assumed on the dark energy potential then it will end up dominating the universe at late times and the universe will not stop this stage of acceleration. On the other hand, the equation of state of dark energy seems to be smaller than -1 as suggested by the cosmological data. We take this as an indication that dark energy does indeed interact with another fluid (we consider fermion fields) and we determine the interaction through the cosmological data and extrapolate it into the future. We study the conditions under which a dark energy can dilute faster or decay into the fermion fields. We show that it is possible to live now in an accelerating epoch dominated by the dark energy and without introducing any fine tuning parameters the dark energy can either dilute faster or decaying into fermions in the future. The acceleration of the universe will then cease.

A. de la Macorra

2007-02-08

149

Dark Energy and Neutrino Model in SUSY

We discuss the effect of the supersymmetry breaking on the Mass Varying Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the gravitational interaction between the hidden sector and the dark energy sector is studied. A model including a chiral superfield in the dark sector and the right-handed neutrino superfield is proposed. Evolutions of the neutrino mass and the equation of state parameter are presented in the model.

Ryo Takahashi; Morimitsu Tanimoto

2006-10-26

150

Weak Lensing: Dark Matter, Dark Energy

The light rays from distant galaxies are deflected by massive structures along the line of sight, causing the galaxy images to be distorted.Measurements of these distortions, known as weak lensing, provide a way of measuring the distribution of dark matter as well as the spatial geometry of the universe. I will describe the ideas underlying this approach to cosmology. With planned large imaging surveys, weak lensing is a powerful probe of dark energy. I will discuss the observational challenges ahead and recent progress in developing multiple, complementary approaches to lensing measurements.

Bhuvnesh Jain

2006-02-27

151

Can Holographic dark energy increase the mass of the wormhole?

In this work, we have studied accretion of dark energy (DE) onto Morris- Thorne wormhole with three different forms, namely, holographic dark energy, holographic Ricci dark energy and modified holographic Ricci dark energy . Considering the scale factor in power-law form we have observed that as the holographic dark energy accretes onto wormhole, the mass of the wormhole is decreasing. In the next phase we considered three parameterization schemes that are able to get hold of quintessence as well as phantom phases. Without any choice of scale factor we reconstructed Hubble parameter from conservation equation and dark energy densities and subsequently got the mass of the wormhole separately for accretion of the three dark energy candidates. It was observed that if these dark energies accrete onto the wormhole, then for quintessence stage, wormhole mass decreases up to a certain finite value and then again increases to aggressively during phantom phase of the universe.

Surajit Chattopadhyay; Davood Momeni; Aziza Altaibayeva; Ratbay Myrzakulov

2014-06-27

152

Can holographic dark energy increase the mass of the wormhole?

NASA Astrophysics Data System (ADS)

In this work, we have studied accretion of dark energy (DE) onto Morris- Thorne wormhole with three different forms, namely, holographic dark energy, holographic Ricci dark energy and modified holographic Ricci dark energy . Considering the scale factor in power-law form we have observed that as the holographic dark energy accretes onto wormhole, the mass of the wormhole is decreasing. In the next phase we considered three parameterization schemes that are able to get hold of quintessence as well as phantom phases. Without any choice of scale factor we reconstructed Hubble parameter from conservation equation and dark energy densities and subsequently got the mass of the wormhole separately for accretion of the three dark energy candidates. It was observed that if these dark energies accrete onto the wormhole, then for quintessence stage, wormhole mass decreases up to a certain finite value and then again increases to aggressively during phantom phase of the universe.

Chattopadhyay, Surajit; Momeni, Davood; Altaibayeva, Aziza; Myrzakulov, Ratbay

2014-12-01

153

NSDL National Science Digital Library

In this lesson, students simulate an experiment in which the discovery of dark energy can be made by plotting modern supernova distances on a Hubble Diagram. Data is provided in an Excel spreadsheet (see related resources). In order to complete this activity, students should be familiar with Hubble's Law and the concepts of absolute luminosity, apparent luminosity, and Doppler shift (particularly redshift). This activity can be done using either a computer graphing program or manually with graph paper. This lesson is part of the "Cosmic Times" teacher's guide and is intended to be used in conjunction with the 2006 Cosmic Times Poster.

154

Holographic Dark Energy Model and Scalar-Tensor Theories

We study the holographic dark energy model in a generalized scalar tensor theory. In a universe filled with cold dark matter and dark energy, the effect of potential of the scalar field is investigated in the equation of state parameter. We show that for a various types of potentials, the equation of state parameter is negative and transition from deceleration to acceleration expansion of the universe is possible.

Yousef Bisabr

2008-08-10

155

Dark energy and particle mixing

We show that the vacuum condensate due to particle mixing is responsible of a dynamically evolving dark energy. In particular, we show that values of the adiabatic index close to -1 for vacuum condensates of neutrinos and quarks imply, at the present epoch, contributions to the vacuum energy compatible with the estimated upper bound on the dark energy.

A. Capolupo; S. Capozziello; G. Vitiello

2008-08-30

156

Dark Energy Survey Simulations

NASA Astrophysics Data System (ADS)

The Dark Energy Survey (DES) is a next generation optical imaging survey that will cover 5000 sq. deg. of the southern sky using a new 520 Megapixel CCD camera that will be mounted on the 4m Blanco telescope at the Cerro Tololo Inter-American Observatory. The DES will probe dark energy using the 4 complementary techniques of galaxy clusters, weak gravitational lensing, baryon acoustic oscillations, and Type Ia supernovae. In preparation for the survey, we have been carrying out detailed catalog- and image-level simulations of the DES, as part of annual data challenges that use the simulated data to help develop and test our data management pipelines and science analysis codes. Here we will describe our latest round of simulations for DES "Data Challenge 5" (DC5). Our DC5 catalog simulations include: dark matter from a "Carmen" N-body simulation box; a galaxy catalog derived using the "ADDGALS" method; galaxy shapes based on COSMOS data; weak lensing convergence and shear derived from ray tracing, plus stronly-lensed arcs; and stars based the "Trilegal" model of the Milky Way. The simulated galaxy and stellar catalogs are then used to populate simulated DES images, which account for a wide range of instrumental and observational effects due to the telescope and corrector, the CCD detectors, and the atmosphere and weather. Using grid computing resources at Fermilab, some 3.5 TB of simulated DES imaging data have been generated for DC5, covering the 5 DES filters (grizy) over some 200 sq. deg. of sky.

Lin, Huan; Kuropatkin, N.; Wechsler, R.; Busha, M.; Becker, M.; Rossetto, B.; da Costa, L.; Makler, M.; Dark Energy Survey Collaboration

2010-01-01

157

Tracking and coupled dark energy as seen by WMAP

The satellite experiment WMAP has produced for the first time a high-coverage, high resolution survey of the microwave sky, releasing publicly available data that are likely to remain unrivalled for years to come. Here we compare the WMAP temperature power spectrum, along with an exhautive compilation of previous experiments, to models of dark energy that allow for a tracking epoch at the present, deriving updated bounds on the dark energy equation of state and the other cosmological parameters. Moreover, we complement the analysis by including a coupling of the dark energy to dark matter. The main results are: a) the WMAP data alone constrains the equation of state of tracking dark energy to be w_\\phi-1), which implies for an inverse power law potential an exponent \\alphadark matter is |\\beta|dark energy equation of state.

Quercellini, L A C

2003-01-01

158

Tracking and coupled dark energy as seen by WMAP

The satellite experiment WMAP has produced for the first time a high-coverage, high resolution survey of the microwave sky, releasing publicly available data that are likely to remain unrivalled for years to come. Here we compare the WMAP temperature power spectrum, along with an exhautive compilation of previous experiments, to models of dark energy that allow for a tracking epoch at the present, deriving updated bounds on the dark energy equation of state and the other cosmological parameters. Moreover, we complement the analysis by including a coupling of the dark energy to dark matter. The main results are: a) the WMAP data alone constrains the equation of state of tracking dark energy to be w_\\phi-1), which implies for an inverse power law potential an exponent \\alphadark matter is |\\beta|dark energy equation of state.

Luca Amendola; Claudia Quercellini

2003-03-11

159

Dark energy in hybrid inflation

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.

Gong, Jinn-Ouk [Department of Physics, KAIST, Daejeon, Republic of Korea (Korea, Republic of); International Center for Astrophysics, KASI, Daejeon (Korea, Republic of); Kim, Seongcheol [Department of Physics, KAIST, Daejeon (Korea, Republic of)

2007-03-15

160

From Dark Energy and Dark Matter to Dark Metric

It is nowadays clear that General Relativity cannot be the definitive theory of Gravitation due to several shortcomings that come out both from theoretical and experimental viewpoints. At large scales (astrophysical and cosmological) the attempts to match it with the latest observational data lead to invoke Dark Energy and Dark Matter as the bulk components of the cosmic fluid. Since no final evidence, at fundamental level, exists for such ingredients, it is clear that General Relativity presents shortcomings at infrared scales. On the other hand, the attempts to formulate more general theories than Einstein's one give rise to mathematical difficulties that need workarounds that, in turn, generate problems from the interpretative viewpoint. We present here a completely new approach to the mathematical objects in terms of which a theory of Gravitation may be written in a first-order (a' la Palatini) formalism, and introduce the concept of Dark Metric which could completely bypass the introduction of disturbing concepts as Dark Energy and Dark Matter.

S. Capozziello; M. De Laurentis; M. Francaviglia; S. Mercadante

2008-08-04

161

Modified Holographic Dark Energy

In this work, motivated by the energy bound suggested by Cohen {\\it et al.}, we propose the modified holographic dark energy (MHDE) model. Choosing the IR cut-off $L=R_{\\rm CC}$ and considering the parameterizations $n^2=2-\\lambda a$, $n^2=2-3\\lambda a^2/(1+3a^2)$ and $n^2=2-\\lambda a^2/(\\beta+a^2)$, we derive all the physical quantities of the non-saturated MHDE model analytically. We find that the non-saturated MHDE models with the parameterizations $n^2=2-\\lambda a$ and $n^2=2-3\\lambda a^2/(1+3a^2)$ are single-parameter models in practice. Also, we consider the cosmological constraints on the non-saturated MHDE, and find that it is well consistent with the observational data.

Hao Wei

2009-05-31

162

Vacuum pressure, dark energy and dark matter

It has been argued that the correct, i.e. positive, sign of quantum vacuum energy density, or more properly, negative sign of quantum vacuum pressure, requires not a very large number, e.g. ~100, of additional, undiscovered fundamental bosonic particle species, absent in the standard model. Interpretation of the new particle species in terms of dark matter ones permits to qualitatively, and even quantitatively, connect all the three concepts given in the title.

Bogus?aw Broda; Micha? Szanecki

2012-01-05

163

On the similarity of Information Energy to Dark Energy

Information energy is shown here to have properties similar to those of dark energy. The energy associated with each information bit of the universe is found to be defined identically to the characteristic energy of a cosmological constant. Two independent methods are used to estimate the universe information content of ~10^91 bits, a value that provides an information energy total comparable to that of the dark energy. Information energy is also found to have a significantly negative equation of state parameter, w energy.

M. P. Gough; T. D. Carozzi; A. M. Buckley

2006-03-03

164

New Agegraphic Dark Energy in $f(R)$ Gravity

In this paper we study cosmological application of new agegraphic dark energy density in the $f(R)$ gravity framework. We employ the new agegraphic model of dark energy to obtain the equation of state for the new agegraphic energy density in spatially flat universe. Our calculation show, taking $nnew agegraphic dark energy model in flat universe in the modified gravity cosmology framework. Also we develop a reconstruction scheme for the modified gravity with $f(R)$ action.

M. R. Setare

2009-08-03

165

On cosmic acceleration without dark energy

We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark-energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if

Edward W. Kolb; Sabino Matarrese; Antonio Riotto

2006-01-01

166

Dynamical system analysis for DBI dark energy interacting with dark matter

A dynamical system analysis related to Dirac Born Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW space time, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

Mahata, Nilanjana

2015-01-01

167

Dynamical system analysis for DBI dark energy interacting with dark matter

A dynamical system analysis related to Dirac Born Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW space time, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

Nilanjana Mahata; Subenoy Chakraborty

2015-01-19

168

Dynamical system analysis for DBI dark energy interacting with dark matter

NASA Astrophysics Data System (ADS)

A dynamical system analysis related to Dirac-Born-Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW spacetime, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

Mahata, Nilanjana; Chakraborty, Subenoy

2015-01-01

169

arXiv:astro-ph/0703364v227Aug2007 Electromagnetic dark energy

arXiv:astro-ph/0703364v227Aug2007 Electromagnetic dark energy Christian Beck School of MathematicalGill University, Montreal, Quebec, Canada (Dated: August 28, 2007) We introduce a new model for dark energy equations, or more generally with the existence of dark energy. The dark energy density consistent

Wright, Francis

170

Dark Energy - Dark Matter Unification: Generalized Chaplygin Gas Model

We review the main features of the generalized Chaplygin gas (GCG) proposal for unification of dark energy and dark matter and discuss how it admits an unique decomposition into dark energy and dark matter components once phantom-like dark energy is excluded. In the context of this approach we consider structure formation and show that unphysical oscillations or blow-up in the matter power spectrum are not present. Moreover, we demonstrate that the dominance of dark energy occurs about the time when energy density fluctuations start evolving away from the linear regime.

Orfeu Bertolami

2005-04-14

171

Revival of the unified dark energy-dark matter model?

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 {delta}{approx}a behavior.

Bento, M.C.; Bertolami, O.; Sen, A.A. [Departamento de Fisica, Instituto Superior Tecnico, Avenida Rovisco Pais, 1049-001 Lisbon (Portugal); Departamento de Fisica and Centro de Fisica das Interaccoes Fundamentais, Instituto Superior Tecnico, Avenida Rovisco Pais, 1049-001 Lisbon (Portugal)

2004-10-15

172

Holographic Dark Energy Like in $f(R)$ Gravity

We investigate the corresponding relation between $f(R)$ gravity and holographic dark energy. We introduce a kind of energy density from $f(R)$ which has role of the same as holographic dark energy. We obtain the differential equation that specify the evolution of the introduced energy density parameter based on varying gravitational constant. We find out a relation for the equation of state parameter to low redshifts which containing varying $G$ correction.

Kh. Saaidi; A. Aghamohammadi

2010-10-12

173

Optimizing New Dark Energy Experiments

Next generation Stage IV dark energy experiments under design during this grant, and now under construction, will enable the determination of the properties of dark energy and dark matter to unprecedented precision using multiple complementary probes. The most pressing challenge in these experiments is the characterization and understanding of the systematic errors present within any given experimental configuration and the resulting impact on the accuracy of our constraints on dark energy physics. The DETF and the P5 panel in their reports recommended Expanded support for ancillary measurements required for the long-term program and for projects that will improve our understanding and reduction of the dominant systematic measurement errors. Looking forward to the next generation Stage IV experiments we have developed a program to address the most important potential systematic errors within these experiments. Using data from current facilities it has been feasible and timely to undertake a detailed investigation of the systematic errors. In this DOE grant we studied of the source and impact of the dominant systematic effects in dark energy measurements, and developed new analysis tools and techniques to minimize their impact. Progress under this grant is briefly reviewed in this technical report. This work was a necessary precursor to the coming generations of wide-deep probes of the nature of dark energy and dark matter. The research has already had an impact on improving the efficiencies of all Stage III and IV dark energy experiments.

Tyson, J. Anthony [University of California, Davis

2013-08-26

174

Ricci Dark Energy in Brans-Dicke theory

A holographic dark energy from Ricci scalar curvature called Ricci dark energy was proposed recently. In this model the future event horizon area is replaced by the inverse of the Ricci scalar curvature. We study the evolution of equation of state of the Ricci dark energy and the transition from decelerated to accelerated expansion of the universe in the Brans-Dicke theory, which is a natural extension of general relativity. We find that the current acceleration of our universe is well explained.

Chao-Jun Feng

2008-06-04

175

Dark Energy and Non-linear Perturbations

Dark energy might have an influence on the formation of non--linear structures during the cosmic history. For example, in models in which dark energy couples to dark matter, it will be non--homogeneous and will influence the collapse of a dark matter overdensity. We use the spherical collapse model to estimate how much influence dark energy might have.

C. van de Bruck; D. F. Mota

2005-01-14

176

Dark energy models through nonextensive Tsallis' statistics

The accelerated expansion of the Universe is one of the greatest challenges of modern physics. One candidate to explain this phenomenon is a new field called dark energy. In this work we have used the Tsallis nonextensive statistical formulation of the Friedmann equation to explore the Barboza-Alcaniz and Chevalier-Polarski-Linder parametric dark energy models and the Wang-Meng and Dalal vacuum decay models. After that, we have discussed the observational tests and the constraints concerning the Tsallis nonextensive parameter.

Rafael da C. Nunes; Edésio M. Barboza Jr.; Everton M. C. Abreu; Jorge Ananias Neto

2014-03-22

177

A note on dark matter and dark energy

NASA Astrophysics Data System (ADS)

Since the geometry of our universe seems to depend very little on baryonic matter, we consider a variational principle involving only dark matter and dark energy which in addition make them depend on each other. There are no adjustable parameters or scalar fields with appropriate equations of state. No quintessence. For a pressure-less, 3-flat FRW model, the cosmological constant is now a function of time, positive by definition and always small. Its time derivative or rather its associated parameter w is always negative and close to -1. The most interesting point is that the age of the universe and w itself are correlated. Moreover, this rather unsophisticated model provides a very limited range for both these quantities and results are in surprising agreement with observed values. The problem of vacuum energy remains what it was; the problem of coincidence is significantly less annoying.

Katz, Joseph

2014-01-01

178

Dark Matter and Dark Energy huncheng@math.mit.edu

Dark Matter and Dark Energy Hung Cheng huncheng@math.mit.edu January 17, 2008 Abstract We suggest that a candidate for dark matter is a meson with spin one the existence of which is dictated by local scale invariance pro- posed by Herman Weyl.. Dark Matter and Scale Invariance Hung Cheng Department of Mathematics

Cheng, Hung

179

Dynamics of Teleparallel Dark Energy

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 $\\xi$ is a great advantage).

Hao Wei

2012-06-01

180

Spherical Collapse Model And Dark Energy(II)

This is a second paper of a series of two. In this paper, we directly correct the problem pointed out in the first paper of this series, dark energy does not cluster on the scale of galaxy clusters, but the current describing the flowing of dark energies outside the clusters is ignored in almost all the previous papers. We set up and solve a first order differential equation which describes the evolution of the clusters in a back ground universe containing dark energies. From the solution we extract the key parameters of the model and find them depending on the equation of state coefficients of dark energies rather non-trivially. We then apply the results in Press-Scheter theory and calculate the number density of galaxy clusters and its evolutions, we find the observable quantities are strongly affected by the equation of state coefficients of dark energies.

Ding-fang Zeng; Yi-hong Gao

2005-05-09

181

Quantum Informational Dark Energy: Dark energy from forgetting

We suggest that dark energy has a quantum informational origin. Landauer's principle associated with the erasure of quantum information at a cosmic horizon implies the non-zero vacuum energy having effective negative pressure. Assuming the holographic principle, the minimum free energy condition, and the Gibbons-Hawking temperature for the cosmic event horizon we obtain the holographic dark energy with the parameter $d\\simeq 1$, which is consistent with the current observational data. It is also shown that both the entanglement energy and the horizon energy can be related to Landauer's principle.

Jae-Weon Lee; Jungjai Lee; Hyeong-Chan Kim

2007-09-01

182

Cosmology from decaying dark energy, primordial at the Planck scale

NASA Astrophysics Data System (ADS)

The consideration of dark energy's quanta, required also by thermodynamics, introduces its chemical potential into the cosmological equations. Isolating its main contribution, we obtain solutions with dark energy decaying to matter or radiation. When dominant, their energy densities tend asymptotically to a constant ratio, explaining today's dark energy-dark matter coincidence, and in agreement with supernova redshift data, and an age-of-the-universe constraint. This also connects the Planck and today's scales through time. This decay may be manifested in the highest-energy cosmic rays, recently detected.

Besprosvany, Jaime

2005-04-01

183

Dark goo: bulk viscosity as an alternative to dark energy

We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an 'effective' pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a dark energy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a dark energy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local equilibrium today for viscous effects to be important.

Gagnon, Jean-Sebastien [Technische Universität Darmstadt, Schlossgartenstrasse 2, 64289, Darmstadt (Germany); Lesgourgues, Julien, E-mail: jean-sebastien.gagnon@physik.tu-darmstadt.de, E-mail: julien.lesgourgues@cern.ch [École Polytechnique Fédérale de Lausanne, CH-1015, Lausanne (Switzerland)

2011-09-01

184

Wormhole solutions supported by interacting dark matter and dark energy

We show that the presence of a nonminimal interaction between dark matter and dark energy may lead to a violation of the null energy condition and to the formation of a configuration with nontrivial topology (a wormhole). In this it is assumed that both dark matter and dark energy satisfy the null energy condition, a violation of which takes place only in the inner high-density regions of the configuration. This is achieved by assuming that, in a high-density environment, a nonminimal coupling function changes its sign in comparison with the case where dark matter and dark energy have relatively low densities which are typical for a cosmological background. For this case, we find regular static, spherically symmetric solutions describing wormholes supported by dark matter nonminimally coupled to dark energy in the form of a quintessence scalar field.

Vladimir Folomeev; Vladimir Dzhunushaliev

2014-03-10

185

Properties of singularities in the (phantom) dark energy universe

The properties of future singularities are investigated in the universe dominated by dark energy including the phantom-type fluid. We classify the finite-time singularities into four classes and explicitly present the models which give rise to these singularities by assuming the form of the equation of state of dark energy. We show the existence of a stable fixed point with an

Shinichi Nojiri; Sergei D. Odintsov; Shinji Tsujikawa

2005-01-01

186

Future supernovae observations as a probe of dark energy

We study the potential impact of improved future supernovae data on our understanding of the dark energy problem. We carefully examine the relative utility of different fitting functions that can be used to parametrize the dark energy models, and provide concrete reasons why a particular choice (based on a parametrization of the equation of state) is better in almost all

Jochen Weller; Andreas Albrecht

2002-01-01

187

Holographic Dark Energy with Time Varying n^2 Parameter in Non-Flat Universe

We consider a holographic dark energy model, with a varying parameter, n, which evolves slowly with time. We obtain the differential equation describing evolution of the dark energy density parameter, $\\Omega_d$, for the flat and non-flat FRW universes. The equation of state parameter in this generalized version of holographic dark energy depends on n.

Bushra Majeed; Mubasher Jamil; Azad A. Siddiqui

2014-11-01

188

Holographic Dark Energy with Time Varying n 2 Parameter in Non-Flat Universe

NASA Astrophysics Data System (ADS)

We consider a holographic dark energy model, with a varying parameter, n, which evolves slowly with time. We obtain the differential equation describing evolution of the dark energy density parameter, ? d , for the flat and non-flat FRW universes. The equation of state parameter in this generalized version of holographic dark energy depends on n.

Majeed, Bushra; Jamil, Mubasher; Siddiqui, Azad A.

2015-01-01

189

A Dynamic Dark Information Energy Consistent with Planck Data

NASA Astrophysics Data System (ADS)

The 2013 cosmology results from the European Space Agency Planck spacecraft provide new limits to the dark energy equation of state parameter. Here we show that Holographic Dark Information Energy (HDIE), a dynamic dark energy model, achieves an optimal fit to the published datasets where Planck data is combined with other astrophysical measurements. HDIE uses Landauer's principle to account for dark energy by the energy equivalent of information, or entropy, of stellar heated gas and dust. Combining Landauer's principle with the Holographic principle yields an equation of state parameter determined solely by star formation history, effectively solving the 'cosmic coincidence problem'. While HDIE mimics a cosmological constant at low red-shifts, z<1, the small difference from a cosmological constant expected at higher red-shifts will only be resolved by the next generation of dark energy instrumentation. The HDIE model is shown to provide a viable alternative to the main cosmological constant/vacuum energy and scalar field/quintessence explanations.

Gough, Michael

2014-03-01

190

Dark energy scaling from dark matter to acceleration

NASA Astrophysics Data System (ADS)

The dark sector of the Universe need not be completely separable into distinct dark matter and dark energy components. We consider a model of early dark energy in which the dark energy mimics a dark matter component in both evolution and perturbations at early times. Barotropic aether dark energy scales as a fixed fraction, possibly greater than one, of the dark matter density and has vanishing sound speed at early times before undergoing a transition. This gives signatures not only in cosmic expansion but in sound speed and inhomogeneities, and in number of effective neutrino species. Model parameters describe the timing, sharpness of the transition, and the relative abundance at early times. Upon comparison with current data, we find viable regimes in which the dark energy behaves like dark matter at early times: for transitions well before recombination the dark energy to dark matter fraction can equal or exceed unity, while for transitions near recombination the ratio can only be a few percent. After the transition, dark energy goes its separate way, ultimately driving cosmic acceleration and approaching a cosmological constant in this scenario.

Bielefeld, Jannis; Caldwell, Robert R.; Linder, Eric V.

2014-08-01

191

In this paper, we give a conceptual explanation of dark energy as a small negative residual scalar curvature present even in empty spacetime. This curvature ultimately results from postulating a discrete spacetime geometry, very closely related to that used in the dynamical triangulations approach to quantum gravity. In this model, there are no states which have total scalar curvature exactly zero. Moreover, numerical evidence in dimension three suggests that, at a fixed volume, the number of discrete-spacetime microstates strongly increases with decreasing curvature. Because of the resulting entropic force, any dynamics which push empty spacetime strongly toward zero scalar curvature would instead produce typically observed states with a small negative curvature. This provides a natural explanation for the empirically observed small positive value for the cosmological constant (Lambda is about 10^(-121) in Planck units.) In fact, we derive the very rough estimate Lambda=10^(-187) from a simple model containing only the two (highly-degenerate) quantum states with total scalar-curvature closest to zero.

Aaron Trout

2012-08-08

192

Dark Energy Rules the Universe

Berkeley Lab theoretical physicist Eric Linder previews his Nov. 24, 2008 talk on the mystery of dark energy. Catch his full lecture here: http://www.osti.gov/sciencecinema/servlets/purl/1007511?format=mp4

Linder, Eric

2008-01-01

193

Decoupling Dark Energy from Matter

We examine the embedding of dark energy in high energy models based upon supergravity and extend the usual phenomenological setting comprising an observable sector and a hidden supersymmetry breaking sector by including a third sector leading to the acceleration of the expansion of the universe. We find that gravitational constraints on the non-existence of a fifth force naturally imply that the dark energy sector must possess an approximate shift symmetry. When exact, the shift symmetry provides an example of a dark energy sector with a runaway potential and a nearly massless dark energy field whose coupling to matter is very weak, contrary to the usual lore that dark energy fields must couple strongly to matter and lead to gravitational inconsistencies. Moreover, the shape of the potential is stable under one-loop radiative corrections. When the shift symmetry is slightly broken by higher order terms in the Kähler potential, the coupling to matter remains small. However, the cosmological dynamics are largely affected by the shift symmetry breaking operators leading to the appearance of a minimum of the scalar potential such that dark energy behaves like an effective cosmological constant from very early on

Carsten Van De Bruck; Jérôme Martin; et al.

2009-01-01

194

Numerical study of halo concentrations in dark-energy cosmologies

We study the concentration parameters, their mass dependence and redshift evolution, of dark-matter halos in different dark-energy cosmologies with constant and time-variable equation of state, and compare them with ``standard'' LambdaCDM and OCDM models. We find that previously proposed algorithms for predicting halo concentrations can be well adapted to dark-energy models. When centred on the analytically expected values, halo concentrations

Klaus Dolag; Matthias Bartelmann; Francesca Perrotta; Carlo Baccigalupi; Lauro Moscardini; Massimo Meneghetti; Giuseppe Tormen

2004-01-01

195

The Influence of Evolving Dark Energy on Cosmology

Observational evidence indicating that the expansion of the universe is accelerating has surprised cosmologists in recent years. Cosmological models have sought to explain this acceleration by incorporating `dark energy', of which the traditional cosmological constant is just one possible candidate. Several cosmological models involving an evolving equation of state of the dark energy have been proposed, as well as possible energy exchange to other components, such as dark matter. This paper summarises the forms of the most prominent models and discusses their implications for cosmology and astrophysics. Finally, this paper examines the current and future observational constraints on the nature of dark energy.

Luke Barnes; Matthew J. Francis; Geraint F. Lewis; Eric V. Linder

2005-10-28

196

Anisotropic charged dark energy star

As the stars carry electrical charges, we present in this paper a model for charged dark energy star which is singularity free. We take Krori-Barua space time. We assume that the radial pressure exerted on the system due to the presence of dark energy is proportional to the isotropic perfect fluid matter density and the difference between tangential and radial pressure is proportional to the square of the electric field intensity. The solution satisfies the physical conditions inside the star

Kanika Das; Nawsad Ali

2014-02-02

197

Dark energy from gravitoelectromagnetic inflation?

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.

Federico Agustin Membiela; Mauricio Bellini

2008-05-23

198

The Dark Energy Camera (DECam)

We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y),

D. L. DePoy; T. Abbott; J. Annis; M. Antonik; M. Barceló; R. Bernstein; B. Bigelow; D. Brooks; E. Buckley-Geer; J. Campa; L. Cardiel; F. Castander; J. Castilla; H. Cease; S. Chappa; E. Dede; G. Derylo; H. T. Diehl; P. Doel; J. DeVicente; J. Estrada; D. Finley; B. Flaugher; E. Gaztanaga; D. Gerdes; M. Gladders; V. Guarino; G. Gutierrez; M. Haney; S. Holland; K. Honscheid; D. Huffman; I. Karliner; D. Kau; S. Kent; M. Kozlovsky; D. Kubik; K. Kuehn; S. Kuhlmann; K. Kuk; F. Leger; H. Lin; G. Martinez; M. Martinez; W. Merritt; J. Mohr; P. Moore; T. Moore; B. Nord; R. Ogando; J. Olsen; B. Onal; J. Peoples; T. Qian; N. Roe; E. Sanchez; V. Scarpine; R. Schmidt; R. Schmitt; M. Schubnell; K. Schultz; M. Selen; T. Shaw; V. Simaitis; J. Slaughter; C. Smith; H. Spinka; A. Stefanik; W. Stuermer; R. Talaga; G. Tarle; J. Thaler; D. Tucker; A. Walker; S. Worswick; A. Zhao

2008-01-01

199

REPORT OF THE DARK ENERGY TASK FORCE

REPORT OF THE DARK ENERGY TASK FORCE (DETF) Dark energy appears to be the dominant component. These circumstances demand an ambitious observational program to determine the dark energy properties as well postulating that 70% of the universe is composed of mysterious "dark energy" that drives the acceleration

Baumgardt, Holger

200

Planck priors for dark energy surveys

Although cosmic microwave background anisotropy data alone cannot constrain simultaneously the spatial curvature and the equation of state of dark energy, CMB data provide a valuable addition to other experimental results. However computing a full CMB power spectrum with a Boltzmann code is quite slow; for instance if we want to work with many dark energy and/or modified gravity models, or would like to optimize experiments where many different configurations need to be tested, it is possible to adopt a quicker and more efficient approach. In this paper we consider the compression of the projected Planck cosmic microwave background data into four parameters, R (scaled distance to last scattering surface), l{sub a} (angular scale of sound horizon at last scattering), {omega}{sub b}h{sup 2} (baryon density fraction) and n{sub s} (powerlaw index of primordial matter power spectrum), all of which can be computed quickly. We show that, although this compression loses information compared to the full likelihood, such information loss becomes negligible when more data is added. We also demonstrate that the method can be used for canonical scalar-field dark energy independently of the parametrization of the equation of state, and discuss how this method should be used for other kinds of dark energy models.

Mukherjee, Pia; Parkinson, David [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom); Kunz, Martin [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom); Department of Theoretical Physics, University of Geneva, 24 Quai E. Ansermet, 1211 Geneve 4 (Switzerland); Wang Yun [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks Street, Norman, Oklahoma (United States)

2008-10-15

201

Planck priors for dark energy surveys

NASA Astrophysics Data System (ADS)

Although cosmic microwave background anisotropy data alone cannot constrain simultaneously the spatial curvature and the equation of state of dark energy, CMB data provide a valuable addition to other experimental results. However computing a full CMB power spectrum with a Boltzmann code is quite slow; for instance if we want to work with many dark energy and/or modified gravity models, or would like to optimize experiments where many different configurations need to be tested, it is possible to adopt a quicker and more efficient approach. In this paper we consider the compression of the projected Planck cosmic microwave background data into four parameters, R (scaled distance to last scattering surface), la (angular scale of sound horizon at last scattering), ?bh2 (baryon density fraction) and ns (powerlaw index of primordial matter power spectrum), all of which can be computed quickly. We show that, although this compression loses information compared to the full likelihood, such information loss becomes negligible when more data is added. We also demonstrate that the method can be used for canonical scalar-field dark energy independently of the parametrization of the equation of state, and discuss how this method should be used for other kinds of dark energy models.

Mukherjee, Pia; Kunz, Martin; Parkinson, David; Wang, Yun

2008-10-01

202

Planck priors for dark energy surveys

Although cosmic microwave background (CMB) anisotropy data alone cannot constrain simultaneously the spatial curvature and the equation of state of dark energy, CMB data provide a valuable addition to other experimental results. However computing a full CMB power spectrum with a Boltzmann code is quite slow; for instance if we want to work with many dark energy and/or modified gravity models, or would like to optimize experiments where many different configurations need to be tested, it is possible to adopt a quicker and more efficient approach. In this paper we consider the compression of the projected Planck CMB data into four parameters, R (scaled distance to last scattering surface), l_a (angular scale of sound horizon at last scattering), Omega_b h^2 (baryon density fraction) and n_s (powerlaw index of primordial matter power spectrum), all of which can be computed quickly. We show that, although this compression loses information compared to the full likelihood, such information loss becomes negligible when more data is added. We also demonstrate that the method can be used for scalar field dark energy independently of the parametrisation of the equation of state, and discuss how this method should be used for other kinds of dark energy models.

Pia Mukherjee; Martin Kunz; David Parkinson; Yun Wang

2008-03-11

203

Dynamical Behavior of Interacting Dark Energy in Loop Quantum Cosmology

NASA Astrophysics Data System (ADS)

The dynamical behaviors of interacting dark energy in loop quantum cosmology are discussed in this paper. Based on three defined dimensionless variables, we simplify the equations of the fixed points. The fixed points for interacting dark energy can be determined by the Friedmann equation coupled with the dynamical equations in Einstein cosmology. But in loop quantum cosmology, besides the Friedmann equation, the conversation equation also gives a constrain on the fixed points. The difference of stability properties for the fixed points in loop quantum cosmology and the ones in Einstein cosmology are also discussed.

Xiao, Kui; Zhu, Jian-Yang

204

Dark energy model with generalized cosmological horizon

NASA Astrophysics Data System (ADS)

We discuss the evolution of the newly proposed dark-energy model with a generalized event horizon (a generalized form of the holographic dark-energy model with a future event horizon) in the flat and nonflat universes. We consider the interacting scenario of this model with cold dark matter. We use the well-known logarithmic approach to evaluate the equation of state parameter and explore its present values. It is found that this parameter shows phantom crossing in some cases of the generalized event horizon parameters. The ?-?' plane is also developed for three different cases of the generalized event horizon parameters. The corresponding phase plane provides thawing and freezing regions. Finally, the validity of a generalized second law of thermodynamics is explored which holds in certain ranges of constant parameters.

Sharif, M.; Jawad, A.

2014-10-01

205

Stable dark energy stars: An alternative to black holes?

In this work, a generalization of the Mazur-Mottola gravastar model is explored, by considering a matching of an interior solution governed by the dark energy equation of state, $\\omega\\equiv p/ \\rhoenergy is a possible candidate.

Francisco S. N. Lobo

2006-12-05

206

Dark Energy and Dark Matter as Inertial Effects

A globally rotating model of the universe is postulated. It is shown that dark energy and dark matter are cosmic inertial effects resulting from such a cosmic rotation, corresponding to centrifugal and a combination of centrifugal and the Coriolis forces, respectively. The physics and the cosmological and galactic parameters obtained from the model closely match those attributed to dark energy and dark matter in the standard {\\Lambda}-CDM model.

Serkan Zorba

2012-10-20

207

Constraining Neutrinos and Dark Energy with Galaxy Clustering in the Dark Energy Survey

We determine the forecast errors on the absolute neutrino mass scale and the equation of state of dark energy by combining synthetic data from the Dark Energy Survey (DES) and the Cosmic Microwave Background (CMB) Planck surveyor. We use angular clustering of galaxies for DES in 7 redshift shells up to $z\\sim 1.7$ including cross-correlations between different redshift shells. We study models with massless and massive neutrinos and three different dark energy models: $\\Lambda$CDM ($w=-1$), wCDM (constant $w$), and waCDM (evolving equation of state parameter $w(a)=w_0 + w_{a}(1-a)$). We include the impact of uncertainties in modeling galaxy bias using a constant and a redshift-evolving bias model. For the $\\Lambda$CDM model we obtain an upper limit for the sum of neutrino masses from DES+Planck of $\\Sigma m_\

Zablocki, Alan

2014-01-01

208

Phase-space analysis of teleparallel dark energy

We perform a detailed dynamical analysis of the teleparallel dark energy scenario, which is based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. We find that the universe can result in the quintessence-like, dark-energy-dominated solution, or to the stiff dark-energy late-time attractor, similarly to standard quintessence. However, teleparallel dark energy possesses an additional late-time solution, in which dark energy behaves like a cosmological constant, independently of the specific values of the model parameters. Finally, during the evolution the dark energy equation-of-state parameter can be either above or below -1, offering a good description for its observed dynamical behavior and its stabilization close to the cosmological-constant value.

Xu, Chen [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Saridakis, Emmanuel N. [Physics Division, National Technical University of Athens, 15780 Zografou Campus, Athens (Greece); Leon, Genly, E-mail: xuc1990@126.com, E-mail: Emmanuel_Saridakis@baylor.edu, E-mail: genly@uclv.edu.cu [Department of Mathematics, Universidad Central de Las Villas, Santa Clara, CP 54830 (Cuba)

2012-07-01

209

Distribution of dark energy in the vicinity of compact objects

The distribution of dark energy density in the vicinity of compact static objects is analyzed. Dark energy is assumed to be in the form of a scalar field with three parameters: the background density, the equation of state parameter and the effective sound speed. Compact object is assumed to be a homogeneous spherical object of constant radius. We use the solutions of the hydrodynamical equations for dark energy in the gravitational fields of such objects for cases of static distribution of dark energy in the vicinity of star and stationary accretion onto black hole in order to analyze the possibility of constraining of the parameters of dark energy from astrophysical data. We show that dependence of density of dark energy in the vicinity of such object on the effective sound speed, background density and equation of state parameter of dark energy makes it possible to try such tests. Here we exploit the accuracy of determination of masses of Sun and black hole in the center of Milky Way to obtain the lower limit on the effective sound speed of dark energy.

M. Tsizh; B. Novosyadlyj; Yu. Kulinich

2014-12-23

210

Non-adiabatic perturbations in Ricci dark energy model

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 ? of Ricci dark energy equals to 1/2. In the case where ? = 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.

Karwan, Khamphee; Thitapura, Thiti, E-mail: pk_karwan@yahoo.com, E-mail: nanodsci2523@hotmail.com [Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900 (Thailand)

2012-01-01

211

Voids and overdensities of coupled Dark Energy

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 |{delta}{sub {phi}}| {approx} O(10{sup -6}) to |{delta}{sub {phi}}| {approx} O(10{sup -4}) indicating an almost homogeneous Dark Energy component.

Mainini, Roberto, E-mail: roberto.mainini@astro.uio.no [Institute of Theoretical Astrophysics, University of Oslo, Box 1029, 0315 Oslo (Norway)] [Institute of Theoretical Astrophysics, University of Oslo, Box 1029, 0315 Oslo (Norway)

2009-04-15

212

Reissner-Nordstrom black hole in dark energy background

In this paper we propose a stationary solution of Einstein's field equations describing Reissner-Nordstrom black hole in dark energy background. It is to be regarded as the Reissner-Nordstrom black hole is embedded into the dark energy solution producing Reissner-Nordstrom-dark energy black hole. We find that the space-time geometry of Reissner-Nordstrom-dark energy solution is Petrov type $D$ in the classification of space-times. It is also shown that the embedded space-time possesses an energy-momentum tensor of the electromagnetic field interacting with the dark energy having negative pressure. We find the energy-momentum tensor for dark energy violates the the strong energy condition due to the negative pressure, whereas that of the electromagnetic field obeys the strong energy condition. It is shown that the time-like vector field for an observer in the Reissner-Nordstrom-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity of the horizons for the embedded dark energy black hole. The characteristic properties of relativistic dark energy based on the de Sitter solution is discussed in an appendix.

Ngangbam Ishwarchandra; Ng. Ibohal; K. Yugindro Singh

2014-11-29

213

New physics at low energies and dark matter-dark energy transmutation

A field theory is proposed where the regular fermionic matter and the dark fermionic matter can be different states of the same "primordial" fermion fields. In regime of the fermion densities typical for normal particle physics, the primordial fermions split into three families identified with regular fermions. When fermion energy density becomes comparable with dark energy density, the theory allows transition to new type of states. The possibility of such Cosmo-Low Energy Physics (CLEP) states is demonstrated by means of solutions of the field theory equations describing FRW universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos. Neutrinos in CLEP state are drawn into cosmological expansion by means of dynamically changing their own parameters. One of the features of the fermions in CLEP state is that in the late time universe their masses increase as a^{3/2} (a=a(t) is the scale factor). The energy density of the cold dark matter consisting of neutrinos in CLEP state scales as a sort of dark energy; this cold dark matter possesses negative pressure and for the late time universe its equation of state approaches that of the cosmological constant. The total energy density of such universe is less than it would be in the universe free of fermionic matter at all.

E. I. Guendelman; A. B. Kaganovich

2004-04-14

214

UTILIZING DARK SILICON TO SAVE ENERGY WITH

DARK SILICON TO SAVE ENERGY WITH COMPUTATIONAL SPRINTING ................................................................................................................................................................................................................... COMPUTATIONAL SPRINTING ACTIVATES DARK SILICON TO IMPROVE RESPONSIVENESS BY BRIEFLY BUT INTENSELY EXCEEDING AT THE PLATFORM'S THERMAL LIMIT. ......Researchers predict increasingly underutilized chip area (dark silicon

Martin, Milo M. K.

215

Cosmological constraints on a dark matter -- dark energy interaction

It is generally assumed that the two dark components of the energy density of the universe, a smooth component called dark energy and a fluid of nonrelativistic weakly interacting particles called dark matter, are independent of each other and interact only through gravity. In this paper, we consider a class of models in which the dark matter and dark energy interact directly. The dark matter particle mass is proportional to the value of a scalar field, and the energy density of this scalar field comprises the dark energy. We study the phenomenology of these models and calculate the luminosity distance as a function of redshift and the CMB anisotropy spectrum for several cases. We find that the phenomenology of these models can differ significantly from the standard case, and current observations can already rule out the simplest models.

Mark B. Hoffman

2003-07-18

216

Dark energy and formation of classical scalar fields

We present a quintessence model for the dark energy in which the quintessence scalar field is produced by the decay of a super heavy dark matter and gradually condensate to a classical scalar field. This model can explain both the smallness and the latest observations by WMAP for the equation of state of the dark energy which has $w \\sim -1.06$. We review both classical and field theoretical treatment of this model and briefly explain the most important parameters for obtaining the observed characteristic of the dark energy.

Houri Ziaeepour

2006-04-03

217

Dark Energy and dark matter of the universe from one-loop renormalization of riccion

Here, creation of the universe is obtained only from gravity sector. The dynamical universe begins with two basic ingredients (i) vacuum energy, also called dark energy (as vacuum energy is not observed) and (ii) background radiation. These two are obtained through one-loop renormalization of riccion. Solutions of renormalization group equations yield initial value of vaccum energy density $\\\\rho_{\\\\Lambda_{\\\\rm ew}} =

S. K. Srivastava

2004-01-01

218

Cosmological dark energy effects from entanglement

The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical dark energy results as byproduct of quantum entanglement.

S. Capozziello; O. Luongo; S. Mancini

2013-02-24

219

Neutrino generated dynamical dark energy with no dark energy field

NASA Astrophysics Data System (ADS)

Dynamical dark energy (DE) phenomenon emerges as a geometrical effect accompanying the cosmological expansion of nonrelativistic fermionic matter. This occurs without the need for any fluid, like dynamical scalar field (quintessence, cosmon, etc.), and with conventional form of the Einstein equations in contrast to other known geometrical DE models. The phenomenon results from first principles in the framework of the two measures field theory where, in the Einstein frame, both fermion masses and the cosmological constant (CC) turn into functions of the cold fermion density n. This n dependence becomes negligible in regular (laboratory) conditions, but it may have an important role in cosmology. In the 4D gravity model where the original action involves only CC and massive fermions without self-interaction, for different (but wide) regions in the parameter space, we have found two possible classes of scenarios for the late universe starting from the cold matter domination era. We argue that the fermions which drive the variable CC should be associated with cold neutrinos disposed in voids and supervoids. The cosmological dynamics of the first class practically coincides with that of the ?CDM model, while the dynamics of the second class is of the phantomlike regime with a pseudo-rip scenario. Crossing the phantom divide happens due to a new type of the neutrino DE effect where neutrinos pass through the state with zero mass and with the vacuumlike EoS P?=-??.

Guendelman, E. I.; Kaganovich, A. B.

2013-02-01

220

Dark Energy vs. Dark Matter: Towards a Unifying Scalar Field?

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 both components. After a quick review of the cosmological constraints on this unifying dark fluid, we will present a model of dark fluid based on a complex scalar field and discuss the problem of the choice of the potential.

A. Arbey

2008-12-18

221

Destiny, The Dark Energy Space Telescope

NASA Astrophysics Data System (ADS)

Destiny is a simple, direct, low cost mission to determine the properties of dark energy by obtaining a cosmologically deep supernova (SN) type Ia Hubble diagram. Operated at L2, its science instrument is a 1.65m space telescope, featuring a grism-fed near-infrared (NIR) (0.85-1.7?m) survey camera/spectrometer with a 0.12 square degree field of view. During its two-year primary mission, Destiny will detect, observe, and characterize 3000 SN Ia events over the redshift interval 0.4

Lauer, Tod R.

2007-04-01

222

Structure formation in inhomogeneous Early Dark Energy models

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 ?CDM 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 ?{sub 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 ?CDM 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 ?CDM model than its homogeneous counterparts.

Batista, R.C. [Escola de Cięncias e Tecnologia, Universidade Federal do Rio Grande do Norte, Caixa Postal 1524, 59072-970, Natal, Rio Grande do Norte (Brazil); Pace, F., E-mail: rbatista@ect.ufrn.br, E-mail: francesco.pace@port.ac.uk [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth, PO1 3FX (United Kingdom)

2013-06-01

223

Gravitation and regular Universe without dark energy and dark matter

It is shown that isotropic cosmology in the Riemann-Cartan spacetime allows to solve the problem of cosmological singularity as well as the problems of invisible matter components - dark energy and dark matter. All cosmological models filled with usual gravitating matter satisfying energy dominance conditions are regular with respect to energy density, spacetime metrics and the Hubble parameter. At asymptotics cosmological solutions of spatially flat models describe accelerating Universe without dark energy and dark matter, and quantitatively their behaviour is identical to that of standard cosmological \\Lambda CDM-model.

A. V. Minkevich

2011-02-03

224

Dark matter, dark energy and gravitational proprieties of antimatter

We suggest that the eventual gravitational repulsion between matter and antimatter may be a key for understanding of the nature of dark matter and dark energy. If there is gravitational repulsion, virtual particle-antiparticle pairs in the vacuum, may be considered as gravitational dipoles. We use a simple toy model to reveal a first indication that the gravitational polarization of such a vacuum, caused by baryonic matter in a Galaxy, may produce the same effect as supposed existence of dark matter. In addition, we argue that cancellation of gravitational charges in virtual particle-antiparticle pairs, may be a basis for a solution of the cosmological constant problem and identification of dark energy with vacuum energy. Hence, it may be that dark matter and dark energy are not new, unknown forms of matter-energy but an effect of complex interaction between quantum vacuum and known baryonic matter.

Dragan Slavkov Hajdukovic

2009-10-21

225

Unified Dark Energy-Dark Matter model with Inverse Quintessence

We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-conventional 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.

Stefano Ansoldi; Eduardo I. Guendelman

2012-09-21

226

Unified dark energy-dark matter model with inverse quintessence

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.

Ansoldi, Stefano [ICRA International Center for Relativistic Astrophysics, INFN Istituto Nazionale di Fisica Nucleare, and Dipartimento di Matematica e Informatica, Universitŕ 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

227

Enhanced Big Rip without Conventional Dark Energy

A modified Friedmann equation which arises in an extension of general relativity which accommodates a time-dependent fundamental length $L(t)$ leads to cosmological models where the scale factor diverges with an essential singularity at a finite future time. Such models have no dark energy in the conventional sense of energy possessing a truly simple pressure-energy relationship. Data on supernovae restrict the time from the present until the Rip to be generically longer than the current age of the Universe.

Paul H. Frampton

2004-07-16

228

Spherical Collapse Model And Dark Energy(I)

In existing literatures about the top-hat spherical collapse model of galaxy clusters formation in cosmology containing dark energies, dark energies are usually assumed not to cluster on this scale. But all these literatures ignored the current describing the flowing of dark energies outside the clusters which should exist under this assumption, so the conclusions of these literatures are worth further explorations. In this paper we study this model in QCDM or Phantom-CDM cosmologies(flat) by assuming that dark energies will cluster synchronously with ordinary matters on the scale of galaxy clusters so the dark energy current flowing outside the clusters does not exist at all and find that in this case, the key parameters of the model exhibit rather non-trivial and remarkable dependence on the equation of state coefficients of dark energies. We then apply the results in Press-Scheter theory and calculate the number density of galaxy clusters and its evolutions. We find that this two quantities are both affected exponentially by the equation of state coefficients of dark energies. We leave the study of this model with the assumption that dark energies do not cluster on the scale of galaxy clusters at all as the topic of another paper where similar conclusions will be obtained also.

Ding-fang Zeng; Yi-hong Gao

2005-05-09

229

On the determination of dark energy

I consider some of the issues we face in trying to understand dark energy. Huge fluctuations in the unknown dark energy equation of state can be hidden in distance data, so I argue that model-independent tests which signal if the cosmological constant is wrong are valuable. These can be constructed to remove degeneracies with the cosmological parameters. Gravitational effects can play an important role. Even small inhomogeneity clouds our ability to say something definite about dark energy. I discuss how the averaging problem confuses our potential understanding of dark energy by considering the backreaction from density perturbations to second-order in the concordance model: this effect leads to at least a 10% increase in the dynamical value of the deceleration parameter, and could be significantly higher. Large Hubble-scale inhomogeneity has not been investigated in detail, and could conceivably be the cause of apparent cosmic acceleration. I discuss void models which defy the Copernican principle in our Hubble patch, and describe how we can potentially rule out these models.This article is a summary of two talks given at the Invisible Universe Conference, Paris, 2009.

Clarkson, Chris [Cosmology and Gravity Group, Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701 (South Africa)

2010-06-23

230

Cosmology with Coupled Gravity and Dark Energy

Dark energy is a fundamental constituent of our universe, its status in the cosmological field equation should be equivalent to that of gravity. Here we construct a dark energy and matter gravity coupling (DEMC) model of cosmology in a way that dark energy and gravity are introduced into the cosmological field equation in parallel with each other from the beginning. The DEMC universe possesses a composite symmetry from global Galileo invariance and local Lorentz invariance. The observed evolution of the universe expansion rate at redshift z>1 is in tension with the standard LCDM model, but can be well predicted by the DEMC model from measurements of only nearby epochs. The so far most precise measured expansion rate at high z is quite a bit slower than the expectations from LCDM, but remarkably consistent with that from DEMC. It is hoped that the DEMC scenario can also help to solve other existing challenges to cosmology: large scale anomalies in CMB maps and large structures up to about 10^3 Mpc of a quasar group. The DEMC universe is a well defined mechanical system. From measurements we can quantitatively evaluate its total rest energy, present absolute radius and expanding speed.

Ti-Pei Li

2015-01-13

231

Cosmology with Coupled Gravity and Dark Energy

Dark energy is a fundamental constituent of our universe, its status in the cosmological field equation should be equivalent to that of gravity. Here we construct a dark energy and matter gravity coupling (DEMC) model of cosmology in a way that dark energy and gravity are introduced into the cosmological field equation in parallel with each other from the beginning. The DEMC universe possesses a composite symmetry from global Galileo invariance and local Lorentz invariance. The observed evolution of the universe expansion rate at redshift z>1 is in tension with the standard LCDM model, but can be well predicted by the DEMC model from measurements of only nearby epochs. The so far most precise measured expansion rate at high z is quite a bit slower than the expectations from LCDM, but remarkably consistent with that from DEMC. It is hoped that the DEMC scenario can also help to solve other existing challenges to cosmology: large scale anomalies in CMB maps and large structures up to about 10^3 Mpc of a quasar group. The DEMC universe is a well defined mechanical system. From measurements we can quantitatively evaluate its total rest energy, present absolute radius and expanding speed.

Ti-Pei Li

2014-09-01

232

Dark energy interacting with neutrinos and dark matter: a phenomenological theory

A model for a flat homogeneous and isotropic Universe composed of dark energy, dark matter, neutrinos, radiation and baryons is analyzed. The fields of dark matter and neutrinos are supposed to interact with the dark energy. The dark energy is considered to obey either the van der Waals or the Chaplygin equations of state. The ratio between the pressure and the energy density of the neutrinos varies with the red-shift simulating massive and non-relativistic neutrinos at small red-shifts and non-massive relativistic neutrinos at high red-shifts. The model can reproduce the expected red-shift behaviors of the deceleration parameter and of the density parameters of each constituent.

G. M. Kremer

2007-04-03

233

The Hubble constant and dark energy from cosmological distance measures

We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia supernovae. When one investigates dark energy, the Hubble constant is often a nuisance parameter; thus it is usually marginalized over. On the other hand, when one focuses on the Hubble constant, simple dark energy models such as a cosmological constant and a constant equation of state are usually assumed. Since we do not know the nature of dark energy yet, it is interesting to investigate the Hubble constant assuming some types of dark energy and see to what extent the constraint on the Hubble constant is affected by the assumption concerning dark energy. We show that the constraint on the Hubble constant is not affected much by the assumption for dark energy. We furthermore show that this holds true even if we remove the assumption that the universe is flat. We also discuss how the prior on the Hubble constant affects the constraints on dark energy and/or the curvature of the universe.

Ichikawa, Kazuhide [Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 277-8582 (Japan); Takahashi, Tomo, E-mail: kazuhide@icrr.u-tokyo.ac.jp, E-mail: tomot@cc.saga-u.ac.jp [Department of Physics, Saga University, Saga 840-8502 (Japan)

2008-04-15

234

QCD modified ghost scalar field dark energy models

Within the framework of FRW cosmology, we study the QCD modified ghost scalar field models of dark energy in the presence of both interaction and viscosity. For a spatially non-flat FRW universe containing modified ghost dark energy (MGDE) and dark matter, we obtain the equation of state of MGDE, the deceleration parameter as well as a differential equation governing the MGDE density parameter. We also investigate the growth of structure formation for our model in a linear perturbation regime. Furthermore, we reconstruct both the dynamics and potentials of the quintessence, tachyon, K-essence and dilaton scalar field DE models according to the evolution of the MGDE density.

K. Karami; S. Asadzadeh; M. Mousivand; Z. Safari

2012-09-05

235

Neutron stars with dark energy

NASA Astrophysics Data System (ADS)

After a short review on the possible experimental observations to verify pseudocomplex General Relativity, neutron stars as a particular object of interest are investigated. Dark energy is added to the structure of a neutron star, while for the nuclear part the chiral SU(3) model is used. For the coupling of matter to dark energy a special assumption is made. The consequences are discussed. We show that neutron stars of up to six solar masses are obtained, which already behave similar to a black hole.

Hess, P. O.; Rodríguez, I.; Greiner, W.; Boller, T.

2015-01-01

236

Constraining Dark Energy with the Dark Energy Survey: Theoretical Challenges

The Dark Energy Survey (DES) will use a new imaging camera on the Blanco 4-m telescope at CTIO to image 5000 square degrees of sky in the South Galactic Cap in four optical bands, and to carry out repeat imaging over a smaller area to identify and measure lightcurves of Type Ia supernovae. The main imaging area overlaps the planned Sunyaev-Zel'dovich survey of the South Pole Telescope. The idea behind DES is to use four distinct and largely independent methods to probe the properties of dark energy: baryon oscillations of the power spectrum, abundance and spatial distribution of clusters, weak gravitational lensing, and Type Ia supernovae. This white paper outlines, in broad terms, some of the theoretical issues associated with the first three of these probes (the issues for supernovae are mostly different in character), and with the general task of characterizing dark energy and distinguishing it from alternative explanations for cosmic acceleration. A companion white paper discusses the kind of numerical simulations and other theoretical tools that will be needed to address the these issues and to create mock catalogs that allow end-to-end tests of analysis procedures. Although we have been thinking about these problems in the specific context of DES, many of them are also relevant to other planned dark energy studies.

James Annis; Sarah Bridle; Francisco J. Castander; August E. Evrard; Pablo Fosalba; Joshua A. Frieman; Enrique Gaztanaga; Bhuvnesh Jain; Andrey V. Kravtsov; Ofer Lahav; Huan Lin; Joseph Mohr; Albert Stebbins; Terence P. Walker; Risa H. Wechsler; David H. Weinberg; Jochen Weller

2005-10-06

237

Distribution of dark energy in the vicinity of compact objects

The distribution of dark energy density in the vicinity of compact static objects is analyzed. Dark energy is assumed to be in the form of a scalar field with three parameters: the background density, the equation of state parameter and the effective sound speed. Compact object is assumed to be a homogeneous spherical object of constant radius. We use the solutions of the hydrodynamical equations for dark energy in the gravitational fields of such objects for cases of static distribution of dark energy in the vicinity of star and stationary accretion onto black hole in order to analyze the possibility of constraining of the parameters of dark energy from astrophysical data. We show that dependence of density of dark energy in the vicinity of such object on the effective sound speed, background density and equation of state parameter of dark energy makes it possible to try such tests. Here we exploit the accuracy of determination of masses of Sun and black hole in the center of Milky Way to obtain the lower li...

Tsizh, M; Kulinich, Yu

2014-01-01

238

Dark energy rest frame and the CMB dipole

If dark energy can be described as a perfect fluid, then, apart from its equation of state relating energy density and pressure, we should also especify the corresponding rest frame. Since dark energy is typically decoupled from the rest of components of the universe, in principle such a frame could be different from that of matter and radiation. In this work we consider the potential observable effects of the motion of dark energy and the possibility to measure the dark energy velocity relative to matter. In particular we consider the modification of the usual interpretation of the CMB dipole and its implications for the determination of matter bulk flows on very large scales. We also comment on the possible origin of a dark energy flow and its evolution in different models.

Antonio L. Maroto

2006-09-08

239

Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.

Chapline, G

2005-03-08

240

NASA Astrophysics Data System (ADS)

We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energy-momentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter space-time, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary Robertson-Walker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed Robertson-Walker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on sub-Hubble scales as in standard cold dark matter scenarios.

Albareti, F. D.; Cembranos, J. A. R.; Maroto, A. L.

2014-12-01

241

It is proposed that after the macroscopic fluctuation of energy density that is responsible for inflation dies away, a class of microscopic fluctuations, always present, survives to give the present day dark energy. This latter is simply a reinterpretation of the causet mechanism of Ahmed, Dodelson, Green and Sorkin, wherein the emergence of space is dropped but only energy considerations are maintained. At postinflation times, energy is exchanged between the "cisplanckian" cosmos and an unknown foam-like transplanckian reservoir. Whereas during inflation, the energy flows only from the latter to the former after inflation it fluctuates in sign thereby accounting for the tiny effective cosmological constant that seems to account for dark energy.

Robert Brout

2005-08-04

242

w and w' of Scalar Field Models of Dark Energy

Important observables to reveal the nature of dark energy are the equation of state $w$ and its time derivative in units of the Hubble time $w'$. Recently, it is shown that the simplest scalar field models of dark energy (quintessence) occupy rather narrow regions in the $w-w'$ plane. We extend the $w-w'$ plane to $wdark energy. We also derive bounds on tracker k-essence.

Takeshi Chiba

2005-10-20

243

The cosmological constant and dark energy

Physics welcomes the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, Lambda; today the concept is termed dark energy or quintessence. Physics also suggests that dark energy could be dynamical, allowing for the arguably appealing picture of an evolving dark-energy density approaching its natural value, zero, and small now because the expanding universe is

P. J. Peebles; Bharat Ratra

2003-01-01

244

Dark energy and 3-manifold topology

We show that the differential-geometric description of matter by differential structures of spacetime leads to a unifying model of the three types of energy in the cosmos: matter, dark matter and dark energy. Using this model we are able to calculate the ratio of dark energy to the total energy of the cosmos.

Torsten Asselmeyer-Maluga; Helge Rose

2007-10-08

245

Cosmic inflation, deceleration, acceleration, dark matter, and dark `energy' in one coherent package

Cosmic inflation, deceleration, acceleration, dark matter, and dark `energy' in one coherent, baryonic particles of primordial matter and as the continuously created, invisible particles of the `dark. DARK MATTER AND DARK `ENERGY' 17 A. Drainholes 17 B. Dark matter and dark `energy' from drainholes 19

Ellis, Homer

246

Cosmological anisotropy from non-comoving dark matter and dark energy

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 plausible and viable working hypothesis.

Harko, Tiberiu [Department of Mathematics, University College London, Gower Street, London, WC1E 6BT (United Kingdom); Lobo, Francisco S. N., E-mail: t.harko@ucl.ac.uk, E-mail: flobo@cii.fc.ul.pt [Centro de Astronomia e Astrofísica da Universidade de Lisboa, Campo Grande, Edificio C8 1749-016 Lisboa (Portugal)

2013-07-01

247

Dark Energy: Is It of Torsion Origin?

{\\it "Dark Energy"} is a term recently used to interpret supernovae type Ia observation. In the present work we give two arguments on a possible relation between dark energy and torsion of space-time.

M. I. Wanas

2010-06-10

248

It is argued that dark energy -or something dynamically equivalent at the background level- is necessary if the expanding universe is to behave as an ordinary macroscopic system; that is, if it is to tend to some thermodynamic equilibrium state in the long run.

Diego Pavón; Ninfa Radicella

2012-12-31

249

Cosmological dark energy and entanglement

Astrophysical observations of recent years indicate that the universe is composed of a large amount of dark energy (DE) responsible for an accelerated expansion of the universe. Here, we argue that DE can arise entirely from the standard principles of strong interaction physics and quantum entanglement. Good quantitative agreement of our estimate with the observation, without the need for any adjustable parameters, is encouraging.

Ghosh, Sanjay K.; Raha, Sibaji [Department of Physics, Bose Institute, 93/1 A.P.C. Road, Kolkata-700009, India Centre for Astroparticle Physics and Space Science, Bose Institute, Block EN, Sector V, Kolkata 700091 (India)

2011-09-23

250

Constraints on the sound speed of dark energy

We have studied constraints on the equation of state, $w$, and speed of sound, c_s, of the dark energy from a joint analysis of data from the cosmic microwave background, large scale structure and type-Ia supernovae. We find that current observations have no significant sensitivity to c_s. However, there is a slight difference between models in which there are no dark energy perturbations and models in which dark energy behaves as a fluid. Assuming that there are no dark energy perturbations shifts the allowed region for $w$ to slightly higher values. At present models with and without dark energy perturbations provide roughly equally good fits to observations, but the difference is potentially important for future parameter estimations. Finally, we have also performed error forecasts for future measurements of c_s.

Steen Hannestad

2005-04-01

251

Validity of Thermodynamical Laws in Dark Energy Filled Universe

We have considered the flat FRW model of the universe which is filled with only dark energy. The general descriptions of first and second laws of thermodynamics are investigated on the apparent horizon and event horizon of the universe. We have assumed the equation of state of three different types of dark energy models. We have examined the validity of first and second laws of thermodynamics on apparent and event horizons for these dark energies. For these dark energy models, it has been found that on the apparent horizon, first and second laws are always valid. On the event horizon, the laws are break down for dark energy models 1 and 2. For model 3, first law cannot be satisfied on the event horizon, but second law may be satisfied at the late stage of the evolution of the universe and so the validity of second law on the event horizon depends on the values of the parameters only.

Samarpita Bhattacharya; Ujjal Debnath

2010-12-26

252

The South Pole Telescope: A white paper for the Dark Energy Task Force

The South Pole Telescope: A white paper for the Dark Energy Task Force J. E. Carlstrom, C. Chang, T constraints on the nature of dark energy by measuring its impact on the growth of structure, specifically redshifts, the statistical power of the survey yields are sufficient to measure the dark energy equation

Collar, Juan I.

253

Simple implementation of general dark energy models

NASA Astrophysics Data System (ADS)

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.

Bloomfield, Jolyon K.; Pearson, Jonathan A.

2014-03-01

254

Dark Matter and Dark Energy in the Universe

NASA Astrophysics Data System (ADS)

For the first time, we have a plausible and complete accounting of matter and energy in the Universe. Expressed a fraction of the critical density it goes like this: neutrinos, between 0.3% and 15%; stars, between 0.3% and 0.6%; baryons (total), 5% ą 0.5%; matter (total), 40% ą 10%; smooth, dark energy, 80% ą 20%; totaling to the critical density (within the errors). This accounting is consistent with the inflationary prediction of a flat Universe and measurements of the anisotropy of the CBR. It also defines three "dark problems": Where are the dark baryons? What is the nonbaryonic dark matter? What is the nature of the dark energy? The leading candidate for the (optically) dark baryons is diffuse hot gas; the leading candidates for the nonbaryonic dark matter are slowly moving elementary particles left over from the earliest moments (cold dark matter), such as axions or neutralinos; the leading candidates for the dark energy involve fundamental physics and include a cosmological constant (vacuum energy), a rolling scalar field (quintessence), and a network of light, frustrated topological defects.

Turner, Michael S.

2001-03-01

255

Dark Matter and Dark Energy in the Universe

NASA Astrophysics Data System (ADS)

For the first time, we have a plausible, complete accounting of matter and energy in the Universe. Expressed a fraction of the critical density it goes like this: neutrinos, between 0.3% and 15%; stars, 0.5%; baryons (total), 5%; matter (total), 40%; smooth, dark energy, 60%; adding up to the critical density (summarized in Fig. ref{fig:omega}). This accounting is consistent with the inflationary prediction of a flat Universe and defines three dark-matter problems: Where are the dark baryons? What is the nonbaryonic dark matter? What is the nature of the dark energy? The leading candidate for the (optically) dark baryons is diffuse hot gas; the leading candidates for the nonbaryonic dark matter are slowly moving elementary particles left over from the earliest moments (cold dark matter), such as axions or neutralinos; the leading candidates for the dark energy involve fundamental physics and include a cosmological constant (vacuum energy), a rolling scalar field (quintessence), and light, frustrated topological defects.

Turner, Michael S.

256

Interacting agegraphic tachyon model of dark energy

Scalar-field dark energy models like tachyon are often regarded as an effective description of an underlying theory of dark energy. In this Letter, we implement the interacting agegraphic dark energy models with tachyon field. We demonstrate that the interacting agegraphic evolution of the universe can be described completely by a single tachyon scalar field. We thus reconstruct the potential as well as the dynamics of the tachyon field according to the evolutionary behavior of interacting agegraphic dark energy.

A. Sheykhi

2009-07-15

257

Testing the Cosmic Coincidence Problem and the Nature of Dark Energy

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 non-canonical scaling of the ratio of dark matter and dark energy with the Robertson-Walker scale factor a(t). Upcoming observations, such as a high redshift supernova survey, application of the Alcock-Paczynski test to quasar pairs, and cluster evolution, will strongly constrain the relative scaling of dark matter and dark energy as well as the equation of state of the dark energy. Thus, whether there actually is a coincidence problem, and the extent of cosmic coincidence in the universe's recent past can be answered observationally in the near future. Determining whether today is a special time in the history of the universe will be a SNAP.

Neal Dalal; Kevork Abazajian; Elizabeth Jenkins; Aneesh V. Manohar

2001-05-18

258

Dark energy and dark matter as curvature effects

Astrophysical observations are pointing out huge amounts of dark matter and dark energy needed to explain the observed large scale structures and cosmic accelerating expansion. Up to now, no experimental evidence has been found, at fundamental level, to explain such mysterious components. The problem could be completely reversed considering dark matter and dark energy as shortcomings of General Relativity and claiming for the correct theory of gravity as that derived by matching the largest number of observational data. As a result, accelerating behavior of cosmic fluid and rotation curves of spiral galaxies are reproduced by means of curvature effects.

S. Capozziello; V. F. Cardone; A. Troisi

2006-03-20

259

The Dark Force: Astrophysical Repulsion from Dark Energy

Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance. We discuss possible astrophysical effects of this "dark" force. For example, the dark force overcomes the gravitational attraction from an object (e.g., dwarf galaxy) of mass $10^7 M_\\odot$ at a distance of $~ 23$ kpc. It seems possible that observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure the dark energy density.

Ho, Chiu Man

2015-01-01

260

The Dark Force: Astrophysical Repulsion from Dark Energy

Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance. We discuss possible astrophysical effects of this "dark" force. For example, the dark force overcomes the gravitational attraction from an object (e.g., dwarf galaxy) of mass $10^7 M_\\odot$ at a distance of $~ 23$ kpc. It seems possible that observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure the dark energy density.

Chiu Man Ho; Stephen D. H. Hsu

2015-01-23

261

Metamaterial model of tachyonic dark energy

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.

Igor I. Smolyaninov

2014-02-07

262

Observational approaches to understanding dark energy

Illuminating the nature of dark energy is one of the most important challenges in cosmology today. In this review I discuss several promising observational approaches to understanding dark energy, in the context of the recommendations by the U.S. Dark Energy Task Force and the ESA-ESO Working Group on Fundamental Cosmology.

Yun Wang

2007-12-01

263

Cosmic structure growth and dark energy

Dark energy has a dramatic effect on the dynamics of the Universe, causing the recently discovered acceleration of the expansion. The dynamics are also central to the behaviour of the growth of large-scale structure, offering the possibility that observations of structure formation provide a sensitive probe of the cosmology and dark energy characteristics. In particular, dark energy with a time-varying

Eric V. Linder; Adrian Jenkins

2003-01-01

264

REPORT OF THE DARK ENERGY TASK FORCE

REPORT OF THE DARK ENERGY TASK FORCE Andreas Albrecht, University of California, Davis Gary. Suntzeff, Texas A&M University Dark energy appears to be the dominant component of the physical Universe a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among

Hu, Wayne

265

Dark Matter and Dark Energy are Mirage

It is known (Quznetsov, 2010) that probabilities of pointlike events are defined by some generalization of Dirac equation. One part of such generalized equation corresponds to the Dirac's leptonic equation, and the other part corresponds to the Dirac's quark equation. The quark part of this equation is invariant under the oscillations of chromatic states. And it turns out that these oscillations bend space-time so that at large distance space expands with acceleration according to Hubble's law. And these oscillations bend space-time so that here appears the discrepancy between quantity of the luminous matter in the space structures and the traditional picture of gravitational interaction of stars in these structures.

Gunn Quznetsov

2010-04-26

266

New holographic dark energy model with non-linear interaction

In this paper the cosmological evolution of a holographic dark energy model with a non-linear interaction between the dark energy and dark matter components in a FRW type flat universe is analysed. In this context, the deceleration parameter $q$ and the equation state $w_{\\Lambda}$ are obtained. We found that, as the square of the speed of sound remains positive, the model is stable under perturbations since early times; it also shows that the evolution of the matter and dark energy densities are of the same order for a long period of time, avoiding the so--called coincidence problem. We have also made the correspondence of the model with the dark energy densities and pressures for the quintessence and tachyon fields. From this correspondence we have reconstructed the potential of scalar fields and their dynamics.

Oliveros, A

2014-01-01

267

Figures of merit for present and future dark energy probes

We compare current and forecasted constraints on dynamical dark energy models from Type Ia supernovae and the cosmic microwave background using figures of merit based on the volume of the allowed dark energy parameter space. For a two-parameter dark energy equation of state that varies linearly with the scale factor, and assuming a flat universe, the area of the error ellipse can be reduced by a factor of {approx}10 relative to current constraints by future space-based supernova data and CMB measurements from the Planck satellite. If the dark energy equation of state is described by a more general basis of principal components, the expected improvement in volume-based figures of merit is much greater. While the forecasted precision for any single parameter is only a factor of 2-5 smaller than current uncertainties, the constraints on dark energy models bounded by -1{<=}w{<=}1 improve for approximately 6 independent dark energy parameters resulting in a reduction of the total allowed volume of principal component parameter space by a factor of {approx}100. Typical quintessence models can be adequately described by just 2-3 of these parameters even given the precision of future data, leading to a more modest but still significant improvement. In addition to advances in supernova and CMB data, percent-level measurement of absolute distance and/or the expansion rate is required to ensure that dark energy constraints remain robust to variations in spatial curvature.

Mortonson, Michael J. [Center for Cosmology and AstroParticle Physics, Ohio State University, Columbus, Ohio 43210 (United States); Huterer, Dragan [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States); Hu, Wayne [Kavli Institute for Cosmological Physics, Department of Astronomy and Astrophysics, and Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States)

2010-09-15

268

Studies of dark energy with X-ray observatories.

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. PMID:20404207

Vikhlinin, Alexey

2010-04-20

269

From confinement to dark energy

The infrared divergence of the self-energy of a color charge is due to an enhancement of the long wavelength modes of the color Coulomb potential field. There are also long wavelength contributions to the QCD vacuum energy that are similarly enhanced. Vacuum modes of Hubble scale wavelengths may be affected in a cosmological setting and this can lead to a residual positive energy density of the form $H^d\\Lambda_{\\rm QCD}^{4-d}$. Lattice studies constrain $d$. If the dark energy takes this form then the universe is driven towards de Sitter expansion, and we briefly study this cosmology when $d$ is just slightly above unity.

B. Holdom

2010-12-02

270

Dark energy from discrete spacetime.

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. PMID:24312502

Trout, Aaron D

2013-01-01

271

Dark Energy from Discrete Spacetime

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, 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. PMID:24312502

Trout, Aaron D.

2013-01-01

272

Cosmological evolution of a quintom model of dark energy

We investigate in this Letter the cosmological evolution of a dark energy model with two scalar fields where one of the scalar has canonical kinetic energy and another scalar has negative kinetic energy term. For such a system with exponential potentials we find that during the evolution of the universe the equation of state w changes from w??1 to w?1,

Zong-Kuan Guo; Yun-Song Piao; Xinmin Zhang; Yuan-Zhong Zhang

2005-01-01

273

Validity of Thermodynamical Laws in Dark Energy Filled Universe

We have considered the flat FRW model of the universe which is filled with only dark energy. The general descriptions of first\\u000a and second laws of thermodynamics are investigated on the apparent horizon and event horizon of the universe. We have assumed\\u000a the equation of state of three different types of dark energy models. We have examined the validity of

Samarpita Bhattacharyaand; Ujjal Debnath

2011-01-01

274

Unified dark energy and dark matter from a scalar field different from quintessence

We explore unification of dark matter and dark energy in a theory containing a scalar field of non-Lagrangian type, obtained by direct insertion of a kinetic term into the energy-momentum tensor. This scalar is different from quintessence, having an equation of state between -1 and 0 and a zero sound speed in its rest frame. We solve the equations of motion for an exponential potential via a rewriting as an autonomous system, and demonstrate the observational viability of the scenario, for sufficiently small exponential potential parameter {lambda}, by comparison to a compilation of kinematical cosmological data.

Gao Changjun [National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 (China); Kunz, Martin [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom); Departement de Physique Theorique, Universite de Geneve, 24 quai Ernest Ansermet, CH-1211 Geneve 4 (Switzerland); Liddle, Andrew R.; Parkinson, David [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom)

2010-02-15

275

One of the most pressing, modern cosmological mysteries is the cause of the accelerated expansion of the universe. The energy density required to cause this large scale opposition to gravity is known to be both far in ...

Jackson, Brendan Marc

2011-11-23

276

1. DARK ENERGY DETECTION: AN EXPERIMENTAL PROBLEM

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

Martin L. Perl

277

Reconstructing Quintom from Ricci Dark Energy

The holographic dark energy with Ricci scalar as IR cutoff called Ricci dark energy(RDE) probes the nature of dark energy with respect to the holographic principle of quantum gravity theory. The scalar field dark energy models like quintom are often viewed as effective description of the underlying field theory of dark energy. In this letter, we assume RDE model as the underlying field theory to find how the generalized ghost condensate model(GGC) that can easily realize quintom behavior can be used to effectively describe it and reconstruct the function $h(\\phi)$ of the generalized ghost condensate model.

Chao-Jun Feng

2008-10-15

278

Radiative inflation and dark energy

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 < or approx. n{sub 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.

Di Bari, Pasquale; King, Stephen F. [School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Luhn, Christoph [Institute for Particle Physics Phenomenology, Ogden Centre for Fundamental Physics, Department of Physics, University of Durham, Science Laboratories, South Road, Durham DH1 3LE (United Kingdom); Merle, Alexander [Max-Planck-Institut fuer Kernphysik, Postfach 10 39 80, 69029 Heidelberg (Germany); Department of Theoretical Physics, School of Engineering Sciences, Royal Institute of Technology (KTH) - AlbaNova University Centre, Roslagstullsbacken 21, 106 91 Stockholm (Sweden); Schmidt-May, Angnis [Department of Physics and Oskar Klein Centre, Stockholm University, AlbaNova University Centre, SE-106 91 Stockholm (Sweden)

2011-10-15

279

Designing dark energy afterglow experiments

Chameleon fields, which are scalar field dark energy candidates, can evade fifth force constraints by becoming massive in high-density regions. However, this property allows chameleon particles to be trapped inside a vacuum chamber with dense walls. Afterglow experiments constrain photon-coupled chameleon fields by attempting to produce and trap chameleon particles inside such a vacuum chamber, from which they will emit an afterglow as they regenerate photons. Here we discuss several theoretical and systematic effects underlying the design and analysis of the GammeV and CHASE afterglow experiments. We consider chameleon particle interactions with photons, Fermions, and other chameleon particles, as well as with macroscopic magnetic fields and matter. The afterglow signal in each experiment is predicted, and its sensitivity to various properties of the experimental apparatus is studied. Finally, we use CHASE data to exclude a wide range of photon-coupled chameleon dark energy models.

Amol Upadhye; Jason H. Steffen; Aaron S. Chou

2012-04-24

280

Dark energy versus modified gravity.

There is now strong observational evidence that the expansion of the Universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead general relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. Here we show that this may not be so easy, demonstrating explicitly that a generalized dark energy model can match the growth rate of the Dvali-Gabadadze-Porrati model and reproduce the 3+1 dimensional metric perturbations. Cosmological observations are then unable to distinguish the two cases. PMID:17501110

Kunz, Martin; Sapone, Domenico

2007-03-23

281

Genesis of Dark Energy: Dark Energy as a Consequence of Cosmological Nuclear Energy

Recent observations on Type-Ia supernovae and low density measurement of matter (including dark matter) suggest that the present day universe consists mainly of repulsive-gravity type exotic-matter with negative-pressure often referred as dark-energy. But the mystery is about the nature of dark-energy and its puzzling questions such as why, how, where & when about the dark- energy are intriguing. In the present paper the author attempts to answer these questions while making an effort to reveal the genesis of dark-energy, and suggests that the cosmological nuclear-binding-energy liberated during primordial nucleo-synthesis remains trapped for 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=+1for 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. This thus almost solves the dark-energy mystery of negative-pressure & repulsive-gravity. It is concluded that dark-energy is a consequence of released-free nuclear-energy of cosmos. The proposed theory makes several estimates / predictions, which agree reasonably well with the astrophysical constraints & observations.

R. C. Gupta

2004-12-07

282

Dark Energy, Gravitation and Electromagnetism

In the context of the fact that the existence of dark energy causing the accelerated expansion of the universe has been confirmed by the WMAP and the Sloan Digital Sky Survey, we re-examine gravitation itself, starting with the formulation of Sakharov and show that it is possible to obtain gravitation in terms of the electromagnetic charge of elementary particles, once the ZPF and its effects at the Compton scale are taken into account.

B. G. Sidharth

2004-01-08

283

Inhomogeneous alternative to dark energy?

Recently, there have been suggestions that the apparent accelerated expansion of the universe is not caused by repulsive gravitation due to dark energy, but is rather a result of inhomogeneities in the distribution of matter. In this work, we investigate the behavior of a dust-dominated inhomogeneous Lemaître-Tolman-Bondi universe model, and confront it with various astrophysical observations. We find that such

Hĺvard Alnes; Morad Amarzguioui; Řyvind Grřn

2006-01-01

284

Fingerprinting Dark Energy III: distinctive marks of viscosity

The characterisation of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed $\\cs$ and the anisotropic stress $\\sigma$. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in \\cite{Sapone:2009mb}, we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed which depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the Integrated Sachs-Wolfe effect in the Cosmic Microwave Background.

Domenico Sapone; Elisabetta Majerotto

2012-03-09

285

About the Geometric Solution to the Problems of Dark Energy

In this paper is proposed a geometric solution to the dark energy, assuming that the space can be divided into regions of size $\\sim L_{p}$ and energy $\\sim E_{p}$. Significantly this assumption generate a energy density similar to the energy density observed for the vaccum energy, the correct solution for the coincidence problem and the state equation characteristic of quintessence in the comoving coordinates. Similarly is studied the ultraviolet and infrarred limits and the amount of dark energy in the Universe.

Miguel Angel García-Aspeitia

2010-11-19

286

Curvature of the universe and the dark energy potential

The flatness of an accelerating universe model (characterized by a dark energy scalar field $\\chi$) is mimicked from a curved model that is filled with, apart from the cold dark matter component, a quintessencelike scalar field $Q$. In this process, we characterize the original scalar potential $V(Q)$ and the mimicked scalar potential $V(\\chi)$ associated to the scalar fields $Q$ and $\\chi$, respectively. The parameters of the original model are fixed through the mimicked quantities that we relate to the present astronomical data, such that the equation state parameter $w_{_{\\chi}}$ and the dark energy density parameter $\\Omega_{\\chi}$.

Sergio del Campo

2002-11-20

287

Correspondence of pilgrim dark energy with scalar field models

NASA Astrophysics Data System (ADS)

In this paper, we consider interacting pilgrim dark energy (Hubble horizon as an infrared cutoff) with cold dark matter in flat universe. We develop the equation of state parameter in this scenario which shows the consistency with pilgrim dark energy phenomenon. In this framework, we analyze the behavior of scalar field and corresponding scalar potentials (which describe the dynamics of the scalar fields) of various scalar field models, graphically. The dynamics of scalar fields and potentials indicate accelerated expansion of the universe which is consistent with the current observations.

Jawad, Abdul; Majeed, Asim

2015-01-01

288

Cuscuton cosmology: Dark energy meets modified gravity

NASA Astrophysics Data System (ADS)

In a companion paper, we have introduced a model of scalar field dark energy, Cuscuton, which can be realized as the incompressible (or infinite speed of sound) limit of a k-essence fluid. In this paper, we study how Cuscuton modifies the constraint sector of Einstein gravity. In particular, we study Cuscuton cosmology and show that even though Cuscuton can have an arbitrary equation of state, or time dependence, and is thus inhomogeneous, its perturbations do not introduce any additional dynamical degree of freedom and only satisfy a constraint equation, amounting to an effective modification of gravity on large scales. Therefore, Cuscuton can be considered to be a minimal theory of evolving dark energy, or a minimal modification of a cosmological constant, as it has no internal dynamics. Moreover, this is the only modification of Einstein gravity to our knowledge, that does not introduce any additional degrees of freedom (and is not conformally equivalent to the Einstein gravity). We then study two simple Cuscuton models, with quadratic and exponential potentials. The quadratic model has the exact same expansion history as ?CDM, and yet contains an early dark energy component with constant energy fraction, which is constrained to ?Q?2%, mainly from WMAP Cosmic Microwave Background and Sloan Digital Sky Survey Lyman-? forest observations. The exponential model has the same expansion history as the Dvali-Gabadadze-Poratti self-accelerating brane-world model, but generates a much smaller Integrated Sachs-Wolfe effect, and is thus consistent with the Cosmic Microwave Background observations. Finally, we show that the evolution is local on superhorizon scales, implying that there is no gross violation of causality, despite Cuscutons infinite speed of sound.

Afshordi, Niayesh; Chung, Daniel J. H.; Doran, Michael; Geshnizjani, Ghazal

2007-06-01

289

Spacetime Foam and Dark Energy

Due to quantum fluctuations, spacetime is foamy on small scales. The degree of foaminess is found to be consistent with the holographic principle. One way to detect spacetime foam is to look for halos in the images of distant quasars. Applying the holographic foam model to cosmology we "predict" that the cosmic energy density takes on the critical value; and basing only on existing archived data on active galactic nuclei from the Hubble Space Telescope, we also "predict" the existence of dark energy which, we argue, is composed of an enormous number of inert "particles" of extremely long wavelength. We speculate that these "particles" obey infinite statistics.

Y. Jack Ng

2008-08-08

290

Bulk-Brane Interaction and Holographic Dark Energy

In this paper we consider the bulk-brane interaction to obtain the equation of state for the holographic energy density in non-flat universe enclosed by the event horizon measured from the sphere of horizon named $L$. We assumes that the cold dark matter energy density on the brane is conserved, but the holographic dark energy density on the brane is not conserved due to brane-bulk energy exchange. Our calculation show, taking $\\Omega_{\\Lambda}=0.73$ for the present time, the lower bound of $w_{\\rm \\Lambda}^{eff}$ is -0.9. This implies that one can not generate phantom-like equation of state from an interacting holographic dark energy model in non-flat universe.

M R Setare

2006-09-14

291

Rotating dark matter solution admitting dark fluid

In this paper we present an exact solution of Einstein's fields equations describing dark matter possessing dark energy with negative pressure and energy equation of state parameter having minus sign.

Ng. Ibohal; Ngangbam Ishwarchandra; K. Yugindro Singh

2009-04-25

292

Dark Energy Constraints from Galaxy Cluster Peculiar Velocities

Future multifrequency microwave background experiments with arcminute resolution and micro-Kelvin temperature sensitivity will be able to detect the kinetic Sunyaev-Zeldovich (kSZ) effect, providing a way to measure radial peculiar velocities of massive galaxy clusters. We show that cluster peculiar velocities have the potential to constrain several dark energy parameters. We compare three velocity statistics (the distribution of radial velocities, the mean pairwise streaming velocity, and the velocity correlation function) and analyze the relative merits of these statistics in constraining dark energy parameters. Of the three statistics, mean pairwise streaming velocity provides constraints that are least sensitive to velocity errors: the constraints on parameters degrades only by a factor of two when the random error is increased from 100 to 500 km/s. We also compare cluster velocities with other dark energy probes proposed in the Dark Energy Task Force report. For cluster velocity measurements with realistic priors, the eventual constraints on the dark energy density, the dark energy equation of state and its evolution are comparable to constraints from supernovae measurements, and better than cluster counts and baryon acoustic oscillations; adding velocity to other dark energy probes improves constraints on the figure of merit by more than a factor of two. For upcoming Sunyaev-Zeldovich galaxy cluster surveys, even velocity measurements with errors as large as 1000 km/s will substantially improve the cosmological constraints compared to using the cluster number density alone.

Suman Bhattacharya; Arthur Kosowsky

2007-12-01

293

Constraining dark energy with clusters: Complementarity with other probes

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 {gamma}. 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.

Cunha, Carlos; Huterer, Dragan [Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109-1040 (United States); Frieman, Joshua A. [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510 (United States); Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637 (United States)

2009-09-15

294

A Kinematical Approach to Dark Energy Studies

We present and employ a new kinematical approach to cosmological ''dark energy'' studies. We construct models in terms of the dimensionless second and third derivatives of the scale factor a(t) with respect to cosmic time t, namely the present-day value of the deceleration parameter q{sub 0} and the cosmic jerk parameter, j(t). An elegant feature of this parameterization is that all {Lambda}CDM models have j(t) = 1 (constant), which facilitates simple tests for departures from the {Lambda}CDM paradigm. Applying our model to the three best available sets of redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements, we obtain clear statistical evidence for a late time transition from a decelerating to an accelerating phase. For a flat model with constant jerk, j(t) = j, we measure q{sub 0} = -0.81 {+-} 0.14 and j = 2.16{sub -0.75}{sup +0.81}, results that are consistent with {Lambda}CDM at about the 1{sigma} confidence level. A standard ''dynamical'' analysis of the same data, employing the Friedmann equations and modeling the dark energy as a fluid with an equation of state parameter, w (constant), gives {Omega}{sub m} = 0.306{sub -0.040}{sup +0.042} and w = -1.15{sub -0.18}{sup +0.14}, also consistent with {Lambda}CDM at about the 1{sigma} level. In comparison to dynamical analyses, the kinematical approach uses a different model set and employs a minimum of prior information, being independent of any particular gravity theory. The results obtained with this new approach therefore provide important additional information and we argue that both kinematical and dynamical techniques should be employed in future dark energy studies, where possible. Our results provide further interesting support for the concordance {Lambda}CDM paradigm.

Rapetti, David; Allen, Steven W.; Amin, Mustafa A.; Blandford, Roger D.; /KIPAC, Menlo Park

2006-06-06

295

New agegraphic dark energy in Ho?ava-Lifshitz cosmology

We investigate the new agegraphic dark energy scenario in a universe governed by Ho?ava-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 Ho?ava-Lifshitz running parameter ?, of the new agegraphic dark energy parameter n, and of the interaction coupling b. We find that w{sub 0} = ?0.82{sup +0.08}{sub ?0.08} and w{sub 1} = 0.08{sup +0.09}{sub ?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 Ho?ava-Lifshitz gravity.

Jamil, Mubasher [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, H-12, Islamabad (Pakistan); Saridakis, Emmanuel N., E-mail: mjamil@camp.edu.pk, E-mail: msaridak@phys.uoa.gr [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing, 400065 (China)

2010-07-01

296

Reconstruction of dark energy and expansion dynamics using Gaussian processes

An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space, as the errors found depend strongly on the parametrisation considered. We present a new non-parametric approach to reconstructing the history of the expansion rate and dark energy using Gaussian Processes, which is a fully Bayesian approach for smoothing data. We present a pedagogical introduction to Gaussian Processes, and discuss how it can be used to robustly differentiate data in a suitable way. Using this method we show that the Dark Energy Survey - Supernova Survey (DES) can accurately recover a slowly evolving equation of state to ?{sub w} = ą0.05 (95% CL) at z = 0 and ą0.25 at z = 0.7, with a minimum error of ą0.025 at the sweet-spot at z ? 0.16, provided the other parameters of the model are known. Errors on the expansion history are an order of magnitude smaller, yet make no assumptions about dark energy whatsoever. A code for calculating functions and their first three derivatives using Gaussian processes has been developed and is available for download.

Seikel, Marina; Clarkson, Chris; Smith, Mathew, E-mail: marina.seikel@uct.ac.za, E-mail: chris.clarkson@uct.ac.za, E-mail: mathew.smith@uct.ac.za [Astrophysics, Cosmology and Gravity Centre (ACGC), and Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch, 7701 (South Africa)

2012-06-01

297

A new class of parametrization for dark energy without divergence

A new class of parametrization of the equation of state of dark energy is proposed in this paper. In contrast with the famous CPL parametrization, the equation of state with this new kind of parametrization does not divergent during the evolution of the Universe even in the future. By using the Markov Chain Monte Carlo (MCMC) method, we perform an observational constraint on two simplest dark energy models belonging to this new class of parametrization with the combined latest observational data from the type Ia supernova compilations including Union2(557), cosmic microwave background, and baryon acoustic oscillation.

Feng, Chao-Jun; Shen, Xian-Yong; Li, Ping; Li, Xin-Zhou, E-mail: fengcj@shnu.edu.cn, E-mail: 1000304237@smail.shnu.edu.cn, E-mail: li57120@126.com, E-mail: kychz@shnu.edu.cn [Shanghai United Center for Astrophysics (SUCA), Shanghai Normal University, 100 Guilin Road, Shanghai 200234, P.R.China (China)

2012-09-01

298

Growth Diagnostics for Dark Energy models and EUCLID forecast

In this work we introduce a new set of parameters $(r_{g}, s_{g})$ involving the linear growth of matter perturbation that can distinguish and constrain different dark energy models very efficiently. Interestingly, for $\\Lambda$CDM model these parameters take exact value $(1,1)$ at all red shifts whereas for models different from $\\Lambda$CDM, they follow different trajectories in the $(r_{g}, s_{g})$ phase plane. By considering the parametrization for the dark energy equation of state ($w$) and for the linear growth rate ($f_{g}$), we show that different dark energy behaviours with similar evolution of the linear density contrast, can produce distinguishable trajectories in the $(r_{g}, s_{g})$ phase plane. Moreover, one can put stringent constraint on these phase plane using future measurements like EUCLID ruling out some of the dark energy behaviours.

Sampurnanand; Anjan A. Sen

2013-01-06

299

Stability of Ghost Dark Energy in CBD Model of Gravity

We study the stability of the ghost dark energy model versus perturbation. Since this kind of dark energy is instable in Einsteinian general relativity theory, then we study a new type of Brans-Dicke theory which has non-minimal coupling with matter which is called chameleon Brans-Dicke (CBD) model of gravity. Due to this coupling the equation of conservation energy is modified. For considering the stability of the model we use the adiabatic squared sound speed, $c_s^2$, whose sign of it determines the stability of the model in which for $c_s^2 >0 $ the model is stable and for $c_s^2 <0 $ the model is instable. However, we study the interacting and non-interacting version of chameleon Brans-Dicke ghost dark energy (CBDGDE) with cold dark matter in non flat FLRW metric. We show that in all cases of investigation the model is stable with a suitable choice of parameters.

Khaled Saaidi

2012-02-18

300

How Sensitive Are Weak Lensing Statistics to Dark Energy Content?

Future weak lensing surveys will directly probe the clustering of dark matter, in addition to providing a test for various cosmological models. Recent studies have provided us with the tools which can be used to construct the complete probability distribution function for convergence fields. It is also possible to construct the bias associated with the hot-spots in convergence maps. These techniques can be used in both the quasi-linear and the highly nonlinear regimes using various well developed numerical methods. We use these results here to study the weak lensing statistics of cosmological models with dark energy. We study how well various classes of dark energy models can be distinguished from models with a cosmological constant. We find that the ratio of the square root of the variance of convergence is complementary to the convergence skewness $S_3$ in probing dark energy equation of state; it can be used to predict the expected difference in weak lensing statistics between various dark energy models, and for choosing optimized smoothing angles to constrain a given class of dark energy models. Our results should be useful for probing dark energy using future weak lensing data with high statistics from galaxy weak lensing surveys and supernova pencil beam surveys.

Dipak Munshi; Yun Wang

2002-06-27

301

Parametrized post-Friedmann framework for interacting dark energy

NASA Astrophysics Data System (ADS)

Dark energy might directly interact with cold dark matter. However, in such a scenario, an early-time large-scale instability occurs occasionally, which may be due to the incorrect treatment for the pressure perturbation of dark energy as a nonadiabatic fluid. To avoid this nonphysical instability, we establish a new framework to correctly calculate the cosmological perturbations in the interacting dark energy models. Inspired by the well-known parametrized post-Friedmann approach, the condition of the dark energy pressure perturbation is replaced with the relationship between the momentum density of dark energy and that of other components on large scales. By reconciling the perturbation evolutions on the large and small scales, one can complete the perturbation equations system. The large-scale instability can be successfully avoided and the well-behaved density and metric perturbations are obtained within this framework. Our test results show that this new framework works very well and is applicable to all the interacting dark energy models.

Li, Yun-He; Zhang, Jing-Fei; Zhang, Xin

2014-09-01

302

Holographic principle and dark energy

We discuss the relationship between holographic entropy bounds and gravitating systems. In order to obtain a holographic energy density, we introduce the Bekenstein-Hawking entropy $S_{\\rm BH}$ and its corresponding energy $E_{\\rm BH}$ using the Friedman equation. We show that the holographic energy bound proposed by Cohen {\\it et al} comes from the Bekenstein-Hawking bound for a weakly gravitating system. Also we find that the holographic energy density with the future event horizon deriving an accelerating universe could be given by vacuum fluctuations of the energy density.

Yun Soo Myung

2004-12-20

303

Probing dark energy using galaxy clustering data

NASA Astrophysics Data System (ADS)

Dark energy is the most important unsolved mystery in cosmology today. Galaxy clustering provides one of the prime probes of dark energy. This work is focused on developing robust analysis techniques for interpreting galaxy clustering data. These are crucial for probing dark energy using galaxy clustering data. First, we present a method to measure the effective distance to z = 0.35, DV(0.35) from the overall shape of the spherically-averaged two-point correlation function (2PCF) of the Sloan Digital Sky Survey Data Release 7 luminous red galaxy sample. We find DV (0.35) = 1428+74-73 Mpc without assuming a dark energy model or a flat Universe. We find that the derived measurement of rs(z d)/DV(0.35) = 0.1143 +/- 0.0030 (the ratio of the sound horizon at the drag epoch to the effective distance to z = 0.35) has tighter constraint and is more robust with respect to possible systematic effects. It is also nearly uncorrelated to O mh2 which might be sensitive to systematic effects. Then, we generalize the method to measure the Hubble parameter, H(z), and angular diameter distance, D A(z), from the two-dimensional 2PCF, and we find H(0.35) = 82.1+4.8-4.9 km s-1 Mpc-1, D A(0.35) = 1048+60-58 Mpc. We also find that the derived measurements of {H(0.35) rs(zd), rs( zd)/DA(0.35)} = {13020 +/- 530(km/s), 0.1518 +/- 0.0062} (with the correlation coefficient r = -0.0584) are nearly uncorrelated, have tighter constraints and are more robust with respect to possible systematic effects. Combining our results with the cosmic microwave background and supernova data, we obtain O k = -0.0004 +/- 0.0070 and w = -0.996 +/- 0.043 (assuming a constant dark energy equation of state). Our results represent the first measurements of H( z) and DA(z) from galaxy clustering data. Our work has significant implications for future surveys in establishing the feasibility of measuring both H( z) and DA(z) from galaxy clustering data.

Chuang, Chia-Hsun

304

The idea that we live near the centre of a large, nonlinear void has attracted attention recently as an alternative to dark energy or modified gravity. We show that an appropriate void profile can fit both the latest cosmic microwave background and supernova data. However, this requires either a fine-tuned primordial spectrum or a Hubble rate so low as to rule these models out. We also show that measurements of the radial baryon acoustic scale can provide very strong constraints. Our results present a serious challenge to void models of acceleration.

J. P. Zibin; A. Moss; D. Scott

2008-09-22

305

The idea that we live near the center of a large, nonlinear void has attracted attention recently as an alternative to dark energy or modified gravity. We show that an appropriate void profile can fit both the latest cosmic microwave background and supernova data. However, this requires either a fine-tuned primordial spectrum or a Hubble rate so low as to rule these models out. We also show that measurements of the radial baryon acoustic scale can provide very strong constraints. Our results present a serious challenge to void models of acceleration. PMID:19113691

Zibin, James P; Moss, Adam; Scott, Douglas

2008-12-19

306

Leptogenesis, Dark Energy, Dark Matter and the neutrinos

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.

Utpal Sarkar

2007-12-17

307

A two measure model of dark energy and dark matter

In this work we construct a unified model of dark energy and dark matter. This is done with the following three elements: a gravitating scalar field, ? with a non-conventional kinetic term, as in the string theory tachyon; an arbitrary potential, V(?); two measures a metric measure ((?g){sup 1/2}) and a non-metric measure (?). The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar field. (ii) The form of the dark energy and dark matter that results from this model is fairly insensitive to the exact form of the scalar field potential.

Guendelman, Eduardo [Department of Physics, Ben-Gurion University, Beer-Sheva (Israel); Singleton, Douglas; Yongram, N., E-mail: guendel@bgu.ac.il, E-mail: dougs@csufresno.edu, E-mail: nattapongy@nu.ac.th [Physics Department, California State University Fresno, Fresno, CA 93740 (United States)

2012-11-01

308

Dark Energy and Neutrino CPT Violation

In this paper we study the dynamical CPT violation in the neutrino sector induced by the dark energy of the Universe. Specifically we consider a dark energy model where the dark energy scalar derivatively interacts with the right-handed neutrinos. This type of derivative coupling leads to a cosmological CPT violation during the evolution of the background field of the dark energy. We calculate the induced CPT violation of left-handed neutrinos and find the CPT violation produced in this way is consistent with the present experimental limit and sensitive to the future neutrino oscillation experiments, such as the neutrino factory.

Pei-Hong Gu; Xiao-Jun Bi; Xinmin Zhang

2005-11-03

309

Entropy-Corrected Holographic Dark Energy

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).

Hao Wei

2009-09-07

310

Dark energy interacting with dark matter and unparticle

We study dynamical behaviors of the dark energy models interacting with dark matter and unparticle in the standard flat FRW cosmology. We considered four different interacting models and examined the stability of the critical points. We find that there exist late-time scaling attractors corresponding to an accelerating Universe and the alleviation of the coincidence problem depends on the choice of parameters in the models.

Songbai Chen; Jiliang Jing

2009-07-16

311

Dark matter and dark energy from quark bag model

We calculate the present expansion of our Universe endowed with relict colored objects quarks and gluons that survived hadronization either as isolated islands of quark-gluon ''nuggets'' or spread uniformly in the Universe. In the first scenario, the QNs can play the role of dark matter. In the second scenario, we demonstrate that uniform colored objects can play the role of dark energy providing the late-time accelerating expansion of the Universe.

Brilenkov, Maxim [Department of Theoretical Physics, Odessa National University, Dvoryanskaya st. 2, Odessa 65082 (Ukraine); Eingorn, Maxim [Physics Department, North Carolina Central University, Fayetteville st. 1801, Durham, North Carolina 27707 (United States); Jenkovszky, Laszlo [Bogolyubov Institute for Theoretical Physics, Kiev 03680 (Ukraine); Zhuk, Alexander, E-mail: maxim.brilenkov@gmail.com, E-mail: maxim.eingorn@gmail.com, E-mail: jenk@bitp.kiev.ua, E-mail: ai.zhuk2@gmail.com [Astronomical Observatory, Odessa National University, Dvoryanskaya st. 2, Odessa 65082 (Ukraine)

2013-08-01

312

The Dark Energy Camera (DECam)

In this paper we describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). It consists of a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), a modern data acquisition and control system and the associated infrastructure for operation in the prime focus cage. The focal plane includes of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of view and 12 smaller 2K x 2K CCDs for guiding, focus and alignment. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.

K. Honscheid; D. L. DePoy; for the DES Collaboration

2008-10-20

313

Generalized Chaplygin Gas Model: Dark Energy - Dark Matter Unification and CMBR Constraints

The generalized Chaplygin gas (GCG) model allows for an unified description of the recent accelerated expansion of the Universe and the evolution of energy density perturbations. This dark energy - dark matter unification is achieved through an exotic background fluid whose equation of state is given by $p = - A/\\rho^{\\alpha}$, where $A$ is a positive constant and $0 < \\alpha \\le 1$. Stringent constraints on the model parameters can be obtained from recent WMAP and BOOMERanG bounds on the locations of the first few peaks and troughs of the Cosmic Microwave Background Radiation (CMBR) power spectrum as well as SNe Ia data.

M. C. Bento; O. Bertolami; A. A. Sen

2003-05-22

314

Unification of Gravitation, Gauge Field and Dark Energy

This paper is composed of two correlated topics: 1. unification of gravitation with gauge fields; 2. the coupling between the daor field and other fields and the origin of dark energy. After introducing the concept of ``daor field" and discussing the daor geometry, we indicate that the complex daor field has two kinds of symmetry transformations. Hence the gravitation and SU(1,3) gauge field are unified under the framework of the complex connection. We propose a first-order nonlinear coupling equation of the daor field, which includes the coupling between the daor field and SU(1,3) gauge field and the coupling between the daor field and the curvature, and from which Einstein's gravitational equation can be deduced. The cosmological observations imply that dark energy cannot be zero, and which will dominate the doom of our Universe. The real part of the daor field self-coupling equation can be regarded as Einstein's equation endowed with the cosmological constant. It shows that dark energy originates from the self-coupling of the space-time curvature, and the energy-momentum tensor is proportional to the square of coupling constant \\lambda. The dark energy density given by our scenario is in agreement with astronomical observations. Furthermore, the Newtonian gravitational constant G and the coupling constant \\epsilon of gauge field satisfy G= \\lambda^{2}\\epsilon^{2}.

Xin-Bing Huang

2005-08-26

315

Imperfect dark energy from kinetic gravity braiding

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.

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); Pujolŕs, 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

316

Nonparametric dark energy reconstruction from supernova data.

Understanding the origin of the accelerated expansion of the Universe poses one of the greatest challenges in physics today. Lacking a compelling fundamental theory to test, observational efforts are targeted at a better characterization of the underlying cause. If a new form of mass-energy, dark energy, is driving the acceleration, the redshift evolution of the equation of state parameter w(z) will hold essential clues as to its origin. To best exploit data from observations it is necessary to develop a robust and accurate reconstruction approach, with controlled errors, for w(z). We introduce a new, nonparametric method for solving the associated statistical inverse problem based on Gaussian process modeling and Markov chain Monte Carlo sampling. Applying this method to recent supernova measurements, we reconstruct the continuous history of w out to redshift z=1.5. PMID:21231517

Holsclaw, Tracy; Alam, Ujjaini; Sansó, Bruno; Lee, Herbert; Heitmann, Katrin; Habib, Salman; Higdon, David

2010-12-10

317

Topology and dark energy: testing gravity in voids.

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. PMID:24483641

Spolyar, Douglas; Sahlén, Martin; Silk, Joe

2013-12-13

318

Nonlocal String Tachyon as a Model for Cosmological Dark Energy

There are many different phenomenological models describing the cosmological dark energy and accelerating Universe by choosing adjustable functions. In this paper we consider a specific model of scalar tachyon field which is derived from the NSR string field theory and study its cosmological applications. We find that in the effective field theory approximation the equation of state parameter w <

I. Ya

319

Hessence: a new view of quintom dark energy

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

Hao Wei; Rong-Gen Cai; Ding-Fang Zeng

2005-01-01

320

Dark energy: Vacuum fluctuations, the effective phantom phase, and holography

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 omega being less than -1 ) emerges even

Emilio Elizalde; Shin'ichi Nojiri; S. D. Odintsov; Peng Wang

2005-01-01

321

Cosmological Surprises from Braneworld models of Dark Energy

Properties of Braneworld models of dark energy are reviewed. Braneworld models admit the following interesting possibilities: (i) The effective equation of state can be w -1. In the former case the expansion of the universe is well behaved at all times and the universe does not run into a future `Big Rip' singularity which is usually encountered by Phantom models.

Varun Sahni

2005-01-01

322

The "Big Wave" theory for Dark Energy Blake Temple

The "Big Wave" theory for Dark Energy Blake Temple (Joint work with Joel Smoller) Abstract. We to the displacement of nearby galaxies by a wave that propagated during the radiation phase of the Big Bang equations of General Relativity (GR) that contain the standard model during the radiation phase of the Big

Temple, Blake

323

Dark Energy and the Cosmological Constant: A Brief Introduction

ERIC Educational Resources Information Center

The recently observed acceleration of the expansion of the universe is a topic of intense interest. The favoured causes are the "cosmological constant" or "dark energy". The former, which appears in the Einstein equations as the term [lambda]g[subscript [mu]v], provides an extremely simple, well-defined mechanism for the acceleration. However,

Harvey, Alex

2009-01-01

324

GALAXY CLUSTERS AS A PROBE OF EARLY DARK ENERGY

We study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and show that these models may be successfully constrained using future observations of galaxy clusters, in particular the redshift abundance, and the Sunyaev-Zel'dovich (SZ) power spectrum. We make predictions for EDE models, as well as {Lambda}CDM for incoming X-ray (eROSITA) and microwave (South Pole Telescope) observations. We show that galaxy clusters' mass function and the SZ power spectrum will put strong constraints both on the equation of state of dark energy today and the redshift at which EDE transits to present-day {Lambda}CDM-like behavior for these models, thus providing complementary information to the geometric probes of dark energy. Not including perturbations in EDE models leads to those models being practically indistinguishable from {Lambda}CDM. An MCMC analysis of future galaxy cluster surveys provides constraints for EDE parameters that are competitive with and complementary to background expansion observations such as supernovae.

Alam, Ujjaini [ISR-1, ISR Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Lukic, Zarija; Bhattacharya, Suman, E-mail: ujjaini@lanl.gov, E-mail: zarija@lanl.gov, E-mail: sumanb@lanl.gov [T-2, T Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2011-02-01

325

Primordial Magnetic Fields from Dark Energy

Evidences indicate that the dark energy constitutes about two thirds of the critical density of the universe. If the dark energy is an evolving pseudo scalar field that couples to electromagnetism, a cosmic magnetic seed field can be produced via spinoidal instability during the formation of large-scale structures.

Da-Shin Lee; Wolung Lee; Kin-Wang Ng

2002-08-30

326

The case for dynamical dark energy revisited

We investigate the behaviour of dark energy using the recently released supernova data of Riess et al 2004 and a model independent parametrization for dark energy (DE). We find that, if no priors are imposed on Omega0m and h, DE which evolves with time provides a better fit to the SNe data than LambdaCDM. This is also true if we

Ujjaini Alam; Varun Sahni; A. A. Starobinsky

2004-01-01

327

Probing dark energy: Methods and strategies

The presence of dark energy in the Universe is inferred directly from the accelerated expansion of the Universe, and, indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Dark energy contributes about two-thirds of the critical density, is smoothly distributed, has large negative pressure, and is very mysterious. For now, all of its discernible cosmological consequences follow from its effect

Dragan Huterer; Michael S. Turner

2001-01-01

328

Singularity-free dark energy star

We propose a model for an anisotropic dark energy star where we assume that the radial pressure exerted on the system due to the presence of dark energy is proportional to the isotropic perfect fluid matter density. We discuss various physical features of our model and show that the model satisfies all the regularity conditions and stable as well as singularity-free.

Farook Rahaman; Anil Kumar Yadav; Saibal Ray; Raju Maulick; Ranjan Sharma

2011-02-07

329

The Dark Energy Survey instrument design

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 {approx}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&D is underway and delivery of DECam to CTIO is scheduled for 2009.

Flaugher, B.; /Fermilab

2006-05-01

330

Examining the evidence for dynamical dark energy.

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 z~0.25 to 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 ?CDM model by observations such as Planck and Euclid-like surveys. PMID:23215174

Zhao, Gong-Bo; Crittenden, Robert G; Pogosian, Levon; Zhang, Xinmin

2012-10-26

331

[Dark matter and dark energy of the universe].

At the turn of the 20th Century, the Universe was thought to consist of our solar system, the Sun, planets, satellites and comets, floating under the Milky Way. The astronomers were ignorant of the existence of galaxies, clusters, quasars and black holes. Over the last ten years the Cosmology has made remarkable progress in our understanding of the composition of the Universe: 23 per cent is in an unknown form called dark matter; 73 per cent in another form called dark energy; 3 per cent is made of free hydrogen and helium atoms; 0.5 per cent makes up all the light we see in the night including the stars, clusters and superclusters; 0.3 per cent is in free neutrino particles; and finally, 0.03 per cent is in the heavier nuclei of which the Sun, the Earth and ourselves are made. In this work we study specially the dark matter and the dark energy. The first one appears to be attached to galaxies, and astronomers agree that it is cold, meaning that the particles that make up that matter are not moving fast. Very recently astronomers discovered that a tremendous amount of the so-cahled dark energy exists and that it is pushing and accelerating the expansion of the Universe. Should this expansion continue for another 14,000 million years, the sky will darken with only a handful of galaxies remaining visible. PMID:16463572

Aguilar Peris, José

2005-01-01

332

Bistable dark solitons of a cubic-quintic Helmholtz equation

We provide a report on exact analytical bistable dark spatial solitons of a nonlinear Helmholtz equation with a cubic-quintic refractive-index model. Our analysis begins with an investigation of the modulational instability characteristics of Helmholtz plane waves. We then derive a dark soliton by mapping the desired asymptotic form onto a uniform background field and obtain a more general solution by deploying rotational invariance laws in the laboratory frame. The geometry of the new soliton is explored in detail, and a range of new physical predictions is uncovered. Particular attention is paid to the unified phenomena of arbitrary-angle off-axis propagation and nondegenerate bistability. Crucially, the corresponding solution of paraxial theory emerges in a simultaneous multiple limit. We conclude with a set of computer simulations that examine the role of Helmholtz dark solitons as robust attractors.

Christian, J. M.; McDonald, G. S.; Chamorro-Posada, P. [Joule Physics Laboratory, School of Computing, Science and Engineering, Materials and Physics Research Centre, University of Salford, Salford M5 4WT (United Kingdom); Departamento de Teoria de la Senal y Comunicaciones e Ingenieria Telematica, Universidad de Valladolid, ETSI Telecomunicacion, Campus Miguel Delibes s/n, 47011 Valladolid (Spain)

2010-05-15

333

Is there supernova evidence for dark energy metamorphosis?

We reconstruct the equation of state w(z) of dark energy (DE) using a recently released data set containing 172 Type Ia supernovae (SNe) without assuming the prior w(z) >=-1 (in contrast to previous studies). We find that DE evolves rapidly and metamorphoses from dust-like behaviour at high z (w~= 0 at z~ 1) to a strongly negative equation of state

Ujjaini Alam; Varun Sahni; Tarun Deep Saini; A. A. Starobinsky

2004-01-01

334

CMB lensing constraints on neutrinos and dark energy

Signatures of lensing of the cosmic microwave background radiation by gravitational potentials along the line of sight carry with them information on the matter distribution, neutrino masses, and dark energy properties. We examine the constraints that Planck, PolarBear, and CMBpol future data, including from the B-mode polarization or the lensing potential, will be able to place on these quantities. We simultaneously fit for neutrino mass and dark energy equation of state including time variation and early dark energy density, and compare the use of polarization power spectra with an optimal quadratic estimator of the lensing. Results are given as a function of systematics level from residual foreground contamination. A realistic CMBpol experiment can effectively constrain the sum of neutrino masses to within 0.05 eV and the fraction of early dark energy to 0.002. We also present a surprisingly simple prescription for calculating dark energy equation of state constraints in combination with supernova distances from JDEM.

Putter, Roland de; Zahn, Oliver; Linder, Eric V. [Berkeley Lab and Berkeley Center for Cosmological Physics, University of California, Berkeley, California 94720 (United States)

2009-03-15

335

A Dust Universe Solution to the Dark Energy Problem

Astronomical measurements of the Omegas for mass density, cosmological constant lambda and curvature k are shown to be sufficient to produce a unique and detailed cosmological model describing dark energy influences based on the Friedman equations. The equation of state Pressure turns out to be identically zero at all epochs as a result of the theory. The partial omega, for dark energy, has the exact value, minus unity, as a result of the theory and is in exact agreement with the astronomer's measured value. Thus this measurement is redundant as it does not contribute to the construction of the theory for this model. Rather, the value of this omega is predicted from the theory. The model has the characteristic of changing from deceleration to acceleration at exactly half the epoch time at which the input measurements are taken. This is a mysterious feature of the model for which no explanation has so far been found. An attractive feature of the model is that the acceleration change time occurs at a red shift of approximately 0.8 as predicted by the dark energy workers. Using a new definition of dark energy density it is shown that the contribution of this density to the acceleration process is via a negative value for the gravitational constant, -G, exactly on a par with gravitational mass which occurs via the usual positive value for G. This paper also contains an appendix on dark energy dynamics with its own abstract.

James G. Gilson

2010-01-14

336

Inferring "Dark Matter" and "Dark Energy" from Videos Dan Xie , Sinisa Todorovic

Inferring "Dark Matter" and "Dark Energy" from Videos Dan Xie , Sinisa Todorovic , and Song.g., grass lawns). Therefore, functional objects can be viewed as "dark matter", emanating "dark energy to approach "dark matter" and thus sat- isfy their needs, where their motions are subject to a com- posite

Zhu, Song Chun

337

The possible nature of dark energy and dark matter Nathalie Olivi-Tran1,2

The possible nature of dark energy and dark matter Nathalie Olivi-Tran1,2 1 Laboratoire Charles: Nathalie.Olivi-Tran@univ-montp2.fr (Dated: July 23, 2012) Abstract The nature of dark matter is linked the nature of time. Keywords: dark matter; dark energy; nature of time 1 hal-00719998,version1-23Jul2012

Paris-Sud XI, UniversitĂŠ de

338

Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios T. Jenke,1,*

Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios T. Jenke,1,* G) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp > 3.7 Ă? 10-16 (5 this work, we link these new measurements to dark matter and dark energy searches. Observational cosmology

Rotter, Stefan

339

Vacuum quantum fluctuation energy in expanding universe and dark energy

This article is based on the Planckon densely piled vacuum model and the principle of cosmology. With the Planck era as initial conditions and including the early inflation, we have solved the Einstein-Friedmann equations to describe the evolution of the universe. The results are: 1) the ratio of the dark energy density to the vacuum quantum fluctuation energy density is $\\frac{{{\\rho }_{de}}}{{{\\rho }_{vac}}}\\sim{{(\\frac{{{t}_{P}}}{{{T}_{0}}})}^{2}}\\sim{{10}^{-122}} $; 2) at the inflation time ${{t}_{\\inf }}={{10}^{-35}}s$, the calculated universe radiation energy density is $\\rho ({{t}_{\\inf }})\\sim{{10}^{-16}}{{\\rho }_{vac}}$ and the corresponding temperature is ${{E}_{c}}\\sim{{10}^{15}}GeV$ consistent with the GUT phase transition temperature; 3) the expanding universe with vacuum as its environment is a non-equilibrium open system constantly exchanging energy with vacuum; during its expansion, the Planckons in the universe lose quantum fluctuation energy and create the cosmic expansion quanta-cosmons, the energy of cosmons is the lost part of the vacuum quantum fluctuation energy and contributes to the universe energy with the calculated value ${{E}_{\\cos mos}}={{10}^{22}}{{M}_{\\otimes }}{{c}^{2}}$ (where ${{M}_{\\otimes }}$ is solar mass); 4) the total energy of the universe, namely the negative gravity energy plus the positive universe energy is zero; 5) the negative gravity potential and the gravity acceleration related to the creation of cosmons are derived with the nature of outward repulsive force, indicating that the cosmon may be the candidate of the dark energy quantum; 6) both the initial Planck era solution and the infinite asymptotic solution of the Einstein-Friedman equations are unstable: the former tends to expand and the latter tends to shrink, so that the Einstein-Friedman universe will undergo a cyclic evolution of successive expansion and shrinking.

Shun-Jin Wang

2013-01-02

340

Possible dark energy imprints in the gravitational wave spectrum of mixed neutron-dark-energy stars

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.

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

341

Physical evidence for dark energy

The authors present measurements of the angular cross-correlation between luminous red galaxies from the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy Probe. They find a statistically significant achromatic positive correlation between these two data sets, which is consistent with the expected signal from the late Integrated Sachs-Wolfe (ISW) effect. they do not detect any anti-correlation on small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ) effect, although they do see evidence for some SZ effect for their highest redshift samples. Assuming a flat universe, their preliminary detection of the ISW effect provides independent physical evidence for the existence of dark energy.

Scranton, Ryan; Connolly, Andrew J.; Nichol, Robert C.; Stebbins, Albert; Szapudi, Istvan; Eisenstein, Daniel J.; Afshordi, Niayesh; Budavari, Tamas; Csabai, Istvan; Frieman, Joshua A.; Gunn, James E.; Johnston, David; Loh, Yeong-Shang; Lupton, Robert H.; Miller, Christopher J.; Sheldon, Erin Scott; Sheth, Ravi K.; Szalay, Alexander S.; Tegmark, Max; Xu, Yongzhong; Anderson, Scott F.; /Pittsburgh U. /Carnegie Mellon U. /Fermilab /Inst. Astron., Honolulu /Arizona U., Astron. Dept. - Steward Observ. /Princeton U.

2003-07-01

342

Physical Evidence for Dark Energy

We present measurements of the angular cross-correlation between luminous red galaxies from the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy Probe. We find a statistically significant achromatic positive correlation between these two data sets, which is consistent with the expected signal from the late Integrated Sachs-Wolfe (ISW) effect. We do not detect any anti-correlation on small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ) effect, although we do see evidence for some SZ effect for our highest redshift samples. Assuming a flat universe, our preliminary detection of the ISW effect provides independent physical evidence for the existence of dark energy.

R. Scranton; A. J. Connolly; R. C. Nichol; A. Stebbins; I. Szapudi; D. J. Eisenstein; N. Afshordi; T. Budavari; I. Csabai; J. A. Frieman; J. E. Gunn; D. Johnston; Y. Loh; R. H. Lupton; C. J. Miller; E. S. Sheldon; R. S. Sheth; A. S. Szalay; M. Tegmark; Y. Xu

2003-07-20

343

Holographic tachyon model of dark energy

In this paper we consider a correspondence between the holographic dark energy density and tachyon energy density in FRW universe. Then we reconstruct the potential and the dynamics of the tachyon field which describe tachyon cosmology.

M R Setare

2007-05-24

344

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.

Sussman, Roberto A. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico (ICN-UNAM), A. P. 70--543, 04510 Mexico D. F. (Mexico)

2009-01-15

345

Equation of state of dark matter after Planck data

NASA Astrophysics Data System (ADS)

In this paper, we loosen the zero equation of state of dark matter to a constant wdm. By using the currently available cosmic observations, which include the type-Ia supernovae, the baryon acoustic oscillation, the WiggleZ measurements of matter power spectrum, and the cosmic microwave background radiation from the firs release of Planck data through the Markov chain Monte Carlo method, we found the equation of state of dark matter in 3? regions: wdm=0.000707-0.000747-0.00149-0.00196+0.000746+0.00146+0.00193. The difference between the minimum of ?2 between the ?CDM and ?wDM models is ??min?2=0.446 for one extra model parameter wdm. Although the currently available cosmic observations favor the ?wDM mildly, no significant deviation from the ?CDM model is found in 1? regions.

Xu, Lixin; Chang, Yadong

2013-12-01

346

Dark Energy from Fifth-Dimensional Brans-Dicke Theory

NASA Astrophysics Data System (ADS)

Following the approach of the induced-matter theory, we investigate the cosmological implications of a five-dimensional Brans-Dicke (BD) theory, and propose to explain the acceleration of the universe. After inducing in a four-dimensional hypersurface, we classify the energy-momentum tensor into two parts in a way that, one part represents all kind of the matter (the baryonic and dark) and the other one contains every extra terms emerging from the scale factor of the fifth dimension and the scalar field, which we consider as the energy-momentum tensor of dark energy. We also separate the energy-momentum conservation equation into two conservation equations, one for matter and the other for dark energy. We perform this procedure for different cases, without interacting term and with two particular (suitable) interacting terms between the two parts. By assuming the parameter of the state equation for dark energy to be constant, the equations of the model admit the power-law solutions. Though, the noninteracting case does not give any accelerated universe, but the interacting cases give both decelerated and accelerated universes. For the interacting cases, we figure out analytically the acceptable ranges of some parameters of the model, and also investigate the data analysis to test the model parameter values consistency with the observational data of the distance modulus of 580 SNe Ia compiled in Union2.1. For one of these interacting cases, the best fitted values suggest that BD coupling constant (?) is ? -7.75, however, it also gives the state parameter of dark energy (wX) equal to ? -0.67. In addition, the model gives the Hubble and deceleration parameters at the present time to be H? ? 69.4 (km/s)/Mpc and q? ? -0.38 (within their confidence intervals), where the scale factor of the fifth dimension shrinks with the time.

Bahrehbakhsh, Amir F.; Farhoudi, Mehrdad; Vakili, Hajar

2013-08-01

347

Nonflat time-variable dark energy cosmology

We generalize the time-variable dark energy scalar field $\\Phi$ model ($\\Phi$CDM) to nonflat space. We show that even in the space-curvature-dominated epoch the scalar field solution is a time-dependent fixed point or attractor, with scalar field energy density that grows relative to the energy density in spatial curvature. This is the first example of a physically consistent and complete model of dynamical dark energy in a nonflat geometry.

Anatoly Pavlov; Shawn Westmoreland; Khaled Saaidi; Bharat Ratra

2013-12-19

348

A quantum model of dark energy

We propose a quantum model of dark energy. The proposed candidate for dark energy is gluon field, as is well-known, gluons are the elementary particles. We assume that gluons may not be completely massless but have tiny masses, thus the gluon field can provide a non-zero energy-momentum tensor. This model corresponds to Einstein's cosmological constant which is one of the generally accepted models for dark energy. Besides the gluon field, we also discuss the properties of electroweak boson field and compare our results with previous known results.

Chang-Yu Zhu; Heng Fan

2009-11-20

349

Ray-tracing simulations of coupled dark energy models

NASA Astrophysics Data System (ADS)

Dark matter and dark energy are usually assumed to couple only gravitationally. An extension to this picture is to model dark energy as a scalar field coupled directly to cold dark matter. This coupling leads to new physical effects, such as a fifth force and a time-dependent dark matter particle mass. In this work we examine the impact that coupling has on weak lensing statistics by constructing realistic simulated weak lensing maps using ray-tracing techniques through N-body cosmological simulations. We construct maps for different lensing quantities, covering a range of scales from a few arcminutes to several degrees. The concordance ? cold dark matter (?CDM) model is compared to different coupled dark energy models, described either by an exponential scalar field potential (standard coupled dark energy scenario) or by a SUGRA potential (bouncing model). We analyse several statistical quantities and our results, with sources at low redshifts are largely consistent with previous work on cosmic microwave background lensing by Carbone et al. The most significant differences from the ?CDM model are due to the enhanced growth of the perturbations and to the effective friction term in non-linear dynamics. For the most extreme models, we see differences in the power spectra up to 40 per cent compared to the ?CDM model. The different time evolution of the linear matter overdensity can account for most of the differences, but when controlling for this using a ?CDM model having the same normalization, the overall signal is smaller due to the effect of the friction term appearing in the equation of motion for dark matter particles.

Pace, Francesco; Baldi, Marco; Moscardini, Lauro; Bacon, David; Crittenden, Robert

2015-02-01

350

Can we test Dark Energy with Running Fundamental Constants ?

We investigate a link between the running of the fine structure constant $\\alpha$ and a time evolving scalar dark energy field. Employing a versatile parameterization for the equation of state, we exhaustively cover the space of dark energy models. Under the assumption that the change in $\\alpha$ is to first order given by the evolution of the Quintessence field, we show that current Oklo, Quasi Stellar Objects and Equivalence Principle observations restrict the model parameters considerably stronger than observations of the Cosmic Microwave Background, Large Scale Structure and Supernovae Ia combined.

Michael Doran

2005-04-26

351

Constraining Perturbative Early Dark Energy with Current Observations

NASA Astrophysics Data System (ADS)

In this work, we study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and constrain these models using current observations. We consider EDE models in which the dark energy equation of state is at least wm >~ -0.1 at early times, which could lead to an EDE density of up to ?_{{DE}} (z_CMB)= 0.03 ?_m(z_CMB). Our analysis shows that marginalizing over the non-DE parameters such as ?m, H 0, andns , current CMB observations alone can constrain the scale factor of transition from EDE to late-time dark energy to at >~ 0.44 and width of transition to ? t <~ 0.37. The equation of state at present is somewhat weakly constrained to w 0 <~ -0.6, if we allow H 0 < 60 km s-1 Mpc-1. Taken together with other observations, such as SNe, Hubble Space Telescope, and Sloan Digital Sky Survey luminous red galaxies, w 0 is constrained much more tightly to w 0 <~ -0.9, while redshift of transition and width of transition are also tightly constrained to at <~ 0.19 and? t <~ 0.21. The evolution of the equation of state for EDE models is thus tightly constrained to ?CDM-like behavior at low redshifts. Incorrectly assuming dark energy perturbations to be negligible leads to different constraints on the equation of state parametersw 0 <~ -0.8, at <~ 0.33, and? t <~ 0.31, thus highlighting the necessity of self-consistently including dark energy perturbations in the analysis. If we allow the spatial curvature to be a free parameter, then the constraints are relaxed to w 0 <~ -0.77, at <~ 0.35, and? t <~ 0.35 with -0.014 < ?? < 0.031 for CMB + other observations. For perturbed EDE models, the 2? lower limit on ?8 (?8 >= 0.59) is much lower than that in ?CDM (?8 >= 0.72), thus raising the interesting possibility of discriminating EDE from ?CDM using future observations such as halo mass functions or the Sunyaev-Zeldovich power spectrum.

Alam, Ujjaini

2010-05-01

352

Quintom dark energy models with nearly flat potentials

We examine quintom dark energy models, produced by the combined consideration of a canonical and a phantom field, with nearly flat potentials and dark energy equation-of-state parameter w{sub DE} close to -1. We find that all such models converge to a single expression for w{sub DE}(z), depending only on the initial field values and their derivatives. We show that this quintom paradigm allows for a description of the transition through -1 in the near cosmological past. In addition, we provide the necessary conditions for the determination of the direction of the -1 crossing.

Setare, M. R.; Saridakis, E. N. [Department of Science, Payame Noor University, Bijar (Iran, Islamic Republic of); Department of Physics, University of Athens, GR-15771 Athens (Greece)

2009-02-15

353

Motivated by the observed cosmic matter distribution, we present the following conjecture: due to the formation of voids and opaque structures, the average matter density on the path of the light from the well-observed objects changes from Omega_M ~ 1 in the homogeneous early universe to Omega_M ~ 0 in the clumpy late universe, so that the average expansion rate increases along our line of sight from EdS expansion Ht ~ 2/3 at high redshifts to free expansion Ht ~ 1 at low redshifts. To calculate the modified observable distance-redshift relations, we introduce a generalized Dyer-Roeder method that allows for two crucial physical properties of the universe: inhomogeneities in the expansion rate and the growth of the nonlinear structures. By treating the transition redshift to the void-dominated era as a free parameter, we find a phenomenological fit to the observations from the CMB anisotropy, the position of the baryon oscillation peak, the magnitude-redshift relations of type Ia supernovae, the local Hubble flow and the nucleosynthesis, resulting in a concordant model of the universe with 90% dark matter, 10% baryons, no dark energy, 15 Gyr as the age of the universe and a natural value for the transition redshift z_0=0.35. Unlike a large local void, the model respects the cosmological principle, further offering an explanation for the late onset of the perceived acceleration as a consequence of the forming nonlinear structures. Additional tests, such as quantitative predictions for angular deviations due to an anisotropic void distribution and a theoretical derivation of the model, can vindicate or falsify the interpretation that light propagation in voids is responsible for the perceived acceleration.

Teppo Mattsson

2007-11-27

354

Dark Energy and Matter Evolution from Lensing Tomography

Reconstructed from lensing tomography, the evolution of the dark matter density field in the well-understood linear regime can provide model-independent constraints on the growth function of structure and the evolution of the dark energy density. We examine this potential in the context that high-redshift cosmology has in the future been fixed by CMB measurements. We construct sharp tests for the existence of multiple dark matter components or a dark energy component that is not a cosmological constant. These functional constraints can be transformed into physically motivated model parameters. From the growth function, the fraction of the dark matter in a smooth component, such as a light neutrino, may be constrained to a statistical precision of sigma(f)= 0.0006 fsky^{-1/2} by a survey covering a fraction of sky fsky with redshift resolution dz=0.1. For the dark energy, a parameterization in terms of the present energy density Omega_{DE}, equation of state w and its redshift derivative w', the constraints correspond to sigma(w)=0.016 fsky^{-1/2} and a degenerate combination of the other two parameters. For a fixed Omega_{DE}, sigma(w') = 0.046 fsky^{-1/2}; for Omega_{DE} marginalized, sigma(w') = 0.069 fsky^{-1/2}.

Wayne Hu

2002-08-05

355

Revealing the Nature of Dark Energy Using Bayesian Evidence

We apply the Bayesian concept of `evidence' to reveal systematically the nature of dark energy from present and future supernova luminosity distance measurements. We express the unknown dark energy equation of state w(z) as a low order polynomial in redshift and use evidence to find the polynomial order, thereby establishing the minimum order required by the data. We apply this method to the current supernova data, and with a prior -1 < w(z) < 1 and Omega_m = 0.3 \\pm 0.05, obtain a large probability of 91% for the cosmological constant model, with the remaining 9% assigned to the two more complex models tested. We also investigate the use of evidence for future supernova data sets such as distances obtainable from surveys like the Supernova Acceleration Probe (SNAP). Given a low uncertainty on the present day matter density we find that, if the underlying dark energy model is only modestly evolving, then a constant $w(z)$ fit is sufficient. However, if the evolution of the dark energy equation of state to linear order is larger than |w_1| ~ 0.5, then the evolution can be established with statistical significance. For models where we can assume the prior -1 < w(z) < 1, the correct polynomial order can be established even for modestly evolving equations of state.

T. D. Saini; J. Weller; S. L. Bridle

2003-05-28

356

An investigation of cosmic dark energy using type Ia supernovae

NASA Astrophysics Data System (ADS)

The ESSENCE project is a 5-year observational program with the goal of discovering ~ 200 type Ia supernovae and measuring their luminosity distances and redshifts in order to better constrain the equation of state of the cosmic Dark Energy. There exists today compelling evidence from at least three independent lines of investigation (type Ia supernovae, the cosmic microwave background, and large scale structure measurements) for the presence of "dark energy" in the universe, which in recent times has fueled an acceleration in the cosmic expansion rate. A number of explanations for the physics of the dark energy have been proposed, such as a cosmological constant or a scalar field ("quintessence"). By constraining the equation of state., we can begin to test these models. In particular, testing whether w = -1 allows us to determine whether or not a cosmological constant is consistent with observations. In its first 3 years of operation at the Cerro Tololo 4m telescope in Chile, the project has successfully discovered 88 type Ia supernovae. We describe here the work done to establish the observing strategy for the survey and the software used to rapidly reduce nightly data and identify candidate supernovae. We also provide a detailed description of the photometric calibration of these data and the attendant sources of systematic error. We then describe the estimation of luminosity distances to these objects and present the cosmological analysis of these data. We give preliminary constraints on the dark energy equation of state parameter, w , and discuss sources of systematic error.

Miknaitis, Gajus A.

357

Dark Energy: Observational Evidence and Theoretical Models

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.

Novosyadlyj, B; Shtanov, Yu; Zhuk, A

2015-01-01

358

Fluid Mechanics Explains Cosmology, Dark Matter, Dark Energy, and Life

Observations of the interstellar medium by the Herschel, Planck etc. infrared satellites throw doubt on standard {\\Lambda}CDMHC cosmological processes to form gravitational structures. According to the Hydro-Gravitational-Dynamics (HGD) cosmology of Gibson (1996), and the quasar microlensing observations of Schild (1996), the dark matter of galaxies consists of Proto-Globular-star-Cluster (PGC) clumps of Earth-mass primordial gas planets in metastable equilibrium since PGCs began star production at 0.3 Myr by planet mergers. Dark energy and the accelerating expansion of the universe inferred from SuperNovae Ia are systematic dimming errors produced as frozen gas dark matter planets evaporate to form stars. Collisionless cold dark matter that clumps and hierarchically clusters does not exist. Clumps of PGCs began diffusion from the Milky Way Proto-Galaxy upon freezing at 14 Myr to give the Magellanic Clouds and the faint dwarf galaxies of the 10^22 m diameter baryonic dark matter Galaxy halo. The first stars persist as old globular star clusters (OGCs). Water oceans and the biological big bang occurred at 2-8 Myr. Life inevitably formed and evolved in the cosmological primordial organic soup provided by 10^80 big bang planets and their hot oceans as they gently merged to form larger binary planets and small binary stars.

Carl H. Gibson

2012-11-02

359

Dark Matter and Dark Energy in the Universe

For the first time, we have a plausible and complete accounting of matter and energy in the Universe. Expressed a fraction of the critical density it goes like this: neutrinos, between 0.3% and 15%; stars, between 0.3% and 0.6%; baryons (total), 5% ą 0.5%; matter (total), 40% ą 10%; smooth, dark energy, 80% ą 20%; totaling to the critical density

Michael S. Turner

2000-01-01

360

Report of the Dark Energy Task Force

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

Andreas Albrecht; Gary Bernstein; Robert Cahn; Wendy L. Freedman; Jacqueline Hewitt; Wayne Hu; John Huth; Marc Kamionkowski; Edward W. Kolb; Lloyd Knox; John C. Mather; Suzanne Staggs; Nicholas B. Suntzeff

2006-01-01

361

Instability of holographic dark energy models

We investigate the difference between holographic dark energy, Chaplygin gas, and tachyon model with constant potential. For this purpose, we examine their squared speeds of sound which are evaluated to zeroth order in perturbation theory and hence depends only on time. We find that the squared speed for holographic dark energy is always negative when choosing the future event horizon as the IR cutoff, while those for Chaplygin gas and tachyon are non-negative. This means that the perfect fluid for holographic dark energy is classically unstable. Hence the holographic interpretation for Chaplygin gas and tachyon is problematic.

Yun Soo Myung

2007-07-20

362

Spinor Dark Energy and Cosmological Coincidence Problem

Recently, the so-called Elko spinor field has been proposed to be a candidate of dark energy. It is a non-standard spinor and has unusual properties. When the Elko spinor field is used in cosmology, its unusual properties could bring some interesting consequences. In the present work, we discuss the cosmological coincidence problem in the spinor dark energy models by using the dynamical system method. Our results show that the cosmological coincidence problem should be taken to heart in the investigations of spinor dark energy models.

Hao Wei

2010-12-20

363

Is Hubble's Expansion due to Dark Energy

{\\it The universe is expanding} is known (through Galaxy observations) since 1929 through Hubble's discovery ($V = H D$). Recently in 1999, it is found (through Supernovae observations) that the universe is not simply expanding but is accelerating too. We, however, hardly know only $4\\%$ of the universe. The Wilkinson Microwave Anisotropy Probe (WMAP) satellite observational data suggest $73\\%$ content of the universe in the form of dark-energy, $23\\%$ in the form of non-baryonic dark-matter and the rest $4\\%$ in the form of the usual baryonic matter. The acceleration of the universe is ascribed to this dark-energy with bizarre properties (repulsive-gravity). The question is that whether Hubble's expansion is just due to the shock of big-bang & inflation or it is due to the repulsive-gravity of dark-energy? Now, it is believed to be due to dark-energy, say, by re-introducing the once-discarded cosmological-constant $\\Lambda$. In the present paper, it is shown that `the formula for acceleration due to dark-energy' is (almost) exactly of same-form as `the acceleration formula from the Hubble's law'. Hence, it is concluded that: yes, `indeed it is the dark-energy responsible for the Hubble's expansion too, in-addition to the current on-going acceleration of the universe'.

R. C. Gupta; Anirudh Pradhan

2010-10-19

364

Tommaso Treu, UC Santa Barbara What is the nature of dark energy and dark matter?

Tommaso Treu, UC Santa Barbara What is the nature of dark energy and dark matter? I will describe of the cold dark matter model, i.e. that galaxies should be surrounded by large numbers of dark satellite exotic alternatives like warm dark matter. I will show first results from this experiment based on Keck

Glashausser, Charles

365

Voids as a precision probe of dark energy

The shapes of cosmic voids, as measured in spectroscopic galaxy redshift surveys, constitute a promising new probe of dark energy (DE). We forecast constraints on the DE equation of state and its variation from current and future surveys and find that the promise of void shape measurements compares favorably to that of standard methods such as supernovae and cluster counts even for currently available data. Owing to the complementary nature of the constraints, void shape measurements improve the Dark Energy Task Force figure of merit by 2 orders of magnitude for a future large scale experiment such as EUCLID when combined with other probes of dark energy available on a similar time scale. Modeling several observational and theoretical systematics has only moderate effects on these forecasts. We discuss additional systematics which will require further study using simulations.

Biswas, Rahul; Alizadeh, Esfandiar [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States); Wandelt, Benjamin D. [UPMC Universite Paris-06, Institut d'Astrophysique de Paris, 98 bis, boulevard Arago, 75014 Paris (France); Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States); Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, Illinois 61801 (United States)

2010-07-15

366

Measuring Dark Energy Clustering with CMB-Galaxy Correlations

The integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB) as measured through its correlation with galaxies provides a unique opportunity to study the dynamics of the dark energy through its large scale clustering properties. Ultimately, a deep all-sky galaxy survey out to z~2 can make a 10sigma or ~10% measurement of the correlation and limit ~3% changes in the gravitational potential or total density fluctuation due to dark energy clustering on the Gpc scale. A canonical single scalar field or quintessence model predicts that these clustering effects will appear on the horizon scale with a strength that reflects the evolution of the dark energy density. In terms of a constant equation of state, this would allow tests of the quintessence prediction for models where |1+w| > 0.05.

Wayne Hu; Ryan Scranton

2004-12-01

367

What We Know About Dark Energy From Supernovae

The measured distances of type Ia (white dwarf) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of dark energy (X) having a negative pressure. Combining all of the data with existing results from large-scale structure surveys, we find a best fit for Omega M and Omega X of 0.28 and 0.72 (respectively), in excellent agreement with the values derived independently from WMAP measurements of the cosmic microwave background radiation. Thus far, the best-fit value for the dark energy equation-of-state parameter is -1, and its first derivative is consistent with zero, suggesting that the dark energy may indeed be Einstein's cosmological constant.

Alex Filippenko

2008-05-21

368

Estimating the uncorrelated dark energy evolution in the Planck era

NASA Astrophysics Data System (ADS)

The equation of state (EOS), w(z), is the most important parameter of dark energy. We reconstruct the evolution of this EOS in a model-independent way using the latest cosmic microwave background (CMB) data from Planck and other observations, such as type Ia supernovae, the baryonic acoustic oscillation measurements (SDSS, 6dF, BOSS, and WiggleZ), and the Hubble parameter value H(z). The results show that the EOS is consistent with the cosmological constant at the 2? confidence level, not preferring a dynamical dark energy. The uncorrelated EOS of dark energy constraints from Planck CMB data are much tighter than those from the WMAP 9-year CMB data.

Wang, F. Y.; Dai, Z. G.

2014-01-01

369

What We Know About Dark Energy From Supernovae

The measured distances of type Ia (white dwarf) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of dark energy (X) having a negative pressure. Combining all of the data with existing results from large-scale structure surveys, we find a best fit for Omega M and Omega X of 0.28 and 0.72 (respectively), in excellent agreement with the values derived independently from WMAP measurements of the cosmic microwave background radiation. Thus far, the best-fit value for the dark energy equation-of-state parameter is -1, and its first derivative is consistent with zero, suggesting that the dark energy may indeed be Einstein's cosmological constant.

Alex Filippenko

2010-01-08

370

Comparison of Supernovae datasets Constraints on Dark Energy

Cosmological measurements suggest that our universe contains a dark energy component. In order to study the dark energy evolution, we constrain a parameterized dark energy equation of state $w(z)=w_0 + w_1 \\frac{z}{1+z}$ using the recent observational datasets: 157 Gold type Ia supernovae and the newly released 182 Gold type Ia supernovae by maximum likelihood method. It is found that the best fit $w(z)$ crosses -1 in the past and the present best fit value of $w(0)<-1$ obtained from 157 Gold type Ia supernovae. The crossing of -1 is not realized and $w_0=-1$ is not ruled out in $1\\sigma$ confidence level for the 182 Gold type Ia supernovae. We also find that the range of parameter $w_0$ is wide even in $1\\sigma$ confidence level and the best fit $w(z)$ is sensitive to the prior of $\\Omega_m$.

Chengwu Zhang; Lixin Xu; Baorong Chang; Hongya Liu

2007-04-23

371

Tachyon field as a dark energy in Bianchi type-V spacetime

NASA Astrophysics Data System (ADS)

In this paper, we consider Bianchi type-V spacetime and study a cosmological model of dark energy based on tachyon scalar field. We assumed three different kinds of matter without possibility of interaction with scalar dark energy. Assuming power law Hubble parameter in terms of scale factor we obtain evolution of scalar field, scalar potential and equation of state parameter.

Sadeghi, J.; Farahani, H.

2015-01-01

372

Dark Energy and Tachyon Field in Bianchi Type-V Space-time

In this paper, we consider Bianchi type-V space-time and study a cosmological model of dark energy based on Tachyon scalar field. We assumed three different kinds of matter without possibility of interaction with scalar dark energy. Assuming power law Hubble parameter in terms of scale factor we obtain evolution of scalar field, scalar potential and equation of state parameter.

J. Sadeghi; H. Farahani

2014-04-15

373

NASA Astrophysics Data System (ADS)

In this paper, the authors have investigated the Kaluza Klein universe with magnetized anisotropic dark energy in the context of Lyra manifold. Exponential and power law volumetric expansion is assumed to obtain the solution of the field equations. It is observed that magnetic field plays significant role in isotropization of the dark energy. The physical parameters of the models have been discussed in detail.

Katore, S. D.; Hatkar, S. P.

2015-01-01

374

Direct Detection Rates of Dark Matter Coupled to Dark Energy

We investigate the effect of a coupling between dark matter and dark energy on the rates for the direct detection of dark matter. The magnitude of the effect depends on the strength $\\kappa$ of this new interaction relative to gravity. The resulting isothermal velocity distribution for dark matter in galaxy halos is still Maxwell-Boltzmann (M-B), but the characteristic velocity and the escape velocity are increased by $\\sqrt{1+\\kappa^2}$. We adopt a phenomenological approach and consider values of $\\kappa$ near unity. For such values we find that: (i) The (time averaged) event rate increases for light WIMPs, while it is somewhat reduced for WIMP masses larger than 100 GeV. (ii) The time dependence of the rate arising from the modulation amplitude is decreased compared to the standard M-B velocity distribution. (iii) The average and maximum WIMP energy increase proportionally to $1+\\kappa^2$, which, for sufficiently massive WIMPs, allows the possibility of designing experiments measuring $\\gamma$ rays following nuclear de-excitation.

N. Tetradis; J. D. Vergados; Amand Faessler

2006-09-07

375

Why we need to see the dark matter to understand the dark energy

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.

Martin Kunz

2007-10-30

376

In this work, we consider the cosmological constraints on the holographic Ricci dark energy proposed by Gao et al.[Phys. Rev. D 79, 043511 (2009)], by using the observational data currently available. The main characteristic of holographic Ricci dark energy is governed by a positive numerical parameter {alpha} in the model. When {alpha}<1/2, the holographic Ricci dark energy will exhibit a quintomlike behavior; i.e., its equation of state will evolve across the cosmological-constant boundary w=-1. The parameter {alpha} can be determined only by observations. Thus, in order to characterize the evolving feature of dark energy and to predict the fate of the Universe, it is of extraordinary importance to constrain the parameter {alpha} by using the observational data. In this paper, we derive constraints on the holographic Ricci dark energy model from the latest observational data including the Union sample of 307 type Ia supernovae, the shift parameter of the cosmic microwave background given by the five-year Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey. The joint analysis gives the best-fit results (with 1{sigma} uncertainty): {alpha}=0.359{sub -0.025}{sup +0.024} and {omega}{sub m0}=0.318{sub -0.024}{sup +0.026}. That is to say, according to the observations, the holographic Ricci dark energy takes on the quintom feature. Finally, in light of the results of the cosmological constraints, we discuss the issue of the scalar-field dark energy reconstruction, based on the scenario of the holographic Ricci vacuum energy.

Zhang Xin [Department of Physics, College of Sciences, Northeastern University, Shenyang 110004 (China); Kavli Institute for Theoretical Physics China, Chinese Academy of Sciences, Beijing 100080 (China)

2009-05-15

377

Holographic Dark Energy in Brans-Dicke Theory

In this paper, the holographic dark energy model is considered in Brans-Dicke theory where the holographic dark energy density $\\rho_{\\Lambda} =3c^2 M^{2}_{pl} L^{-2}$ is replaced with $\\rho_{h}=3c^2 \\Phi(t)L^{-2}$. Here $\\Phi(t)=\\frac{1}{8\\pi G}$ is a time variable Newton constant. With this replacement, it is found that no accelerated expansion universe will be achieved when the Hubble horizon is taken as the role of IR cut-off. When the event horizon is adopted as the IR cut-off, an accelerated expansion universe is obtained. In this case, the equation of state of holographic dark energy $w_h$ takes a modified form $w_h=-{1/3}(1+\\alpha+\\frac{2}{c}\\sqrt{\\Omega_{h}})$. In the limit $\\alpha\\to 0$, the 'standard' holographic dark energy is recovered. In the holographic dark energy dominated epoch, power-law and de Sitter time-space solutions are obtained.

Lixin Xu; Wenbo Li; Jianbo Lu

2008-04-18

378

Distance Measurements from Supernovae and Dark Energy Constraints

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''of set 397 SNe Ia. Combining the SN Ia data with CMB data from WMAP five year observations, the Sloan Digital Sky Survey baryon acoustic oscillation measurements, the data of 69 gammay-ray bursts, and the Hubble constant measurement from the HST project SHOES, we measure the dark energy density function X(z)=\\rho_X(z)/\\rho_X(0) as a free function of redshift (assumed to be a constant at z>1 or z>1.5). Without 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 098% confidence level for z1). We quantify dark energy constraints without assuming a flat universe using the dark energy Figure-of-Merit (FoM) for both $X(z)$ and a dark energy equation-of-state linear in the cosmic scale factor.

Yun Wang

2009-10-14

379

Unknowns and unknown unknowns: from dark sky to dark matter and dark energy

NASA Astrophysics Data System (ADS)

Answering well-known fundamental questions is usually regarded as the major goal of science. Discovery of other unknown and fundamental questions is, however, even more important. Recognition that "we didn't know anything" is the basic scientific driver for the next generation. Cosmology indeed enjoys such an exciting epoch. What is the composition of our universe ? This is one of the well-known fundamental questions that philosophers, astronomers and physicists have tried to answer for centuries. Around the end of the last century, cosmologists finally recognized that "We didn't know anything". Except for atoms that comprise slightly less than 5% of the universe, our universe is apparently dominated by unknown components; 23% is the known unknown (dark matter), and 72% is the unknown unknown (dark energy). In the course of answering a known fundamental question, we have discovered an unknown, even more fundamental, question: "What is dark matter? What is dark energy?" There are a variety of realistic particle physics models for dark matter, and its experimental detection may be within reach. On the other hand, it is fair to say that there is no widely accepted theoretical framework to describe the nature of dark energy. This is exactly why astronomical observations will play a key role in unveiling its nature. I will review our current understanding of the "dark sky", and then present on-going Japanese project, SuMIRe, to discover even more unexpected questions.

Suto, Yasushi

2010-07-01

380

Holographic dark energy in the DGP model

The braneworld model proposed by Dvali, Gabadadze and Porrati leads to an accelerated universe without cosmological constant or other form of dark energy. Nevertheless, we have investigated the consequences of this model when an holo- graphic dark energy is included, taken the Hubble scale as IR cutoff. We have found that the holographic dark energy leads to an accelerated universe flat (de Sitter like expansion) for the two branch: {\\ko} = \\pm1 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. Manuscript

Norman Cruz; Samuel Lepe; Francisco Peńa

2011-09-09

381

Particle mixing, flavor condensate and dark energy

The mixing of neutrinos and quarks generate a vacuum condensate that, at the present epoch, behaves as a cosmological constant. The value of the dark energy is constrained today by the very small breaking of the Lorentz invariance.

Massimo Blasone; Antonio Capolupo; Giuseppe Vitiello

2009-12-08

382

Neutrino mixing, flavor states and dark energy

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.

M. Blasone; A. Capolupo; S. Capozziello; G. Vitiello

2007-11-06

383

Non-vacuum conformally flat space-times: dark energy

NASA Astrophysics Data System (ADS)

In this paper we propose a class of exact solutions (stationary and non-stationary) of Einstein's field equations. We find that the space-time geometries of the solutions are non-vacuum and conformally flat, whose energy-momentum tensors possess dark energy with negative pressure and the energy equation of state parameter w=-1/2. We also find that the time-like vector fields of the matter distributions of the solutions are expanding, shearing with acceleration and zero-twist. It is also found that, due to the negative pressure, the energy-momentum tensors violate the strong energy conditions leading to the repulsive gravitational fields of the space-time geometries. Energy-momentum tensors for the solutions also obey the energy conservation equations. From these physical properties of the matter distribution we may refer the space-times to as examples of exact solutions of the Einstein's field equations admitting dark energy with negative pressure. It is to note that the approximate sizes of the masses of the (stationary and non-stationary) solutions are less than (1/2)×10-60 in Bousso's length scale r>1060. We also find that the surface gravities on the horizons are directly proportional to their respective masses.

Ibohal, N.; Ishwarchandra, Ngangbam; Singh, K. Yugindro

2011-10-01

384

Towards Dark Energy from String-Theory

We discuss vacuum energy in string and M-theory with a focus on heterotic M-theory. In the latter theory a mechanism is described for maintaining zero vacuum energy after supersymmetry breaking. Higher-order corrections can be expected to give a sufficiently small amount of vacuum energy to possibly account for dark energy.

Axel Krause

2007-12-31

385

On dark energy models of single scalar field

In this paper we revisit the dynamical dark energy model building based on single scalar field involving higher derivative terms. By imposing a degenerate condition on the higher derivatives in curved spacetime, one can select the models which are free from the ghost mode and the equation of state is able to cross the cosmological constant boundary smoothly, dynamically violate the null energy condition. Generally the Lagrangian of this type of dark energy models depends on the second derivatives linearly. It behaves like an imperfect fluid, thus its cosmological perturbation theory needs to be generalized. We also study such a model with explicit form of degenerate Lagrangian and show that its equation of state may cross -1 without any instability.

Li, Mingzhe [Department of Physics, Nanjing University, Nanjing 210093 (China); Qiu, Taotao [Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan (China); Cai, Yifu [Department of Physics, Arizona State University, Tempe, AZ 85287 (United States); Zhang, Xinmin, E-mail: limz@nju.edu.cn, E-mail: xsjqiu@gmail.com, E-mail: ycai21@asu.edu, E-mail: xmzhang@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918-4, Beijing 100049 (China)

2012-04-01

386

Gravity resonance spectroscopy constrains dark energy and dark matter scenarios.

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 ?>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 ?=20???m (95% C.L.). PMID:24785025

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

387

Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios

NASA Astrophysics Data System (ADS)

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 ? >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 ? =20 ?m (95% C.L.).

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.

2014-04-01

388

Interacting dark energy collapse with matter components separation

We use the spherical collapse model of structure formation to investigate the separation in the collapse of uncoupled matter (essentially baryons) and coupled dark matter in an interacting dark energy scenario. Following the usual assumption of a single radius of collapse for all species, we show that we only need to evolve the uncoupled matter sector to obtain the evolution for all matter components. This gives us more information on the collapse with a simplified set of evolution equations compared with the usual approaches. We then apply these results to four quintessence potentials and show how we can discriminate between different quintessence models.

Delliou, M. Le [Departamento de Física Matemática, Instituto de Física, Universidade de Săo Paulo, CP 66.318 05314-970, Săo Paulo, SP (Brazil); Barreiro, T., E-mail: delliou@cii.fc.ul.pt, E-mail: tmbarreiro@ulusofona.pt [Departamento de Matemática da FFMCC, Universidade Lusófona de Humanidades e Tecnologias, Campo Grande, 376 1749-024 Lisboa (Portugal)

2013-02-01

389

Topology and Dark Energy: Testing Gravity in Voids

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 (EOS) 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 EOS 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.

Douglas Spolyar; Martin Sahlén; Joe Silk

2013-12-16

390

Evolution of perturbations in distinct classes of canonical scalar field models of dark energy

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.

Jassal, H. K. [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211 019 (India)

2010-04-15

391

How early is early dark energy?

We investigate constraints on early dark energy (EDE) from the Cosmic Microwave Background (CMB) anisotropy, taking into account data from WMAP9 combined with latest small scale measurements from the South Pole Telescope (SPT). For a constant EDE fraction we propose a new parametrization with one less parameter but still enough to provide similar results to the ones previously studied in literature. The main emphasis of our analysis, however, compares a new set of different EDE parametrizations that reveal how CMB constraints depend on the redshift epoch at which Dark Energy was non negligible. We find that bounds on EDE get substantially weaker if dark energy starts to be non-negligible later, with early dark energy fraction Omega_e free to go up to about 5% at 2 sigma if the onset of EDE happens at z dark energy is present at last scattering, even if its effects switch off afterwards. We show that the CMB mainly constrains the presence of Dark Energy at the time of its emission, while EDE-modifications of the subsequent growth of structure are less important.

Valeria Pettorino; Luca Amendola; Christof Wetterich

2013-01-22

392

Dark Energy Found Stifling Growth in Universe

NASA Astrophysics Data System (ADS)

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 development to slow down." Vikhlinin and his colleagues used Chandra to observe the hot gas in dozens of galaxy clusters, which are the largest collapsed objects in the universe. Some of these clusters are relatively close and others are more than halfway across the universe. The results show the increase in mass of the galaxy clusters over time aligns with a universe dominated by dark energy. It is more difficult for objects like galaxy clusters to grow when space is stretched, as caused by dark energy. Vikhlinin and his team see this effect clearly in their data. The results are remarkably consistent with those from the distance measurements, revealing general relativity applies, as expected, on large scales. "For years, scientists have wanted to start testing how gravity works on large scales and now, we finally have," said William Forman, a co-author of the study from the Smithsonian Astrophysical Observatory. "This is a test that general relativity could have failed." When combined with other clues -- supernovas, the study of the cosmic microwave background, and the distribution of galaxies -- this new X-ray result gives scientists the best insight to date on the properties of dark energy. The study strengthens the evidence that dark energy is the cosmological constant. Although it is the leading candidate to explain dark energy, theoretical work suggests it should be about 10 raised to the power of 120 times larger than observed. Therefore, alternatives to general relativity, such as theories involving hidden dimensions, are being explored. "Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that 'nothing weighs something'," said Vikhlinin. "A lot more testing is needed, but so far Einstein's theory is looking as good as ever." These results have consequences for predicting the ultimate fate of the universe. If dark energy is explained by the cosmological constant, the expansion of the universe will cont

2008-12-01

393

Dark Energy-Dark Matter Interaction from the Abell Cluster A586

We find that deviation from the virial equilibrium of the Abell Cluster A586 yields evidence of the interaction between dark matter and dark energy. We argue that this interaction might imply a violation of the Equivalence Principle. Our analysis show that evidence is found in the context of two different models of dark energy-dark matter interaction.

Orfeu Bertolami; Francisco Gil Pedro; Morgan Le Delliou

2007-12-31

394

The accelerating universe and dark energy

NASA Astrophysics Data System (ADS)

The recent discovery by Riess et al.1 and Perlmutter et al.2 that the expansion of the universe is accelerating is one of the most significant discoveries in cosmology in the last few decades. To explain this acceleration a mysterious new component of the universe, dark energy, was hypothesized. Using general relativity (GR), the measured rate of acceleration translates to the present understanding that the baryonic matter, of which the familiar world is made of, is a mere 4% of the total mass-energy of the universe, with nonbaryonic dark matter making up 24% and dark energy making up the majority 72%. Dark matter, by definition, has attractive gravity, and even though we presently do not know what it is, it could be made of the next heavy particles discovered by particle physicists. Dark energy, however, is much more mysterious, in that even though we do not know what it is, it must have some kind of repulsive gravity and negative pressure, very unusual properties that are not part of the present understanding of physics. Investigating the nature of dark energy is therefore one of the most important areas of cosmology. In this review, the cosmology of an expanding universe, based on GR, is discussed. The methods of studying the acceleration of the universe, and the nature of dark energy, are presented. A large amount of experimentation on this topic has taken place in the decade since the discovery of the acceleration. These are discussed and the present state of knowledge of the cosmological parameters is summarized in Table 7 below. A vigorous program to further these studies is under way. These are presented and the expected results are summarized in Table 10 below. The hope is that at the end of this program, it would be possible to tell whether dark energy is due to Einstein's cosmological constant or is some other new constituent of the universe, or alternately the apparent acceleration is due to some modification of GR.

Baltay, Charles

2014-05-01

395

Thermodynamics of viscous dark energy in an RSII braneworld

We show that for an RSII braneworld filled with interacting viscous dark energy and dark matter, one can always rewrite the Friedmann equation in the form of the first law of thermodynamics, $dE=T_hdS_h+WdV$, at apparent horizon. In addition, the generalized second law of thermodynamics can fulfilled in a region enclosed by the apparent horizon on the brane for both constant and time variable 5-dynamical Newton's constant $G_5$. These results hold regardless of the specific form of the dark energy. Our study further support that in an accelerating universe with spatial curvature, the apparent horizon is a physical boundary from the thermodynamical point of view.

M. R. Setare; A. Sheykhi

2011-03-05

396

Dark Energy, Dark Matter and Science with Constellation-X

NASA Technical Reports Server (NTRS)

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.

Cardiff, Ann Hornschemeier

2005-01-01

397

Dark energy constraints after the new Planck data

NASA Astrophysics Data System (ADS)

The Planck Collaboration has recently published maps of the cosmic microwave background radiation with the highest precision. In the standard flat ? cold dark matter framework, Planck data show that the Hubble constant H0 is in tension with that measured by the several direct probes on H0. In this paper, we perform a global analysis from the current observational data in the general dark energy models and find that resolving this tension requires the dark energy model with its equation of state (EOS) w?-1. Firstly, assuming the w to be a constant, the Planck data favor w<-1 at about 2? confidence level when combining with the supernovae supernova legacy survey compilation. Consequently the value derived on H0, H0=71.3ą2.0kms-1Mpc-1 (68% C.L.) is consistent with that from direct H0 probes. We then investigate the dark energy model with a time-evolving w, and obtain the 68% C.L. constraints w0=-0.81ą0.19 and wa=-1.9ą1.1 from the Planck data and the supernova legacy survey compilation. Current data still slightly favor the quintom dark energy scenario with EOS across the cosmological constant boundary w?-1.

Xia, Jun-Qing; Li, Hong; Zhang, Xinmin

2013-09-01

398

Coupling dark energy with Standard Model states

In this contribution one examines the coupling of dark energy to the gauge fields, to neutrinos, and to the Higgs field. In the first case, one shows how a putative evolution of the fundamental couplings of strong and weak interactions via coupling to dark energy through a generalized Bekenstein-type model may cause deviations on the statistical nuclear decay Rutherford-Soddy law. Existing bounds for the weak interaction exclude any significant deviation. For neutrinos, a perturbative approach is developed which allows for considering viable varying mass neutrino models coupled to any quintessence-type field. The generalized Chaplygin model is considered as an example. For the coupling with the Higgs field one obtains an interesting cosmological solution which includes the unification of dark energy and dark matter.

M. C. Bento; A. E. Bernardini; O. Bertolami

2009-04-13

399

Effective dark energy models and dark energy models with bounce in frames of F( T) gravity

NASA Astrophysics Data System (ADS)

Various cosmological models in frames of F( T) gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with ?CDM model. The dynamics of universe governed by F( T) gravity can mimics ?CDM evolution in past but declines from it in a future. We also construct some dark energy models with the "real" (non-effective) equation-of-state parameter w such that w?-1. It is showed that in F( T) gravity the Universe filled phantom field not necessarily ends its existence in singularity. There are two possible mechanisms permitting the final singularity. Firstly due to the nonlinear dependence between energy density and H 2 ( H is the Hubble parameter) the universe can expands not so fast as in the general relativity and in fact Little Rip regime take place instead Big Rip. We also considered the models with possible bounce in future. In these models the universe expansion can mimics the dynamics with future singularity but due to bounce in future universe begin contracts.

Astashenok, Artyom V.

2014-05-01

400

Cosmic Acceleration, Dark Energy and Fundamental Physics

A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic (p\\sim -rho), very smooth form of energy called ``dark energy'' accounting for about 75% of the Universe. The ``simplest'' explanation for dark energy is the zero-point energy density associated with the quantum vacuum; however, all estimates for its value are many orders-of-magnitude too large. Other ideas for dark energy include a very light scalar field or a tangled network of topological defects. An alternate explanation invokes gravitational physics beyond general relativity. Observations and experiments underway and more precise cosmological measurements and laboratory experiments planned for the next decade will test whether or not dark energy is the quantum energy of the vacuum or something more exotic, and whether or not general relativity can self consistently explain cosmic acceleration. Dark energy is the most conspicuous example of physics beyond the standard model and perhaps the most profound mystery in all of science.

Michael S. Turner; Dragan Huterer

2007-06-14

401

A Casimir approach to dark energy

We calculate the gravitational self-energy of vacuum quantum field fluctuations using a Casimir approach. We find that the Casimir gravitational self-energy density can account for the measured dark energy density when the SUSY-breaking energy is approximately 5 TeV, in good agreement with current estimates. Furthermore, the Casimir gravitational self-energy appears to provide a quantum mechanism for the well-know geometric relation between the Planck, SUSY and cosmological constant energy scales.

Allan Rosencwaig

2006-06-26

402

First-order formalism for the quintom model of dark energy

The present paper deals to the quintom model of dark energy. We introduce a first-order formalism, which shows how to relate the potential that specifies the scalar field model to Hubble parameter. Reviewing briefly the quintom scenario of dark energy, we present a general procedure to solve the equations of motion for quintom model driven by a couple scalar fields with first-order differential equations.

M. R. Setare; J. Sadeghi

2008-05-08

403

We present constraints on the dark energy equation-of-state parameter, w=P\\/(rhoc2), using 60 SNe Ia from the ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat universe. By including constraints on (OmegaM, w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w=-1.05+0.13-0.12 (stat 1 sigma)+\\/-0.13 (sys)

W. Michael Wood-Vasey; G. Miknaitis; C. W. Stubbs; S. Jha; A. G. Riess; P. M. Garnavich; R. P. Kirshner; C. Aguilera; A. C. Becker; J. W. Blackman; S. Blondin; P. Challis; A. Clocchiatti; A. Conley; R. Covarrubias; T. M. Davis; A. V. Filippenko; R. J. Foley; A. Garg; M. Hicken; K. Krisciunas; B. Leibundgut; W. Li; T. Matheson; A. Miceli; G. Narayan; G. Pignata; J. L. Prieto; A. Rest; M. E. Salvo; B. P. Schmidt; R. C. Smith; J. Sollerman; J. Spyromilio; J. L. Tonry; N. B. Suntzeff; A. Zenteno

2007-01-01

404

Clarifying spherical collapse in coupled dark energy cosmologies

The spherical collapse model is often used to follow the evolution of overdensities into the nonlinear regime. We describe the correct approach to be used in coupled dark energy cosmologies, where a fifth force, different from gravity and mediated by the dark energy scalar field, influences the collapse. We reformulate the spherical collapse description by deriving it directly from the set of nonlinear hydrodynamical Navier-Stokes equations. By comparing with the corresponding relativistic equations, we show how the fifth force should be taken into account within the spherical collapse picture and clarify the problems arising when an inhomogeneous scalar field is considered within a spherical collapse picture. We then apply our method to the case of coupled quintessence, where the fifth force acts among cold dark matter particles, and to growing neutrino quintessence, where the fifth force acts between neutrinos. Furthermore, we review this method within standard cosmologies and apply our analysis to minimally coupled quintessence. We also check past results for early dark energy parametrizations.

Wintergerst, Nico [Arnold-Sommerfeld-Center, Ludwig-Maximilians-Universitaet, Theresienstrasse 37, D-80333 Muenchen (Germany); Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany); Pettorino, Valeria [SISSA, Via Bonomea 265, 34136 Trieste (Italy); Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany)

2010-11-15

405

Entropic-force dark energy reconsidered

We reconsider the entropic-force model in which both kind of Hubble terms ${\\dot H}$ and $H^{2}$ appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions, namely the scale factor, deceleration parameter, matter density and growth of linear matter perturbations. However, we find that the entropic-force model is not viable at the background and perturbation levels due to the fact that the entropic formulation does not add a constant term in the Friedmann equations. On the other hand, if on mere phenomenological grounds we replace the ${\\dot H}$ dependence of the effective DE density with a linear term $H$ without including a constant additive term, we find that the transition from deceleration to acceleration becomes possible but the recent structure formation data strongly disfavors this cosmological scenario. Finally, we briefly compare the entropic-force models with some related DE models (based on dynamical vacuum energy) which overcome these difficulties and are compatible with the present observations.

Spyros Basilakos; Joan Sola

2014-05-21

406

Entropic-force dark energy reconsidered

NASA Astrophysics Data System (ADS)

We reconsider the entropic-force model in which both kinds of Hubble terms, H? and H2, appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions, namely, the scale factor, deceleration parameter, matter density, and growth of linear matter perturbations. However, we find that the entropic-force model is not viable at the background and perturbation levels due to the fact that the entropic formulation does not add a constant term in the Friedmann equations. On the other hand, if on mere phenomenological grounds we replace the H ? dependence of the effective DE density with a linear term H without including a constant additive term, we find that the transition from deceleration to acceleration becomes possible, but the recent structure formation data strongly disfavor this cosmological scenario. Finally, we briefly compare the entropic-force models with some related DE models (based on dynamical vacuum energy) which overcome these difficulties and are compatible with the present observations.

Basilakos, Spyros; Solŕ, Joan

2014-07-01

407

A Regularized Free Form Estimator for Dark Energy

We construct a simple, regularized estimator for the dark energy equation of state by using the recently introduced linear response approximation. We show that even a simple regularization substantially improves the performance of the free form fitting approach. The use of linear response approximation allows an analytic construction of maximum likelihood estimator, in a convenient and easy to use matrix form. We show that in principle, such regularized free form fitting can give us an unbiased estimate of the functional form of the equation of state of dark energy. We show the efficacy of this approach on a simulated SNAP class data, but it is easy to generalize this method to include other cosmological tests. We provide a possible explanation for the sweet spots seen in other reconstruction methods.

Tarun Deep Saini

2003-02-14

408

Viscous Dark Energy and Generalized Second Law of Thermodynamics

We examine the validity of the generalized second law of thermodynamics in a non-flat universe in the presence of viscous dark energy. First we assume that the universe is filled only with viscous dark energy. Then, we extend our study to the case where there is an interaction between viscous dark energy and pressureless dark matter. We examine the time

M. R. Setare; A. Sheykhi

2010-01-01

409

Falsification of dark energy by fluid mechanics

The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating supernovae dimness, suggesting a remarkable change in the expansion rate of the Universe from a decrease since the big bang to an increase, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and dark energy concepts. Kinematic viscosity is neglected in current standard models of self-gravitational structure formation, which rely on cold dark matter CDM condensations and clusterings that are also falsified by fluid mechanics. Weakly collisional CDM particles do not condense but diffuse away. Photon viscosity predicts superclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies and merge to form their stars. Dark energy is a systematic dimming error for Supernovae Ia caused by dark matter planets near hot white dwarf stars at the Chandrasekhar carbon limit. Evaporated planet atmospheres may or may not scatter light from the events depending on the line of sight.

Carl H. Gibson

2012-03-23

410

"Dark energy" in the Local Void

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 ($\\sim5\\times10^{15}\\,M_\\odot$) 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.

M. Villata

2012-01-18

411

Fermion field as inflaton, dark energy and dark matter

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.

Guilherme Grams; Rudinei C. de Souza; Gilberto M. Kremer

2014-07-21

412

Fermion field as inflaton, dark energy and dark matter

NASA Astrophysics Data System (ADS)

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.

Grams, Guilherme; de Souza, Rudinei C.; Kremer, Gilberto M.

2014-09-01

413

Prepared for submission to JCAP Interacting dark energy collapse

Prepared for submission to JCAP Interacting dark energy collapse with matter components separation in the collapse of uncoupled matter (including dark matter and baryons) and coupled dark matter in an interacting how we can discriminate between different quintessence models. Keywords: dark matter simulations, dark

414

Transient and late time attractor tachyon dark energy: Can we distinguish it from quintessence?

The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter w varies from 0 to -1. In the case of tachyon field potential V({phi}){yields}0 slower (faster) than 1/{phi}{sup 2} at infinity, dark energy (dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that w is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly the same as that of the thawing quintessence.

Ali, Amna; Sami, M.; Sen, A. A. [Centre of Theoretical Physics, Jamia Millia Islamia, New Delhi-110025 (India)

2009-06-15

415

Semi-analytic galaxy formation in early dark energy cosmologies

NASA Astrophysics Data System (ADS)

We study the impact of early dark energy (EDE) cosmologies on galaxy properties by coupling high-resolution numerical simulations with semi-analytic modelling (SAM) of galaxy formation and evolution. EDE models are characterized by a non-vanishing high-redshift contribution of dark energy, producing an earlier growth of structures and a modification of large-scale structure evolution. They can be viewed as typical representatives of non-standard dark energy models in which only the expansion history is modified, and hence the impact on galaxy formation is indirect. We show that in EDE cosmologies the predicted space density of galaxies is enhanced at all scales with respect to the standard ? cold dark matter (?CDM ) scenario, and the corresponding cosmic star formation history and stellar mass density are increased at high redshift. We compare these results with a set of theoretical predictions obtained with alternative SAMs applied to our reference ?CDM simulation, yielding a rough measure of the systematic uncertainty of the models. We find that the modifications in galaxy properties induced by EDE cosmologies are of the same order of magnitude as intra-SAM variations for a standard ?CDM realization (unless rather extreme EDE models are considered), suggesting that it is difficult to use such predictions alone to disentangle between different cosmological scenarios. However, when independent information on the underlying properties of host dark matter haloes is included, the SAM predictions on galaxy bias may provide important clues to the expansion history and the equation-of-state evolution.

Fontanot, Fabio; Springel, Volker; Angulo, Raul E.; Henriques, Bruno

2012-11-01

416

Dark energy in thermal equilibrium with the cosmological horizon?

NASA Astrophysics Data System (ADS)

According to a generalization of black hole thermodynamics to a cosmological framework, it is possible to define a temperature for the cosmological horizon. The hypothesis of thermal equilibrium between the dark energy and the horizon has been considered by many authors. We find the restrictions imposed by this hypothesis on the energy transfer rate (Qi) between the cosmological fluids, assuming that the temperature of the horizon has the form T =b/2?R, where R is the radius of the horizon. We more specifically consider two types of dark energy: Chaplygin gas (CG) and dark energy with a constant equation of state parameter (wDE). In each case, we show that for a given radius R, there is a unique term Qde that is consistent with thermal equilibrium. We also consider the situation where, in addition to dark energy, other fluids (cold matter, radiation) are in thermal equilibrium with the horizon. We find that the interaction terms required for this will generally violate energy conservation (

Poitras, Vincent

2014-03-01

417

The Revival of the Unified Dark Energy-Dark Matter Model ?

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 phantom-like dark energy is excluded. Within this framework, we study structure formation and show that difficulties associated to unphysical oscillations or blow-up 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 $\\delta \\sim a$ behaviour.

M. C. Bento; O. Bertolami; A. A. Sen

2004-07-16

418

Can Strong Gravitational Lensing Constrain Dark Energy?

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, $(D_{ds}/D_{s})^{\\Lambda}$ and that for other dark energy models, $(D_{ds}/D_{s})^{\\rm{other}}$ 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 ($\\theta_E$), which is proportional to both $D_{ds}/D_s$ and velocity dispersion squared, $\\sigma_v^2$. $D_{ds}/D_s$ values depend on the parameters of each dark energy model individually. However, $(D_{ds}/D_s)^{\\Lambda} - (D_{ds}/D_{s})^{\\rm{other}}$ for the various dark energy models, is well within the error of $\\sigma_v$ 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.

Seokcheon Lee; Kin-Wang Ng

2007-07-12

419

Cosmological Bardeen-Cooper-Schrieffer condensate as dark energy

We argue that the occurrence of late-time acceleration can conveniently be described by first-order general relativity covariantly coupled to fermions. Dark energy arises as a Bardeen-Cooper-Schrieffer condensate of fermions which forms in the early universe. At late times, the gap and chemical potential evolve to have an equation of state with effective negative pressure, thus naturally leading to acceleration.

Alexander, Stephon; Biswas, Tirthabir; Calcagni, Gianluca [Department of Physics and Astronomy, Haverford College, Haverford, Pennsylvania 19041 (United States); Institute for Gravitation and the Cosmos, Department of Physics, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States)

2010-02-15

420

Dark energy constraints from the cosmic age and supernova

Using the low limit of cosmic ages from globular cluster and the white dwarfs: t0>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?m0.4 or 0.1?mh20.16. We find cosmic age limit plays a

Bo Feng; Xiulian Wang; Xinmin Zhang

2005-01-01

421

Braneworlds, Conformal Fields and Dark Energy

In the Randall-Sundrum scenario we analize the dynamics of a spherically symmetric 3-brane when matter fields propagate in the bulk. For a well defined class of conformal fields of weight -4 we determine a new set of exact 5-dimensional solutions which localize gravity in the vicinity of the brane and are stable under radion field perturbations. Geometries which describe the dynamics of inhomogeneous dust, generalized dark radiation and homogeneous polytropic dark energy are shown to belong to this set.

Rui Neves

2006-01-06

422

Dark Energy and the Accelerating Universe

The discovery ten years ago that the expansion of the Universe is\\u000aaccelerating put in place the last major building block of the present\\u000acosmological model, in which the Universe is composed of 4% baryons, 20% dark\\u000amatter, and 76% dark energy. At the same time, it posed one of the most\\u000aprofound mysteries in all of science, with deep

Joshua A. Frieman; Michael S. Turner; Dragan Huterer

2008-01-01

423

NASA Astrophysics Data System (ADS)

The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein's field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.

Sarkar, Sanjay

2014-02-01

424

Topics in microlensing and dark energy

NASA Astrophysics Data System (ADS)

In this dissertation we describe two separate research projects. The first project involves the utilization and development of reddening models, color magnitude diagrams (CMDs), and microlensing population models of the Large Magellanic Cloud (LMC) to constrain the locations of micro-lensing source stars and micro-lensing objects in the Large Magellanic Cloud and the Milky Way (MW) halo using data of 13 microlensing source stars obtained by the MACHO (massive compact halo objects) collaboration with the Hubble Space Telescope. This analysis suggests that the source stars are located in the LMC disk and the lenses are located in the MW halo. For the second project, we report on the results of a Markov Chain Monte Carlo (MCMC) analysis of an inverse power law (IPL) quintessence model using the Dark Energy Task Force (DETF) simulated data models as a representation of future dark energy experiments. Simulated data sets were generated for a Lambda cold dark matter (L CDM ) background cosmology as well as a case where the dark energy is provided by a specific IPL fiducial model. The results are presented in the form of error contours generated by these two background cosmologies which are then used to consider the effects of future dark energy projects on IPL scalar field models and are able to demonstrate the power of DETF Stage 4 data sets in the context of the IPL model. We find that the respective increase in constraining power with higher quality data sets produced by our analysis gives results that are broadly consistent with the DETF results for the w 0 - w a parameterization of dark energy. Finally, using our simulated data sets constructed around a fiducial IPL model, we find that for a universe containing dark energy described by such a scalar field, a cosmological constant can be excluded by Stage 4 data at the 3s level.

Yashar, Mark

425

The signature of dark energy perturbations in galaxy cluster surveys

Models of dynamical dark energy unavoidably possess fluctuations in the energy density and pressure of that new component. In this paper we estimate the impact of dark energy fluctuations on the number of galaxy clusters in the Universe using a generalization of the spherical collapse model and the Press-Schechter formalism. The observations we consider are several hypothetical Sunyaev-Zel'dovich and weak lensing (shear maps) cluster surveys, with limiting masses similar to ongoing (SPT, DES) as well as future (LSST, Euclid) surveys. Our statistical analysis is performed in a 7-dimensional cosmological parameter space using the Fisher matrix method. We find that, in some scenarios, the impact of these fluctuations is large enough that their effect could already be detected by existing instruments such as the South Pole Telescope, when priors from other standard cosmological probes are included. We also show how dark energy fluctuations can be a nuisance for constraining cosmological parameters with cluster counts, and point to a degeneracy between the parameter that describes dark energy pressure on small scales (the effective sound speed) and the parameters describing its equation of state.

Abramo, L.R.; Batista, R.C. [Instituto de Física, Universidade de Săo Paulo, CP 66318, 05314-970, Săo Paulo (Brazil); Rosenfeld, R., E-mail: abramo@fma.if.usp.br, E-mail: rbatista@fma.if.usp.br, E-mail: rosenfel@ift.unesp.br [Instituto de Física Teórica, Universidade Estadual Paulista, R. Dr. Bento Teobaldo Ferraz 271, 01140-070, Săo Paulo (Brazil)

2009-07-01

426

Dark Energy Density in Brane World

We present a possible explanation to the tiny positive cosmological constant under the frame of AdS$_5$ spacetime embedded by a dS$_4$ brane. We calculate the dark energy density by summing the zero point energy of massive scalar fields in AdS$_5$ spacetime. Under the assumption that the radius of AdS$_5$ spacetime is of the same magnitude as the radius of observable universe, the dark energy density in dS$_4$ brane is obtained, which is smaller than the observational value. The reasons are also discussed.

Hai-Bao Wen; Xin-Bing Huang

2005-02-08

427

Distinguishing Modified Gravity from Dark Energy

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 super-horizon scales and scale-dependent on sub-horizon scales. For scale-independent modifications, utilizing the conservation of the curvature scalar and a parameterized 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 parameterization for the gravitational coupling $G$ and the post-Newtonian parameter $\\gamma$. These parameterizations 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.

Edmund Bertschinger; Phillip Zukin

2008-01-16

428

Might Dark Matter and Energy be Intrinsic Properties of Space?

NASA Astrophysics Data System (ADS)

It is shown that if a volume element V, of space is assumed to have intrinsic energy E, then basic principles of mechanics, thermodynamics and special relativity lead to the equation of state: E= pV, where p is the pressure. When this equation of state is incorporated in the Einstein equations it leads to the prediction that the orbital speed of matter circling a visible galaxy embedded in a spherical galactic halo should be relativistic, in disagreement with observations. However, it also leads directly to the interesting notion that the inertial mass of such a medium can be understood as a resistance to being compressed via Lorentz contraction. It is then shown that the mathematical structure of thermodynamics suggests another plausible definition of pressure if we allow for the possibility that the intrinsic energy of spacetime may not be described by the same work-energy relationship as ordinary matter. This additional possibility leads to the equation of state: E=- pV. While both of these equations of state describe forms of energy that are quite unlike ordinary energy, neither alone is able to account for observed rotational velocity curves of matter orbiting visible galaxies. Therefore, the possibility that space has two distinct components of energy is investigated. This results in a plausible, two-component equation of state in which the former equation of state is tentatively identified as the dark matter (DM) component, the latter as the dark energy (DE) component. The effective equation of state of space, accounting for the presence of both components, may then be written in the form: p= w ?, where ? is the total energy density, p the total pressure, and w represents the fractional excess of DM over DE (and therefore satisfies: -1? w?+1). Given the wide range of possible spacetime properties implied by this equation it appears to be a viable candidate for explaining observations presently attributed to the presence of both DM and DE. Specifically, the static, spherically symmetric solution of Einsteins field equations, neglecting effects of ordinary matter, predicts the inverse r 2 distribution of intrinsic space energy required to explain observed constant rotational velocity curves for matter in circular orbits around visible galaxies embedded within spherically symmetric galactic halos. The proposed equation of state is also capable of describing regions of space undergoing accelerated expansion as regions where DE is dominant (i.e., w<-1/3).

Bruner, Ronald F.

2009-09-01

429

Dark Energy: Mystery of the Millennium

Nearly seventy per cent of the energy density in the universe is unclustered and exerts negative pressure. This conclusion - now supported by numerous observations - poses the greatest challenge for theoretical physics today. I discuss this issue with special emphasis on the cosmological constant as the possible choice for the dark energy. Several curious features of a universe with

T. Padmanabhan

2006-01-01

430

Cosmic Acceleration, Dark Energy, and Fundamental Physics

A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic ( p-rho), very smooth form of energy called ``dark energy'' accounting for about 75% of the Universe.

Michael S. Turner; Dragan Huterer

2007-01-01

431

Dynamics of dark energy in the gravitational fields of matter inhomogeneities

NASA Astrophysics Data System (ADS)

We study the dynamical properties and space distribution of dark energy in the weak and strong gravitational fields caused by inhomogeneities of matter in the static world of galaxies and clusters. We show that the dark energy in the weak gravitational fields of matter density perturbations can condense or dilute, but amplitudes of its perturbations remain very small on all scales. We illustrate also how the "accretion" of the phantom dark energy onto the matter overdensity forms the dark energy underdensity. We analyze the behavior of dark energy in the gravitational fields of stars and black holes with the Schwarzschild metric. It is shown that, in the case of stars, the static solution of the differential equations for energy-momentum conservation exists and describes the distribution of density of dark energy inside and outside of a star. We have found that for stars and galaxies its value differs slightly from the average and is a bit higher for the quintessential scalar field as dark energy and a bit lower for the phantom one. The difference grows with the decrease of the effective sound speed of dark energy and is large in the neighborhood of neutron stars. We obtain and analyze also the solutions of equations that describe the stationary accretion of the dark energy as a test component onto the Schwarzschild black hole. It is shown that the rate of change of mass of the dark energy is positive in the case of quintessential dark energy and is negative in the case of the phantom one.

Novosyadlyj, Bohdan; Kulinich, Yurij; Tsizh, Maksym

2014-09-01

432

Axion-Dilaton Cosmology and Dark Energy

We discuss a class of flat FRW cosmological models based on D=4 axion-dilaton gravity universally coupled to cosmological background fluids. In particular, we investigate the possibility of recurrent acceleration, which was recently shown to be generically realized in a wide class of axion-dilaton models, but in absence of cosmological background fluids. We observe that, once we impose the existence of radiation -and matter- dominated earlier stages of cosmic evolution, the axion-dilaton dynamics is altered significantly with respect to the case of pure axion-dilaton gravity. During the matter dominated epoch the scalar fields remain either frozen, due to the large expansion rate, or enter a cosmological scaling regime. In both cases, oscillations of the effective equation of state around the acceleration boundary value are impossible. Models which enter an oscillatory stage in the low redshift regime, on the other hand, are disfavored by observations. We also comment on the viability of the axion-dilaton system as a candidate for dynamical dark energy. In a certain subclass of models, an intermediate scaling regime is succeeded by eternal acceleration. We also briefly discuss the issue of dependence on initial conditions.

Riccardo Catena; Jan Möller

2007-09-12

433

Emergent Cosmology, Inflation and Dark Energy

A new class of gravity-matter models defined in terms of two independent non-Riemannian volume forms (alternative generally covariant integration measure densities) on the space-time manifold are studied in some detail. These models involve an additional $R^2$ (square of the scalar curvature) term as well as scalar matter field potentials of appropriate form so that the pertinent action is invariant under global Weyl-scale symmetry. Scale invariance is spontaneously broken upon integration of the equations of motion for the auxiliary volume-form degrees of freedom. After performing transition to the physical Einstein frame we obtain: (i) An effective potential for the scalar field with two flat regions which allows for a unified description of both early universe inflation as well as of present dark energy epoch; (ii) For a definite parameter range the model possesses a non-singular "emergent universe" solution which describes an initial phase of evolution that precedes the inflationary phase; (iii) For a reasonable choice of the parameters the present model conforms to the Planck Collaboration data.

Eduardo Guendelman; Ramón Herrera; Pedro Labrańa; Emil Nissimov; Svetlana Pacheva

2015-01-08

434

Emergent cosmology, inflation and dark energy

NASA Astrophysics Data System (ADS)

A new class of gravity-matter models defined in terms of two independent non-Riemannian volume forms (alternative generally covariant integration measure densities) on the space-time manifold are studied in some detail. These models involve an additional (square of the scalar curvature) term as well as scalar matter field potentials of appropriate form so that the pertinent action is invariant under global Weyl-scale symmetry. Scale invariance is spontaneously broken upon integration of the equations of motion for the auxiliary volume-form degrees of freedom. After performing transition to the physical Einstein frame we obtain: (1) an effective potential for the scalar field with two flat regions which allows for a unified description of both early universe inflation as well as of present dark energy epoch; (2) for a definite parameter range the model possesses a non-singular "emergent universe" solution which describes an initial phase of evolution that precedes the inflationary phase; (3) for a reasonable choice of the parameters the present model conforms to the Planck Collaboration data.

Guendelman, Eduardo; Herrera, Ramón; Labrana, Pedro; Nissimov, Emil; Pacheva, Svetlana

2015-02-01

435

Probing dark energy with lensing magnification in photometric surveys.

I present an estimator for the angular cross correlation of two tracers of the cosmological large-scale structure that utilizes redshift information to isolate separate physical contributions. The estimator is derived by solving the Limber equation for a reweighting of the foreground tracer that nulls either clustering or lensing contributions to the cross correlation function. Applied to future photometric surveys, the estimator can enhance the measurement of gravitational lensing magnification effects to provide a competitive independent constraint on the dark energy equation of state. PMID:24580685

Schneider, Michael D

2014-02-14

436

New Perspectives: Wave Mechanical Interpretations of Dark Matter, Baryon and Dark Energy

NASA Astrophysics Data System (ADS)

We model the cosmic components: dark matter, dark energy and baryon distributions in the Cosmic Web by means of highly nonlinear Schrodinger type and reaction diffusion type wave mechanical descriptions. The construction of these wave mechanical models of the structure formation is achieved by introducing the Fisher information measure and its comparison with highly nonlinear term which has dynamical analogy to infamous quantum potential in the wave equations. Strikingly, the comparison of this nonlinear term and the Fisher information measure provides a dynamical distinction between lack of self-organization and self-organization in the dynamical evolution of the cosmic components. Mathematically equivalent to the standard cosmic fluid equations, these approaches make it possible to follow the evolution of the matter distribution even into the highly nonlinear regime by circumventing singularities. Also, numerical realizations of the emerging web-like patterns are presented from the nonlinear dynamics of the baryon component while dark energy component shows Gaussian type dynamics corresponding to soliton-like solutions.

Russell, Esra

437

Dark soliton solution for higher-order nonlinear Schrödinger equation with variable coefficients

In this paper, we consider the generalized higher-order nonlinear Schrödinger equation model with variable coefficients and obtain an exact dark soliton solution in explicit form for specified soliton management conditions. As an example, we consider a soliton control system, and present the main features of the dark soliton solution. Further, the stability of the dark soliton solution is numerically studied

Rongcao Yang; Ruiyu Hao; Lu Li; Zhonghao Li; Guosheng Zhou

2004-01-01

438

Dark energy properties from large future galaxy surveys

NASA Astrophysics Data System (ADS)

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 (?(wp)?(wa))-1, we find a value of 690 for Euclid-like data combined with Planck-like measurements of the cosmic microwave background anisotropies in a 10-dimensional cosmological parameter space, assuming a ?CDM fiducial cosmology. For the more commonly used 7-parameter model, we find a figure-of-merit of 1900 for the same data combination. 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 w0 deviates from -1 by as much as is currently observationally allowed, models with hat cs2 = 10-6 and hat cs2 = 1 can be distinguished from one another at more than 2? significance. We emphasise that constraints on the dark energy sound speed from cluster measurements are strongly dependent on the modelling of the cluster mass function; significantly weaker sensitivities ensue if we modify our model to include fewer features of nonlinear dark energy clustering. Finally, we find that the sum of neutrino masses can be measured with a 1? precision of 0.015 eV, even in complex cosmological models in which the dark energy equation of state varies with time. The 1? sensitivity to the effective number of relativistic species Neffml is approximately 0.03, meaning that the small deviation of 0.046 from 3 in the standard value of Neffml due to non-instantaneous decoupling and finite temperature effects can be probed with 1? precision for the first time.

Basse, Tobias; Eggers Bjćlde, Ole; Hamann, Jan; Hannestad, Steen; Wong, Yvonne Y. Y.

2014-05-01

439

Neutrino Condensate as Origin of Dark Energy

We propose a new solution to the origin of dark energy. We suggest that it was created dynamically from the condensate of a singlet neutrino at a late epoch of the early Universe through its effective self interaction. This singlet neutrino is also the Dirac partner of one of the three observed neutrinos, hence dark energy is related to neutrino mass. The onset of this condensate formation in the early Universe is also related to matter density and offers an explanation of the coincidence problem of why dark energy (70%) and total matter (30%) are comparable at the present time. We demonstrate this idea in a model of neutrino mass with (right-handed) singlet neutrinos and a singlet scalar.

Jitesh R. Bhatt; Bipin R. Desai; Ernest Ma; G. Rajasekaran; Utpal Sarkar

2009-11-26

440

Evolution of dark energy perturbations in scalar-tensor cosmologies

We solve analytically and numerically the generalized Einstein equations in scalar-tensor cosmologies to obtain the evolution of dark energy and matter linear perturbations. We compare our results with the corresponding results for minimally coupled quintessence perturbations. We find that scalar-tensor dark energy density perturbations are amplified by a factor of about 10{sup 4} compared to minimally coupled quintessence perturbations on scales less than about 1000 h{sup -1} Mpc (sub-Hubble scales). On these scales dark energy perturbations constitute a fraction of about 10% compared to matter density perturbations. Scalar-tensor dark energy density perturbations are anticorrelated with matter linear perturbations on sub-Hubble scales. This anticorrelation of matter with negative pressure perturbations induces a mild amplification of matter perturbations by about 10% on sub-Hubble scales. The evolution of scalar field perturbations on sub-Hubble scales is scale independent and therefore corresponds to a vanishing effective speed of sound (c{sub s{Phi}=}0). We briefly discuss the observational implications of our results, which may include predictions for galaxy and cluster halo profiles that are modified compared to {Lambda}CDM. The observed properties of these profiles are known to be in some tension with the predictions of {Lambda}CDM.

Bueno Sanchez, J. C.; Perivolaropoulos, L. [Department of Physics, University of Ioannina, Ioannina (Greece)

2010-05-15

441

Evolution of spherical overdensities in holographic dark energy models

In this work we investigate the spherical collapse model in flat FRW dark energy universes. We consider the Holographic Dark Energy (HDE) model as a dynamical dark energy scenario with a slowly time-varying equation-of-state (EoS) parameter $w_{\\rm de}$ in order to evaluate the effects of the dark energy component on structure formation in the universe. We first calculate the evolution of density perturbations in the linear regime for both phantom and quintessence behavior of the HDE model and compare the results with standard Einstein-de Sitter (EdS) and $\\Lambda$CDM models. We then calculate the evolution of two characterizing parameters in the spherical collapse model, i.e., the linear density threshold $\\delta_{\\rm c}$ and the virial overdensity parameter $\\Delta_{\\rm vir}$. We show that in HDE cosmologies the growth factor $g(a)$ and the linear overdensity parameter $\\delta_{\\rm c}$ fall behind the values for a $\\Lambda$CDM universe while the virial overdensity $\\Delta_{\\rm vir}$ is larger in HDE models ...

Naderi, Tayebe; Pace, Francesco

2014-01-01

442

Physical alternative to the dark energy paradigm

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 ...

Sapar, Arved

2014-01-01

443

Quintessence in a quandary: Prior dependence in dark energy models

NASA Astrophysics Data System (ADS)

The archetypal theory of dark energy is quintessence: a minimally coupled scalar field with a canonical kinetic energy and potential. By studying random potentials, we show that quintessence imposes a restricted set of priors on the equation of state of dark energy. Focusing on the commonly used parametrization, w (a )?w0+wa(1 -a ) , we show that there is a natural scale and direction in the (w0,wa) plane that distinguishes quintessence as a general framework. We calculate the expected information gain for a given survey and show that, because of the nontrivial prior information, it is a function of more than just the figure of merit. This allows us to make a quantitative case for novel survey strategies. We show that the scale of the prior sets target observational requirements for gaining significant information. This corresponds to a figure of merit FOM ?200 , a requirement that future galaxy redshift surveys will meet.

Marsh, David J. E.; Bull, Philip; Ferreira, Pedro G.; Pontzen, Andrew

2014-11-01

444

DESTINY, The Dark Energy Space Telescope

NASA Technical Reports Server (NTRS)

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.

Pasquale, Bert A.; Woodruff, Robert A.; Benford, Dominic J.; Lauer, Tod

2007-01-01

445

Dark Energy Studies: Challenges to Computational Cosmology

The ability to test the nature of dark mass-energy components in the universe through large-scale structure studies hinges on accurate predictions of sky survey expectations within a given world model. Numerical simulations predict key survey signatures with varying degrees of confidence, limited mainly by the complex astrophysics of galaxy formation. As surveys grow in size and scale, systematic uncertainties in theoretical modeling can become dominant. Dark energy studies will challenge the computational cosmology community to critically assess current techniques, develop new approaches to maximize accuracy, and establish new tools and practices to efficiently employ globally networked computing resources.

James Annis; Francisco J. Castander; August E. Evrard; Joshua A. Frieman; Enrique Gaztanaga; Bhuvnesh Jain; Andrey V. Kravtsov; Ofer Lahav; Huan Lin; Joseph Mohr; Paul M. Ricker; Albert Stebbins; Risa H. Wechsler; David H. Weinberg; Jochen Weller

2005-10-06

446

Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios

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 the 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 gravity-like interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant~$\\beta > 5.8\\times10^8$ at~95% confidence level~(C.L.), and an attractive (repulsive) dark matter axion-like spin-mass coupling is excluded for the coupling strength $g_sg_p > 3.7\\times10^{-16}$~($5.3\\times10^{-16}$)~at a Yukawa length of~$\\lambda = 20$~{\\textmu}m~(95% (C.L.).

T. Jenke; G. Cronenberg; J. Burgdörfer; L. A. Chizhova; P. Geltenbort; A. N. Ivanov; T. Lauer; T. Lins; S. Rotter; H. Saul; U. Schmidt; H. Abele

2014-04-15

447

Zero cosmological constant and nonzero dark energy from the holographic principle

NASA Astrophysics Data System (ADS)

The first law of thermodynamics and the holographic principle applied to an arbitrary large cosmic causal horizon are shown to naturally demand a zero cosmological constant and a non-zero dynamical dark energy in the form of the holographic dark energy. A semiclassical analysis shows that the holographic dark energy has a parameter d = 1 and an equation of state comparable to current observational data if the entropy of the horizon saturates the Bekenstein-Hawking bound. This result indicates that quantum field theory should be modified on a large scale to explain the dark energy. The relations among the dark energy, the quantum vacuum energy and the entropic gravity are also discussed.

Lee, Jae-Weon

2013-09-01

448

The nonlinear Schrödinger equation for ultrashort pulse propagation in metamaterials with a nonlinear polarization is solved by an extended tanh function expansion method, and the dark solitary wave solutions for various conditions are obtained. The role of the dispersive magnetic permeability, which manifests itself as self-steepening and higher order nonlinear dispersion terms in the nonlinear Schrödinger equation in dark solitary

Xi Cheng; Binxian Zhuang; Xiaoyu Dai; Wenhua Su; Shuangchun Wen

2009-01-01

449

Chaotic scalar fields as models for dark energy Christian Beck*

Chaotic scalar fields as models for dark energy Christian Beck* Kavli Institute for Theoretical stochastically quantized self-interacting scalar fields as suitable models to generate dark energy is the exis- tence of vacuum energy or, in a more general setting, of dark energy. The observations suggest

Beck, Christian

450

Dark matter interacts with variable vacuum energy

We investigate a spatially flat Friedmann-Robertson-Walker (FRW) scenario with two interacting components, dark matter and variable vacuum energy (VVE) densities, plus two decoupled components, one is a baryon term while the other behaves as a radiation component. We consider a linear interaction in the derivative dark component density. We apply the $\\chi^2$ method to the observational Hubble data for constraining the cosmological parameters and analyze the amount of dark energy in the radiation era for the model. It turns out that our model fulfills the severe bound of $\\Omega_{x}(z\\simeq 1100)age problem at high redshift associated with the old quasar APM 08279+5255 and estimate the age of the universe today.

Iván E. Sánchez G

2014-09-21

451

Can dark energy viscosity be detected with the Euclid survey?

Recent work has demonstrated that it is important to constrain the dynamics of cosmological perturbations, in addition to the evolution of the background, if we want to distinguish among different models of the dark sector. Especially the anisotropic stress of the (possibly effective) dark energy fluid has been shown to be an important discriminator between modified gravity and dark energy models. In this paper we use approximate analytical solutions of the perturbation equations in the presence of viscosity to study how the anisotropic stress affects the weak lensing and galaxy power spectrum. We then forecast how sensitive the photometric and spectroscopic Euclid surveys will be to both the speed of sound and the viscosity of our effective dark energy fluid when using weak lensing tomography and the galaxy power spectrum. We find that Euclid alone can only constrain models with very small speed of sound and viscosity, while it will need the help of other observables in order to give interesting constraints on models with a sound speed close to one. This conclusion is also supported by the expected Bayes factor between models.

Domenico Sapone; Elisabetta Majerotto; Martin Kunz; Bianca Garilli

2013-05-08

452

Viscous dark energy and generalized second law of thermodynamics

We examine the validity of the generalized second law of thermodynamics in a non-flat universe in the presence of viscous dark energy. At first we assume that the universe filled only with viscous dark energy. Then, we extend our study to the case where there is an interaction between viscous dark energy and pressureless dark matter. We examine the time evolution of the total entropy, including the entropy associated with the apparent horizon and the entropy of the viscous dark energy inside the apparent horizon. Our study show that the generalized second law of thermodynamics is always protected in a universe filled with interacting viscous dark energy and dark matter in a region enclosed by the apparent horizon. Finally, we show that the the generalized second law of thermodynamics is fulfilled for a universe filled with interacting viscous dark energy and dark matter in the sense that we take into account the Casimir effect.

M. R. Setare; A. Sheykhi

2011-03-05

453

A geometric measure of dark energy with pairs of galaxies.

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 AlcockPaczynski test), which would provide an independent way of investigating the abundance (?(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 ?(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

Marinoni, Christian; Buzzi, Adeline

2010-11-25

454

THE LIGHT/DARK UNIVERSE Light from Galaxies, Dark Matter and Dark Energy

NASA Astrophysics Data System (ADS)

1. The enigma of the dark night sky. 1.1. Why is the sky dark at night? 1.2. "By reason of distance". 1.3. Island Universe. 1.4. Non-uniform sources. 1.5. Tired light. 1.6. Absorption. 1.7. Fractal Universe. 1.8. Finite age. 1.9. Dark stars. 1.10. Curvature. 1.11. Ether voids. 1.12. Insufficient energy. 1.13. Light-matter interconversion. 1.14. Cosmic expansion. 1.15. Olbers' paradox today -- 2. The intensity of cosmic background light. 2.1. Bolometric intensity. 2.2. Time and redshift. 2.3. Matter, energy and expansion. 2.4. How important is expansion?. 2.5. Simple flat models. 2.6. Curved and multi-fluid models. 2.7. A bright sky at night? -- 3. The spectrum of cosmic background light. 3.1. Spectral intensity. 3.2. Luminosity density. 3.3. The delta function. 3.4. The normal distribution. 3.5. The thermal spectrum. 3.6. The spectra of galaxies. 3.7. The light of the night sky. 3.8. R.I.P. Olbers' paradox -- 4. Dark cosmology. 4.1. The four dark elements. 4.2. Baryons. 4.3. Dark matter. 4.4. Neutrinos. 4.5. Dark energy. 4.6. Cosmological concordance. 4.7. The coincidental Universe -- 5. The radio and microwave backgrounds. 5.1. The cosmological "constant". 5.2. The scalar field. 5.3. Decaying dark energy. 5.4. Energy density. 5.5. Source luminosity. 5.6. Bolometric intensity. 5.7. Spectral energy distribution. 5.8. Dark energy and the background light -- 6. The infrared and visible backgrounds. 6.1. Decaying axions. 6.2. Axion halos. 6.3. Bolometric intensity. 6.4. Axions and the background light -- 7. The ultraviolet background. 7.1. Decaying neutrinos. 7.2. Neutrino halos. 7.3. Halo luminosity. 7.4. Free-streaming neutrinos. 7.5. Extinction by gas and dust. 7.6. Neutrinos and the background light -- 8. The x-ray and gamma-ray backgrounds. 8.1. Weakly interacting massive particles. 8.2. Pair annihilation. 8.3. One-loop decay. 8.4. Tree-level decay. 8.5. Gravitinos. 8.6. WIMPs and the background light -- 9. The high-energy gamma-ray background. 9.1. Primordial black holes. 9.2. Evolution and density. 9.3. Spectral energy distribution. 9.4. Bolometric intensity. 9.5. Spectral intensity. 9.6. Higher dimensions -- 10. The universe seen darkly.

Overduin, James M.; Wesson, Paul S.

455

Dark Energy and The Dark Matter Relic Abundance

Two mechanisms by which the quintessence scalar could enhance the relic abundance of dark matter particles are discussed. These effects can have an impact on supersymmetric candidates for dark matter.

Rosati, Francesca [Universita di Padova, Dipartimento di Fisica 'Galileo Galilei', via Marzolo 8, 35131 Padova (Italy); INFN - Sezione di Padova, via Marzolo 8, 35131 Padova (Italy)

2004-11-17

456

Unification of dark matter and dark energy: the inhomogeneous Chaplygin gas

We extend the world model of Kamenshchik et al. to large perturbations by formulating a Zeldovich-like approximation. We sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.

Neven Bili?

2002-01-01