scholarly journals RECONSTRUCTING GENERALIZED GHOST CONDENSATE MODEL WITH DYNAMICAL DARK ENERGY PARAMETRIZATIONS AND OBSERVATIONAL DATASETS

2008 ◽  
Vol 23 (02) ◽  
pp. 139-152 ◽  
Author(s):  
JINGFEI ZHANG ◽  
XIN ZHANG ◽  
HONGYA LIU
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
High Redshift ◽  
State Parameter ◽  
Current Data ◽  
Cosmic Acceleration ◽  
Microwave Background ◽  
Type Ia ◽  
Ia Supernovae ◽  
Dynamical Dark Energy

Observations of high-redshift supernovae indicate that the universe is accelerating at the present stage, and we refer to the cause for this cosmic acceleration as "dark energy". In particular, the analysis of current data of type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic microwave background (CMB) anisotropy implies that, with some possibility, the equation-of-state parameter of dark energy may cross the cosmological-constant boundary (w = -1) during the recent evolution stage. The model of "quintom" has been proposed to describe this w = -1 crossing behavior for dark energy. As a single-real-scalar-field model of dark energy, the generalized ghost condensate model provides us with a successful mechanism for realizing the quintom-like behavior. In this paper, we reconstruct the generalized ghost condensate model in the light of three forms of parametrization for dynamical dark energy, with the best-fit results of up-to-date observational data.

scholarly journals ANISOTROPIC DARK ENERGY AND ELLIPSOIDAL UNIVERSE

2011 ◽  
Vol 20 (06) ◽  
pp. 1153-1166 ◽  
Author(s):  
L. CAMPANELLI ◽  
P. CEA ◽  
G. L. FOGLI ◽  
L. TEDESCO
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Background Radiation ◽  
Microwave Background ◽  
Anisotropic Dark Energy ◽  
Large Scale Geometry ◽  
Microwave Background Radiation ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe

A cosmological model with anisotropic dark energy is analyzed. The amount of deviation from isotropy of the equation of state of dark energy, the skewness δ, generates an anisotropization of the large-scale geometry of the Universe, quantifiable by means of the actual shear Σ0. Requiring that the level of cosmic anisotropization at the time of decoupling be such that we can solve the "quadrupole problem" of cosmic microwave background radiation, we find that |δ| ~ 10-4 and |Σ_0| ~10-5, compatible with existing limits derived from the magnitude redshift data on Type Ia supernovae.

scholarly journals A gravitational puzzle

2011 ◽  
Vol 369 (1957) ◽  
pp. 4998-5002
Author(s):  
Robert R. Caldwell
Keyword(s):  
Gravitational Lensing ◽  
Large Scale ◽  
Current Data ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Microwave Background ◽  
Scale Free ◽  
Cosmological Observations ◽  
Stress Energy ◽  
The Relationship

The challenge to understand the physical origin of the cosmic acceleration is framed as a problem of gravitation. Specifically, does the relationship between stress–energy and space–time curvature differ on large scales from the predictions of general relativity. In this article, we describe efforts to model and test a generalized relationship between the matter and the metric using cosmological observations. Late-time tracers of large-scale structure, including the cosmic microwave background, weak gravitational lensing, and clustering are shown to provide good tests of the proposed solution. Current data are very close to proving a critical test, leaving only a small window in parameter space in the case that the generalized relationship is scale free above galactic scales.

A PARAMETRIZED VARIABLE DARK ENERGY MODEL: STRUCTURE FORMATION AND OBSERVATIONAL CONSTRAINTS

2006 ◽  
Vol 15 (09) ◽  
pp. 1455-1472 ◽  
Author(s):  
S. ARBABI BIDGOLI ◽  
M. SADEGH MOVAHED ◽  
S. RAHVAR
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Large Scale ◽  
High Redshift ◽  
Growth Index ◽  
Energy Model ◽  
Linear Perturbation ◽  
Model Parameters ◽  
Type Ia ◽  
Parametrization Scheme

In this paper we investigate a simple parametrization scheme of the quintessence model given by Wetterich [Phys. Lett. B594, 17 (2004)]. The crucial parameter of this model is the bending parameter b, which is related to the amount of dark energy in the early universe. Using the linear perturbation and the spherical infall approximations, we investigate the evolution of matter density perturbations in the variable dark energy model, and obtain an analytical expression for the growth index f. We show that increasing b leads to less growth of the density contrast δ, and also decreases the growth index. Giving a fitting formula for the growth index at the present time, we verify that the approximation relation [Formula: see text] also holds in this model. To compare predictions of the model with observations, we use the Supernovae type Ia (SNIa) Gold Sample and the parameters of the large scale structure determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS). The best fit values for the model parameters by marginalizing on the remained ones, are [Formula: see text], [Formula: see text] and [Formula: see text] at 1σ confidence level. As a final test we calculate the age of universe for different choices of the free parameters in this model and compare it with the age of old stars and some high redshift objects. Then we show that the predictions of this variable dark energy model are consistent with the age observation of old star and can solve the "age crisis" problem.

scholarly journals Model-independent cosmic acceleration and redshift-dependent intrinsic luminosity in type-Ia supernovae

2019 ◽  
Vol 625 ◽  
pp. A15 ◽  
Author(s):  
I. Tutusaus ◽  
B. Lamine ◽  
A. Blanchard
Keyword(s):  
Spline Interpolation ◽  
High Redshift ◽  
Cosmic Acceleration ◽  
Expansion Rate ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe ◽  
Intrinsic Luminosity

Context. The cosmological concordance model (ΛCDM) is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type-Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has been some debate in the literature concerning the statistical treatment of SNIa, and their stature as proof of cosmic acceleration. Aims. In this paper we relax the standard assumption that SNIa intrinsic luminosity is independent of redshift, and examine whether it may have an impact on our cosmological knowledge and more precisely on the accelerated nature of the expansion of the universe. Methods. To maximise the scope of this study, we do not specify a given cosmological model, but we reconstruct the expansion rate of the universe through a cubic spline interpolation fitting the observations of the different cosmological probes: SNIa, baryon acoustic oscillations (BAO), and the high-redshift information from the cosmic microwave background (CMB). Results. We show that when SNIa intrinsic luminosity is not allowed to vary as a function of redshift, cosmic acceleration is definitely proven in a model-independent approach. However, allowing for redshift dependence, a nonaccelerated reconstruction of the expansion rate is able to fit, at the same level of ΛCDM, the combination of SNIa and BAO data, both treating the BAO standard ruler rd as a free parameter (not entering on the physics governing the BAO), and adding the recently published prior from CMB observations. We further extend the analysis by including the CMB data. In this case we also consider a third way to combine the different probes by explicitly computing rd from the physics of the early universe, and we show that a nonaccelerated reconstruction is able to nicely fit this combination of low- and high-redshift data. We also check that this reconstruction is compatible with the latest measurements of the growth rate of matter perturbations. We finally show that the value of the Hubble constant (H0) predicted by this reconstruction is in tension with model-independent measurements. Conclusions. We present a model-independent reconstruction of a nonaccelerated expansion rate of the universe that is able to fit all the main background cosmological probes nicely. However, the predicted value of H0 is in tension with recent direct measurements. Our analysis points out that a final reliable and consensual value for H0 is critical to definitively prove cosmic acceleration in a model-independent way.

scholarly journals Improving dark energy constraints with high-redshift Type Ia supernovae from CANDELS and CLASH

2013 ◽  
Vol 557 ◽  
pp. A64 ◽  
Author(s):  
Vincenzo Salzano ◽  
Steven A. Rodney ◽  
Irene Sendra ◽  
Ruth Lazkoz ◽  
Adam G. Riess ◽  
...  
Keyword(s):  
Dark Energy ◽  
High Redshift ◽  
Type Ia Supernovae ◽  
Energy Constraints ◽  
Type Ia ◽  
Ia Supernovae

Probing the nature of dark energy

2015 ◽  
Vol 30 (28n29) ◽  
pp. 1545010
Author(s):  
Yun Wang
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Structure Type ◽  
Type Ia Supernovae ◽  
Galaxy Clustering ◽  
Growth History ◽  
Type Ia ◽  
History Of ◽  
Expansion Of The Universe ◽  
Ia Supernovae

The cause for the observed acceleration in the expansion of the Universe is unknown, and referred to as “dark energy” for convenience. Dark energy could be an unknown energy component, or a modification of Einstein’s general relativity. This dictates the measurements that are optimal in unveiling the nature of dark energy: the cosmic expansion history, and the growth history of cosmic large scale structure. Type Ia supernovae, galaxy clustering, and weak lensing are generally considered the most powerful observational probes of dark energy. I will examine Type Ia supernovae and galaxy clustering as dark energy probes, and discuss the recent results and future prospects.

scholarly journals COSMIC CONSTRAINT ON RICCI DARK ENERGY MODEL

2009 ◽  
Vol 24 (17) ◽  
pp. 1355-1360 ◽  
Author(s):  
LIXIN XU ◽  
WENBO LI ◽  
JIANBO LU
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Energy Model ◽  
Likelihood Method ◽  
Acoustic Oscillations ◽  
Microwave Background ◽  
Ricci Dark Energy ◽  
Type Ia ◽  
Ia Supernovae ◽  
Best Fit

In this paper, a holographic dark energy model, dubbed Ricci dark energy, is confronted with cosmological observational data from type Ia Supernovae (SN Ia), baryon acoustic oscillations (BAO) and cosmic microwave background (CMB). By using maximum likelihood method, we found that Ricci dark energy model is a viable candidate of dark energy model with the best fit parameters: Ωm0 = 0.34 ± 0.04, α = 0.38 ± 0.03 with 1σ error. Here, α is a dimensionless parameter related to Ricci dark energy ρR and Ricci scalar R, i.e. ρR ∝ αR.

scholarly journals CONSTRAINTS ON THE SOUND SPEED OF DYNAMICAL DARK ENERGY

2008 ◽  
Vol 17 (08) ◽  
pp. 1229-1243 ◽  
Author(s):  
JUN-QING XIA ◽  
YI-FU CAI ◽  
TAO-TAO QIU ◽  
GONG-BO ZHAO ◽  
XINMIN ZHANG
Keyword(s):  
Monte Carlo ◽  
Markov Chain ◽  
Dark Energy ◽  
Sound Speed ◽  
Global Analysis ◽  
Precision Measurements ◽  
Microwave Background ◽  
Angular Scale ◽  
Type Ia ◽  
Dynamical Dark Energy

In this paper we study in detail the sound speed — [Formula: see text], which is directly related to the classical perturbations — of dynamical dark energy (DE). We consider especially the case with an equation of state crossing the cosmological constant boundary, and show its implications for cosmic microwave background (CMB) anisotropy. With the present observational data on the CMB, the Type Ia supernova (SNIa) and galaxy clustering, we perform a global analysis to constrain the sound speed of DE, using the Markov chain Monte Carlo method. We find that the sound speed of DE is weakly constrained by current observations, and thus futuristic precision measurements of the CMB on a very large angular scale (low multipoles) are necessary.

scholarly journals PROBING FOR DYNAMICS OF DARK-ENERGY IN MASS VARYING NEUTRINOS: COSMIC MICROWAVE BACKGROUND RADIATION AND LARGE SCALE STRUCTURE

2007 ◽  
Vol 22 (25n28) ◽  
pp. 2131-2142 ◽  
Author(s):  
YONG-YEON KEUM
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmic Microwave Background ◽  
Large Scale ◽  
Background Radiation ◽  
Coupling Parameter ◽  
Cosmic Acceleration ◽  
Microwave Background ◽  
Cosmological Perturbation ◽  
Cosmological Perturbation Theory

We present cosmological perturbation theory in neutrino probe interacting dark-energy models, and calculate cosmic microwave background anisotropies and matter power spectrum. In these models, the evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for the cosmic acceleration today. We consider several types of scalar field potentials and put constraints on the coupling parameter between neutrinos and dark energy. Assuming the flatness of the universe, the constraint we can derive from the current observation is Σ mν < 0.87eV at the 95 % confidence level for the sum over three species of neutrinos.

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