scholarly journals Variable Equation of State for Generalized Dark Energy Model

2011 ◽  
Vol 50 (9) ◽  
pp. 2687-2696 ◽  
Author(s):  
Saibal Ray ◽  
Farook Rahaman ◽  
Utpal Mukhopadhyay ◽  
Ruby Sarkar
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Energy Model ◽  
Variable Equation

scholarly journals Cosmological Implications of the Generalized Entropy Based Holographic Dark Energy Models in Dynamical Chern-Simons Modified Gravity

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
M. Younas ◽  
Abdul Jawad ◽  
Saba Qummer ◽  
H. Moradpour ◽  
Shamaila Rani
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Modified Gravity ◽  
Dark Energy Model ◽  
State Parameter ◽  
Energy Model ◽  
Evolutionary Equation ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Chern Simons

Recently, Tsallis, Rényi, and Sharma-Mittal entropies have widely been used to study the gravitational and cosmological setups. We consider a flat FRW universe with linear interaction between dark energy and dark matter. We discuss the dark energy models using Tsallis, Rényi, and Sharma-Mittal entropies in the framework of Chern-Simons modified gravity. We explore various cosmological parameters (equation of state parameter, squared sound of speed ) and cosmological plane (ωd-ωd′, where ωd′ is the evolutionary equation of state parameter). It is observed that the equation of state parameter gives quintessence-like nature of the universe in most of the cases. Also, the squared speed of sound shows stability of Tsallis and Rényi dark energy model but unstable behavior for Sharma-Mittal dark energy model. The ωd-ωd′ plane represents the thawing region for all dark energy models.

scholarly journals HOLOGRAPHIC DARK ENERGY MODEL CHARACTERIZED BY THE CONFORMAL-AGE-LIKE LENGTH

2012 ◽  
Vol 27 (16) ◽  
pp. 1250085 ◽  
Author(s):  
ZHUO-PENG HUANG ◽  
YUE-LIANG WU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Dimensional Space ◽  
Early Time ◽  
Energy Model ◽  
Holographic Dark Energy Model ◽  
Frw Universe

A holographic dark energy model characterized by the conformal-age-like length scale [Formula: see text] is motivated from the four-dimensional space–time volume at cosmic time t in the flat Friedmann–Robertson–Walker (FRW) universe. It is shown that when the background constituent with constant equation of state wm dominates the universe in the early time, the fractional energy density of the dark energy scales as [Formula: see text] with the equation of state given by [Formula: see text]. The value of wm is taken to be wm≃-1 during inflation, wm = ⅓ in radiation-dominated epoch and wm = 0 in matter-dominated epoch, respectively. When the model parameter d takes the normal value at order one, the fractional density of dark energy is naturally negligible in the early universe, Ω de ≪1 at a ≪1. With such an analytic feature, the model can be regarded as a single-parameter model like the ΛCDM model, so that the present fractional energy density Ω de (a = 1) can solely be determined by solving the differential equation of Ωde once d is given. We further extend the model to the general case in which both matter and radiation are present. The scenario involving possible interaction between the dark energy and the background constituent is also discussed.

scholarly journals THEORETICAL ASPECTS OF QUINTOM MODELS

2010 ◽  
Vol 25 (11n12) ◽  
pp. 909-921 ◽  
Author(s):  
TAOTAO QIU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Early Universe ◽  
Dark Energy Model ◽  
Phenomenological Study ◽  
Energy Model

Quintom models, with its Equation of State being able to cross the cosmological constant boundary w = -1, turns out to be attractive for phenomenological study. It can not only be applicable for dark energy model for current universe, but also lead to a bounce scenario in the early universe.

scholarly journals COSMOLOGICAL CONSTRAINT AND ANALYSIS ON HOLOGRAPHIC DARK ENERGY MODEL CHARACTERIZED BY THE CONFORMAL-AGE-LIKE LENGTH

2012 ◽  
Vol 27 (22) ◽  
pp. 1250130 ◽  
Author(s):  
ZHUO-PENG HUANG ◽  
YUE-LIANG WU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Energy Model ◽  
Single Parameter ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Holographic Dark Energy Model ◽  
Λcdm Model

We present a best-fit analysis on the single-parameter holographic dark energy model characterized by the conformal-age-like length, [Formula: see text]. Based on the Union2 compilation of 557 supernova Ia (SNIa) data, the baryon acoustic oscillation (BAO) results from the Sloan Digital Sky Survey data release 7 (SDSS DR7) and the cosmic microwave background radiation (CMB) data from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7), we show that the model gives the minimal [Formula: see text], which is comparable to [Formula: see text] for the ΛCDM model. The single parameter d concerned in the model is found to be d = 0.232±0.006±0.009. Since the fractional density of dark energy Ωde~ d2a2at a ≪ 1, the fraction of dark energy is naturally negligible in the early universe, Ωde≪ 1 at a ≪ 1. The resulting constraints on the present fractional energy density of matter and the equation of state are [Formula: see text] and [Formula: see text] respectively. We also provide a systematic analysis on the cosmic evolutions of the fractional energy density of dark energy, the equation of state of dark energy, the deceleration parameter and the statefinder. It is noticed that the equation of state crosses from wde> -1 to wde< -1, the universe transits from decelerated expansion (q > 0) to accelerated expansion (q < 0) recently, and the statefinder may serve as a sensitive diagnostic to distinguish the CHDE model with the ΛCDM model.

scholarly journals STATEFINDER DIAGNOSTIC FOR THE YANG–MILLS DARK ENERGY MODEL

2008 ◽  
Vol 17 (08) ◽  
pp. 1245-1254 ◽  
Author(s):  
WEN ZHAO
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Energy Model ◽  
Statefinder Parameters ◽  
Yang Mills ◽  
Energy Models

We study the statefinder parameters in the Yang–Mills condensate dark energy models, and find that the evolving trajectories of these models are different from those of other dark energy models. We also define two eigenfunctions of the Yang–Mills condensate dark energy models. The values of these eigenfunctions are quite close to zero if the equation of state of the Yang–Mills condensate is not far from -1, which can be used to simply differentiate between the Yang–Mills condensate models and other dark energy models.

scholarly journals A TRACKER SOLUTION FOR A HOLOGRAPHIC DARK ENERGY MODEL

2006 ◽  
Vol 15 (06) ◽  
pp. 869-877 ◽  
Author(s):  
HUI LI ◽  
ZONG-KUAN GUO ◽  
YUAN-ZHONG ZHANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Energy Model ◽  
Holographic Dark Energy Model ◽  
Coincidence Problem ◽  
Accelerating Expansion ◽  
State 1

We investigate a kind of holographic dark energy model with a future event horizon being IR cutoff and the equation of state -1. In this model, the constraint on the equation of state automatically specifies an interaction between matter and dark energy. With this interaction included, an accelerating expansion is obtained as well as the transition from deceleration to acceleration. It is found that there exists a stable tracker solution for the numerical parameter d > 1, and d smaller than one will not lead to a physical solution. This model provides another possible phenomenological framework to alleviate the cosmological coincidence problem in the context of holographic dark energy. Some properties of the evolution which are relevant to cosmological parameters are also discussed.

TWO-FIELD MODELS OF DARK ENERGY WITH EQUATION OF STATE ACROSS -1

2006 ◽  
Vol 21 (03) ◽  
pp. 231-241 ◽  
Author(s):  
XIAO-FEI ZHANG ◽  
HONG LI ◽  
YUN-SONG PIAO ◽  
XINMIN ZHANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Spinor Field ◽  
Dark Energy Model ◽  
Scalar Fields ◽  
Energy Model ◽  
Simple Realization ◽  
Dynamical Dark Energy

In this paper, we study the possibility of building two-field models of dark energy with equation of state across -1. Specifically we will consider two classes of models: one consists of two scalar fields (quintessence + phantom) and another includes one scalar (phantom) and one spinor field (neutrino). Our studies indicate to some extent that two-field models give rise to a simple realization of the dynamical dark energy model with the equation of state across w=-1.

scholarly journals PROBING FOR THE COSMOLOGICAL PARAMETERS WITH PLANCK MEASUREMENT

2008 ◽  
Vol 17 (11) ◽  
pp. 2025-2048 ◽  
Author(s):  
JUN-QING XIA ◽  
HONG LI ◽  
GONG-BO ZHAO ◽  
XINMIN ZHANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Neutrino Mass ◽  
Dark Energy Model ◽  
Cosmological Parameters ◽  
Energy Model ◽  
Cpt Symmetry ◽  
Λcdm Model ◽  
Inflationary Parameters ◽  
Dynamical Dark Energy

In this paper we investigate the constraints on the cosmological parameters, especially the equation of state of dynamical dark energy w DE , the inflationary parameters ns, αs and r, the total neutrino mass ∑ mν and the curvature of the universe ΩK, using the simulated data of future Planck measurement. First, we determine the cosmological parameters with the current observations, including ESSENCE (192 samples), Three-Year WMAP (WMAP3), Boomerang-2K2, CBI, VSA, ACBAR, SDSS LRG and 2dFGRS, and then we take the best-fit model as the fiducial model in the ensuing simulations. In the simulations we pay particular attention to the effects of the dynamical dark energy in the determination of the cosmological parameters. For this reason, in order to make our constraints more robust, we have added the simulated SNAP data to our simulations. Using the present data, we find that the Quintom dark energy model is mildly favored, while the ΛCDM model remains a good fit. In the framework of the dynamical dark energy model, the constraints on the inflationary parameters, ∑ mν and ΩK, become weak, compared with the constraints in the ΛCDM model. Intriguingly, we find that the inflationary models with a "blue" tilt, which are excluded about 2σ in the ΛCDM model, are well within the 2σ region with the presence of the dynamics of dark energy. The upper limits of neutrino mass are weakened by a factor of 2 (95% CL) — say, ∑ mν < 1.59 eV and ∑ mν < 1.53 eV for two forms of parametrization of the equation of state of dark energy. The flat universe is a good fit to the current data, namely |ΩK| < 0.03 (95% CL). With the simulated Planck and SNAP data, the dynamical dark energy model and the ΛCDM model might be distinguished at the 4σ confidence level. And the uncertainties of the inflationary parameters, ∑ mν and ΩK, can be reduced significantly in the framework of the dynamical dark energy model. We also constrain the rotation angle Δα, denoting the possible CPT violation, from the simulated Planck and CMBpol data and find that our results are much more stringent than the current constraint and will be used to verify the CPT symmetry with a higher precision.

Cosmic evolution of ghost dark energy models in f(G,T) gravity

2019 ◽  
Vol 35 (10) ◽  
pp. 2050063
Author(s):  
M. Sharif ◽  
Saadia Saba
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Dark Energy Model ◽  
State Parameter ◽  
Energy Model ◽  
Frw Universe ◽  
Ghost Dark Energy ◽  
Energy Models ◽  
Generalized Ghost Dark Energy

The aim of this paper is to study the reconstruction paradigm for both ghost as well as generalized ghost dark energy models in the context of [Formula: see text] gravity. To accomplish this, we use correspondence scenario for pressureless flat FRW universe with power-law scale factor. The cosmological behavior of reconstructed models is analyzed through graphical analysis of deceleration, equation of state, squared speed of sound parameters and phase planes. It is found that the deceleration parameter represents accelerated epoch for both models whereas equation of state parameter indicates phantom era of the universe for ghost dark energy model and quintessence for its generalized version. The phase planes [Formula: see text] and [Formula: see text] indicate the freezing region with phantom phase for both reconstructed dark energy models. We conclude that the squared speed of sound parameter leads to the stability of generalized ghost dark energy model only.

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