VALIDITY OF THE THERMODYNAMICAL PROPERTIES OF THE DARK ENERGY MODEL WITH THE EQUATION OF STATE: w = w0 + w1 · z(1 + z)/(1 + z2)

2011 ◽  
Vol 26 (12) ◽  
pp. 885-892 ◽  
Author(s):  
LILI XING ◽  
JIANBIN CHEN ◽  
YUANXING GUI ◽  
ERIC M. SCHLEGEL ◽  
JIANBO LU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Event Horizon ◽  
Dark Energy Model ◽  
Apparent Horizon ◽  
Parametric Model ◽  
Isotropic Universe ◽  
Thermodynamical Properties ◽  
Spatially Homogeneous ◽  
The Universe

We investigate the validity of the thermodynamical properties of the universe in a new parametric model of dark energy with the equation of state w = w0 + w1 · z(1 + z)/(1 + z2). In the spatially homogeneous and isotropic universe, assuming that the temperature and entropy in cosmology is as in a black hole, we examine the thermodynamical properties of the universe bounded by the apparent horizon and the event horizon respectively. By analysis, we find that the first and the second laws of thermodynamics are valid inside the apparent horizon, while they break down inside the event horizon.

Viability of specific reconstructed f(T,𝒯 ) models

2019 ◽  
Vol 34 (30) ◽  
pp. 1950184
Author(s):  
M. Umair Shahzad ◽  
Nadeem Azhar ◽  
Abdul Jawad ◽  
Shamaila Rani
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
State Parameter ◽  
Pilgrim Dark Energy ◽  
Ghost Dark Energy ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Hubble Horizon ◽  
The Universe

The reconstruction scenario of well-established dark energy models such as pilgrim dark energy model and generalized ghost dark energy with Hubble horizon and [Formula: see text] models is being considered. We have established [Formula: see text] models and analyzed their viability through equation of state parameter and [Formula: see text] (where prime denotes derivative with respect to [Formula: see text]) plane. The equation of state parameter evolutes the universe in three different phases such as quintessence, vacuum and phantom. However, the [Formula: see text] plane also describes the thawing as well as freezing region of the universe. The recent observational data also favor our results.

scholarly journals Thermodynamics of the viscous f(T,B) gravity in the new agegraphic dark energy model

2020 ◽  
Vol 35 (20) ◽  
pp. 2050166 ◽  
Author(s):  
A. Pourbagher ◽  
Alireza Amani
Keyword(s):  
Dark Energy ◽  
Hubble Parameter ◽  
Dark Energy Model ◽  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Energy Model ◽  
Accelerated Expansion ◽  
Agegraphic Dark Energy ◽  
New Agegraphic Dark Energy ◽  
The Universe

In this paper, we first obtain the energy density by the approach of the new agegraphic dark energy model, and then the [Formula: see text] gravity model is studied as an alternative to the dark energy in a viscous fluid by flat-FRW background, in which [Formula: see text] and [Formula: see text] are torsion scalar and boundary term. The Friedmann equations will be obtained in the framework of modified teleparallel gravity by tetrad components. We consider that the universe dominates with components such as matter and dark energy by an interacting model. The Hubble parameter is parameterized by the power-law for the scale factor, and then we fit the corresponding Hubble parameter with observational data constraints. The variation of the equation of state (EoS) for dark energy is plotted as a function of the redshift parameter, and the accelerated expansion of the universe is explored. In what follows, the stability of the model is also studied on the base of the sound speed parameter. Finally, the generalized second law of thermodynamics is investigated by entropies of inside and on the boundary of the apparent horizon in thermodynamics equilibrium.

scholarly journals Tsallis agegraphic dark energy model

2019 ◽  
Vol 34 (11) ◽  
pp. 1950086 ◽  
Author(s):  
M. Abdollahi Zadeh ◽  
A. Sheykhi ◽  
H. Moradpour
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Late Time ◽  
Conformal Time ◽  
Classical Level ◽  
Agegraphic Dark Energy ◽  
Energy Models ◽  
Age Of The Universe ◽  
The Universe

Using the non-extensive Tsallis entropy and the holographic hypothesis, we propose a new dark energy (DE) model with timescale as infrared (IR) cutoff. Considering the age of the Universe as well as the conformal time as IR cutoffs, we investigate the cosmological consequences of the proposed DE models and study the evolution of the Universe filled by a pressureless matter and the obtained DE candidates. We find that although this model can describe the late time acceleration and the density, deceleration and the equation of state parameters show satisfactory behavior by themselves, these models are classically unstable unless the interaction between the two dark sectors of the Universe is taken into account. In addition, the results of the existence of a mutual interaction between the cosmos sectors are also addressed. We find out that the interacting models are stable at the classical level which is in contrast to the original interacting agegraphic dark energy models which are classically unstable [K. Y. Kim, H. W. Lee and Y. S. Myung, Phys. Lett. B 660, 118 (2008)].

scholarly journals THERMODYNAMICAL PROPERTIES OF DARK ENERGY IN LOOP QUANTUM COSMOLOGY

2011 ◽  
Vol 20 (02) ◽  
pp. 169-179
Author(s):  
KUI XIAO ◽  
JIAN-YANG ZHU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Quantum Cosmology ◽  
Thermal Equilibrium ◽  
Apparent Horizon ◽  
State Parameter ◽  
Loop Quantum Cosmology ◽  
Thermodynamical Properties ◽  
The One ◽  
Modified Entropy

Considering an arbitrary, varying equation of state parameter, the thermodynamical properties of dark energy fluid in the semiclassical loop quantum cosmology scenario, where we consider the inverse volume modification, are studied. The equation of state parameters are corrected when we consider the effective behavior. Assuming that the apparent horizon has Hawking temperature, the modified entropy–area relation is obtained, and we find that this relation is different from the one which is obtained by considering the holonomy correction. Considering that the dark energy is in thermal equilibrium with the Hawking radiation of the apparent horizon, we get the expression for the entropy of the dark energy fluid.

scholarly journals DARK ENERGY AND THE FUTURE FATE OF THE UNIVERSE

2007 ◽  
Vol 22 (35) ◽  
pp. 2689-2699
Author(s):  
YUNGUI GONG ◽  
YUAN-ZHONG ZHANG
Keyword(s):  
Dark Energy ◽  
Event Horizon ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Scale Factor ◽  
Energy Model ◽  
Holographic Dark Energy Model ◽  
Hubble Horizon ◽  
Size Criterion ◽  
The Universe

We consider the possibility of observing the onset of the late time inflation of our patch of the Universe. The Hubble size criterion and the event horizon criterion are applied to several dark energy models to discuss the problem of future inflation of the Universe. We find that the acceleration has not lasted long enough to confirm the onset of inflation by present observations for the dark energy model with constant equation of state, the holographic dark energy model and the generalized Chaplygin gas (GCG) model. For the flat ΛCDM model with Ωm0 = 0.3, we find that if we use the Hubble size criterion, we need to wait until the av which is the scale factor at the time when the onset of inflation is observed reaches 3.59 times of the scale factor aT when the Universe started acceleration, and we need to wait until av = 2.3aT to see the onset of inflation if we use the event horizon criterion. For the flat holographic dark energy model with d = 1, we find that av = 3.46aT with the Hubble horizon and av = 2.34aT with the event horizon, respectively. For the flat GCG model with the best supernova fitting parameter α = 1.2, we find that av = 5.50aT with the Hubble horizon and av = 2.08aT with the event horizon, respectively.

Isotropic cosmological models in F(T,TG) theory

2016 ◽  
Vol 31 (30) ◽  
pp. 1650175 ◽  
Author(s):  
M. Sharif ◽  
Kanwal Nazir
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Models ◽  
Isotropic Universe ◽  
Eos Parameter ◽  
Torsion Scalar ◽  
The Universe ◽  
Reconstructed Model ◽  
Universe Models ◽  
Relativistic Matter

This paper is devoted to study evolution of the isotropic universe models in the framework of [Formula: see text] gravity ([Formula: see text] represents torsion scalar and [Formula: see text] is the teleparallel equivalent of the Gauss–Bonnet (GB) term). We construct [Formula: see text] models by taking different eras of the universe like non-relativistic and relativistic matter eras, dark energy (DE) dominated era and their combinations. It is found that the reconstructed models indicate decreasing behavior for DE dominated era and its combination with other eras. We also discuss stability of each reconstructed model. Finally, we evaluate equation of state (EoS) parameter by considering two models and study its behavior graphically.

Bianchi type-III holographic dark energy model with quintessence

2018 ◽  
Vol 15 (09) ◽  
pp. 1850161 ◽  
Author(s):  
M. Vijaya Santhi ◽  
V. U. M. Rao ◽  
Daba Meshesha Gusu ◽  
Y. Aditya
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Bianchi Type ◽  
Holographic Dark Energy ◽  
Scale Factor ◽  
Holographic Dark Energy Model ◽  
The Universe ◽  
Average Scale Factor

In this study, we investigate an anisotropic Bianchi type-[Formula: see text] space-time in the presence of matter and holographic dark energy components within the framework of general relativity. We obtained the solution of the field equations by assuming (i) the expansion scalar [Formula: see text] in the model is proportional to shear scalar [Formula: see text], (ii) hybrid expansion law for average scale factor (keeping an eye on the recent scenario of accelerating nature of the universe). We develop cosmological parameters like deceleration and equation of state parameters. These parameters are plotted versus redshift [Formula: see text] for different values of power component of average scale factor [Formula: see text]. We observe that the equation of state varies in quintessence region ([Formula: see text]) and ultimately tends to [Formula: see text]CDM model ([Formula: see text]). The deceleration parameter exhibits a smooth transition from early decelerated epoch to present accelerated era. In addition, we establish the correspondence between our holographic dark energy model and quintessence scalar field. We also express the self-interacting potential [Formula: see text] and scalar field [Formula: see text] of quintessence model as functions of cosmic time [Formula: see text], which describes the accelerated expansion of the universe.

scholarly journals Amended FRW Metric and Rényi Dark Energy Model

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Sarfraz Ali ◽  
Sabir Iqbal ◽  
Khuram Ali Khan ◽  
Hamid Reza Moradi
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Modified Gravity ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Energy Model ◽  
Field Equations ◽  
First Case ◽  
Chern Simons ◽  
The Universe

This article is devoted to exploring the Rényi holographic dark energy model in the theory of Chern-Simons modified gravity. We studied the deceleration parameter, equation of state, and cosmological plane considering the Amended FRW modal. Modified field equations of -gravity theory gave two independent solutions. In the first case, this model provided the transitional change from deceleration to acceleration compatible with collected observational data. However, it supported a decelerating phase of expansion only in the second case. It was noted that the Equation of State advocated the dominance era under the influence of dark energy in the first case and the second predicted the influence of Λ CDM. In both cases, ω < 0 , ω ′ < 0 voted that the universe is in a freezing region and its cosmic expansion is more rapidly accelerated in the background of Chern-Simons modified gravity.

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.

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