scholarly journals HOLOGRAPHIC DARK ENERGY AND VALIDITY OF THE GENERALIZED SECOND LAW OF THERMODYNAMICS IN THE DGP BRANEWORLD

2010 ◽  
Vol 25 (36) ◽  
pp. 3069-3079 ◽  
Author(s):  
JIBITESH DUTTA ◽  
SUBENOY CHAKRABORTY ◽  
M. ANSARI
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Fluid System ◽  
Generalized Second Law ◽  
The Universe ◽  
Two Fluid ◽  
Dgp Braneworld

In this paper, we investigate the validity of the generalized second law of thermodynamics (GSLT) in the DGP braneworld. The boundary of the universe is assumed to be enclosed by the dynamical apparent horizon or the event horizon. The universe is chosen to be homogeneous and isotropic and the validity of the first law has been assumed here. The matter in the universe is taken in the form of non-interacting two-fluid system: one component is the holographic dark energy and the other component is in the form of dust.

scholarly journals VISCOUS DARK ENERGY AND GENERALIZED SECOND LAW OF THERMODYNAMICS

2010 ◽  
Vol 19 (07) ◽  
pp. 1205-1215 ◽  
Author(s):  
M. R. SETARE ◽  
A. SHEYKHI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Time Evolution ◽  
Casimir Effect ◽  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Total Entropy ◽  
Generalized Second Law ◽  
The Universe

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 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 shows 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 by taking into account the Casimir effect.

Viscous Ricci dark energy and generalized second law of thermodynamics in modified f(R, T) gravity

2018 ◽  
Vol 33 (38) ◽  
pp. 1850225 ◽  
Author(s):  
C. P. Singh ◽  
Ajay Kumar
Keyword(s):  
Dark Energy ◽  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Fluid Viscosity ◽  
Ricci Dark Energy ◽  
Evolution Of The Universe ◽  
Generalized Second Law ◽  
The Future ◽  
The Universe

The motivation of this paper is to study the bulk viscosity effect in Ricci dark energy (RDE) model within the framework of modified f(R, T) gravity, where R is the Ricci scalar and T is the trace of the energy–momentum tensor. As most studies assume that the universe is filled with a perfect fluid, viscosity is expected to present at least during some stages, especially in the early stage of the evolution of the universe but it could still become significant in the future. We assume the universe is filled with viscous RDE and pressureless dark matter. We consider the total bulk viscous coefficient is in the form of [Formula: see text][Formula: see text]H, where [Formula: see text] and [Formula: see text] are the constants. We obtain the solutions to the modified field equations by assuming a form f(R, T) = R [Formula: see text] T, where [Formula: see text] is a constant. We find the scale factor and deceleration parameter, and classify all possible evolutions of the universe. We briefly discuss the future finite-time singularity and show that the Big Rip singularity appears in viscous RDE model. We investigate two geometrical diagnostics, statefinder parameter and Om to analyze the dynamics of evolution of the universe. The trajectories of statefinder parameter reveal that the model behaves like quintessence for small [Formula: see text], and for large [Formula: see text] it shows the Chaplygin gas-like. However, in late time both the models approach [Formula: see text]CDM. The model shows a transition from decelerated phase to accelerated phase. Similarly, the Om analysis reveals that the model behaves like quintessence for small [Formula: see text] and phantom-like for large [Formula: see text]. We extend our study to analyze the time evolution of the total entropy and generalized second law of thermodynamics of viscous RDE model in f(R, T) theory inside the apparent horizon. Our study shows that the generalized second law of thermodynamics always preserves in viscous RDE model in a region enclosed by the apparent horizon under the suitable constraints of viscous coefficients.

scholarly journals The generalized second law of thermodynamics with Barrow entropy

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Emmanuel N. Saridakis ◽  
Spyros Basilakos
Keyword(s):  
Black Hole ◽  
Dark Energy ◽  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Gravitational Effects ◽  
Generalized Second Law ◽  
Horizon Entropy ◽  
The Universe ◽  
Universe Evolution

AbstractWe investigate the validity of the generalized second law of thermodynamics, applying Barrow entropy for the horizon entropy. The former arises from the fact that the black-hole surface may be deformed due to quantum-gravitational effects, quantified by a new exponent $$\Delta $$ Δ . We calculate the entropy time-variation in a universe filled with the matter and dark energy fluids, as well as the corresponding quantity for the apparent horizon. We show that although in the case $$\Delta =0$$ Δ = 0 , which corresponds to usual entropy, the sum of the entropy enclosed by the apparent horizon plus the entropy of the horizon itself is always a non-decreasing function of time and thus the generalized second law of thermodynamics is valid, in the case of Barrow entropy this is not true anymore, and the generalized second law of thermodynamics may be violated, depending on the universe evolution. Hence, in order not to have violation, the deformation from standard Bekenstein–Hawking expression should be small as expected.

scholarly journals THERMODYNAMICS IN KALUZA–KLEIN UNIVERSE

2013 ◽  
Vol 28 (17) ◽  
pp. 1350072 ◽  
Author(s):  
M. SHARIF ◽  
RABIA SALEEM
Keyword(s):  
Dark Energy ◽  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Model Parameters ◽  
Ricci Dark Energy ◽  
Generalized Second Law ◽  
Energy Models ◽  
Fixed Radius ◽  
Kaluza Klein

This paper is devoted to check the validity of laws of thermodynamics for Kaluza–Klein universe in the state of thermal equilibrium, composed of dark matter and dark energy. The generalized holographic dark energy and generalized Ricci dark energy models are considered here. It is proved that the first and generalized second law of thermodynamics are valid on the apparent horizon for both of these models. Further, we take a horizon of radius L with modified holographic or Ricci dark energy. We conclude that these models do not obey the first and generalized second law of thermodynamics on the horizon of fixed radius L for a specific range of model parameters.

A unified picture of cosmological entropy on apparent horizon in F(R, G) gravity

2017 ◽  
Vol 32 (33) ◽  
pp. 1750182 ◽  
Author(s):  
Ali İhsan Keskin ◽  
Irfan Acikgoz
Keyword(s):  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Hawking Temperature ◽  
Second Law ◽  
Field Equations ◽  
Frw Universe ◽  
Generalized Second Law ◽  
History Of ◽  
The Universe ◽  
Friedmann Robertson Walker

In this study, the validity of the generalized second law of thermodynamics (GSLT) has been investigated in F(R, G) gravity. We consider that the boundary of the universe is surrounded by an apparent horizon in the spatially flat Friedmann–Robertson–Walker (FRW) universe, and we take into account the Hawking temperature on the horizons. The unified solutions of the field equations corresponding to gravity theory have been applied to the validity of the GSLT frame, and in this way, both the solutions have been verified and all the expansion history of the universe has been shown in a unified picture.

Cosmology in scalar–tensor–vector theory via thermodynamics

2018 ◽  
Vol 33 (24) ◽  
pp. 1850137 ◽  
Author(s):  
Onur Siginc ◽  
Mustafa Salti ◽  
Hilmi Yanar ◽  
Oktay Aydogdu
Keyword(s):  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Entropy Function ◽  
Second Law ◽  
Generalized Second Law ◽  
Vector Theory ◽  
Theory Of Gravity ◽  
The Universe ◽  
Non Equilibrium

Assuming the universe as a thermodynamical system, the second law of thermodynamics can be extended to another form including the sum of matter and horizon entropies, which is called the generalized second law of thermodynamics. The generalized form of the second law (GSL) is universal which means it holds both in non-equilibrium and equilibrium pictures of thermodynamics. Considering the universe is bounded by a dynamical apparent horizon, we investigate the nature of entropy function for the validity of GSL in the scalar–tensor–vector (STEVE) theory of gravity.

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