scholarly journals Generalized second law of thermodynamics on the apparent horizon in modified Gauss–Bonnet gravity

2016 ◽  
Vol 25 (04) ◽  
pp. 1650040 ◽  
Author(s):  
A. Abdolmaleki ◽  
T. Najafi
Keyword(s):  
Deceleration Parameter ◽  
Apparent Horizon ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Second Law ◽  
De Sitter ◽  
Frw Universe ◽  
Curvature Invariant ◽  
Generalized Second Law ◽  
The Universe

Modified gravity (MG) and generalized second law (GSL) of thermodynamics are interesting topics in the modern cosmology. In this regard, we investigate the GSL of gravitational thermodynamics in the framework of modified Gauss–Bonnet (GB) gravity or [Formula: see text]-gravity. We consider a spatially FRW universe filled with the pressureless matter and radiation enclosed by the dynamical apparent horizon with the Hawking temperature. For two viable [Formula: see text] models, we first numerically solve the set of differential equations governing the dynamics of [Formula: see text]-gravity. Then, we obtain the evolutions of the Hubble parameter, the GB curvature invariant term, the density and equation of state (EoS) parameters as well as the deceleration parameter. In addition, we check the energy conditions for both models and finally examine the validity of the GSL. For the selected [Formula: see text] models, we conclude that both models have a stable de Sitter attractor. The EoS parameters behave quite similar to those of the [Formula: see text]CDM model in the radiation/matter dominated epochs, then they enter the phantom region before reaching the de Sitter attractor with [Formula: see text]. The deceleration parameter starts from the radiation/matter dominated eras, then transits from a cosmic deceleration to acceleration and finally approaches a de Sitter regime at late times, as expected. Furthermore, the GSL is respected for both models during the standard radiation/matter dominated epochs. Thereafter when the universe becomes accelerating, the GSL is violated in some ranges of scale factor. At late times, the evolution of the GSL predicts an adiabatic behavior for the accelerated expansion of the universe.

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.

scholarly journals The generalized second law of thermodynamics for interacting f(R) gravity

2014 ◽  
Vol 23 (08) ◽  
pp. 1450071 ◽  
Author(s):  
Ramón Herrera ◽  
Nelson Videla
Keyword(s):  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Effective Equation ◽  
Frw Universe ◽  
Total Energy Density ◽  
Generalized Second Law ◽  
Interaction Term ◽  
The Universe ◽  
Gravitational Thermodynamics

In this paper, we examine the validity of the generalized second law (GSL) of gravitational thermodynamics in the context of interacting f(R) gravity. We take into account that the boundary of the universe to be confined by the dynamical apparent horizon in a flat FRW universe. We study the effective equation of state, deceleration parameter and GSL in this interaction-framework. We find that the evolution of the total entropy increases through the interaction term. As an example, we consider a f(R) gravity with a power-law dependence on the curvature R. Here, we find exact solutions for a model in which the interaction term is related to the total energy density of matter.

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.

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.

scholarly journals Qualitative aspects of Rastall gravity with barotropic fluid

2021 ◽  
Author(s):  
Ashutosh Singh ◽  
Rakesh Raushan ◽  
R. Chaubey
Keyword(s):  
Dynamical System ◽  
Equation Of State ◽  
System Approach ◽  
Apparent Horizon ◽  
Dynamical Evolution ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Frw Universe ◽  
Barotropic Fluid ◽  
Generalized Second Law

We investigate the dynamical evolution of homogeneous and isotropic flat-FRW universe filled with a barotropic fluid satisfying linear equation of state in Rastall gravity. Using dynamical system approach, we find the fixed points of the system and study their stability. We further explore the thermodynamic aspects at the apparent horizon by investigating the validity of generalized second law of thermodynamics with equilibrium description.

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 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.

Sign in / Sign up

Export Citation Format

Share Document