scholarly journals THERMODYNAMICS IN KALUZA–KLEIN UNIVERSE

2013 ◽  
Vol 28 (17) ◽  
pp. 1350072 ◽  
Author(s):  
M. SHARIF ◽  
RABIA SALEEM

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.

2018 ◽  
Vol 33 (38) ◽  
pp. 1850225 ◽  
Author(s):  
C. P. Singh ◽  
Ajay Kumar

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.


2012 ◽  
Vol 27 (33) ◽  
pp. 1250187 ◽  
Author(s):  
M. SHARIF ◽  
RABIA SALEEM

This paper is devoted to check validity of the laws of thermodynamics for locally rotationally symmetric (LRS) Bianchi type I (BI) universe model which is filled with combination of dark matter and dark energy (DE). We take two types of DE models, i.e. generalized holographic DE (HDE) and generalized Ricci DE (RDE). It is proved that the first and generalized second law of thermodynamics (GSLT) are valid on the apparent horizon for both the models. Further, we take fixed radius L of the apparent horizon with original holographic or RDE. We conclude that the first and GSLT do not hold on the horizon of fixed radius L for both the models.


2010 ◽  
Vol 19 (07) ◽  
pp. 1205-1215 ◽  
Author(s):  
M. R. SETARE ◽  
A. SHEYKHI

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.


2018 ◽  
Vol 15 (03) ◽  
pp. 1850033
Author(s):  
Abdul Jawad ◽  
Shamaila Rani ◽  
Tanzeela Nawaz

We investigate the generalized second law of thermodynamics by assuming the interaction of dark energy and dark matter in Chern–Simons modified gravity. We consider a family of holographic dark energy models by assuming its various cutoffs such as Hubble horizon, event horizon, their combination, Ricci scalar and its generalized form. The general criteria of generalized second law of thermodynamics in terms of coincidence parameter is being developed. This criterion is being applied for the above-mentioned holographic dark energy models to check the validity of the generalized second law of thermodynamics and the constraints where it is respected are referred.


2010 ◽  
Vol 25 (36) ◽  
pp. 3069-3079 ◽  
Author(s):  
JIBITESH DUTTA ◽  
SUBENOY CHAKRABORTY ◽  
M. ANSARI

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.


2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Emmanuel N. Saridakis ◽  
Spyros Basilakos

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.


2019 ◽  
Vol 35 (04) ◽  
pp. 1950360 ◽  
Author(s):  
A. S. Sefiedgar ◽  
M. Mirzazadeh

Thermodynamics of the evolving Lorentzian wormhole at the apparent horizon is investigated in [Formula: see text] gravity. Redefining the energy density and the pressure, the continuity equation is satisfied and the field equations in [Formula: see text] gravity reduce to the ones in general relativity. However, the energy–momentum tensor includes all the corrections from [Formula: see text] gravity. Therefore, one can apply the standard entropy-area relation within [Formula: see text] gravity. It is shown that there may be an equivalency between the field equations and the first law of thermodynamics. It seems that an equilibrium thermodynamics may be held on the apparent horizon. The validity of the generalized second law of thermodynamics (GSL) is also investigated in the wormholes.


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