Thermodynamics of gravitationally induced particle creation scenario in DGP braneworld

In this paper, we discuss the thermodynamical analysis for gravitationally induced particle creation scenario in the framework of DGP braneworld model. For this purpose, we consider apparent horizon as the boundary of the universe. We take three types of entropy such as Bakenstein entropy, logarithmic corrected entropy and power law corrected entropy with ordinary creation rate \(\Gamma \). We analyze the first law and generalized second law of thermodynamics analytically for these entropies which hold under some constraints. The behavior of total entropy in each case is also discussed which implies the validity of generalized second law of thermodynamics. Also, we check the thermodynamical equilibrium condition for two phases of creation rate, that is constant and variable \(\Gamma \) and found its vitality in all cases of entropy.     

Fluctuation probes of quark deconfinement

A classical and quantum mechanical generalized second law of thermodynamics in cosmology implies constraints on the effective equation of state of the universe in the form of energy conditions, obeyed by many known cosmological solutions, forbids certain cosmological singularities, and is compatible with entropy bounds. This second law is based on the conjecture that causal boundaries and not only event horizons have geometric entropies proportional to their area. In string cosmology the second law provides new information about nonsingular solutions.     

Interacting three fluid system and thermodynamics of the universe bounded by the event horizon

The work deals with the thermodynamics of the universe bounded by the event horizon. The matter in the universe has three constituents namely dark energy, dark matter and radiation in nature and interaction between then is assumed. The variation of entropy of the surface of the horizon is obtained from unified first law while matter entropy variation is calculated from the Gibbss’ law. Finally, validity of the generalized second law of thermodynamics is examined and conclusions are written point wise.     

Holographic dark energy: Quantum correlations against thermodynamical description

Classical and quantum entropic properties of holographic dark energy (HDE) are considered in view of the fact that its entropy is far more restrictive than the entropy of a black hole of the same size. In cosmological settings (in which HDE is promoted to a plausible candidate for being the dark energy of the universe), HDE should be viewed as a combined state composed of the event horizon and the stuff inside the horizon. By any interaction of the subsystems, the horizon and the interior become entangled, raising thereby a possibility that their quantum correlations be responsible for the almost purity of the combined state. Under this circumstances, the entanglement entropy is almost the same for both subsystems, being also of the same order as the thermal (coarse grained) entropy of the interior or the horizon. In the context of thermodynamics, however, only additive coarse grained entropies matter, so we use these entropies to test the generalized second law (GSL) of gravitational thermodynamics in this framework. While we find that the original Li's model passes the GSL test for a special choice of parameters, in a saturated model with the choice for the IR cutoff in the form of the Hubble parameter, the GSL always breaks down.     

Generalized Second Law of Thermodynamics in Parabolic LTB Inhomogeneous Cosmology

We study thermodynamics of the parabolic Lemaitre-Tolman-Bondi (LTB) cosmology supported by a perfect fluid source. This model is the natural generalization of the flat Friedmann-Robertson-Walker (FRW) universe, and describes an inhomogeneous universe with spherical symmetry. After reviewing some basic equations in the parabolic LTB cosmology, we obtain a relation for the deceleration parameter in this model. We also obtain a condition for which the universe undergoes an accelerating phase at the present time. We use the first law of thermodynamics on the apparent horizon together with the Einstein field equations to get a relation for the apparent horizon entropy in LTB cosmology. We find out that in LTB model of cosmology, the apparent horizon's entropy could be feeded by a term, which incorporates the effects of the inhomogeneity. We consider this result and get a relation for the total entropy evolution, which is used to examine the generalized second law of thermodynamics for an accelerating universe. We also verify the validity of the second law and the generalized second law of thermodynamics for a universe filled with some kinds of matters bounded by the event horizon in the framework of the parabolic LTB model.     

Generalized Second Law of Thermodynamics in Parabolic LTB Inhomogeneous Cosmology

We study thermodynamics of the parabolic Lemaitre-Tolman-Bondi(LTB) cosmology supported by a perfect Suid source.This model is the natural generalization of the Sat Friedmann-Robertson-Walker(FRW) universe,and describes an inhomogeneous universe with spherical symmetry.After reviewing some basic equations in the parabolic LTB cosmology,we obtain a relation for the deceleration parameter in this model.We also obtain a condition for which the universe undergoes an accelerating phase at the present time.We use the first law of thermodynamics on the apparent horizon together with the Einstein field equations to get a relation for the apparent horizon entropy in LTB cosmology.We find out that in LTB model of cosmology,the apparent horizon's entropy could be feeded by a term,which incorporates the effects of the inhomogeneity.We consider this result and get a relation for the total entropy evolution,which is used to examine the generalized second law of thermodynamics for an accelerating universe.We also verify the validity of the second law and the generalized second law of thermodynamics for a universe filled with some kinds of matters bounded by the event horizon in the framework of the parabolic LTB model.     

Validity of the generalized second law of thermodynamics of the universe bounded by the event horizon in holographic dark energy model

In this paper, we investigate the validity of the generalized second law of thermodynamics of the universe bounded by the event horizon in the holographic dark energy (DE) model. 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 DE model and the other component is in the form of dust.     

Thermodynamics of Chaplygin Gas Interacting with Cold Dark Matter

The main goal of the present work is to investigate the validity of the second law of gravitational thermodynamics in an expanding Gödel-type universe filled with generalized Chaplygin gas interacting with cold dark matter. By assuming the Universe as a thermodynamical system bounded by the apparent horizon, and calculating separately the entropy variation for generalized Chaplygin gas, cold dark matter and for the horizon itself, we obtained an expression for the time derivative of the total entropy. We conclude that the 2nd law of gravitational thermodynamics is conditionally valid in the cosmological scenario where the generalized Chaplygin gas interacts with cold dark matter.     

The Generalized Second Law for the Interacting New Agegraphic Dark Energy in a Non-flat FRW Universe Enclosed by the Dynamical Apparent Horizon

We investigate the validity of the generalized second law of gravitational thermodynamics on the dynamical apparent horizon in a non-flat FRW universe containing the interacting new agegraphic dark energy with dark matter. We show that for this model, the equation of state parameter can cross the phantom divide line. We also present that for the selected model under thermal equilibrium with the Hawking radiation, the generalized second law is always satisfied throughout the history of the universe. Whereas, the evolution of the entropy of the universe and dynamical apparent horizon, separately, depends on the equation of state parameter of the interacting new agegraphic dark energy model.     

Generalized Second Law of Thermodynamics on the Event Horizon for Interacting Dark Energy

Here we are trying to find the conditions for the validity of the generalized second law of thermodynamics (GSLT) assuming the first law of thermodynamics on the event horizon in both cases when the FRW universe is filled with interacting two fluid system- one in the form of cold dark matter and the other is either holographic dark energy or new age graphic dark energy.     

Semi-holographic universe

By assuming that a dark component (dark energy) in the universe strictly obeys the holographic principle, that is, its entropy is one fourth of the apparent horizon, we find that the existence of the other dark component (dark matter) is compulsory, as a compensation of dark energy, based on the first law of thermodynamics. By using the method of dynamical system analysis, we find that there exists a stable dark energy-dark matter scaling solution at late time, which is helpful to solve the coincidence problem. For reasonable parameters, the deceleration parameter is well consistent with current observations.     

Effect of arbitrary matter-geometry coupling on thermodynamics in f(R) theories of gravity

In this paper, the thermodynamics of the Friedmann–Lemaître–Robertson–Walker universe have been explored in f(R) theories of gravity with arbitrary matter-geometry coupling. The equivalence between the modified Friedmann equations with any spatial curvature and the first law of thermodynamics is confirmed, where the assumption of the entropy plays a crucial role. Then laws of thermodynamics in our considering case are obtained. They can reduce to the ones given in Einstein’s general theory of relativity under certain conditions. Moreover, a particular model is investigated through the obtained generalized second law of thermodynamics with observational results of cosmographic parameters.     

Non-minimal gravitational coupling of phantom and big rip singularity

We consider a non-minimal coupling of a perfect fluid matter system with geometry, which the coupling function is taken to be an arbitrary function of the Ricci scalar. Due to such a coupling, the matter stress tensor is no longer conserved and there is an energy transfer between the two components. By solving the conservation equation and applying the second law of thermodynamics, we show that direction of the energy transfer depends on the equation of state of the matter fluid. In particular, a phantom fluid should loose energy with expansion of the universe. This energy reduction can avoid the universe to end with a cosmic doomsday.     

Statefinder and Om Diagnostics for Interacting New Holographic Dark Energy Model and Generalized Second Law of Thermodynamics

In this work, we have considered that the flat FRW universe is filled with the mixture of dark matter and the new holographic dark energy. If there is an interaction, we have investigated the natures of deceleration parameter, statefinder and Om diagnostics. We have examined the validity of the first and generalized second laws of thermodynamics under these interactions on the event as well as apparent horizon. It has been observed that the first law is violated on the event horizon. However, the generalized second law is valid throughout the evolution of the universe enveloped by the apparent horizon. When the event horizon is considered as the enveloping horizon, the generalized second law is found to break down excepting at late stage of the universe.     

Generalized Second Law of Thermodynamics in Emergent Universe

In this letter, we have considered the FRW model of the emergent universe, which was presented in our previous work (Debnath, in Class. Quantum Gravity 25:205019, 2008). We have chosen one of the form of scale factor in such a way that the emergent scenario is possible in the universe. We have also considered the universe as a thermodynamical system with the horizon surface as a boundary of the system. The entropy and the radius of the event horizon have been calculated in the emergent scenario. When the emergent scenario occurs, we have shown that the generalized second law of thermodynamics is always satisfied for open, flat and closed models of the universe.     

A study of generalized second law of thermodynamics in magnetic universe in the light of non-linear electrodynamics

In this work, we have considered the magnetic universe in non-linear electrodynamics. The Einstein field equations for non-flat FRW model have been considered when the universe is filled with the matter and magnetic field only. We have discussed the validity of the generalized second law of thermodynamics of the magnetic universe bounded by Hubble, apparent, particle and event horizons using Gibbs? law and the first law of thermodynamics for interacting and non-interacting scenarios. It has been shown that the GSL is always satisfied for Hubble, apparent and particle horizons but for event horizon, the GSL is violated initially and satisfied at late stage of the universe.     

Thermodynamics of apparent horizon and modified Friedmann equations

Starting from the first law of thermodynamics, dE=T _h ? dS _h +W? dV, at the apparent horizon of a FRW universe, and assuming that the associated entropy with apparent horizon has a quantum-corrected relation, $S=\frac{A}{4G}-\alpha \ln \frac{A}{4G}+\beta \frac{4G}{A}$ , we derive modified Friedmann equations describing the dynamics of the universe with any spatial curvature. We also examine the time evolution of the total entropy including the quantum-corrected entropy associated with the apparent horizon together with the matter field entropy inside the apparent horizon. Our study shows that, with the local equilibrium assumption, the generalized second law of thermodynamics is fulfilled in a region enclosed by the apparent horizon.