Second Law Of Gravitational Thermodynamics Research Articles

Apparent Horizon and Gravitational Thermodynamics of Universe in the Eddington-Born-Infeld Theory

The thermodynamics of Universe in the Eddington-Born-Infeld (EBI) theory was restudied by utilizing the holographic-style gravitational equations that dominate the dynamics of the cosmical apparent horizon ΥA and the evolution of Universe. We started in rewriting the EBI action of the Palatini approach into the Bigravity-type action with an extra metric qμν. With the help of the holographic-style dynamical equations, we discussed the property of the cosmical apparent horizon ΥA including timelike, spacelike, and null characters, which depends on the value of the parameter of state wm in EBI Universe. The unified first law for the gravitational thermodynamics and the total energy differential for the open system enveloped by ΥA in EBI Universe were obtained. Finally, applying the positive-heat-out sign convention, we derived the generalized second law of gravitational thermodynamics in EBI Universe.

Super inflation mechanism and dark energy from a cosmological entropy perspective

Various approaches are developed that provide a unification of the early inflationary epoch of the universe and dark energy (cosmic accelerating expansion case). In one respect, we express this unification in a universal thermodynamic framework within the context of F ( T , T G ) role=presentation> F ( T , T G ) F ( T , T G ) F\left( T,T_{G} \right) gravity, where T role=presentation> T T T represents the torsion invariant and T G role=presentation> T G T G T_{G} is the teleparallel equivalent of the Gauss--Bonnet term. For a Friedmann-Robertson-Walker universe model bounded by the dynamical apparent horizon, we explore the generalized second law of gravitational thermodynamics (GSLT). Finally, we discuss the super inflation mechanism, the deceleration case (radiation and dust regions), and the late time cosmic acceleration of the universe into the validity of the GSLT that we obtain.

Holographicf(T)-gravity model with power-law entropy correction

Using a correspondence between the f(T)-gravity with the power-law entropy corrected version of the holographic dark energy model, we reconstruct the holographic f(T)-gravity model with power-law entropy correction. We fit the model parameters by using the latest observational data including type Ia supernovea, baryon acoustic oscillation, cosmic microwave background, and Hubble parameter data. We also check the viability of our model using a cosmographic analysis approach. Using the best-fit values of the model, we obtain the evolutionary behaviors of the effective torsion equation of state parameter of the power-law entropy corrected holographic f(T)-gravity model as well as the deceleration parameter of the universe. We also investigate different energy conditions in our model. Furthermore, we examine the validity of the generalized second law of gravitational thermodynamics. Finally, we point out the growth rate of matter density perturbation in our model. We conclude that in power-law entropy corrected holographic f(T)-gravity model, the universe begins a matter dominated phase and approaches a de Sitter regime at late times, as expected. It also can justify the transition from the quintessence state to the phantom regime in the near past as indicated by recent observations. Moreover, this model is consistent with current data, passes the cosmographic test and fits the data of the growth factor well as the LCDM model.

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 Godel-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 in a non-flat FRW universe containing the interacting new agegraphic dark energy with cold dark matter. The boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. We show that for this model, the equation of state parameter can cross the phantom divide. 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 apparent horizon, separately, depends on the equation of state parameter of the interacting new agegraphic dark energy model.

The generalized second law of gravitational thermodynamics on the apparent and event horizons in FRW cosmology

We investigate the validity of the generalized second law (GSL) of gravitational thermodynamics on the apparent and event horizons in a non-flat Friedmann–Robertson–Walker (FRW) universe containing dark energy interacting with dark matter. We show that for the dynamical apparent horizon, the GSL is always satisfied throughout the history of the universe for any spatial curvature and it is independent of the equation of state parameter of the interacting dark energy model. On the other hand, for the cosmological event horizon, the validity of the GSL depends on the equation of state parameter of the model.

The generalized second law in phantom dominated universes in the presence of black holes

This Letter considers the generalized second law of gravitational thermodynamics in two scenarios featuring a phantom dominated expansion plus a black hole. The law is violated in both scenarios.

Dark energy and the generalized second law

We explore the thermodynamics of dark energy taking into account the existence of the observer's event horizon in accelerated universes. Except for the initial stage of Chaplygin gas dominated expansion, the generalized second law of gravitational thermodynamics is fulfilled and the temperature of the phantom fluid results positive. This substantially extends the work of Pollock and Singh [M.D. Pollock, T.P. Singh, Class. Quantum Grav. 6 (1989) 901] on the thermodynamics of super-inflationary expansion.

Relic gravitational waves and the generalized second law

The generalized second law of gravitational thermodynamics is applied to the present era of accelerated expansion of the Universe. In spite of the fact that the entropy of matter and relic gravitational waves inside the event horizon diminish, the mentioned law is fulfilled provided that the expression for the entropy density of the gravitational waves satisfies a certain condition.