Scalar-Tensor Theory of Gravity and Generalized Second Law of Thermodynamics on the Event Horizon

TL;DR

This paper investigates the conditions under which the generalized second law of thermodynamics holds in a universe bounded by an event horizon within scalar-tensor gravity, considering different dark energy models and eras.

Contribution

It introduces a framework to analyze the validity of the GSLT in scalar-tensor theories with arbitrary entropy functions on the event horizon, covering both quintessence and phantom eras.

Findings

Conditions for GSLT validity derived for different scalar field models.

Restrictions on the equation of state for the validity of GSLT.

Analysis applicable to universes with perfect fluid and holographic dark energy.

Abstract

In blackhole physics, the second law of thermodynamics is generally valid whether the blackhole is a static or a non-static one. Considering the universe as a thermodynamical system the second law of blackhole dynamics extends to the non-negativity of the sum of the entropy of the matter and the horizon, known as generalized second law of thermodynamics(GSLT). Here, we have assumed the universe to be bounded by the event-horizon or filled with perfect fluid and holographic dark energy in two cases. Thus considering entropy to be an arbitrary function of the area of the event-horizon, we have tried to find the conditions and the restrictions over the scalar field and equation of state for the validity of the GSLT and both in quintessence-era and in phantom-era in scalar tensor theory.