Thermodynamics of flat FLRW universe in Rastall Theory

TL;DR

This paper explores the thermodynamics of a flat FLRW universe within Rastall theory, deriving entropy relations, constraints on parameters, and examining the second law of thermodynamics.

Contribution

It introduces a novel entropy relation for the apparent horizon in Rastall theory and analyzes thermodynamic laws within this framework.

Findings

Derived a relation for horizon entropy in Rastall theory

Established constraints on Rastall parameters from entropy positivity

Confirmed the validity of thermodynamic laws in the model

Abstract

In this paper, after referring to the Rastall theory, we address some of its cosmological consequences. Moreover, bearing the Clausius relation in mind, using Friedman equations in Rastall theory and the Cai-Kim temperature, we obtain a relation for the apparent horizon entropy of a flat FLRW universe. In addition, we impose the entropy positivity condition on the obtained relation for the horizon entropy, to find some constraints on the Rastall parameters. Moreover, we investigate the second and generalized second laws of thermodynamics. The results of considering a dominated prefect fluid with constant state parameter are also addressed helping us familiarize with the Rastall theory.