Irreversible Geometrothermodynamics of Open Systems in Modified Gravity

TL;DR

This paper investigates the thermodynamics of open systems within modified gravity, focusing on particle production due to non-conservation of energy-momentum, leading to a generalized cosmological model that includes matter creation and entropy evolution.

Contribution

It introduces a thermodynamic framework for open systems in scalar-tensor $f(R,T)$ gravity, linking particle production to gravitational effects and extending the $ ext{Lambda}$CDM model.

Findings

Derived expressions for particle creation rate and entropy evolution.

Proposed a generalized cosmological model with matter and entropy production.

Showed that modified gravity can describe universe evolution from empty conditions.

Abstract

In this work, we explore the formalism of the irreversible thermodynamics of open systems and the possibility of gravitationally generated particle production in modified gravity. More specifically, we consider the scalar-tensor representation of $f(R,T)$ gravity, in which the matter energy-momentum tensor is not conserved due to a nonminimal curvature-matter coupling. In the context of the irreversible thermodynamics of open systems, this non-conservation of the energy-momentum tensor can be interpreted as an irreversible flow of energy from the gravitational sector to the matter sector, which, in general, could result in particle creation. We obtain and discuss the expressions for the particle creation rate, the creation pressure, and the entropy and temperature evolutions. Applied together with the modified field equations of scalar-tensor $f(R,T)$ gravity, the thermodynamics of open systems lead to a generalization of the $\Lambda$CDM cosmological paradigm, in which the particle creation rate and pressure are considered effectively as components of the cosmological fluid energy-momentum tensor. Thus, generally, modified theories of gravity in which these two quantities do not vanish provide a macroscopic phenomenological description of particle production in the cosmological fluid filling the Universe and also lead to the possibility of cosmological models that start from empty conditions and gradually build up matter and entropy.