Gravitationally induced particle production in scalar-tensor $f(R,T)$ gravity

TL;DR

This paper investigates how gravitational effects in scalar-tensor $f(R,T)$ gravity can lead to particle production, affecting cosmological evolution and offering a generalization of the standard $\\Lambda$CDM model, with implications for entropy and thermodynamics.

Contribution

It introduces a covariant thermodynamic framework for particle production in $f(R,T)$ gravity and compares specific models with observational data.

Findings

Particle creation rates vary with redshift.

The generalized model aligns with observational Hubble data.

Entropy increases due to gravitational matter production.

Abstract

We explore the possibility of gravitationally generated particle production in the scalar-tensor representation of $f(R,T)$ gravity. Due to the explicit nonminimal curvature-matter coupling in the theory, the divergence of the matter energy-momentum tensor does not vanish. We explore the physical and cosmological implications of this property by using the formalism of irreversible thermodynamics of open systems in the presence of matter creation/annihilation. The particle creation rates, pressure, temperature evolution and the expression of the comoving entropy are obtained in a covariant formulation and discussed in detail. Applied together with the gravitational field equations, the thermodynamics of open systems lead to a generalization of the standard $\Lambda$CDM cosmological paradigm, in which the particle creation rates and pressures are effectively considered as components of the cosmological fluid energy-momentum tensor. We also consider specific models, and compare the scalar-tensor $f(R,T)$ cosmology with the $\Lambda$CDM scenario and the observational data for the Hubble function. The properties of the particle creation rates, of the creation pressures, and entropy generation through gravitational matter production are further investigated in both the low and high redshift limits.