Irreversible Processes in Inflationary Cosmological Models

TL;DR

This paper models the early universe as an irreversible process involving particle production, using thermodynamics and general relativity, leading to insights on inflation and the evolution of cosmic parameters.

Contribution

It introduces a cosmological model incorporating irreversible particle production via non-equilibrium pressure, linking thermodynamics with inflationary dynamics.

Findings

Positive acceleration regimes simulate inflation

Acceleration decreases and vanishes as matter density peaks

Model connects particle production with cosmic evolution

Abstract

By using the thermodynamic theory of irreversible processes and Einstein general relativity, a cosmological model is proposed where the early universe is considered as a mixture of a scalar field with a matter field. The scalar field refers to the inflaton while the matter field to the classical particles. The irreversibility is related to a particle production process at the expense of the gravitational energy and of the inflaton energy. The particle production process is represented by a non-equilibrium pressure in the energy-momentum tensor. The non-equilibrium pressure is proportional to the Hubble parameter and its proportionality factor is identified with the coefficient of bulk viscosity. The dynamic equations of the inflaton and the Einstein field equations determine the time evolution of the cosmic scale factor, the Hubble parameter, the acceleration and of the energy densities of the inflaton and matter. Among other results it is shown that in some regimes the acceleration is positive which simulates an inflation. Moreover, the acceleration decreases and tends to zero in the instant of time where the energy density of matter attains its maximum value.