A thermodynamic model of inflation without inflaton field

TL;DR

This paper proposes a thermodynamic model of cosmic inflation that does not require an inflaton field, using a novel fluid approach within geometrothermodynamics to address key cosmological problems.

Contribution

It introduces a new inflationary model based on thermodynamics and fluid dynamics, avoiding scalar fields and connecting early and late universe acceleration.

Findings

Addresses flatness and horizon problems with a novel fluid model

Calculates temperatures and out-of-equilibrium properties during inflation

Suggests a unification of inflation and late-time acceleration via a cosmological constant

Abstract

In the framework of geometrothermodynamics, we explore how to construct an inflationary cosmic fluid without requiring inflaton fields. To do so, we employ standard radiation and matter as barotropic background, speculating on the existence of a further real fluid, interpreted as a possible matter with pressure constituent. We thus illustrate its main characteristics, showing how it may face the flatness and horizon problems, yielding an equivalent number of e-foldings, compatible with theoretical expectations. Moreover, we calculate the associated equilibrium and kinetic temperatures, and compute out-of-equilibrium properties, in terms of particle production and effective reheating mechanism. Accordingly, we revise how inflation ends and how to fix the free parameters of our model from observations. Last but not least, we propose how to obtain a bare cosmological constant that could relate the late-time acceleration to inflation, aiming to unify the two approaches. Finally, we discuss the corresponding theoretical implications of our treatment in contrast to the standard approach reliant on scalar field potentials, emphasizing the main advantages and disadvantages.