A non-singular early-time viscous cosmological model

TL;DR

This paper analyzes a non-singular early universe model with viscosity, demonstrating it can describe radiation era conditions while satisfying thermodynamical and stability criteria within Eckart's framework.

Contribution

It introduces a viscous cosmological model that is mathematically stable, thermodynamically consistent, and non-singular, extending previous work by verifying key physical conditions.

Findings

Model describes radiation domination era of ΛCDM

Satisfies near equilibrium, stability, and entropy conditions

Features positive energy density and infinite initial temperature

Abstract

In this paper, we study the thermodynamical and mathematical consistencies for a non-singular early-time viscous cosmological model known as soft-Big Bang, which was previously found in [N. Cruz, E. Gonz\'alez, and J. Jovel, Phys. Rev. D \textbf{105}, 024047 (2022)]. This model represents a flat homogeneous and isotropic universe filled with a dissipative radiation fluid and a cosmological constant $\Lambda$, which is small but not negligible, in the framework of Eckart's theory. In particular, we discuss the capability of the solution in the fulfillment of the three following conditions: (i) the near equilibrium condition, which is assumed in Eckart's theory of non-perfect fluids, (ii) the mathematical stability of the solution under small perturbations, and (iii) the positiveness of the entropy production. We have found that this viscous model can describe the radiation domination era of the $\Lambda$CDM model and, at the same time, fulfill the three conditions mentioned by the fulfillment of a single constraint on the bulk viscous coefficient $\xi_{0}$, finding also that this non-singular model has a positive energy density in the infinity past which is infinity hotter with a constant entropy.