Thermodynamic class II Szekeres-Szafron solutions. Regular models

TL;DR

This paper investigates regular, non-symmetric Szekeres-Szafron solutions of class II in local thermal equilibrium, analyzing their thermodynamic properties and physical viability, especially those compatible with ideal gas equations of state.

Contribution

It extends previous work on singular models to regular solutions, providing thermodynamic schemes and analyzing their physical and cosmological implications.

Findings

Models satisfy physical reality conditions in wide spacetime domains.

Identifies thermodynamic schemes compatible with ideal gas behavior.

Analyzes models with homogeneous temperature akin to FLRW cosmology.

Abstract

In a recent paper (Coll {\em et al} 2019 {\it Class. Quantum Grav.} {\bf 36} 175004) we have studied a family of Szekeres-Szafron solutions of class II in local thermal equilibrium (singular models). In this paper we deal with a similar study for all other class II Szekeres-Szafron solutions without symmetries. These models in local thermal equilibrium (regular models) are analyzed and their associated thermodynamic schemes are obtained. In particular, we focus on the subfamily of solutions which are compatible with the generic ideal gas equation of state ($p = \tilde{k} n \Theta$), and we analyze in depth two notable interpretations that follow on from the choice of two specific thermodynamic schemes: firstly, as a generic ideal gas in local thermal equilibrium and, secondly, as a model having the homogeneous temperature of the FLRW limit. The models above are shown to fulfill the general necessary macroscopic requirements for physical reality (positivity of matter density, internal energy and temperature, energy conditions and compressibility conditions) in wide domains of the spacetime.