Cosmological model with variable equations of state for matter and dark energy

TL;DR

This paper develops a cosmological model with time-varying equations of state for matter and dark energy, exploring how these variations influence universe expansion and differ from standard CDM models, including scenarios like generalized Chaplygin gas.

Contribution

It introduces a flexible cosmological model with variable EoS for matter and dark energy, extending CDM models to include evolving components and multiple expansion phases.

Findings

Variable EoS can cause multiple transitions between deceleration and acceleration.

The model encompasses generalized Chaplygin gas as a special case.

Evolving dark energy can mimic pressureless dust at late times.

Abstract

We construct a cosmological model which is physically reasonable, mathematically tractable, and extends the study of CDM models to the case where the equations of state (EoS) for matter and dark energy (DE) vary with time. It is based on the assumptions of (i) flatness, (ii) validity of general relativity, (iii) the presence of a DE component that varies between two asymptotic values, (iv) the matter of the universe smoothly evolves from an initial radiation stage - or a barotropic perfect fluid - to a phase where it behaves as cosmological dust at late times. The model approximates the CDM ones for small $z$ but significantly differ from them for large $z$. We focus our attention on how the evolving EoS for matter and DE can modify the CDM paradigm. We discuss a number of physical scenarios. One of them includes, as a particular case, the so-called generalized Chaplygin gas models where DE evolves from non-relativistic dust. Another kind of models shows that the current accelerated expansion is compatible with a DE that behaves like pressureless dust at late times. We also find that a universe with variable DE can go from decelerated to accelerated expansion, and vice versa, several times.