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

Abstract

We construct a cosmological model which is physically reasonable, mathematically tractable, and extends the study of cold dark matter (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.