Exact solution and exotic fluid in cosmology

TL;DR

This paper explores a cosmological model combining a nonlinear sigma model with a cosmological fluid, revealing exact solutions that transition from matter dominance to dark energy, consistent with observations for specific fluid equations of state.

Contribution

It introduces an exact cosmological solution within a nonlinear sigma model framework coupled to a fluid, extending previous models and analyzing its observational viability.

Findings

The model exhibits a transition from matter to dark energy dominance.

The universe's age calculated matches observations for certain fluid equations of state.

The model's behavior aligns with ΛCDM under specific conditions.

Abstract

We investigate cosmological consequences of nonlinear sigma model coupled with a cosmological fluid which satisfies the continuity equation. The target space action is of de Sitter type and is composed of four scalar fields. The potential which is a function of only one of the scalar fields is also introduced. We perform a general analysis of the ensuing cosmological equations and give various critical points and their properties. Then, we show that the model exhibits exact cosmological solution which yields a transition from matter domination into dark energy and compare it with the $\Lambda$CDM behavior. Especially, we calculate the age of the Universe and show that it is consistent with the observational value if the equation of the state $\omega_f$ for the cosmological fluid is within the range of $0.13 < \omega_f < 0.22.$ Some implication of this result is also discussed.