Observational constraints on the Emergent Universe with interacting non-linear fluids and its stability analysis

TL;DR

This paper explores a stable, singularity-free Emergent Universe model with interacting nonlinear fluids, constrained by observational data, and analyzes its classical stability over cosmic evolution.

Contribution

It introduces a novel Emergent Universe model with nonlinear equations of state and fluid interactions, constrained by observational data, and assesses its classical stability.

Findings

Model can be stable theoretically but unstable at present epoch.

Observational data constrains model parameters.

Universe transitions from early dark energy and radiation to matter and dark energy dominance.

Abstract

We investigate a flat Emergent Universe (EU) with a nonlinear equation of state which is equivalent to three different compositions of fluids. In the EU, initially, the evolution of the universe began with no interaction, but as time evolves, an interaction sets in among the three fluids leading to the observed universe. The characteristic of an EU is that it is a singularity-free universe that evolves with all the basic features of the early evolution. A given nonlinear equation of state parameter permits a universe with three different fluids. We get a universe with dark energy, cosmic string, and radiation domination to begin with, which at a later epoch transits into a universe with three different fluids with matter domination, dark matter, and dark energy for a given interaction strength among the cosmic fluids. Later the model parameters are constrained using the observed Hubble data and Type Ia Supernova (SnIa) data from the Pantheon data set. The classical stability analysis of the model is performed using the square speed of sound. It is found that a theoretically stable cosmological model can be obtained in this case, however, the model becomes classically unstable at the present epoch when the observational bounds on the model parameters are taken into account.