Observationally constrained emergent universe scenario with non-conventional late-time dynamics

TL;DR

This paper explores an emergent universe model driven by extended Chaplygin gas, which explains late-time cosmic acceleration, exhibits non-conventional behavior, and fits observational data better than the standard b1-CDM model.

Contribution

It introduces a novel emergent universe scenario using extended Chaplygin gas with quadratic modifications, providing a viable alternative to b1-CDM and addressing initial singularity issues.

Findings

Dark energy crosses the phantom divide in the past and present.

Model fits observational data better than b1-CDM at certain redshifts.

The universe transitions into a decelerating phase, making dark energy transient.

Abstract

In this paper, we attempt to explore the possibility of a obtaining a viable emergent universe scenario supported by a type of fluid known as the extended Chaplygin gas, which extends a modification to the equation of state of the well known modified Chaplygin gas by considering additional higher order barotropic fluid terms. We consider quadratic modification only. Such a fluid is capable of explaining the present cosmic acceleration and is a possible dark energy candidate. We construct a theoretical model of the emergent universe assuming it is dominated by such a fluid at late times. Our model results in non-conventional late-time behavior and deviates from the standard $\Lambda$-CDM model. Dark energy is found to cross the \textit{phantom} divide in the past and present besides exhibiting \textit{thawing} behaviour in the future, asymptotically leading to transition into a decelerating phase making dark energy a \textit{transient} phenomenon. The qualitative nature of variation of the cosmological parameters resulting from model parameters observationally constrained through Markov Chain Monte Carlo sampling of Pantheon+OHD data is interestingly found to resemble the DESI results. Also,the value of $H(z)$ at a redshift $z=2.34$ and present value of Hubble parameter fits much better than $\Lambda$-CDM with recent observations. This leads us to the realization that such a fluid is not only a probable candidate for dark energy, but also sources an emergent universe unlike modified Chaplygin gas and the initial singularity problem can be resolved in a flat universe within the standard relativistic context.