Cosmological constraints on polytropic gas model

TL;DR

This paper investigates the polytropic gas model as a unification of dark matter and dark energy, fitting it to observational data to constrain its parameters and analyze its cosmological implications.

Contribution

It provides the first comprehensive observational constraints on the polytropic gas model and demonstrates its ability to naturally solve the cosmic coincidence problem.

Findings

The universe transitions from matter domination to a de Sitter phase.

Accelerated expansion begins at redshift z_t=0.74.

The model fits observational data well and addresses the coincidence problem.

Abstract

We study the polytropic gas scenario as the unification of dark matter and dark energy. We fit the model parameters by using the latest observational data including type Ia supernovae, baryon acoustic oscillation, cosmic microwave background, and Hubble parameter data. At 68.3% and 95.4% confidence levels, we find the best fit values of the model parameters as $\tilde{K}=0.742_{-0.024}^{+0.024}(1\sigma)_{-0.049}^{+0.048}(2\sigma)$ and $n=-1.05_{-0.08}^{+0.08}(1\sigma)_{-0.16}^{+0.15}(2\sigma)$. Using the best fit values of the model, we obtain the evolutionary behaviors of the equation of state parameters of the polytropic gas model and dark energy, the deceleration parameter of the universe as well as the dimensionless density parameters of dark matter and dark energy. We conclude that in this model, the universe starts from the matter dominated epoch and approaches a de Sitter phase at late times, as expected. Also the universe begins to accelerate at redshift $z_{\rm t}=0.74$. Furthermore in contrary to the $\Lambda$CDM model, the cosmic coincidence problem is solved naturally in the polytropic gas scenario.