Cosmological constraints on a decomposed Chaplygin gas

TL;DR

This paper investigates cosmological constraints on a decomposed Chaplygin gas model, analyzing two interaction scenarios and deriving tight bounds on model parameters using observational data.

Contribution

It provides the first observational constraints on a generalized Chaplygin gas cosmology with different interaction models, highlighting their proximity to the standard Lambda-CDM model.

Findings

Barotropic model constrained to $ ext{alpha}<5.66\times10^{-6}$

Geodesic model allows $-0.15<\text{alpha}<0.26$

Barotropic model must be very close to Lambda-CDM

Abstract

Any unified dark matter cosmology can be decomposed into dark matter interacting with vacuum energy, without introducing any additional degrees of freedom. We present observational constraints on an interacting vacuum plus dark energy corresponding to a generalised Chaplygin gas cosmology. We consider two distinct models for the interaction leading to either a barotropic equation of state or dark matter that follows geodesics, corresponding to a rest-frame sound speed equal to the adiabatic sound speed or zero sound speed, respectively. For the barotropic model, the most stringent constraint on $\alpha$ comes from the combination of CMB+SNIa+LSS(m) gives $\alpha<5.66\times10^{-6}$ at the 95% confidence level, which indicates that the barotropic model must be extremely close to the $\Lambda$CDM cosmology. For the case where the dark matter follows geodesics, perturbations have zero sound speed, and CMB+SNIa+gISW then gives the much weaker constraint $-0.15<\alpha<0.26$ at the 95% confidence level.