Unified models of the cosmological dark sector

TL;DR

This paper proposes a viscous fluid model for the dark sector that unifies dark matter and dark energy, fitting observational data and favoring a baryon-like matter content with a negative deceleration parameter.

Contribution

It introduces a unified viscous fluid model for the dark sector that aligns with observational data and differs from previous models by favoring baryonic matter levels and a negative deceleration parameter.

Findings

Compatible with 2dFGRS and SDSS data

Maximum probability for negative deceleration parameter q0 ≈ -0.53

Favors baryonic matter abundance from nucleosynthesis

Abstract

We model the cosmological substratum by a viscous fluid that is supposed to provide a unified description of the dark sector and pressureless baryonic matter. In the homogeneous and isotropic background the \textit{total} energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically non-adiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value $q_{0} \approx - 0.53$ of the deceleration parameter. Moreover, different from other approaches, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis.