Bulk viscous cosmology: unified dark matter

TL;DR

This paper explores a cosmological model where a single viscous fluid explains dark matter and dark energy, connecting bulk viscosity to the universe's expansion and fitting the model to supernova data.

Contribution

It introduces a unified dark matter model with bulk viscosity, deriving the Hubble parameter's relation to viscosity and fitting the model to observational data.

Findings

The viscous model can reproduce the observed expansion history.

The Hubble parameter relates directly to the bulk viscosity coefficient.

Model fitting with SNe Ia data supports the viability of viscous unified dark matter.

Abstract

The bulk viscosity is introduced to model unified dark matter. The viscous unified model assumes the universe is filled with a single fluid with the bulk viscosity. We review the general framework of the viscous cosmology. The Hubble parameter has a direct connection with the bulk viscosity coefficient. For concrete form of the bulk viscosity, the Hubble parameter which has the scaling relation with the redshift can be obtained. We discuss two viscosity models and the cosmological evolution to which they lead. Using SNe Ia data, the viscosity model can be fitted. We briefly review the fitting method here.