Cosmic bulk viscosity through backreaction

TL;DR

This paper models cosmic bulk viscosity as a backreaction effect of inhomogeneities using Buchert's formalism, comparing the resulting luminosity distance to supernova data and finding marginal differences from standard cosmology.

Contribution

It introduces a novel approach to cosmic bulk viscosity via backreaction effects with a time-dependent curvature, providing a new way to interpret supernova observations.

Findings

Luminosity distance differs slightly from flat bulk viscous models.

Model aligns with ΛCDM within current observational uncertainties.

Future data could distinguish this backreaction model from standard cosmology.

Abstract

We consider an effective viscous pressure as the result of a backreaction of inhomogeneities within Buchert's formalism. The use of an effective metric with a time-dependent curvature radius allows us to calculate the luminosity distance of the backreaction model. This quantity is different from its counterpart for a "conventional" spatially flat bulk viscous fluid universe. Both expressions are tested against the SNIa data of the Union2.1 sample with only marginally different results for the distance-redshift relation and in accordance with the $\Lambda$CDM model. Future observations are expected to be able to discriminate among these models on the basis of indirect measurements of the curvature evolution.