Accelerating cosmological expansion from shear and bulk viscosity

TL;DR

This paper investigates how shear and bulk viscosity in the dark sector can influence the universe's expansion rate, potentially explaining cosmic acceleration through backreaction effects of velocity perturbations.

Contribution

It introduces a model linking viscosity effects in the dark sector to the acceleration of cosmic expansion, highlighting the role of perturbation spectra.

Findings

Viscosity effects can significantly impact cosmic expansion dynamics.

Backreaction from velocity perturbations may explain acceleration without dark energy.

Material properties of the dark sector influence cosmological evolution.

Abstract

The dissipation of energy from local velocity perturbations in the cosmological fluid affects the time evolution of spatially averaged fluid dynamic fields and the cosmological solution of Einstein's field equations. We show how this backreaction effect depends on shear and bulk viscosity and other material properties of the dark sector, as well as the spectrum of perturbations. If sufficiently large, this effect could account for the acceleration of the cosmological expansion.