Late time anisotropy as an imprint of cosmological backreaction

TL;DR

This paper investigates how large-scale structure backreaction induces local anisotropy in cosmic flow, with implications for understanding late-time acceleration and constraining dark energy models.

Contribution

It provides a perturbative calculation of the averaged shear caused by backreaction, linking anisotropy to cosmological parameters and matter power spectrum.

Findings

Averaged shear ranges from 2% to 37% at redshift ~0.5.

Backreaction-induced shear differs from homogeneous shear in evolution and amplitude.

Isotropy of Hubble flow can constrain backreaction models.

Abstract

Backreaction effects of the large scale structure on the background dynamics have been claimed to lead to a renormalization of the background dynamics that may account for the late time acceleration of the cosmic expansion. This article emphasizes that generically the averaged flow is locally anisotropic, a property that can be related to observation. Focusing on perturbation theory, the spatially averaged shear, that characterizes the anisotropy of the flow, is computed. It is shown that this shear arising from backreaction differs from a homogeneous shear: its time evolution is different and its amplitude is completely determined by the cosmological parameters and the matter power spectrum. It ranges within (2-37)% at a redshift of order 0.5 so that the isotropy of the Hubble flow may allow to constrain the backreaction approach to dark energy.