Scale dependence of cosmological backreaction

TL;DR

This paper investigates how cosmic inhomogeneities affect the universe's evolution through backreaction, analyzing scale dependence up to higher orders and comparing results with Newtonian cosmology and observational data.

Contribution

It provides a perturbative analysis of backreaction effects as a function of scale, identifying critical scales where effects become significant and highlighting the dominant role of spatial curvature.

Findings

A 10% backreaction effect appears at scales of 200 Mpc.

The local Hubble rate variance is 10% at 40 Mpc and 5% at 60 Mpc.

A comparison with Newtonian cosmology and observational data is presented.

Abstract

Due to the non-commutation of spatial averaging and temporal evolution, inhomogeneities and anisotropies (cosmic structures) influence the evolution of the averaged Universe via the cosmological backreaction mechanism. We study the backreaction effect as a function of averaging scale in a perturbative approach up to higher orders. We calculate the hierarchy of the critical scales, at which 10% effects show up from averaging at different orders. The dominant contribution comes from the averaged spatial curvature, observable up to scales of 200 Mpc. The cosmic variance of the local Hubble rate is 10% (5%) for spherical regions of radius 40 (60) Mpc. We compare our result to the one from Newtonian cosmology and Hubble Space Telescope Key Project data.