The cosmological backreaction: gauge (in)dependence, observers and scalars

Abstract

We discuss several issues related to a recent proposal for defining classical spatial averages to be used in the so-called cosmological backreaction problem. In the large averaging-volume limit all gauge dependence disappears and different averages can be univocally characterized by the observers associated with different scalar fields. The relation between such averaging procedure and the standard one is emphasized and a gauge invariant way to select different observers is presented. For finite averaging volumes we show that, within our proposal, a residual gauge dependence is left, but is suppressed by several effects.

16 pages, no figures. Comments and references added, errors and typos corrected, conclusions unchanged. Comment added and typos corrected, version published in JCAP

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• Tensor Mode Backreaction During Slow-roll Inflation
• Kullback-Leibler entropy and Penrose conjecture in the Lemaitre-Tolman-Bondi model