Gauge invariant averages for the cosmological backreaction

Abstract

We show how to provide suitable gauge invariant prescriptions for the classical spatial averages (resp. quantum expectation values) that are needed in the evaluation of classical (resp. quantum) backreaction effects. We also present examples illustrating how the use of gauge invariant prescriptions can avoid interpretation problems and prevent misleading conclusions.Comment: 21 pages, no figures. Comments and references added, typos corrected. Small corrections and reference added, matches version published in JCA