HEP Theory Journal Club

Gauge-Invariant Corrections to the Expansion Rate

Vincent Comeau

McGill

In my talk, I will show how one can compute gauge-invariant perturbative corrections to the average expansion rate of an expanding spacetime, at any order in perturbation theory. I will focus exclusively on the classical theory (Einstein's gravity), and deal more specifically with the case of a spacetime containing a perfect fluid. As an example, I will compute the first-order correction to the average expansion rate generated by the scalar metric perturbations. I will show that such a correction is the same in different gauges, and that it grows with time for backgrounds where the conformal time increases with the scale factor.