Quantum gravitational backreaction in the case of the local Hubble rate

Markus Frob (Leipzig/York)

6 March 2019

We determine corrections to the Hubble rate due to graviton loops in a cosmological background spacetime of constant deceleration parameter. The corrections are gauge-invariant, based on a recent proposal for all-order gauge-invariant observables in perturbative quantum gravity.

We find explicit expressions for the cases of matter – and radiation-dominated eras and slow-roll inflation with vanishing second slow-roll parameter. Interestingly, in the latter case the corrections can be described by a quantum-corrected first slow-roll parameter, which brings the spacetime closer to de Sitter space (based on arXiv:1806.11124).