Quantum gravitational backreaction in the case of the local Hubble rate
Markus Frob (Leipzig/York)
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).