Semiclassical relations and IR effects in de Sitter and slow-roll space-times
Steven B. Giddings, Martin S. Sloth
TL;DR
This paper shows that infrared gravitons generate leading one-loop corrections to scalar and tensor correlators in de Sitter and slow-roll space-times, which can be captured by simple semiclassical consistency relations. These IR effects accumulate over long inflation and can shift key observables such as the tensor-to-scalar ratio and non-Gaussianity, potentially driving perturbation theory into a non-perturbative regime for sufficiently prolonged inflation. The authors verify the semiclassical predictions with explicit in-in calculations and discuss limitations of the $\delta N$ approach in capturing tensor IR effects, drawing intriguing parallels to non-perturbative dynamics in black hole physics. The work highlights the need for a non-perturbative description of IR gravitational effects and explores their implications for chaotic inflation scenarios and the late-time behavior of cosmological fluctuations.
Abstract
We calculate IR divergent graviton one-loop corrections to scalar correlators in de Sitter space, and show that the leading IR contribution may be reproduced via simple semiclassical consistency relations. One can likewise use such semiclassical relations to calculate leading IR corrections to correlators in slow-roll inflation. The regulated corrections shift the tensor/scalar ratio and consistency relation of single field inflation, and non-gaussianity parameters averaged over very large distances. For inflation of sufficient duration, for example arising from a chaotic inflationary scenario, these corrections become of order unity. First-order corrections of this size indicate a breakdown of the perturbative expansion, and suggest the need for a non-perturbative description of the corresponding regime. This is analogous to a situation argued to arise in black hole evolution, and to interfere with a sharp perturbative calculation of "missing information" in Hawking radiation.