IR Divergences in Inflation and Entropy Perturbations

TL;DR

This paper investigates infrared divergences in inflationary perturbations, revealing that entropy mode loops cause power-law divergences and impose constraints on interaction couplings, affecting the stability of de Sitter space.

Contribution

It provides a detailed analysis of IR divergences from entropy modes in inflation, highlighting their severity and implications for perturbation theory validity and de Sitter stability.

Findings

Infrared divergences are power-law, not logarithmic.

Perturbation theory breaks down if entropy self-coupling exceeds a critical value.

Quantum effects on de Sitter stability are amplified by entropy fluctuations.

Abstract

We study leading order perturbative corrections to the two point correlation function of the scalar field describing the curvature perturbation in a slow-roll inflationary background, paying particular attention to the contribution of entropy mode loops. We find that the infrared divergences are worse than in pure de Sitter space: they are power law rather than logarithmic. The validity of perturbation theory and thus of the effective field theory of cosmological perturbations leads to stringent constraints on the coupling constants describing the interactions, in our model the quartic self-interaction coupling constant of the entropy field. If the self coupling constant is larger than some critical value which depends in particular on the duration of the inflationary phase, then perturbation theory breaks down. Our analysis may have implications for the stability of de Sitter space: the quantum effects which lead to an instability of de Sitter space will be larger in magnitude in the presence of entropy fluctuations.