Effective field theory of waterfall in hybrid inflation

TL;DR

This paper investigates the validity of the classical approximation during the waterfall phase of hybrid inflation using effective field theory, revealing that waterfall field fluctuations can dominate and spoil classical predictions.

Contribution

It constructs an EFT for hybrid inflation's waterfall phase and derives conditions under which the classical approximation remains valid.

Findings

Waterfall field fluctuations can dominate early in the phase.

Classical approximation may be invalid due to backreaction.

Derived constraints ensure EFT validity during waterfall transition.

Abstract

We examine the validity of the classical approximation of the waterfall phase transition in hybrid inflation from an effective field theory (EFT) point of view. The EFT is constructed by integrating out the waterfall field fluctuations, up to one-loop order in the perturbative expansion. Assuming slow-roll conditions are obeyed, right after the onset of the waterfall phase, we find the backreaction of the waterfall field fluctuations to the evolution of the system can be dominant. In this case the classical approximation is completely spoiled. We derive the necessary constraint that ensures the validity of the EFT.