Issues concerning the waterfall of hybrid inflation

TL;DR

This paper examines the waterfall phase in hybrid inflation, focusing on quantum fluctuations and their impact on primordial curvature perturbations, concluding that the contribution is negligible on cosmological scales.

Contribution

It provides a simplified analysis of the waterfall process in hybrid inflation, addressing quantum fluctuation treatment and curvature perturbation contributions.

Findings

Quantum fluctuations of the waterfall field are negligible on cosmological scales.

The spectrum of curvature perturbations generated during the waterfall is strongly blue.

The analysis applies to GUT-scale inflation models.

Abstract

We discuss the waterfall that ends hybrid inflation. Making some simplifying assumptions, that may be satisfied by GUT inflation models, two issues are addressed. First, the procedure of keeping the quantum fluctuation of the waterfall field only in the regime where it can be regarded as classical. Second, the contribution to the primordial curvature perturbation that is generated during the waterfall. Because the waterfall field is heavy during inflation, the spectrum of this contribution is strongly blue and hence is negligible on cosmological scales.