Contribution of the hybrid inflation waterfall to the primordial curvature perturbation

TL;DR

This paper investigates the contribution of the waterfall phase in hybrid inflation to the primordial curvature perturbation, highlighting potential implications for small-scale structure and black hole formation.

Contribution

It provides a corrected calculation of the curvature perturbation generated during the waterfall phase in standard hybrid inflation, addressing inaccuracies in previous studies.

Findings

The waterfall contribution can be significant on small scales.

Earlier calculations of this contribution were incorrect.

The corrected calculation clarifies the impact on primordial perturbations.

Abstract

A contribution $\zeta_\chi$ to the curvature perturbation will be generated during the waterfall that ends hybrid inflation, that may be significant on small scales. In particular, it may lead to excessive black hole formation. We here consider standard hybrid inflation, where the tachyonic mass of the waterfall field is much bigger than the Hubble parameter. We calculate $\zeta_\chi$ in the simplest case, and see why earlier calculations of $\zeta_\chi$ are incorrect.