Modulation of the waterfall by a gauge field

TL;DR

This paper calculates how a gauge field coupled to the waterfall field during hybrid inflation influences curvature perturbations, revealing anisotropic signatures and a new varyon mechanism affecting inflaton dynamics.

Contribution

It provides the first complete calculation of curvature perturbations during the waterfall phase with gauge field coupling and introduces the varyon mechanism affecting inflaton variation.

Findings

Gauge field coupling induces anisotropic perturbations.

The varyon mechanism alters inflaton contribution during waterfall.

Observable anisotropic bispectrum may be detectable.

Abstract

We present the first complete calculation of the curvature perturbation generated during the hybrid inflation waterfall, caused by the coupling of the waterfall field to a gauge field A whose kinetic function f^2 depends on the inflaton field. We impose an upper bound on the field W=f*A which ensures that it has a negligible effect before the waterfall. We confirm the claim of Soda and Yokoyama, that the perturbation \delta W generates a statistically anisotropic spectrum and bispectrum, which could easily be observable. We also discover a new phenomenon, whereby the time-dependent `varyon' field W causes the inflaton contribution to vary during the waterfall. The varyon mechanism might be implemented also with a scalar field and might not involve the waterfall.