Hybrid inflation and gravitational waves from accidentally light scalars

TL;DR

This paper presents a hybrid inflation model with radiatively generated potential, predicting specific CMB correlations and gravitational waves from tachyonic preheating, potentially detectable by future experiments and consistent with pulsar timing array observations.

Contribution

It introduces a minimal hybrid inflation model with radiative potential generation and links gravitational wave production to tachyonic preheating and topological defects.

Findings

Predicts specific correlations among CMB observables.

Gravitational waves from tachyonic preheating may be detectable.

Topological defects produce a stochastic gravitational wave background.

Abstract

We construct a hybrid-inflation model where the inflaton potential is generated radiatively, as gauge symmetries guarantee it to be accidentally flat at tree level. The model can be regarded as a small-field version of Natural Inflation, with inflation ending when the mass of a second scalar, the waterfall field, turns tachyonic. This provides a minimal, robust realization of hybrid inflation, which predicts specific correlations among Cosmic Microwave Background observables. Tachyonic preheating leads to the production of gravitational waves which, for a low inflationary scale, might be detected by upcoming experiments. Simple variations of the model can give rise to topological defects, such as unstable domain walls. Their dynamics produces a stochastic gravitational wave background, which can be compatible with the recent detection by pulsar timing arrays.