Meso-inflationary Peccei-Quinn symmetry breaking with non-minimal coupling

TL;DR

This paper explores a novel inflationary model where the Peccei-Quinn symmetry is broken during inflation due to non-minimal gravity coupling, leading to distinctive scalar perturbations and gravitational wave signatures.

Contribution

It introduces a two-stage inflationary scenario with PQ symmetry breaking facilitated by non-minimal coupling, and analyzes resulting perturbations and gravitational wave signals.

Findings

Scalar perturbations are amplified at small scales.

Generated isocurvature perturbations lead to detectable gravitational waves.

The model predicts specific signatures for next-generation experiments.

Abstract

We study a realization of the inflationary scenario where the Peccei-Quinn (PQ) symmetry is spontaneously broken during inflation, facilitated by its non-minimal coupling to gravity. This results in effectively two-field inflation: the early stage is driven by an inflaton field with the PQ symmetry intact, and the later stage is driven by the PQ scalar after its effective mass becomes tachyonic, causing destabilization from the origin. The non-minimal coupling serves the dual purpose of restoring the PQ symmetry during early inflation and flattening the PQ potential post-tachyonic shift, allowing for continued slow roll. We analyze the inflationary background solutions and scalar perturbations, which are amplified at small scales via significant isocurvature perturbations generated near the symmetry-breaking epoch. These perturbations lead to second-order gravitational waves, detectable by next-generation space-based experiments.