Not So Minimal Warm Inflation

TL;DR

This paper investigates the viability of minimal warm inflation models driven by axion-like inflatons coupled to gauge bosons, focusing on the hierarchy of decay constants and observational constraints.

Contribution

It critically assesses the clockwork mechanism's ability to produce necessary hierarchies and explores effective descriptions consistent with observations.

Findings

Clockwork mechanism cannot generate the required hierarchy.

Partial-wave unitarity bounds allow effective models consistent with observations.

Thermal friction can sustain inflation from cold initial conditions.

Abstract

An axion-like inflaton coupled to non-Abelian gauge bosons provides a compelling microphysical framework for warm inflation. Starting even from cold initial conditions, in these systems, sphaleron heating may generate thermal friction sufficient to sustain finite temperatures throughout the inflationary epoch. Insisting on shift-symmetric potentials, in this work we revisit the viability of these scenarios under the designation of Minimal Warm Inflation. We examine both observational constraints and model-building limitations on models with a hierarchy between the decay constants appearing in the friction rate and in the inflaton potential. We conclude that the popular clockwork mechanism cannot generate the required hierarchy; however, partial-wave unitarity bounds admit effective descriptions that remain consistent with observations.