Warm-assisted natural inflation

TL;DR

This paper explores warm natural inflation with a temperature-dependent dissipation, showing it can align with Planck 2018 data, especially favoring weak dissipation and constraining the inflation scale.

Contribution

It introduces a warm inflation model with a T^3-dependent dissipation coefficient, analyzing its compatibility with observational data and exploring its parameter space.

Findings

Weak dissipative regime is preferred for f=5 M_pl.

Inflation begins cold and transitions to thermal dominance.

f<1 M_pl is excluded by observational constraints.

Abstract

We consider natural inflation in a warm inflation framework with a temperature-dependent dissipative coefficient $\Gamma \propto T^3$. Natural inflation can be compatible with the Planck 2018 results with such warm assistance. With no a priori assumptions on the dissipative effect's magnitude, we find that the Planck results prefer a weak dissipative regime for our benchmark scale $f=5 M_{\rm pl}$, which lies outside the $2\sigma$ region in the cold case. The inflation starts in the cold regime and evolves with a growing thermal fluctuation that dominates over quantum fluctuation before the end of the inflation. The observed spectral tilt puts stringent constraints on the model's parameter space. We find that $f< 1 M_{\rm pl}$ is excluded. A possible origin of such dissipative coefficient from axion-like coupling to gauge fields and tests of the model are also discussed.