Dilution of axion dark radiation by thermal inflation

TL;DR

This paper investigates how thermal inflation driven by a gauged Higgs field can dilute axion dark radiation, addressing conflicts with dark radiation constraints and exploring implications for baryogenesis in models with a gauged $U(1)$ symmetry.

Contribution

It introduces a mechanism where thermal inflation driven by a gauged Higgs field dilutes axion dark radiation, with implications for $U(1)_{B-L}$ symmetry and baryogenesis.

Findings

Thermal inflation can significantly reduce axion dark radiation density.

The model is compatible with baryogenesis mechanisms.

Implications for local $B-L$ symmetry in early universe cosmology.

Abstract

Axions in the Peccei-Quinn (PQ) mechanism provide a promising solution to the strong CP problem in the standard model of particle physics. Coherently generated PQ scalar fields could dominate the energy density in the early Universe and decay into relativistic axions, which would conflict with the current dark radiation constraints. We study the possibility that a thermal inflation driven by a $U(1)$ gauged Higgs field dilutes such axions. A well-motivated extra gauged $U(1)$ would be the local $B-L$ symmetry. We also discuss the implication for the case of $U(1)_{B-L}$ and an available baryogenesis mechanism in such cosmology.