Axion Models with High Scale Inflation

TL;DR

This paper explores how to prevent excessive axion dark radiation in high-scale inflation models by considering thermal dissipation effects and late-time decay of heavy scalars, offering new solutions to overproduction issues.

Contribution

It demonstrates that finite-temperature dissipation and late decay of heavy scalars can relax axion overproduction constraints in high-scale inflation scenarios.

Findings

Finite-temperature dissipation reduces axion overproduction.

Late decay of heavy scalars further relaxes constraints.

Thermal plasma interactions enable axion models to be consistent with observations.

Abstract

We revisit the cosmological aspects of axion models. In the high-scale inflation scenario, the Peccei-Quinn (PQ) symmetry is likely to be restored during/after inflation. If the curvature of the PQ scalar potential at the origin is smaller than its vacuum expectation value; for instance in a class of SUSY axion models, thermal inflation happens before the radial component of the PQ scalar (saxion) relaxes into the global minimum of the potential and the decay of saxion coherent oscillation would produce too much axion dark radiation. In this paper, we study how to avoid the overproduction of axion dark radiation with some concrete examples. We show that, by taking account of the finite-temperature dissipation effect appropriately, the overproduction constraint can be relaxed since the PQ scalar can take part in the thermal plasma again even after the PQ phase transition. We also show that it can be further relaxed owing to the late time decay of another heavy CP-odd scalar, if it is present.