Multiple Axions Save High-Scale Inflation

TL;DR

Multiple axion theories can enable high-scale inflation with detectable tensor modes by avoiding the domain wall problem, through specific anomaly coefficient conditions ensuring a unique axion potential minimum.

Contribution

The paper demonstrates that theories with multiple axions can circumvent the domain wall problem, allowing high-scale inflation compatible with observable tensor fluctuations without fine-tuning.

Findings

High-scale inflation can produce detectable tensor modes in multi-axion models.

A condition on anomaly coefficients ensures a unique axion potential minimum.

Multi-axion models evade the domain wall problem common in single-axion scenarios.

Abstract

Many models of dark matter QCD axion requires inflation at a scale $H_{\text{inf}} \lesssim 10^{6}$~GeV and hence does not allow for a detectable tensor mode fluctuation. This is because the domain wall problem forces the Peccei--Quinn symmetry to be broken during the inflation and the axions to be produced by the misalignment mechanism. We point out that theories with multiple axions can evade this constraint and allow for a high-scale inflation with detectable tensor mode. It only requires a condition on the anomaly coefficients so that there is a unique minimum for the axion potential without a fine-tuning or small parameters.