Strong CP problem and axion dark matter with small instantons

TL;DR

This paper investigates how small instantons affect the axion mass and CP violation, proposing a high-scale inflation scenario where axion dark matter can have a large decay constant around 10^{15-16} GeV.

Contribution

It introduces a natural scenario for axion dark matter considering small-instanton effects, expanding the viable parameter space for high-scale inflation models.

Findings

Small instantons significantly modify the axion mass and CP phases.

A viable axion dark matter scenario with decay constants up to 10^{16} GeV.

The scenario is compatible with high-scale inflation models.

Abstract

The axion mass receives a large correction from small instantons if the QCD gets strongly coupled at high energies. We discuss the size of the new CP violating phases caused by the fact that the small instantons are sensitive to the UV physics. We also discuss the effects of the mass correction on the axion abundance of the Universe. Taking the small-instanton contributions into account, we propose a natural scenario of axion dark matter where the axion decay constant is as large as $10^{15\text{-}16}$GeV. The scenario works in the high-scale inflation models.