Recent progress on QCD inputs for axion phenomenology

TL;DR

This paper reports on lattice QCD simulations to determine the topological properties of QCD at finite temperatures, providing insights crucial for axion phenomenology and highlighting differences from instanton gas models.

Contribution

The study offers new lattice QCD results for the topological susceptibility at high temperatures with physical quark masses, improving understanding of axion-related QCD properties.

Findings

Topological susceptibility differs from instanton gas predictions in size and temperature dependence.

Results have significant implications for axion mass and coupling estimates.

Provides a basis for future high-temperature QCD studies.

Abstract

The properties of the QCD axion are strictly related to the dependence of strong interactions on the topological parameter theta. We present a determination of the topological properties of QCD for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors and physical quark masses. Numerical results for the topological susceptibility, when compared to instanton gas computations, differ both in size and in the temperature dependence. We discuss the implications of such findings for axion phenomenology, also in comparison to similar studies in the literature, and the prospects for future investigations.