The QCD axion, precisely

TL;DR

This paper demonstrates how to precisely determine the properties of the QCD axion using first-principle QCD calculations, combining chiral perturbation theory and lattice QCD results, with implications for axion detection and cosmology.

Contribution

The paper introduces a method to accurately compute the QCD axion potential, mass, and couplings by integrating lattice QCD and chiral perturbation theory, reducing uncertainties significantly.

Findings

Full axion potential and mass can be reconstructed with percent accuracy.

Axion couplings to nucleons are determined with less than ten percent uncertainty.

Finite temperature effects on the axion potential are computed up to the crossover region.

Abstract

We show how several properties of the QCD axion can be extracted at high precision using only first principle QCD computations. By combining NLO results obtained in chiral perturbation theory with recent Lattice QCD results the full axion potential, its mass and the coupling to photons can be reconstructed with percent precision. Axion couplings to nucleons can also be derived reliably, with uncertainties smaller than ten percent. The approach presented here allows the precision to be further improved as uncertainties on the light quark masses and the effective theory couplings are reduced. We also compute the finite temperature dependence of the axion potential and its mass up to the crossover region. For higher temperature we point out the unreliability of the conventional instanton approach and study its impact on the computation of the axion relic abundance.