The axion-photon coupling from lattice Quantum Chromodynamics

by José Javier Hernández Hernández (Central China Normal University)

Thursday 17 Sept 2026, 15:10 → 16:10 Asia/Shanghai

S408

The axion is a prime dark matter candidate that aditionally solves the strong CP problem. Its experimental detection relies on the axion-photon coupling, which receives a model-independent contribution from Quantum Chromodynamics (QCD). Previously, this contribution was only estimated via different variants of Chiral Perturbation Theory (ChPT) with inconsistent results. We present the first non-perturbative, first-principles determination of the QCD axion-photon coupling using continuum-extrapolated lattice simulations. We obtain $g_{A\gamma\gamma}^{\rm QCD} = -1.77(8)\alpha_{em}/(2\pi f_A)$, which is about 10% smaller in magnitude than the ChPT prediction quoted by the PDG. In this talk we will describe how this quantity can be extracted by studying the response of the QCD vacuum to a time-reversal violating combination of electromagnetic fields and discuss how our result modifies the constraints over the landscape of viable axion models, providing guidance for ongoing and future experimental searches.
Based on arXiv:2603.29153

Bio:
José Javier Hernández Hernández is a postdoctoral researcher at the Institute of Particle Physics, Central China Normal University, in Wuhan, working on lattice QCD in background electromagnetic fields. His current work concerns topology and the restoration of chiral and $U(1)_A$ symmetry in strong magnetic fields. He obtained his PhD from Bielefeld University in 2025 under Gergely Endrődi, with a thesis on QCD topology, axions and electromagnetic fields. During his PhD he established the magnetic-field dependence of the topological susceptibility across the chiral crossover and provided the first lattice determination of the axion–photon coupling.