Speaker
Description
Axions were first proposed as a solution to the strong CP problem, but they also act as prime dark matter candidates. Detection of axions hinges on their conversion to photons, governed by the axion-photon coupling. Besides the direct, modeling dependent part, coupling can be realized through sea effects of the strong interaction. The value of the latter can be calculated directly from QCD. We present the first non-perturbative determination of this contribution, employing CP violating background electromagnetic fields. We also discuss a novel method to estimate the topological charge based on the axial Ward identity. We obtain $g_{a\gamma\gamma}= -1.77(8)\alpha/(2\pi f_a)$, which is about 10% smaller in magnitude than and is in some tension with the ChPT prediction quoted by the PDG.