Axion Phenomenology from Unquenched Lattice QCD

par Prof. Guido Martinelli (Roma La Sapienza)

The properties of the QCD axion can be studied from the dependence of strong interactions on the $\theta$-parameter. We present a study of the moments of the topological charge for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors at the physical quark masses. Our numerical results for the topological susceptibility, when compared to the instanton gas calculation, differ both in size and in the temperature dependence. We discuss the implications of these results for axion phenomenology, a comparison with other more recent studies and the prospects for future investigations. We also present some new results recently obtained at finer lattice spacing using metadynamics to reduce the systematic error due to the topological freezing.
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