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Axion Phenomenology from Unquenched Lattice QCD

by Prof. Guido Martinelli (Roma La Sapienza)

mercredi 24 mai 2017 de à (Europe/Paris)
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.