Temperature-dependence of the QCD topological susceptibility
We recently obtained an estimate of the axion mass based on the hypothesis that axions make up most of the dark matter in the universe. A key ingredient for this calculation was the temperature-dependence of the topological susceptibility of full QCD. In the talk I summarize the calculation of the susceptibility in a range of temperatures from well below the finite temperature cross-over to around 2 GeV. The two main difficulties of the calculation are the poor sampling of nonzero topological sectors at high temperature and an unexpectedly slow convergence of the susceptibility to its continuum limit. I discuss how these problems can be solved by two new techniques, the first one with the integration method and the second one with reweighting using the quark zero modes.
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Nonzero Temperature and Density