Topological observables and θ dependence in high temperature QCD from lattice simulations

A bstract We study topology in Quantum Chromodynamics at high temperatures by means of lattice calculations. Simulations are performed with N f = 2 + 1 + 1 Wilson twisted mass fermions at maximal twist with physical quark masses, and temperatures T ≳ 180 MeV. The results obtained with three lattice spacings ranging between 0 . 057 and 0 . 080 fm are extrapolated to the continuum limit. We compare the results for the topological susceptibility obtained with the field-theoretic definition with those obtained from an observable constructed with the disconnected part of the chiral susceptibility, and we confirm their agreement — within the largish errors — on our range of temperatures. We also study the topological charge distribution, the next order cumulant b 2 and, for the first time, the Free Energy as a function of the θ angle. We find a rapid crossover to the Dilute Instanton Gas behaviour above T ≃ 300 MeV for all the observables we have considered.