• topological susceptibility
• QCD
• axions
• topology

In this work Topology in N_f=2+1 full QCD with staggered fermions at high temperature is studied by means of numerical simulations. In particular, a method which combines the multicanonical algorithm (which allows us to sample correctly the topological charge probability distribution in the high temperature regime) and the spectral projectors method (which, according to a recent study with twisted mass fermions in the zero temperature case, seems to give very small cut-off effects) is used in order to have a more reliable estimation of the topological susceptibility (χ). First of all, the spectral projectors method with staggered fermions is tested in full QCD at zero temperature. In particular, the topological susceptibility in the continuum limit is measured and a comparison with a gluonic definition is done. Then we focus on the high temperature regime. We have investigated two temperatures: T=430 MeV and T=570 MeV. We find that it is possible to suppress O(a^2) corrections and strongly reduce cut-off effects which are larger in the gluonic definition. In this temperature regime, there is no a theoretical estimation of the exact functional form of the topological susceptibility dependence on the temperature so we cannot verify the validity of our results. However, according to the Dilute Instanton Gas Approximation (which is valid at high temperatures), χ(T)= c T^{-D_2} where D_2~8 and c is a constant and our two estimations are compatible with this power law behaviour.