Fermionic Quasiparticles in Higgs Boson and Heavy Neutrino Decay in Leptogenesis

We calculate the decay rate of the lightest heavy Majorana neutrino in a thermal bath using finite temperature cutting rules and effective Green's functions according to the hard thermal loop resummation technique. Analogously, we calculate the Higgs decay rate at higher temperature. Compared to the usual approach where thermal masses are inserted into the kinematics of final states, we find that deviations arise through two different leptonic dispersion relations. The decay rates differ from the usual approach by more than one order of magnitude in the temperature range which is interesting for the weak washout regime. Some aspects of this work have been published in Ref. [1], to which we refer the interested reader.