Decay of heavy Majorana neutrinos using the full Boltzmann equation including its implications for leptogenesis

Abstract

We have studied the two-body production and decay of a heavy, right-handed neutrino to two light states using the full Boltzmann equation instead of the usual integrated Boltzmann equation which assumes kinetic equilibrium of all species. Decays and inverse decays are inefficient for thermalising the distribution function of the heavy neutrino and in some parameter ranges there can be very large deviations from kinetic equilibrium. This leads to substantial numerical differences between the two approaches. Furthermore we study the impact of this difference on the lepton asymmetry production during leptogenesis and find that in the strong washout regime the final asymmetry is changed by 15-30% when the full Boltzmann equation is used.