Further considerations on the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>CP</mml:mi></mml:math>asymmetry in heavy majorana neutrino decays

Abstract

We work out the thermodynamic equations for the decays and scatterings of heavy Majorana neutrinos including the constraints from unitarity. The Boltzmann equations depend on the $\mathrm{CP}$ asymmetry parameter which contains both a self-energy and a vertex correction. At thermal equilibrium there is no net lepton asymmetry due to the $\mathrm{CPT}$ theorem and the unitarity constraint. We show explicitly that deviations from thermal equilibrium create lepton asymmetry.