Abstract
With an emphasis on unitarity and CPT requirements, we study the inclusion of CP-violating processes in baryogenesis at next-to-leading order, particularly those involving the top Yukawa interaction in leptogenesis. We show that there are more contributions than previously considered, but also important cancellations. Some of these involve the interference of connected with disconnected diagrams. We also discuss on the application of the Kinoshita-Lee-Nauenberg theorem to treat the infrared divergences that are common at next-to-leading order. Finally, we calculate the CP asymmetry in the three-body decay of a sterile neutrino into a lepton and top quarks.
Highlights
O λ2t, for arbitrary values of the sterile neutrino masses
With an emphasis on unitarity and CPT requirements, we study the inclusion of CP-violating processes in baryogenesis at next-to-leading order, those involving the top Yukawa interaction in leptogenesis
Using unitarity and CPT invariance we have derived in a simple way the source term of the Boltzmann equations (BE) for the density asymmetry of some particle denoted generically by a
Summary
A widely used and simple approximation to follow the evolution of lepton and baryon asymmetries is to set classical BE in an expanding universe, with quantum effects entering only in the calculation of cross sections and decay rates. A conclusion that stands out is that the only contributions to the source of the BE for ∆fa come from production processes of “a” (or “a”) particles, with an out-of-equilibrium species N in the initial state. They find that the generation of an asymmetry from scatterings (as opposed to decays) with only a single out-of-equilibrium heavy particle is not possible. This is, for instance, the case in “purely flavoured leptogenesis” [29], where flavour effects allow a baryon asymmetry to be generated even when the total CP asymmetry (i.e. summed over all lepton flavours) is zero
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