Leptogenesis from Lepton-Number-Breaking Scalars

Leptogenesis via right-handed neutrino (RHN) decay is a well-motivated model of baryogenesis that arises naturally in models accommodating Standard Model neutrino masses. The origin of the RHN masses is unknown, but if their masses arise dynamically the resulting lepton asymmetry can be suppressed due to the additional RHN interactions present. In this work, we show that in such scenarios there exists a previously unconsidered source of lepton asymmetry from the decays of the Higgs boson responsible for spontaneously breaking lepton number. This new source can greatly exceed the contribution to the asymmetry from to the decay of RHNs themselves, and render leptogenesis viable for parameters that otherwise wouldn't work in the minimal scenario. We present analytic and numerical studies of the asymmetry due to lepton-number-breaking scalar decay, along with cosmological and theoretical considerations for when this new source could be relevant for leptogenesis.