Analysis of leptogenesis in a supersymmetric triplet seesaw model

We analyze leptogenesis in a supersymmetric triplet seesaw scenario that explains the observed neutrino masses, adopting a phenomenological approach where the decay branching ratios of the triplets and the amount of $CP$ violation in its different decay channels are assumed as free parameters. We find that the solutions of the relevant Boltzmann equations lead to a rich phenomenology, in particular, much more complex compared to the nonsupersymmetric case, mainly due to the presence of an additional Higgs doublet. Several unexpected and counter-intuitive behaviors emerge from our analysis: the amount of $CP$ violation in one of the decay channels can prove to be irrelevant to the final lepton asymmetry, leading to successful leptogenesis even in scenarios with a vanishing $CP$ violation in the leptonic sector; gauge annihilations can be the dominant effect in the determination of the evolution of the triplet density up to very high values of its mass, leading anyway to a sizeable final lepton asymmetry, which is also a growing function of the washout parameter $K\ensuremath{\equiv}{\ensuremath{\Gamma}}_{d}/H$, defined as usual as the ratio between the triplet decay amplitude ${\ensuremath{\Gamma}}_{d}$ and the Hubble constant $H$; on the other hand, cancellations in the Boltzmann equations may lead to a vanishing lepton asymmetry if in one of the decay channels both the branching ratio and the amount of $CP$ violation are suppressed, but not vanishing. The present analysis suggests that in the supersymmetric triplet seesaw model successful leptogenesis can be attained in a wide range of scenarios, provided that an asymmetry in the decaying triplets can act as a lepton-number reservoir.