Soft leptogenesis in the inverse seesaw model

We consider leptogenesis induced by soft supersymmetry breaking terms ("softleptogenesis"), in the context of the inverse seesaw mechanism. In this modelthere are lepton number (L) conserving and L-violating softsupersymmetry-breaking B-terms involving the singlet sneutrinos which, togetherwith the -- generically small-- L-violating parameter responsible of theneutrino mass, give a small mass splitting between the four singlet sneutrinostates of a single generation. In combination with the trilinear softsupersymmetry breaking terms they also provide new CP violating phases neededto generate a lepton asymmetry in the singlet sneutrino decays. We obtain thatin this scenario the lepton asymmetry is proportional to the L-conserving softsupersymmetry-breaking B-term, and it is not suppressed by the L-violatingparameters. Consequently we find that, as in the standard see-saw case, thismechanism can lead to sucessful leptogenesis only for relatively small value ofthe relevant soft bilinear coupling. The right-handed neutrino masses can besufficiently low to elude the gravitino problem. Also the corresponding Yukawacouplings involving the lightest of the right-handed neutrinos are constrainedto be \sum |Y_{1k}|^2\lesssim 10^{-7} which generically implies that theneutrino mass spectrum has to be strongly hierarchical.Comment: 28 pages, 1 figure; some references added; final version to appear in JHE