Leptogenesis in the two right-handed neutrino model revisited
Abstract
We revisit leptogenesis in the minimal non-supersymmetric type I see-saw mechanism with two right-handed (RH) neutrinos, including flavour effects and allowing both RH neutrinos N1 and N2 to contribute, rather than just the lightest RH neutrino N1 that has hitherto been considered. By performing scans over parameter space in terms of the single complex angle z of the orthogonal matrix R, for a range of PMNS parameters, we find that in regions around z π/2, for the case of a normal mass hierarchy, the N2 contribution can dominate the contribution to leptogenesis, allowing the lightest RH neutrino mass to be decreased by about an order of magnitude in these regions, down to M1 1.3*1011 GeV for vanishing initial N2-abundance, with the numerical results supported by analytic estimates. We show that the regions around z π /2 correspond to light sequential dominance, so the new results in this paper may be relevant to unified model building.