Leptogenesis in the two right-handed neutrino model revisited

We revisit leptogenesis in the minimal nonsupersymmetric type I seesaw mechanism with two right-handed (RH) neutrinos, including flavor 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 leptonic mixing 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.