Leptogenesis in the two right-handed neutrino model revisited

TL;DR

This paper reexamines leptogenesis in a minimal two right-handed neutrino model, revealing that the second neutrino can significantly contribute, especially near specific parameter values, potentially lowering the required neutrino mass scale.

Contribution

It demonstrates that including the second right-handed neutrino's contribution alters leptogenesis dynamics, especially around certain parameter regions, and connects these findings to light sequential dominance.

Findings

N_2 contribution can dominate leptogenesis near z ≈ ±π/2

Lightest RH neutrino mass can be reduced to ~1.3×10^11 GeV

Results supported by analytic estimates and relevant to model building

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 N_1 and N_2 to contribute, rather than just the lightest RH neutrino N_1 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 \sim \pm \pi/2, for the case of a normal mass hierarchy, the N_2 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 M_1 \sim 1.3*10^11 GeV for vanishing initial N_2-abundance, with the numerical results supported by analytic estimates. We show that the regions around z \sim \pm \pi /2 correspond to light sequential dominance, so the new results in this paper may be relevant to unified model building.