A fuller flavour treatment of N_2-dominated leptogenesis

TL;DR

This paper enhances the understanding of N_2-dominated leptogenesis by including previously neglected flavour effects, especially off-diagonal couplings, revealing new mechanisms like phantom leptogenesis that can significantly alter the final matter-antimatter asymmetry.

Contribution

It introduces analytical formulas accounting for flavour coupling effects at different stages of leptogenesis, expanding the theoretical framework and potential scenarios for baryon asymmetry generation.

Findings

Analytical expressions for final asymmetry with flavour coupling effects.

Identification of phantom leptogenesis where asymmetries escape washout.

New possibilities for N_2-dominated leptogenesis scenarios.

Abstract

We discuss N_2-dominated leptogenesis in the presence of flavour dependent effects that have hitherto been neglected, in particular the off-diagonal entries of the flavour coupling matrix that connects the total flavour asymmetries, distributed in different particle species, to the lepton and Higgs doublet asymmetries. We derive analytical formulae for the final asymmetry including the flavour coupling at the N_2-decay stage as well as at the stage of washout by the lightest right-handed neutrino N_1. Moreover, we point out that in general part of the electron and muon asymmetries (phantom terms), can completely escape the wash-out at the production and a total B-L asymmetry can be generated by the lightest RH neutrino wash-out yielding so called phantom leptogenesis. However, the phantom terms are proportional to the initial N_2 abundance and in particular they vanish for initial zero N_2-abundance. Taking any of these new effects into account can significantly modify the final asymmetry produced by the decays of the next-to-lightest RH neutrinos, opening up new interesting possibilities for N_2-dominated thermal leptogenesis.