Testing constrained sequential dominance models of neutrinos

Abstract

Constrained sequential dominance (CSD) is a natural framework for implementing the see-saw mechanism of neutrino masses which allows the mixing angles and phases to be accurately predicted in terms of relatively few input parameters. We analyze a class of CSD(n) models where, in the flavour basis, two right-handed neutrinos are dominantly responsible for the 'atmospheric' and 'solar' neutrino masses with Yukawa couplings to $({\\nu }_{e},{\\nu }_{\\mu },{\\nu }_{\\tau })$ proportional to $(0,1,1)$ and $(1,n,n-2),$ respectively, where n is a positive integer. These coupling patterns may arise in indirect family symmetry models based on A 4. With two right-handed neutrinos, using a χ 2 test, we find a good agreement with data for CSD(3) and CSD(4) where the entire Pontecorvo–Maki–Nakagawa–Sakata mixing matrix is controlled by a single phase η, which takes simple values, leading to accurate predictions for mixing angles and the magnitude of the oscillation phase $| {\\delta }_{\\mathrm{CP}}| .$ We carefully study the perturbing effect of a third 'decoupled' right-handed neutrino, leading to a bound on the lightest physical neutrino mass ${m}_{1}{\\rm{\\lesssim }}1$ meV for the viable cases, corresponding to a normal neutrino mass hierarchy. We also discuss a direct link between the oscillation phase ${\\delta }_{\\mathrm{CP}}$ and leptogenesis in CSD(n) due to the same see-saw phase η appearing in both the neutrino mass matrix and leptogenesis.