A4 See-Saw Models and Form Dominance

TL;DR

This paper introduces the concept of Form Dominance in the type I see-saw mechanism, linking right-handed neutrino states to physical neutrino masses, and proposes Natural Form Dominance to address cancellation issues.

Contribution

It generalizes Constrained Sequential Dominance by allowing arbitrary neutrino spectra and develops minimal A4 see-saw models satisfying Form Dominance with predictive mass sum rules.

Findings

Models predict closely spaced neutrino masses with normal or inverted ordering.

Form Dominance leads to form diagonalizable effective neutrino mass matrices.

Natural Form Dominance reduces partial cancellations in neutrino mass models.

Abstract

We introduce the idea of Form Dominance in the (type I) see-saw mechanism, according to which a particular right-handed neutrino mass eigenstate is associated with a particular physical neutrino mass eigenstate, leading to a form diagonalizable effective neutrino mass matrix. Form Dominance, which allows an arbitrary neutrino mass spectrum, may be regarded as a generalization of Constrained Sequential Dominance which only allows strongly hierarchical neutrino masses. We consider alternative implementations of the see-saw mechanism in minimal A4 see-saw models and show that such models satisfy Form Dominance, leading to neutrino mass sum rules which predict closely spaced neutrino masses with a normal or inverted neutrino mass ordering. To avoid the partial cancellations inherent in such models we propose Natural Form Dominance, in which a different flavon is associated with each physical neutrino mass eigenstate.