Hierarchical Neutrino Masses and Mixing in Flipped-SU(5)

TL;DR

This paper explores how flipped SU(5) grand unified theory naturally produces hierarchical neutrino masses and mixing angles, including a small theta-13, through a seesaw mechanism involving gauge singlets.

Contribution

It introduces simple ansatze for singlet couplings in flipped SU(5) that generate realistic hierarchical neutrino masses and mixing matrices, with a focus on the role of the Cabbibo parameter.

Findings

Hierarchical neutrino masses emerge naturally in the model.

The mixing angle theta-13 is predicted to be the smallest.

A factorized parametrization of neutrino mass incorporates Cabbibo mixing and singlet sector effects.

Abstract

We consider the problem of neutrino masses and mixing in the framework of flipped SU(5). The right-handed neutrino mass, generated through the operation of a seesaw mechanism by a sector of gauge singlets, leads naturally, at a subsequent level, to the standard seesaw mechanism resulting into three light neutrino states with masses of the desired phenomenological order of magnitude. In this framework we study simple Ansatze for the singlet couplings for which hierarchical neutrino masses emerge naturally, parametrized in terms of the Cabbibo parameter. The resulting neutrino mixing matrices are characterized by a hierarchical structure, in which theta-(13) is always predicted to be the smallest. Finally, we discuss a possible factorized parametrization of the neutrino mass that, in addition to Cabbibo mixing, encodes also mixing due to the singlet sector.