Low scale type I seesaw model for lepton masses and mixings

A E Cárcamo Hernández,Nicolás A Neill,Marcela González

doi:10.1103/physrevd.101.035005

Abstract

In contrast to the original type I seesaw mechanism that requires right-handed Majorana neutrinos at energies much higher than the electroweak scale, the so-called low scale seesaw models allow lighter masses for the additional neutrinos. Here we propose an alternative low scale type I seesaw model, where neither linear nor inverse seesaw mechanisms take place, but the spontaneous breaking of a discrete symmetry at an energy scale much lower than the model cutoff is responsible for the smallness of the light active neutrino masses. In this scenario, the model is defined with minimal particle content, where the right-handed Majorana neutrinos can have masses at the $\sim 50\mbox{ GeV}$ scale. The model is predictive in the neutrino sector having only four effective parameters that allow to successfully reproduce the experimental values of the six low energy neutrino observables.

Highlights

After minimally extending the Standard Model (SM) to include massive neutrinos, the observed fermion mass hierarchy is extended over a range of 13 orders of magnitude, from the lightest active neutrino mass scale up to the top quark mass
In this work we propose an extension of the SM based on the A4 family symmetry, which is supplemented by a Z4 auxiliary symmetry, whose spontaneous breaking at an energy scale much lower than the model cutoff (Λ) produces the small light active neutrino mass scale mν
We propose an extension of the SM where the scalar sector is augmented by the inclusion of four gauge-singlet scalar fields and the SM gauge symmetry is supplemented by the A4 × Z4 discrete group

Summary

INTRODUCTION

After minimally extending the Standard Model (SM) to include massive neutrinos, the observed fermion mass hierarchy is extended over a range of 13 orders of magnitude, from the lightest active neutrino mass scale up to the top quark mass. It would be desirable to build an A4 flavor model which at low energies reduces to the SM model and where the different gauge singlet scalars are accommodated into A4 singlets and one A4 triplet [with VEV pattern in the (1,1,1) A4 direction] which satisfies the minimization condition of the scalar potential for the whole range of values of the parameter space To this end, in this work we propose an extension of the SM based on the A4 family symmetry, which is supplemented by a Z4 auxiliary symmetry, whose spontaneous breaking at an energy scale (vS) much lower than the model cutoff (Λ) produces the small light active neutrino mass scale mν. We provide a concise description of the A4 discrete group

MODEL DESCRIPTION

NEUTRINO MASSES AND MIXINGS

SUMMARY AND CONCLUSIONS