Neutrino Masses and a Fourth Generation of Fermions

TL;DR

This paper investigates how neutrino masses can be generated in models with four fermion generations, analyzing different contributions and their experimental constraints, and exploring flavor symmetry applications in this extended framework.

Contribution

It introduces a comprehensive analysis of neutrino mass generation mechanisms in four-generation models, including new flavor symmetry applications and parameter space exploration.

Findings

Identification of parameter regions where different neutrino mass contributions dominate

Analysis of experimental bounds on mixing and mass parameters

Proposal of flavor symmetry models suitable for four-generation scenarios

Abstract

We study neutrino mass generation in models with four chiral families of leptons and quarks and four right handed neutrinos. Generically, in these models there are three different contributions to the light neutrino masses: the usual see-saw contribution, the tree-level contribution due to mixing of light neutrinos with neutrino of the fourth generation, and the two loop contribution due to the Majorana mass term of the fourth neutrino. We study properties of these contributions and their experimental bounds. The regions of the parameters (mixings of the fourth neutrino, masses of RH neutrino components, etc.) have been identified where various contributions dominate. New possibilities of a realization of the flavour symmetries in the four family context are explored. In particular, we consider applications of the smallest groups, e.g. SG(20,3), with irreducible representation 4.