Theory and phenomenology of Dirac neutrinos

TL;DR

This thesis explores the theoretical possibility of neutrinos being Dirac particles, examining the necessary symmetries, their connections to dark matter, and presenting models with distinctive phenomenological predictions.

Contribution

It provides a comprehensive analysis of Dirac neutrino models, including symmetry requirements, generalized seesaw frameworks, and detailed phenomenological models.

Findings

Extra symmetries are needed to protect Dirac neutrino nature.

Generalized Weinberg operators enable model-independent analysis.

Two models with rich phenomenological predictions are studied in detail.

Abstract

In this thesis I discuss in some detail the possibility that neutrinos are Dirac. If this is indeed the case, some extra symmetries beyond the Standard Model gauge group need to be enforced in order to protect Diracness and the smallness of neutrino mass. These symmetries may have a deep connection with other physics sectors, like Dark Matter stability. I also review the general seesaw framework applied to Dirac neutrinos in a model-independent way thanks to the analysis of generalized Weinberg operators and give some simple, elegant UV complete examples both for seesaw variants and radiative mass models. Finally I study in some detail two models with very rich phenomenological predictions.