Systematic Analysis of Dirac Neutrino Masses at Dimension Five

TL;DR

This paper systematically analyzes how Dirac neutrino masses can originate from a dimension five operator, exploring all tree and one-loop realizations, their particle content, and implications for dark matter candidates.

Contribution

It provides a comprehensive classification of models generating Dirac neutrino masses via a dimension five operator, including symmetry considerations and dark matter connections.

Findings

All possible tree-level and one-loop realizations identified.

Dark matter candidates are associated with loop mediators.

Constraints on model parameters for viable dark matter are discussed.

Abstract

We perform a systematic study of the Dirac neutrino masses which arise from a dimension five effective operator with a singlet scalar. We identify all possible realizations of this operator at tree level and one-loop level. The corresponding predictions for the particle content and neutrino mass matrix are presented. We add a $Z_{2}$ symmetry to forbid the renormalizable Yukawa coupling, and non-abelian discrete flavor symmetry can be used to forbid tree level diagrams in non-genuine one-loop models. The electrically neutral particle mediating the loop diagram could be dark matter candidate. We give the possible dark matter particles and the restrictions on the parameter $\alpha$ for each model.