Seesaw Dirac neutrino mass through dimension-6 operators

TL;DR

This paper explores various pathways to generate Dirac neutrino masses via dimension-6 operators within the Standard Model framework, considering additional scalars and symmetries that may also stabilize dark matter.

Contribution

It systematically analyzes the simplest dimension-6 operators involving new scalar fields and their role in Dirac neutrino mass generation, extending previous work.

Findings

Identified unique and multiple field contraction possibilities for Dirac neutrino masses.

Demonstrated how extra symmetries can simultaneously ensure neutrino Dirac nature and dark matter stability.

Detailed the role of $SU(2)_L$ singlets, doublets, and triplets in these mechanisms.

Abstract

In this paper, a followup of arXiv: 1802.05722, we describe the many pathways to generate Dirac neutrino mass through dimension-6 operators. By using only the Standard Model Higgs doublet in the external legs one gets a unique operator $\frac{1}{\Lambda^2} \, \bar{L}\, \bar{\Phi} \, \bar{\Phi} \, \Phi \, \nu_R $. In contrast, the presence of new scalars implies new possible field contractions, which greatly increase the number of possibilities. Here we study in detail the simplest ones, involving $SU(2)_L$ singlets, doublets and triplets. The extra symmetries needed to ensure the Dirac nature of neutrinos can also be responsible for stabilizing dark matter.