# Systematic classification of two loop d = 4 Dirac neutrino mass models and the Diracness-dark matter stability connection

## TL;DR

This paper systematically classifies all two-loop models for Dirac neutrino masses, exploring their topologies and diagrams, and highlights the link between neutrino Diracness and dark matter stability.

## Contribution

It provides a comprehensive classification framework for two-loop Dirac neutrino mass models and illustrates the connection to dark matter stability with explicit examples.

## Key findings

- Complete classification of two-loop Dirac neutrino mass models
- Identification of model topologies and diagrams
- Explicit models linking neutrino Diracness to dark matter stability

## Abstract

We provide a complete systematic classification of all two-loop realizations of the dimension four operator for Dirac neutrino masses. Our classification is multi-layered, starting first with a classification in terms of all possible distinct two-loop topologies. Then we discuss the possible diagrams for each topology. Model-diagrams originating from each diagram are then considered. The criterion for genuineness is also defined and discussed at length. Finally, as examples, we construct two explicit models which also serve to highlight the intimate connection between the Dirac nature of neutrinos and dark matter stability.