A Model of Radiative Neutrino Mass: with or without Dark Matter

TL;DR

This paper introduces a three-loop neutrino mass model with a softly-broken $Z_2$ symmetry that can naturally include a dark matter candidate without requiring an additional symmetry, linking neutrino mass and dark matter solutions.

Contribution

The model demonstrates a unified approach to neutrino mass and dark matter, with a softly-broken symmetry allowing for long-lived dark matter and potential TeV-scale new physics.

Findings

Long-lived dark matter is possible with small symmetry breaking parameter

The model can produce neutrino masses at the TeV scale

Dark matter candidate can be tested in direct detection experiments

Abstract

We present a three-loop model of neutrino mass whose most-general Lagrangian possesses a softly-broken accidental $Z_2$ symmetry. In the limit that a single parameter vanishes, $\lambda\rightarrow0$, the $Z_2$ symmetry becomes exact and the model contains a stable dark-matter candidate. However, even for finite $\lambda\ll1$, long-lived dark matter is possible, giving a unified solution to the neutrino mass and dark matter problems that does not invoke a new symmetry. Taken purely as a neutrino mass model, the new physics can be at the TeV scale. When dark matter is incorporated, however, only a singlet scalar can remain this light, though the dark matter can be tested in direct-detection experiments.