A realistic model of neutrino masses with a large neutrinoless double beta decay rate

TL;DR

This paper presents a new, testable model for neutrino masses that allows for a large neutrinoless double beta decay rate independent of neutrino mass, with potential observable effects at colliders and in lepton flavor violation experiments.

Contribution

The authors introduce a simple two-loop model where neutrinoless double beta decay can be sizable independently of neutrino masses, differing from standard predictions and linking to observable collider and flavor violation signals.

Findings

Neutrinoless double beta decay can be large despite small neutrino masses.

Model predicts sizable lepton flavor violating rates within experimental reach.

Large third mixing angle $ heta_{13}$ is compatible with current constraints.

Abstract

The minimal Standard Model extension with the Weinberg operator does accommodate the observed neutrino masses and mixing, but predicts a neutrinoless double beta ($0\nu\beta\beta$) decay rate proportional to the effective electron neutrino mass, which can be then arbitrarily small within present experimental limits. However, in general $0\nu\beta\beta$ decay can have an independent origin and be near its present experimental bound; whereas neutrino masses are generated radiatively, contributing negligibly to $0\nu\beta\beta$ decay. We provide a realization of this scenario in a simple, well defined and testable model, with potential LHC effects and calculable neutrino masses, whose two-loop expression we derive exactly. We also discuss the connection of this model to others that have appeared in the literature, and remark on the significant differences that result from various choices of quantum number assignments and symmetry assumptions. In this type of models lepton flavor violating rates are also preferred to be relatively large, at the reach of foreseen experiments. Interestingly enough, in our model this stands for a large third mixing angle, $\sin^2\theta_{13} \gtrsim 0.008$, when $\mu \rightarrow eee$ is required to lie below its present experimental limit.