Observable flavor violation from spontaneous lepton number breaking

TL;DR

This paper introduces a model with spontaneous lepton number breaking that predicts observable flavor-violating decays involving the majoron, potentially explaining the muon g-2 anomaly but facing astrophysical constraints.

Contribution

It presents a simple model where spontaneous lepton number breaking leads to large flavor-violating decays and links to neutrino masses and muon g-2, with implications for experimental bounds.

Findings

Majoron-emitting decays can saturate experimental bounds

The model can explain the muon g-2 anomaly in some parameter regions

Tension exists between muon g-2 explanation and astrophysical bounds

Abstract

We propose a simple model of spontaneous lepton number violation with potentially large flavor violating decays, including the possibility that majoron emitting decays, such as $\mu \to e \, J$, saturate the experimental bounds. In this model the majoron is a singlet-doublet admixture. It generates a type-I seesaw for neutrino masses and contains also a vector-like lepton. As a by-product, the model can explain the anomalous $(g-2)_{\mu}$ in parts of its parameter space, where one expects that the branching ratio of the Higgs to muons is changed with respect to Standard Model expectations. However, the explanation of the muon $g-2$ anomaly would lead to tension with recent astrophysical bounds on the majoron coupling to muons.