Dark matter and observable Lepton Flavour Violation

TL;DR

This paper proposes a model linking large lepton flavor violation rates with dark matter stability, where the same leptonic symmetry explains both phenomena and predicts observable effects in upcoming experiments.

Contribution

It introduces a novel model connecting observable lepton flavor violation with dark matter stability via a leptonic symmetry and a Majoron-like field, with testable predictions.

Findings

Large LFV rates imply dark matter in the keV range.

Active-neutrino interactions with the Majoron could be detected in supernova neutrino bursts.

The model predicts observable $ ext{μ} o e$ conversion signals in near-future experiments.

Abstract

Seesaw models with leptonic symmetries allow right-handed (RH) neutrino masses at the electroweak scale, or even lower, at the same time having large Yukawa couplings with the Standard Model leptons, thus yielding observable effects at current or near-future lepton-flavour-violation (LFV) experiments. These models have been previously considered also in connection to low-scale leptogenesis, but the combination of observable LFV and successful leptogenesis has appeared to be difficult to achieve unless the leptonic symmetry is embedded into a larger one. In this paper, instead, we follow a different route and consider a possible connection between large LFV rates and Dark Matter (DM). We present a model in which the same leptonic symmetry responsible for the large Yukawa couplings guarantees the stability of the DM candidate, identified as the lightest of the RH neutrinos. The spontaneous breaking of this symmetry, caused by a Majoron-like field, also provides a mechanism to produce the observed relic density via the decays of the latter. The phenomenological implications of the model are discussed, finding that large LFV rates, observable in the near-future $\mu \to e$ conversion experiments, require the DM mass to be in the keV range. Moreover, the active-neutrino coupling to the Majoron-like scalar field could be probed in future detections of supernova neutrino bursts.