Neutrinoless double beta decay and the muonium-to-antimuonium transition in models with a doubly charged scalar

TL;DR

This paper explores how models with a doubly charged scalar can induce neutrinoless double beta decay and muonium-to-antimuonium transition, analyzing their potential observability and implications for lepton number violation.

Contribution

It investigates the relationship between these two lepton number violating processes within the doubly charged scalar models and assesses their experimental detectability.

Findings

Muonium-to-antimuonium transition rate can reach current experimental bounds.

Updated bounds on transition rates can distinguish between models.

Extensions to left-right models can induce neutrinoless double beta decay.

Abstract

The lepton number and flavor violations are important possible ingredients of the lepton physics. The neutrinoless double beta decay and the transition of the muonium into antimuonuim are related to those violations. The former can give us an essential part of fundamental physics, and there are plenty of experimental attempts to observe the process. The latter has also been one of the attractive phenomena, and the experimental bound will be updated in planned experiments at new high-intensity muon beamlines. In models with a doubly charged scalar, not only can those two processes be induced, but also the active neutrino masses can be induced radiatively. The flavor violating decays of the charged leptons constrain the flavor parameters of the models. We study how the muonium-to-antimuonium transition rate can be as large as the current experimental bound, and we insist that the updated bound of the transition rate will be useful to distinguish the models to generate the neutrinoless double beta decay via the doubly charged scalar. We also study a possible extension of the model to the left-right model which can induce the neutrinoless double beta decay.