Observable Lepton Number Violation with Predominantly Dirac Nature of Active Neutrinos

TL;DR

This paper explores a model where active neutrinos are mainly Dirac particles with tiny Majorana masses, predicting observable lepton number violation signals and charged lepton flavor violation, while maintaining a decoupled new physics sector.

Contribution

It introduces a specific $SU(2)_R imes SU(2)_L imes U(1)_{B-L}$ model with discrete symmetries where neutrino masses are predominantly Dirac, and lepton number violation signatures are observable despite the decoupled sectors.

Findings

Neutrinos are mainly Dirac with suppressed Majorana masses.

Predicts observable lepton number violation signals like neutrinoless double beta decay.

Forecasts charged lepton flavor violation processes such as $\mu ightarrow 3e$ and $\mu ightarrow e \gamma$.

Abstract

We study a specific version of $SU(2)_R \times SU(2)_L \times U(1)_{B-L}$ models extended by discrete symmetries where the new physics sector responsible for tiny neutrino masses at leading order remains decoupled from the new physics sector that can give rise to observable signatures of lepton number violation such as neutrinoless double beta decay. More specifically, the dominant contribution to light neutrino masses comes from a one-loop Dirac mass. At higher loop level, a tiny Majorana mass also appears which remains suppressed by many order of magnitudes in comparison to the Dirac mass. Such a model where the active neutrinos are predominantly of Dirac type, also predicts observable charged lepton flavour violation like $\mu \rightarrow 3e, \mu \rightarrow e \gamma$ and multi-component dark matter.