# Accessible Lepton-Number-Violating Models and Negligible Neutrino Masses

## TL;DR

This paper identifies models where lepton-number violation occurs without generating significant neutrino masses, allowing for observable lepton-number-violating processes at accessible energy scales, despite tiny neutrino masses.

## Contribution

The paper introduces a complete family of models with lepton-number violation that produce negligible neutrino masses even below 1 TeV, expanding the phenomenological landscape.

## Key findings

- Certain models predict observable $$-conversion rates in upcoming experiments.
- Lepton-number violation can be significant without large neutrino masses.
- Phenomenology includes charged-lepton flavor violation and baryon-number violation.

## Abstract

Lepton-number violation (LNV), in general, implies nonzero Majorana masses for the Standard Model neutrinos. Since neutrino masses are very small, for generic candidate models of the physics responsible for LNV, the rates for almost all experimentally accessible LNV observables -- except for neutrinoless double-beta decay -- are expected to be exceedingly small. Guided by effective-operator considerations of LNV phenomena, we identify a complete family of models where lepton number is violated but the generated Majorana neutrino masses are tiny, even if the new-physics scale is below 1 TeV. We explore the phenomenology of these models, including charged-lepton flavor-violating phenomena and baryon-number-violating phenomena, identifying scenarios where the allowed rates for $\mu^-\to e^+$-conversion in nuclei are potentially accessible to next-generation experiments.