Doubly-Charged Scalars in the Type-II Seesaw Mechanism: Fundamental Symmetry Tests and High-Energy Searches

TL;DR

This paper evaluates how low-energy symmetry tests, especially the MOLLER experiment, can detect interactions from doubly-charged scalars in type-II seesaw models, complementing high-energy collider searches and neutrinoless double beta decay experiments.

Contribution

It compares the sensitivity of low-energy symmetry tests to collider and decay searches for doubly-charged scalars in different seesaw scenarios, highlighting the unique reach of the MOLLER experiment.

Findings

CLFV searches are most sensitive in the simplest scenario.

MOLLER can probe scalar interactions up to ~10 TeV in left-right models.

MOLLER helps clarify the mechanism behind neutrinoless double beta decay.

Abstract

We analyze the sensitivity of low-energy fundamental symmetry tests to interactions mediated by doubly-charged scalars that arise in type-II seesaw models of neutrino mass and their left-right symmetric extensions. We focus on the next generation measurement of the parity-violating asymmetry in M{\o}ller scattering planned by the MOLLER collaboration at Jefferson Laboratory. We compare the MOLLER sensitivity to that of searches for charged lepton flavor violation (CLFV) and neutrinoless double beta-decay ($0\nu\beta\beta$-decay) as well as present and possible future high-energy collider probes. We show that for the simplest type-II seesaw scenario, CLFV searches have the greatest sensitivity. However, in a left-right symmetric extension where the scale of parity-breaking is decoupled from the $SU(2)_R$-breaking scale, the MOLLER experiment will provide a unique probe of scalar triplet interactions in the right-handed sector for a doubly-charged scalar mass up to $\sim$ 10 TeV and help elucidate the mechanism of $0\nu\beta\beta$-decay.