A Survey of Lepton Number Violation Via Effective Operators

TL;DR

This survey reviews 129 lepton number violating effective operators up to dimension eleven, analyzing their experimental signatures, current constraints, and future detection prospects to understand neutrino mass origins.

Contribution

It provides a comprehensive classification of lepton number violating operators and evaluates their experimental implications and constraints, guiding future searches.

Findings

Some operators are already constrained by current data.

Next-generation experiments can probe more operators.

Neutrinoless double-beta decay remains the most promising detection method.

Abstract

We survey 129 lepton number violating effective operators, consistent with the minimal Standard Model gauge group and particle content, of mass dimension up to and including eleven. Upon requiring that each one radiatively generates the observed neutrino masses, we extract an associated characteristic cutoff energy scale which we use to calculate other observable manifestations of these operators for a number of current and future experimental probes, concentrating on lepton number violating phenomena. These include searches for neutrinoless double-beta decay and rare meson, lepton, and gauge boson decays. We also consider searches at hadron/lepton collider facilities in anticipation of the LHC and the future ILC. We find that some operators are already disfavored by current data, while more are ripe to be probed by next-generation experiments. We also find that our current understanding of lepton mixing disfavors a subset of higher dimensional operators. While neutrinoless double-beta decay is the most promising signature of lepton number violation for the majority of operators, a handful is best probed by other means. We argue that a combination of constraints from various independent experimental sources will help to pinpoint the ``correct'' model of neutrino mass, or at least aid in narrowing down the set of possibilities.