Double beta decay and neutrino mass models

TL;DR

This paper analyzes the conditions under which the mass mechanism dominates neutrinoless double beta decay, classifies scalar-mediated contributions by loop level, and examines a specific 2-loop model's phenomenology.

Contribution

It provides a comprehensive classification of short-range contributions based on loop level and discusses their relative importance in neutrino mass models.

Findings

Mass mechanism often dominates but not always in neutrinoless double beta decay.

Short-range contributions vary significantly depending on the loop level of the model.

A detailed phenomenological analysis of a 2-loop model shows potential for competing contributions.

Abstract

Neutrinoless double beta decay allows to constrain lepton number violating extensions of the standard model. If neutrinos are Majorana particles, the mass mechanism will always contribute to the decay rate, however, it is not a priori guaranteed to be the dominant contribution in all models. Here, we discuss whether the mass mechanism dominates or not from the theory point of view. We classify all possible (scalar-mediated) short-range contributions to the decay rate according to the loop level, at which the corresponding models will generate Majorana neutrino masses, and discuss the expected relative size of the different contributions to the decay rate in each class. Our discussion is general for models based on the SM group but does not cover models with an extended gauge. We also work out the phenomenology of one concrete 2-loop model in which both, mass mechanism and short-range diagram, might lead to competitive contributions, in some detail.