Long-range contributions to double beta decay revisited

TL;DR

This paper systematically analyzes dimension-7 lepton number violating operators that contribute to neutrinoless double beta decay, identifying models and constraints, including new ones, and examining their impact on decay amplitudes and neutrino masses.

Contribution

It provides a comprehensive classification of d=7 operators affecting double beta decay and compares constraints from mass mechanisms and decay amplitudes, including novel models.

Findings

d=7 operators produce significant long-range decay contributions

Some models generate neutrino masses at 2-loop level

Certain models fit oscillation data and enhance decay amplitude

Abstract

We discuss the systematic decomposition of all dimension-7 (d=7) lepton number violating operators. These d=7 operators produce momentum enhanced contributions to the long-range part of the neutrinoless double beta decay amplitude and thus are severely constrained by existing half-live limits. In our list of possible models one can find contributions to the long-range amplitude discussed previously in the literature, such as the left-right symmetric model or scalar leptoquarks, as well as some new models not considered before. The d=7 operators generate Majorana neutrino mass terms either at tree-level, 1-loop or 2-loop level. We systematically compare constraints derived from the mass mechanism to those derived from the long-range double beta decay amplitude and classify our list of models accordingly. We also study one particular example decomposition, which produces neutrino masses at 2-loop level, can fit oscillation data and yields a large contribution to the long-range double beta decay amplitude, in some detail.