Systematic decomposition of the neutrinoless double beta decay operator

TL;DR

This paper systematically decomposes the neutrinoless double beta decay operator at dimension nine, identifying known and new mechanisms, and explores their potential signals at the LHC, with implications for neutrino mass measurements.

Contribution

It provides a complete list of tree-level diagrams for neutrinoless double beta decay, including new mechanisms not previously discussed in the literature.

Findings

Identified new possible contributions to neutrinoless double beta decay.

Connected decay mechanisms to potential LHC signals.

Provided a framework to set limits on all contributions based on Lorentz invariance.

Abstract

We discuss the systematic decomposition of the dimension nine neutrinoless double beta decay operator, focusing on mechanisms with potentially small contributions to neutrino mass, while being accessible at the LHC. We first provide a (d=9 tree-level) complete list of diagrams for neutrinoless double beta decay. From this list one can easily recover all previously discussed contributions to the neutrinoless double beta decay process, such as the celebrated mass mechanism or "exotics", such as contributions from left-right symmetric models, R-parity violating supersymmetry and leptoquarks. More interestingly, however, we identify a number of new possibilities which have not been discussed in the literature previously. Contact to earlier works based on a general Lorentz-invariant parametrisation of the neutrinoless double beta decay rate is made, which allows, in principle, to derive limits on all possible contributions. We furthermore discuss possible signals at the LHC for mediators leading to the short-range part of the amplitude with one specific example. The study of such contributions would gain particular importance if there were a tension between different measurements of neutrino mass such as coming from neutrinoless double beta decay and cosmology or single beta decay.