Neutrinoless double beta decay in seesaw models

TL;DR

This paper explores how neutrinoless double beta decay rates depend on the mass of extra states in seesaw models, highlighting the importance of nuclear matrix elements and the potential for cancellations affecting experimental bounds.

Contribution

It provides a comprehensive analysis of the dependence of decay rates on mediating fermion masses and clarifies the interplay between light neutrino contributions and extra states in seesaw models.

Findings

Nuclear matrix elements vary with fermion mass and have associated uncertainties.

Extra states can cancel light neutrino contributions, affecting decay amplitude predictions.

Seesaw models can reconcile large decay rates with cosmological neutrino mass bounds.

Abstract

We study the general phenomenology of neutrinoless double beta decay in seesaw models. In particular, we focus on the dependence of the neutrinoless double beta decay rate on the mass of the extra states introduced to account for the Majorana masses of light neutrinos. For this purpose, we compute the nuclear matrix elements as functions of the mass of the mediating fermions and estimate the associated uncertainties. We then discuss what can be inferred on the seesaw model parameters in the different mass regimes and clarify how the contribution of the light neutrinos should always be taken into account when deriving bounds on the extra parameters. Conversely, the extra states can also have a significant impact, cancelling the Standard Model neutrino contribution for masses lighter than the nuclear scale and leading to vanishing neutrinoless double beta decay amplitudes even if neutrinos are Majorana particles. We also discuss how seesaw models could reconcile large rates of neutrinoless double beta decay with more stringent cosmological bounds on neutrino masses.