Majorana phases beyond neutrinoless double beta decay

TL;DR

This paper investigates how Majorana phases in neutrino mixing can be constrained beyond neutrinoless double beta decay, highlighting potential methods to exclude the minimal Standard Model extension with neutrino masses.

Contribution

It analyzes the potential to obtain information on Majorana phases beyond $0 uetaeta$ decay, emphasizing the implications for the minimal neutrino mass model.

Findings

Current mixing parameters prevent certain lepton number violating processes from vanishing simultaneously.

A no-lose theorem is proposed for excluding the $ u_M{ m SM}$ model based on lepton number violation.

Constraints depend on the lightest neutrino mass and mixing parameters.

Abstract

The $\nu_M{\rm SM}$ is defined as the SM extended to include dimension-5 operators. In this model neutrino masses violate lepton number, and two parameters of the lepton mixing matrix, the Majorana phases, are yet to be constrained. One combination of these phases and the neutrino masses, often denoted by $m_{ee}$, is probed by neutrinoless double beta decays ($0\nu\beta\beta$). We explore what information may be obtained beyond $0\nu\beta\beta$, and how it depends on the lightest neutrino mass. We point out that with current central values of the mixing parameters, $\Delta L_e=2$ and $\Delta L_e=\Delta L_\mu = 1$ (or $\Delta L_e=2$ and $\Delta L_\mu = 2$) processes cannot simultaneously vanish, providing a no-lose theorem, in principle, for excluding the $\nu_M{\rm SM}$, even in the case of normal mass ordering.