A neutrino mass-mixing sum rule from SO(10) and neutrinoless double beta decay

TL;DR

This paper derives a neutrino mass-mixing sum rule from a minimal SO(10) grand unified model, predicting a normal hierarchy, a lower limit on the lightest neutrino mass, and implications for neutrinoless double beta decay.

Contribution

It presents a specific neutrino mass-mixing relation within SO(10) models, linking neutrino parameters to neutrinoless double beta decay predictions and establishing a lower bound on the lightest neutrino mass.

Findings

Normal neutrino mass hierarchy is the only allowed.

A lower limit for the lightest neutrino mass is established.

Implications for neutrinoless double beta decay effective mass parameter.

Abstract

Minimal SO(10) grand unified models provide phenomenological predictions for neutrino mass patterns and mixing. These are the outcome of the interplay of several features, namely: i) the seesaw mechanism; ii) the presence of an intermediate scale where B-L gauge symmetry is broken and the right-handed neutrinos acquire a Majorana mass; iii) a symmetric Dirac neutrino mass matrix whose pattern is close to the up-type quark one. In this framework two natural characteristics emerge. Normal neutrino mass hierarchy is the only allowed, and there is an approximate relation involving both light-neutrino masses and mixing parameters. This differs from what occurring when horizontal flavour symmetries are invoked. In this case, in fact, neutrino mixing or mass relations have been separately obtained in literature. In this paper we discuss an example of such comprehensive mixing-mass relation in a specific realization of SO(10) and, in particular, analyse its impact on the expected neutrinoless double beta decay effective mass parameter $\langle m_{ee} \rangle$, and on the neutrino mass scale. Remarkably a lower limit for the lightest neutrino mass is obtained ($m_{\rm lightest} \gtrsim 7.5 \times 10^{-4}$ eV, at 3 $\sigma$ level).