Neutrino Masses and Mass Hierarchy: Evidence for the Normal Hierarchy

TL;DR

This paper presents Bayesian evidence strongly favoring the normal neutrino mass hierarchy, based on cosmological and laboratory data, with significant implications for future neutrino research and experiments.

Contribution

It provides robust Bayesian evidence for the normal hierarchy, consistent across various prior assumptions, and discusses implications for neutrinoless double beta decay.

Findings

Bayesian odds > 140:1 for normal hierarchy

Evidence remains strong across different prior choices

Implications for future double beta decay experiments

Abstract

The latest cosmological constraints on the sum of neutrino masses, in combination with the latest laboratory measurements on oscillations, provide ``decisive" Bayesian evidence for the normal neutrino mass hierarchy. We show that this result holds across very different prior alternatives by exploring two extremes on the range of prior choices. In fact, while the specific numerical value for the Evidence depends on the choice of prior, the Bayesian odds remain greater than 140:1 across very different prior choices. For Majorana neutrinos this has important implications for the upper limit of the neutrino-less double beta decay half life and thus for the technology and resources needed for future double beta decay experiments.