Cosmology and the neutrino mass ordering

TL;DR

This paper introduces a Bayesian method to assess the likelihood of the neutrino mass ordering using cosmological data, providing a quantitative framework for potential exclusion of the inverted ordering.

Contribution

The paper presents a novel Bayesian approach to evaluate the probability of neutrino mass orderings from cosmological observations, including mock data analysis for future surveys.

Findings

Current data yields a 2:1 posterior odds favoring normal ordering.

Combining cosmology with oscillation data adjusts odds to about 3:2.

Future surveys could exclude inverted ordering if the sum of neutrino masses is measured with 0.02 eV accuracy.

Abstract

We propose a simple method to quantify a possible exclusion of the inverted neutrino mass ordering from cosmological bounds on the sum of the neutrino masses. The method is based on Bayesian inference and allows for a calculation of the posterior odds of normal versus inverted ordering. We apply the method for a specific set of current data from Planck CMB data and large-scale structure surveys, providing an upper bound on the sum of neutrino masses of 0.14 eV at 95% CL. With this analysis we obtain posterior odds for normal versus inverted ordering of about 2:1. If cosmological data is combined with data from oscillation experiments the odds reduce to about 3:2. For an exclusion of the inverted ordering from cosmology at more than 95% CL, an accuracy of better than 0.02 eV is needed for the sum. We demonstrate that such a value could be reached with planned observations of large scale structure by analysing artificial mock data for a EUCLID-like survey.