Determining the Neutrino Mass Hierarchy with Cosmology

TL;DR

Future cosmological surveys combining cosmic shear and CMB data could determine the neutrino mass hierarchy, potentially providing strong evidence for either normal or inverted hierarchies and influencing other cosmological parameters.

Contribution

This study forecasts the capability of upcoming cosmological experiments to distinguish neutrino mass hierarchies using Fisher matrix and Bayesian analysis.

Findings

Planck and Euclid could constrain the mass of a single neutrino species.

Future experiments may provide strong evidence for the neutrino mass hierarchy.

Assuming a hierarchy could bias other cosmological parameter estimates.

Abstract

The combination of current large scale structure and cosmic microwave background (CMB) anisotropies data can place strong constraints on the sum of the neutrino masses. Here we show that future cosmic shear experiments, in combination with CMB constraints, can provide the statistical accuracy required to answer questions about differences in the mass of individual neutrino species. Allowing for the possibility that masses are non-degenerate we combine Fisher matrix forecasts for a weak lensing survey like Euclid with those for the forthcoming Planck experiment. Under the assumption that neutrino mass splitting is described by a normal hierarchy we find that the combination Planck and Euclid will possibly reach enough sensitivity to put a constraint on the mass of a single species. Using a Bayesian evidence calculation we find that such future experiments could provide strong evidence for either a normal or an inverted neutrino hierachy. Finally we show that if a particular neutrino hierachy is assumed then this could bias cosmological parameter constraints, for example the dark energy equation of state parameter, by > 1\sigma, and the sum of masses by 2.3\sigma.