Constraints on massive sterile neutrino species from current and future cosmological data

TL;DR

This paper analyzes current and future cosmological data to constrain the masses and number of sterile neutrino species, exploring their compatibility with cosmological and nucleosynthesis bounds and potential future measurements.

Contribution

It provides updated bounds on sterile neutrino masses and counts from cosmological data and forecasts the impact of future measurements on these parameters.

Findings

(3+2) sterile neutrino models are compatible with current cosmological data within 95% CL.

Big Bang Nucleosynthesis bounds challenge models with thermally decoupled sterile states.

Future cosmological and laboratory measurements could clarify sterile neutrino properties.

Abstract

Sterile massive neutrinos are a natural extension of the Standard Model of elementary particles. The energy density of the extra sterile massive states affects cosmological measurements in an analogous way to that of active neutrino species. We perform here an analysis of current cosmological data and derive bounds on the masses of the active and the sterile neutrino states as well as on the number of sterile states. The so-called (3+2) models with three sub-eV active massive neutrinos plus two sub-eV massive sterile species is well within the 95% CL allowed regions when considering cosmological data only. If the two extra sterile states have thermal abundances at decoupling, Big Bang Nucleosynthesis bounds compromise the viability of (3+2) models. Forecasts from future cosmological data on the active and sterile neutrino parameters are also presented. Independent measurements of the neutrino mass from tritium beta decay experiments and of the Hubble constant could shed light on sub-eV massive sterile neutrino scenarios.