Cornering (quasi) degenerate neutrinos with cosmology

TL;DR

Cosmological data strongly constrains quasi-degenerate neutrino masses, with current observations disfavoring such scenarios at over 5 sigma, and future probes promising even tighter constraints.

Contribution

This paper assesses the current and future cosmological constraints on quasi-degenerate neutrino masses within the standard model extension, highlighting the increasing exclusion power.

Findings

Planck 2018 data disfavors quasi-degenerate neutrinos at 2.4 sigma

Adding BAO data increases the rejection to 5.9 sigma

Future cosmological probes could reject quasi-degeneracy at 17 sigma

Abstract

In light of the improved sensitivities of cosmological observations, we examine the status of quasi-degenerate neutrino mass scenarios. Within the simplest extension of the standard cosmological model with massive neutrinos, we find that quasi-degenerate neutrinos are severely constrained by present cosmological data and neutrino oscillation experiments. % % We find that Planck 2018 observations of cosmic microwave background (CMB) anisotropies disfavour quasi-degenerate neutrino masses at $2.4$ Gaussian $\sigma$'s, while adding Baryon acoustic oscillations (BAO) data brings the rejection to 5.9$\sigma$'s. % The highest statistical significance with which one would be able to rule out quasi-degeneracy would arise if the sum of neutrino masses is $\Sigma m_\nu = 60$ \meV (the minimum allowed by neutrino oscillation experiments); % indeed a sensitivity of 15 meV, as expected from a combination of future cosmological probes, would further improve the rejection level up to 17$\sigma$. % We discuss the robustness of these projections with respect to assumptions on the underlying cosmological model, and also compare them with bounds from $\beta$ decay endpoint and neutrinoless double beta decay studies.