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 \mathrm { 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 .