Cornering (quasi) degenerate neutrinos with cosmology
  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.
