Improved cosmological constraints on the neutrino mass and lifetime
  We present cosmological constraints on the sum of neutrino masses as a
function of the neutrino lifetime, in a framework in which neutrinos decay into
dark radiation after becoming non-relativistic. We find that in this regime the
cosmic microwave background (CMB), baryonic acoustic oscillations (BAO) and
(uncalibrated) luminosity distance to supernovae from the Pantheon catalog
constrain the sum of neutrino masses $\sum m_\nu$ to obey $\sum m_\nu< 0.42$ eV
at (95$\%$ C.L.). While the the bound has improved significantly as compared to
the limits on the same scenario from {\it Planck} 2015, it still represents a
significant relaxation of the constraints as compared to the stable neutrino
case. We show that most of the improvement can be traced to the more precise
measurements of low-$\ell$ polarization data in {\it Planck} 2018, which leads
to tighter constraints on $\tau_{\rm reio}$ (and thereby on $A_s$), breaking
the degeneracy arising from the effect of (large) neutrino masses on the
amplitude of the CMB power spectrum.
