  Neutrino oscillation experiments and direct bounds on absolute masses
constrain neutrino mass differences to fall into the microwave energy range,
for most of the allowed parameter space. As a consequence of these recent
phenomenological advances, older constraints on radiative neutrino decays based
on diffuse background radiations and assuming strongly hierarchical masses in
the eV range are now outdated. We thus derive new bounds on the radiative
neutrino lifetime using the high precision cosmic microwave background spectral
data collected by the Far Infrared Absolute Spectrophotometer instrument on
board of Cosmic Background Explorer. The lower bound on the lifetime is between
a few x 10^19 s and 5 x 10^20 s, depending on the neutrino mass ordering and on
the absolute mass scale. However, due to phase space limitations, the upper
bound in terms of the effective magnetic moment mediating the decay is not
better than ~ 10^-8 Bohr magnetons. We also comment about possible improvements
of these limits, by means of recent diffuse infrared photon background data. We
compare these bounds with pre-existing limits coming from laboratory or
astrophysical arguments. We emphasize the complementarity of our results with
others available in the literature.
