The diffuse supernova neutrino background as a probe of late-time
  neutrino mass generation
  The relic neutrinos from old supernova explosions are among the most ancient
neutrino fluxes within experimental reach. Thus, the diffuse supernova neutrino
background (DSNB) could teach us if neutrino masses were different in the past
(redshifts $z\lesssim 5$). Oscillations inside the supernova depend strongly on
the neutrino mass-squared differences and the values of the mixing angles,
rendering the DSNB energy spectrum sensitive to variations of these parameters.
Considering a purely phenomenological parameterization of the neutrino masses
as a function of redshift, we compute the expected local DSNB spectrum here on
Earth. Given the current knowledge of neutrino oscillation parameters,
specially the fact that $|U_{e3}|^2$ is small, we find that the $\nu_e$
spectrum could be significantly different from standard expectations if
neutrinos were effectively massless at $z\gtrsim1$ as long as the neutrino mass
ordering is normal. On the other hand, the $\overline{\nu}_e$ flux is not
expected to be significantly impacted. Hence, a measurement of both the
neutrino and antineutrino components of the DSNB should allow one to test the
possibility of recent neutrino mass generation.
