Revisiting Supernova 1987A Constraints on Dark Photons
  We revisit constraints on dark photons with masses below ~ 100 MeV from the
observations of Supernova 1987A. If dark photons are produced in sufficient
quantity, they reduce the amount of energy emitted in the form of neutrinos, in
conflict with observations. For the first time, we include the effects of
finite temperature and density on the kinetic-mixing parameter, epsilon, in
this environment. This causes the constraints on epsilon to weaken with the
dark-photon mass below ~ 15 MeV. For large-enough values of epsilon, it is well
known that dark photons can be reabsorbed within the supernova. Since the rates
of reabsorption processes decrease as the dark-photon energy increases, we
point out that dark photons with energies above the Wien peak can escape
without scattering, contributing more to energy loss than is possible assuming
a blackbody spectrum. Furthermore, we estimate the systematic uncertainties on
the cooling bounds by deriving constraints assuming one analytic and four
different simulated temperature and density profiles of the proto-neutron star.
Finally, we estimate also the systematic uncertainty on the bound by varying
the distance across which dark photons must propagate from their point of
production to be able to affect the star. This work clarifies the bounds from
SN1987A on the dark-photon parameter space.
