New stellar constraints on dark photons
  We consider the stellar production of vector states V within the minimal
model of "dark photons". We show that when the Stuckelberg mass of the dark
vector becomes smaller than plasma frequency, the emission rate is dominated by
the production of the longitudinal modes of V, and scales as \kappa^2 m_V^2,
where \kappa and m_V are the mixing angle with the photon and the mass of the
dark state. This is in contrast with earlier erroneous claims in the literature
that the emission rate decouples as the forth power of the mass. We derive
ensuing constraints on the (\kappa, m_V) parameter space by calculating the
cooling rates for the Sun and red giant stars. We find that stellar bounds for
m_V < 10 eV are significantly strengthened, to the extent that all current
"light-shining-through-wall" experiments find themselves within deeply excluded
regions.
