  We study the possibility that a keV-MeV mass hidden photon (HP), i.e. a
hidden sector U(1) gauge boson, accounts for the observed amount of dark
matter. We focus on the case where the HP interacts with the standard model
sector only through kinetic mixing with the photon. The relic abundance is
computed including all relevant plasma effects into the photon's self-energy,
which leads to a resonant yield almost independent of the HP mass. The HP can
decay into three photons. Moreover, if light enough it can be copiously
produced in stars. Including bounds from cosmic photon backgrounds and stellar
evolution, we find that the hidden photon can only give a subdominant
contribution to the dark matter. This negative conclusion may be avoided if
another production mechanism besides kinetic mixing is operative.

High Energy Physics - Phenomenology;Astrophysics