Dark Light, Dark Matter and the Misalignment Mechanism
  We explore the possibility that the dark matter is a condensate of a very light vector boson. Such a condensate could be produced during inflation, provided the vector mass arises via the Steuckelberg mechanism. We derive bounds on the kinetic mixing of the dark matter boson with the photon, and point out several potential signatures of this model. 
Ann E. Nelson and Jakub Scholtz
hep-ph astro-ph.CO