Photon mass from inflation
  We consider vacuum polarization from massless scalar electrodynamics in de Sitter inflation. The theory exhibits a 3+1 dimensional analogue of the Schwinger mechanism in which a photon mass is dynamically generated. The mechanism is generic for light scalar fields that couple minimally to gravity. The non-vanishing of the photon mass during inflation may result in magnetic fields on cosmological scales. 
Tomislav Prokopec (Heidelberg), Ola Tornkvist (Imperial College),   Richard Woodard (Florida)