Fradette, AnthonyPospelov, MaximPradler, JosefRitz, Adam2018-06-272018-06-2720152015Fradette, A., Pospelov, M., Pradler, J. & Ritz, A. (2015). Cosmic Microwave Background Constraints on Very Dark Photons. Physics Procedia, 61, 689-693. https://doi.org/10.1016/j.phpro.2014.12.081http://dx.doi.org/10.1016/j.phpro.2014.12.081http://hdl.handle.net/1828/9529We analyze the effects of a massive dark photon with mV > 1 MeV on the Cosmic Microwave Background (CMB). We calculate the freeze-in abundance and derive limits on the parameter space from energy injections in the CMB. We find that for dark vectors in the mass range 1 MeV < mV < 300 MeV, the model is already ruled out for effective electromagnetic coupling as low as 10−34 – 10-37enDark photonsHidden sectorCosmic Microwave BackgroundArticle