Coffey, John2020-04-212020-04-2120202020-04-21http://hdl.handle.net/1828/11690The purpose of this thesis is to recognize the effects of electromagnetic energy injection into the early Universe from decaying sub-GeV dark vectors. Decay widths and energy spectra for the most prominent channels in the sub-GeV region are calculated for various dark vector models. The models include the kinetic mixing of the dark photon with the Standard Model photon, U(1)_A' , a dark vector boson which couples to the baryon minus the lepton current, U(1)_B-L, and the last three are dark vector bosons which couple one lepton's current minus a different lepton's current, U(1)_Li-Lj where i != j = e, mu, tau . Measurements from Big Bang Nucleosynthesis and the Cosmic Microwave Background are used to constrain the lifetime, mass and coupling constant of the dark vectors.enAvailable to the World Wide WebBig Bang NucleosynthesisCosmic Microwave Backgrounddark vectorssub-GeVCosmological ConstraintsThesis