Small-Scale Structure Formation in Mixed Sterile Neutrino Dark Matter Models*

An observed excess in stacked galaxy X-ray spectra at 3.55 keV can be interpreted as the decay of a 7.1 keV sterile neutrino dark matter particle. Here, we explore various scenarios for the lepton number-driven production of sterile neutrino dark matter in the early universe. We discuss these mixed sterile neutrino dark matter models (sterile neutrinos plus cold dark matter), properties of the sterile neutrino dark matter spectra formed, and how characteristics of these spectra – and the physics that form them – can constrain these models through the formation of small-scale structure.