Mixed Sterile Neutrino Dark Matter Models and the Early Universe Quark-Gluon Plasma

Astrophysics points to the possibility of a 7.1 keV sterile neutrino dark matter particle, inferred from an unidentified 3.55 keV X-ray line in the stacked spectra of galaxies and clusters. Sterile neutrino dark matter provides an interesting way to probe nuclear physics in the early universe, as sterile neutrino dark matter is formed prior to the QCD transition, when the universe is a high-entropy quark gluon plasma (QGP). Consequently, the production of sterile neutrino dark matter is greatly influenced by both the characteristics of the QGP and neutrino interactions within it. In this talk, we consider mixed sterile neutrino dark matter models that combine cold dark matter and sterile neutrino dark matter. Our investigation focuses on how the interplay between properties of the QGP and neutrinos are imprinted on these mixed sterile neutrino dark matter models, along with their consequential astrophysical implications.