Production and evolution of perturbations of sterile neutrino dark matter

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Abstract
Sterile neutrinos, fermions with no standard model couplings [SU(2) singlets], are predicted by most extensions of the standard model, and may be the dark matter. I describe the nonthermal production and linear perturbation evolution in the early universe of this dark matter candidate. I calculate production of sterile neutrino dark matter including effects of Friedmann dynamics dictated by the quark-hadron transition and particle population, the alteration of finite temperature effective mass of active neutrinos due to the presence of thermal leptons, and heating of the coupled species due to the disappearance of degrees of freedom in the plasma. These effects leave the sterile neutrinos with a nontrivial momentum distribution. I also calculate the evolution of sterile neutrino density perturbations in the early universe through the linear regime and provide a fitting function form for the transfer function describing the suppression of small-scale fluctuations for this warm dark matter candidate. The results presented here differ quantitatively from previous work due to the inclusion of the relevant physical effects during the production epoch.