Abstract
We discuss numerous mechanisms for production of sterile neutrinos, which can account for all or a fraction of dark matter, and which can range from warm to effectively cold dark matter, depending on the cosmological scenario. We investigate production by Higgs boson decay, $(B-L)$ gauge boson production at high temperature, as well as production via resonant and nonresonant neutrino oscillations. We calculate the effects on structure formation in these models, some for the first time. If two populations of sterile neutrinos, one warm and one cold, were produced by different mechanisms, or if sterile neutrinos account for only a fraction of dark matter, while the remainder is some other cold dark matter particle, the resulting multi-component dark matter may alleviate some problems in galaxy formation. We examine the X-ray constraints and the candidate signal at 3.5 keV. Finally, we also show that the $\sigma_8$ problem can be a signature of fractional dark matter in the form of sterile neutrinos in several mechanisms.
Highlights
Sterile or right-handed neutrinos are introduced for the purpose of explaining the observed masses of active neutrinos
Since the same mixing parameter controls the production and the decay of sterile neutrinos in the case of oscillation production, the x-ray signatures expected from dark matter are uniquely determined by the particle mass and the mixing that produce the requisite abundance of sterile neutrino dark matter [3,8]
The density of dark matter is given by 1 ξ f3 16π that is, exactly the observed present value of ρDM=T3γ, which corresponds to ΩDM 1⁄4 0.2. This coincidence of scales to produce the proper dark matter density is unique among the models for sterile neutrino dark matter production, and it can be compared with the “weakly interacting massive particle (WIMP) miracle” of electroweak-scale dark matter
Summary
Sterile or right-handed neutrinos are introduced for the purpose of explaining the observed masses of active neutrinos. If one of the Majorana masses is of the order of 1–10 keV, the corresponding particle can be dark matter [2,3] and can affect supernova explosions in ways consistent with observations [4,5] This dark matter candidate arises from a very minimal extension of the Standard Model by one light sterile neutrino. Since the same mixing parameter controls the production and the decay of sterile neutrinos in the case of oscillation production, the x-ray signatures expected from dark matter are uniquely determined by the particle mass and the mixing that produce the requisite abundance of sterile neutrino dark matter [3,8]. For the first time, the linear transfer functions for several production mechanisms—Higgs decay and two types of Grand Unified Theory (GUT-)scale production—to assess their effects on cosmological structure formation, as they cross the regime from cold to warm dark matter
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