Hidden treasures: Sterile neutrinos as dark matter with miraculous abundance, structure formation for different production mechanisms, and a solution to the σ8 problem

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 σ8 problem can be a signature of fractional dark matter in the form of sterile neutrinos in several mechanisms.

Deep Search for Decaying Dark Matter with XMM-Newton Blank-Sky Observations

“…For example, in the Neutrino Minimal Standard Model (νMSM) [27][28][29], which may simultaneously explain the observed neutrino masses, DM density, and baryon asymmetry, the Standard Model is supplemented by three heavier sterile-neutrino states, the lightest of which is the DM candidate. The DM abundance is generated through the mixing of sterile and active neutrinos [1], which can further be resonantly enhanced by a finite lepton chemical potential [2,[29][30][31][32][33][34][35], though other production mechanisms are also possible [3,36,37]. DM models such as axionlike particle DM [38] and moduli DM [39] predict similar UXL signatures from DM decay.…”

Neutrinos in Astrophysics and Cosmology

“…Sterile neutrinos can be much colder than that shown in Fig. 15 if they are produced at high temperature, similar to gravitinos, or if there is a large entropy transfer by new or standard particles into the plasma after the sterile neutrino dark matter is produced [76]. (purple) momentum distributions versus a thermal distribution (red), on arbitrary scales.…”

“…The variety of sterile neutrino production models' relation with structure formation constraints is discussed in Ref. [76].…”

Axion–Sterile Neutrino Dark Matter

“…Yet another motivation for this work is the fact that the well-motivated presence of the axion also significantly enlarges the viable region of parameter space for sterile neutrino DM in the aνMSM, compared to the case 2 X s = 1 (where this region is quite narrow [52,53]): all observational bounds become weaker when the sterile neutrino has to account for only a fraction X s < 1 of DM.…”