New Dark Matter Candidate: Nonthermal Sterile Neutrinos

Abstract

We propose a new and unique dark matter candidate: ∼ 100 eV to ∼ 10 keV sterile neutrinos produced via lepton number-driven resonant MSW (Mikheyev-Smirnov-Wolfenstein) conversion of active neutrinos. The requisite lepton number asymmetries in any of the active neutrino flavors range from 10 −3 to 10 −1 of the photon number -well within primordial nucleosynthesis bounds. The unique feature here is that the adiabaticity condition of the resonance strongly favors the production of lower energy sterile neutrinos. The resulting non-thermal (cold) energy spectrum can cause these sterile neutrinos to revert to non-relativistic kinematics at an early epoch, so that free-streaming lengths at or below the dwarf galaxy scale are possible. Therefore, the main problem associated with light neutrino dark matter candidates can be circumvented in our model.

Bulk QCD thermodynamics and sterile neutrino dark matter

“…Sterile neutrinos with masses of 1 − 100 keV and small mixings with active neutrinos are produced in a nonequilibrium quantum decoherence process associated with the scattering of active neutrinos: either with the usual simplifying assumption of a small universal lepton number [9] (of order of the baryon number) or with the more liberal possibility of a large lepton number in neutrinos (several orders of magnitude larger than the baryon number) [11]. We define the lepton number in a neutrino flavor here as the difference between neutrino and antineutrino number densities normalized by the photon number density, n γ , at a given epoch:…”

“…Sterile neutrinos are a natural candidate for WDM [9,10] and CDM [11,12], and can emerge from models with composite fermions [13], mirror fermions [14] or light ax-inos [15]. Sterile neutrinos with masses of 1 − 100 keV and small mixings with active neutrinos are produced in a nonequilibrium quantum decoherence process associated with the scattering of active neutrinos: either with the usual simplifying assumption of a small universal lepton number [9] (of order of the baryon number) or with the more liberal possibility of a large lepton number in neutrinos (several orders of magnitude larger than the baryon number) [11].…”

A symbiotic scenario for the rapid formation of supermassive black holes

“…However, for a larger initial lepton asymmetry, like L νe ∼ 10 −2 , there is, in addition to non-resonant neutrino scattering, also resonant or matter-enhanced neutrino scattering contributing to the production of dark matter [10]. The latter yields cool sterile neutrinos that have a distorted quasi-degenerate spectrum, with an average energy of about two-thirds of that of the warm sterile neutrinos, due to the resonant Mikheyev-Smirnov-Wolfenstein (MSW) oscillations [14].…”

“…well ahead of the quark-gluon and chiral restoration phase transitions, through incoherent resonant [10] and non-resonant [11] scattering of the active neutrinos. For a wide range of the parameters of the νMSM, the sterile neutrinos are generated out of thermal equilibrium, yielding a sterile neutrino mass fraction of the total mass-energy of this universe which is consistent with that of nonbaryonic dark matter.…”

“…a mixing angle of the sterile neutrino ν s with the active neutrino ν e given by sin 2 ϑ = 10 −13 , and a sterile neutrino mass m = 15 keV/c 2 , the mass fraction of the sterile neutrinos produced in the early universe is indeed Ω νs ∼ 0.24 [10], i.e. equal to that of the nonbaryonic dark matter, derived from the WMAP data [5].…”