Sterile neutrino dark matter as a consequence ofνMSM-induced lepton asymmetry

Abstract

It has been pointed out by one of the authors (Shaposhnikov 2008 Preprint 0804.4542) that in theνMSM (Standard Model extended with three right-handed neutrinos with masses smallerthan the electroweak scale), there is a corner in the parameter space whereCP-violating resonant oscillations among the two heaviest right-handed neutrinos continue tooperate below the freeze-out temperature of sphaleron transitions, leading toa lepton asymmetry which is considerably larger than the baryon asymmetry.Consequently, the lightest right-handed (‘sterile’) neutrinos, which may serve as darkmatter, are generated through an efficient resonant mechanism proposed by Shiand Fuller (1999 Phys. Rev. Lett. 82 2832 [astro-ph/9810076]).We re-compute the dark matter relic density and non-eq uilibrium momentumdistribution function in this situation with quantum field theoretic methods and,confronting the results with existing astrophysical data, derive bounds on theproperties of the lightest right-handed neutrinos. Our spectra can be used as aninput for structure formation simulations in warm dark matter cosmologies, for aLyman-α analysis of the dark matter distribution on small scales, and for studying the properties ofhaloes of dwarf spheroidal galaxies.