Scalar induced resonant sterile neutrino production in the early Universe

It has been recently suggested [F. Bezrukov et al. J. Cosmol. Astropart. Phys. 06 (2017) 051; F Bezrukov et al. Phys. Rev. D 99, 083507 (2019)] that a cosmic scalar field can completely change the keV-scale sterile neutrino production in the early Universe. Its effect may, for various parameter choices, either suppress sterile neutrino production and make moderate active-sterile mixing cosmologically acceptable, or increase the production and generate a considerable dark matter component out of sterile neutrino with otherwise negligible mixing with SM. In this paper, we provide analytic estimates complementing and improving of the numerical calculations performed by F. Bezrukov et al. [Phys. Rev. D 99, 083507 (2019) in the case of the resonant amplification of the sterile neutrino production by the scalar field. We found the substantially cooler velocity distribution of sterile neutrinos as compared to most production mechanisms, opening a new window for warm dark matter, which is otherwise forbidden by structure formation considerations. We also discuss phenomenological and theoretical issues related to the successful implementation of this idea in fully realistic extensions of the Standard Model of particle physics.