Opening a new window for warm dark matter

Abstract

We explore the range of parameters for dark-matter sterile neutrinos in an extention of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the $ν$MSM). This simple model can explain a wide range of phenomena, including neutrino oscillations, baryogenesis, the pulsar velocities, and the early reionization. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). In addition, the primordial production of dark matter sterile neutrinos allows to escape most of the constraints.

Figures (1)

• Figure 1: Restrictions on the mixing angle of sterile neutrino coming from X-ray observations of Boyarsky:2006fg and from the Lyman-$\alpha$ forest data analysis of Seljak:2006qw, assuming that all dark matter is in sterile neutrinos. No region is allowed for sterile neutrinos produced in active-sterile transitions, if their initial concentration was zero. For $N_1$ produced thermally at high energy scale the allowed region is for $M_s > 2.5$ keV and below the shaded area. For primordial production of sterile neutrinos in light inflaton decays Shaposhnikov:2006xi, all values below shaded area and to the right from $M_s =10$ keV are allowed.