  The standard model of particle physics is extended by adding a purely
neutrinophilic dark sector. It is shown that theories which accommodate
standard model neutrinos as dark radiation are resurrected. Sterile neutrinos
bridge the visible and the dark sector and can keep their mutual interactions
effective even after the epoch of big bang nucleosythesis. This prolonged
contact between dark matter and standard model neutrinos solves the well-known
small-scale structure problems of the cosmological standard model. The dark
sector presented in this work satisfies all experimental and observational
constraints from particle physics and cosmology.
