  Dark matter has been recognized as an essential part of matter for over 70
years now, and many suggestions have been made, what it could be. Most of these
ideas have centered on Cold Dark Matter, particles that are expected in
extensions of standard particle physics, such as supersymmetry. Here we explore
the concept that dark matter is sterile neutrinos, a concept that is commonly
referred to as Warm Dark Matter. Such particles have keV masses, and decay over
a very long time, much longer than the Hubble time. In their decay they produce
X-ray photons which modify the ionization balance in the early universe,
increasing the fraction of molecular Hydrogen, and thus help early star
formation. Sterile neutrinos may also help to understand the baryon-asymmetry,
the pulsar kicks, the early growth of black holes, the minimum mass of dwarf
spheroidal galaxies, as well as the shape of dark matter halos. As soon as all
these tests have been quantitative in its various parameters, we may focus on
the creation mechanism of these particles, and could predict the strength of
the sharp X-ray emission line, expected from any large dark matter assembly. A
measurement of this X-ray emission line would be definitive proof for the
existence of may be called weakly interacting neutrinos, or WINs.
