Title:

The Nature of Dark Matter	



Peter L. Biermann
MPIfR, Bonn



Abstract:

	Dark matter could light up the first stars in the universe if the dark
matter is made up of weakly interacting neutrinos, right-handed neutrinos,
or also called sterile neutrinos. We have shown that sterile neutrino decays
could speed up the formation of molecular hydrogen and light up the first
stars as early as 20-100 million years after the big bang. The light from
these first stars could ionize the interstellar gas by 150-400 million years
after the big bang, in accordance with the observations. Formation of
central galactic black holes, as well as structure on subgalactic scales
favor some form of warm dark matter, such as sterile neutrinos, as dark
matter. The consensus of several indirect pieces of evidence leads one to
believe that the long sought-after dark-matter particle may, indeed, be a
sterile neutrino.  The Galactic center black hole and its mass may provide a
crucial limit for the mass of the sterile neutrino:  Assuming that the mass
of the Galactic Center Black hole is all due to dark matter growth, and that
there is little additional baryonic growth, gives a lower limit to the dark
matter particle mass. The main prediction of warm dark matter is, that all
dwarf spheroidal galaxies should have he same dark matter mass, has been
verified; the galaxy mass suggests also a keV dark matter particle.  The
X-ray emission from neighboring dwarf and normal galaxies, the Virgo
cluster as well as the X-ray background  give an upper limit at almost  the
same number; the Lyman $\alpha$-forest gives also a lower limit.  X-ray
observations are scheduled for this proposal in April 2007.  The high pulsar
velocities may also be explained with a transition from normal to sterile
neutrinos.  While all pieces of evidence may find a separate solution, a keV
right handed neutrino could provide a unifying picture.  This may lead to a
decisive step in determining the nature and mass  of the dark matter
particles, suggesting as one solution a Weakly Interacting Neutrino, or WIN,
of a few keV.