  Taken at face value, current experimental data indicate the existence of a
new particle, the sterile neutrino, which must be a singlet under the Standard
Model gauge group. Although they are not detectable through traditional means,
such particles have interesting observable consequences for particle
astrophysics and cosmology. Here we examine these implications and discuss, in
particular, sterile neutrino dark matter and the relationship between
matter-enhanced active-sterile neutrino transformation and the synthesis of
heavy elements in supernovae.
