  Sterile neutrinos in the keV mass range may constitute the galactic dark
matter. Various proposed direct detection and laboratory searches are reviewed.
The most promising method in the near future is complete energy-momentum
reconstruction of individual beta-decay or K-capture events, using atoms
suspended in a magneto-optical trap. A survey of suitable isotopes is
presented, together with the measurement precision required in a typical
experimental configuration. It is concluded that among the most promising are
the K-capture isotopes 131Cs, which requires measurement of an X-ray and
several Auger electrons in addition to the atomic recoil, and 7Be which has
only a single decay product but needs development work to achieve a trapped
source. A number of background effects are discussed. It is concluded that
sterile neutrinos with masses down to the 5-10 keV region would be detectable,
together with relative couplings down to the level 10-10-10-11 in a 1-2 year
running time.
