The combination of COBE data [57] and the distribution of
galaxies on large and small scales is hard to understand on the basis of
simple cold dark matter. One possibility is that in addition to cold dark
matter there is a small admixture [58] of hot dark matter,
presumably due to a massive 
neutrino with a mass in the range
[59]. Even better fits
are obtained if there are two nearly degenerate neutrinos in the
few eV range [60], and speculations on these lines have
been encouraged by the possible LSND observation of
. There are, however,
alternative explanations [61],
such as a 100 eV sterile neutrino, decaying
MeV neutrino,
cosmological constant, topological
defects, low density universe, or a tilted initial spectrum.
If the 
has a mass in the eV range then, unless its mixing
with 
is extremely small, 
oscillations should be observable in the CHORUS and NOMAD experiments
at CERN, and the later E803 at Fermilab, all of which will be sensitive
to 
appearance for very small 
for
in the eV
range.