The recent atmospheric neutrino data from Super-Kamiokande
[46]
provide strong evidence of neutrino oscillations and
therefore of non-zero neutrino mass. These data imply a lower limit
on the hot dark matter (i.e., light neutrino) contribution to the
cosmological density
0.001.
is
actually that low, and therefore cosmologically uninteresting, if
m(
) >>
m(µ), as is
suggested by the hierarchical
pattern of the quark and charged lepton masses. But if the
and µ are nearly
degenerate in mass, as suggested by their
strong mixing, then
could be substantially larger.
Although the Cold + Hot Dark Matter (CHDM) cosmological model with
h 
0.5,
m = 1, and
= 0.2 predicts power
spectra of cosmic density and CMB anisotropies that are in excellent
agreement with the data
[96,
49],
as we have just seen the large
value measured for the Hubble parameter makes such
m = 1 models
dubious. It remains to be seen whether including a significant amount
of hot dark matter in
low-m models
improves their agreement with data. Primack & Gross
[97,
98]
found that the possible improvement of the
low-m flat
(
CDM) cosmological models
with the addition of light neutrinos appears to be rather limited, and
the maximum amount of hot dark matter decreases with decreasing
m
[95].
For m
0.4,
[29]
find that
0.08;
[47]
finds more restrictive upper
limits with the constraint that the primordial power spectrum index
n 
1, but this may not be
well motivated.