The recent atmospheric neutrino data from Super-Kamiokande 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 \Omega _ { \nu } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 0.001 — almost as much as that of all the stars in the universe — and permit higher \Omega _ { \nu } .
The “ standard ” COBE-normalized critical-matter-density ( i.e. , \Omega _ { m } = 1 ) Cold Dark Matter ( CDM ) model has too much power on small scales .
But adding to CDM neutrinos with mass of about 5 eV , corresponding to \Omega _ { \nu } \approx 0.2 , results in a much improved fit to data on the nearby galaxy and cluster distribution .
Indeed , the resulting Cold + Hot Dark Matter ( CHDM ) cosmological model is arguably the most successful \Omega _ { m } = 1 model for structure formation [ 1 , 2 , 3 , 4 ] .
However , other recent data has begun to make the case for \Omega _ { m } \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 0.6 fairly convincing .
In light of all this new data , we reconsider whether cosmology still provides evidence favoring neutrino mass of a few eV in flat models with cosmological constant \Omega _ { \Lambda } = 1 - \Omega _ { m } .
We find that the possible improvement of the low- \Omega _ { m } flat ( \Lambda CDM ) cosmological models with the addition of light neutrinos appears to be rather limited .