Cold + Hot Dark Matter After Super-Kamiokande

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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 Ων> 0.001 --- almost as much as that of all the stars in the universe --- and permit higher Ων. The ``standard'' COBE-normalized critical-matter-density (i.e., Ωₘ=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 Ων≈ 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 Ωₘ=1 model for structure formation. However, other recent data has begun to make the case for Ωₘ < 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 ΩΛ= 1 - Ωₘ. We find that the possible improvement of the low-Ωₘ flat (LCDM) cosmological models with the addition of light neutrinos appears to be rather limited.