Cold + Hot Dark Matter

The Cold + Hot Dark Matter (CHDM) model appears to require about 5 eV of neutrino mass in order to produce early enough galaxy formation. Recent experimental data suggests that this neutrino mass may be divided between two species of neutrinos, each with mass of about 2.4 eV. Here we consider the consequences of such neutrino masses for cosmological models for the formation of galaxies and large scale structure in the universe, which are spatially flat and in which most of the dark matter is cold. The linear calculations and the new N-body simulation that we report here indicate that an Ω = 1 CHDM cosmological model with two neutrinos each of mass ≈ 2.4 eV (we will call this model C v²DM) agrees remarkably well with all available observations. However, we find that this is true only if the Hubble parameter H₀ ≈ 50 km s ^-1 Mpc ^-1. We also consider Cold Dark Matter (CDM) models with a cosmological constant Λ and show that evidence for hot dark matter raises serious difficulties for low-Ω ACDM models.