  The large-scale distribution of cold dark matter halos is generally assumed
to trace the large-scale distribution of matter. In a universe with multiple
types of matter fluctuations, as is the case with massive neutrinos, the
relation between the halo field and the matter fluctuations may be more
complicated. We develop a method for calculating the bias factor relating
fluctuations in the halo number density to fluctuations in the mass density in
the presence of multiple fluctuating components of the energy density. In the
presence of massive neutrinos we find a small but pronounced feature in the
halo bias near the neutrino free-streaming scale. The neutrino feature is a
small step with amplitude that increases with halo mass and neutrino mass
density. The scale-dependent halo bias lessens the suppression of the
small-scale halo power spectrum and should therefore weaken constraints on
neutrino mass from the galaxy auto-power spectrum and correlation function. On
the other hand, the feature in the bias is itself a novel signature of massive
neutrinos that can be studied independently.
