Spoon or slide? The non-linear matter power spectrum in the presence of
  massive neutrinos
  Numerical simulations of massive neutrino cosmologies consistently find a
spoon-like feature in the non-linear matter power spectrum ratios of
cosmological models that differ only in the neutrino mass fraction f_N.
Typically, the ratio approaches unity at low wave numbers k, decreases by ~ 10
f_N at k ~ 1 h/Mpc, and turns up again at large k. Using the halo model of
large-scale structure, we show that this spoon feature originates in the
transition from the two-halo power spectrum to the one-halo power spectrum. The
former's sensitivity to f_N rises with k, while that of the latter decreases
with k. The presence of this spoon feature is robust with respect to different
choices of the halo mass function and the halo density profile, and does not
require any parameter tuning within the halo model. We demonstrate that a
standard halo model calculation is already able to predict the depth, width,
and position of this spoon as well as its evolution with redshift z with
remarkable accuracy. Predictions at z >= 1 can be further improved using
non-linear perturbative inputs.
