Planck constraints on neutrino isocurvature density perturbations
  The recent Cosmic Microwave Background data from the Planck satellite
experiment, when combined with HST determinations of the Hubble constant, are
compatible with a larger, non-standard, number of relativistic degrees of
freedom at recombination, parametrized by the neutrino effective number
$N_{eff}$. In the curvaton scenario, a larger value for $N_{eff}$ could arise
from a non-zero neutrino chemical potential connected to residual neutrino
isocurvature density (NID) perturbations after the decay of the curvaton field,
parametrized by the amplitude $\alpha^{NID}$. Here we present new constraints
on $N_{eff}$ and $\alpha^{NID}$ from an analysis of recent cosmological data.
We found that the Planck+WP dataset does not show any indication for a neutrino
isocurvature component, severly constraining its amplitude, and that current
indications for a non-standard $N_{eff}$ are further relaxed.
