Dark Radiation after Planck
  We present new constraints on the relativistic neutrino effective number
N_eff and on the Cosmic Microwave Background power spectrum lensing amplitude
A_L from the recent Planck 2013 data release. Including observations of the CMB
large angular scale polarization from the WMAP satellite, we obtain the bounds
N_eff = 3.71 +/- 0.40 and A_L = 1.25 +/- 0.13 at 68% c.l.. The Planck dataset
alone is therefore suggesting the presence of a dark radiation component at
91.1% c.l. and hinting for a higher power spectrum lensing amplitude at 94.3%
c.l.. We discuss the agreement of these results with the previous constraints
obtained from the Atacama Cosmology Telescope (ACT) and the South Pole
Telescope (SPT). Considering the constraints on the cosmological parameters, we
found a very good agreement with the previous WMAP+SPT analysis but a tension
with the WMAP+ACT results, with the only exception of the lensing amplitude.
