Planck 2013 results. XVI. Cosmological parameters
  We present the first results based on Planck measurements of the CMB
temperature and lensing-potential power spectra. The Planck spectra at high
multipoles are extremely well described by the standard spatially-flat
six-parameter LCDM cosmology. In this model Planck data determine the
cosmological parameters to high precision. We find a low value of the Hubble
constant, H0=67.3+/-1.2 km/s/Mpc and a high value of the matter density
parameter, Omega_m=0.315+/-0.017 (+/-1 sigma errors) in excellent agreement
with constraints from baryon acoustic oscillation (BAO) surveys. Including
curvature, we find that the Universe is consistent with spatial flatness to
percent-level precision using Planck CMB data alone. We present results from an
analysis of extensions to the standard cosmology, using astrophysical data sets
in addition to Planck and high-resolution CMB data. None of these models are
favoured significantly over standard LCDM. The deviation of the scalar spectral
index from unity is insensitive to the addition of tensor modes and to changes
in the matter content of the Universe. We find a 95% upper limit of r<0.11 on
the tensor-to-scalar ratio. There is no evidence for additional neutrino-like
relativistic particles. Using BAO and CMB data, we find N_eff=3.30+/-0.27 for
the effective number of relativistic degrees of freedom, and an upper limit of
0.23 eV for the summed neutrino mass. Our results are in excellent agreement
with big bang nucleosynthesis and the standard value of N_eff=3.046. We find no
evidence for dynamical dark energy. Despite the success of the standard LCDM
model, this cosmology does not provide a good fit to the CMB power spectrum at
low multipoles, as noted previously by the WMAP team. While not of decisive
significance, this is an anomaly in an otherwise self-consistent analysis of
the Planck temperature data.
