Planck 2013 results. XVI. Cosmological parameters

Articolo

Data di Pubblicazione:

2014

Abstract:

This paper presents the first cosmological results based on Planck
measurements of the cosmic microwave background (CMB) temperature and
lensing-potential power spectra. We find that the Planck spectra at high
multipoles (l ≳ 40) are extremely well described by the
standard spatially-flat six-parameter LambdaCDM cosmology with a
power-law spectrum of adiabatic scalar perturbations. Within the context
of this cosmology, the Planck data determine the cosmological parameters
to high precision: the angular size of the sound horizon at
recombination, the physical densities of baryons and cold dark matter,
and the scalar spectral index are estimated to be
theta_* = (1.04147 � 0.00062) �
10^-2, Omega_bh² = 0.02205 �
0.00028, Omega_ch² = 0.1199 � 0.0027, and
n_s = 0.9603 � 0.0073, respectively(note that in this
abstract we quote 68% errors on measured parameters and 95% upper limits
on other parameters). For this cosmology, we find a low value of the
Hubble constant, H₀ = (67.3 � 1.2) km s^-1
Mpc^-1, and a high value of the matter density parameter,
Omega_m = 0.315 � 0.017. These values are in tension
with recent direct measurements of H₀ and the
magnitude-redshift relation for Type Ia supernovae, but are in excellent
agreement with geometrical 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 use high-resolution CMB data together with Planck to
provide greater control on extragalactic foreground components in an
investigation of extensions to the six-parameter LambdaCDM model. We
present selected results from a large grid of cosmological models, using
a range of additional astrophysical data sets in addition to Planck and
high-resolution CMB data. None of these models are favoured over the
standard six-parameter LambdaCDM cosmology. The deviation of the
scalar spectral index from unity isinsensitive to the addition of tensor
modes and to changes in the matter content of the Universe. We find an
upper limit of r_0.002< 0.11 on the tensor-to-scalar ratio.
There is no evidence for additional neutrino-like relativistic particles
beyond the three families of neutrinos in the standard model. 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 sum of neutrino masses. 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;
using BAO and CMB data, the dark energy equation of state parameter is
constrained to be w = -1.13_-0.10^+0.13. We also use
the Planck data to set limits on a possible variation of the
fine-structure constant, dark matter annihilation and primordial
magnetic fields. Despite the success of the six-parameter LambdaCDM
model in describing the Planck data at high multipoles, we note that
this cosmology does not provide a good fit to the temperature power
spectrum at low multipoles. The unusual shape of the spectrum in the
multipole range 20 ≲ l ≲ 40 was seen previously in the
WMAP data and is a real feature of the primordial CMB anisotropies. The
poor fit to the spectrum at low multipoles is not of decisive
significance, but is an "anomaly" in an otherwise self-consistent
analysis of the Planck temperature data.

Tipologia CRIS:

1.1 Articolo in rivista

Keywords:

cosmic background radiation; cosmological parameters; early Universe; inflation; primordial nucleosynthesis

Elenco autori: