Planck 2018 results. VI. Cosmological parameters
Abstract
We present cosmological parameter results from the final fullmission Planck measurements of the cosmic microwave background (CMB) anisotropies, combining information from the temperature and polarization maps and the lensing reconstruction. Compared to the 2015 results, improved measurements of largescale polarization allow the reionization optical depth to be measured with higher precision, leading to significant gains in the precision of other correlated parameters. Improved modelling of the smallscale polarization leads to more robust constraints on many parameters, with residual modelling uncertainties estimated to affect them only at the 0.5σ level. We find good consistency with the standard spatiallyflat 6parameter ΛCDM cosmology having a powerlaw spectrum of adiabatic scalar perturbations (denoted "base ΛCDM" in this paper), from polarization, temperature, and lensing, separately and in combination. A combined analysis gives dark matter density Ω_{c}h^{2} = 0.120 ± 0.001, baryon density Ω_{b}h^{2} = 0.0224 ± 0.0001, scalar spectral index n_{s} = 0.965 ± 0.004, and optical depth τ = 0.054 ± 0.007 (in this abstract we quote 68% confidence regions on measured parameters and 95% on upper limits). The angular acoustic scale is measured to 0.03% precision, with 100θ_{*} = 1.0411 ± 0.0003. These results are only weakly dependent on the cosmological model and remain stable, with somewhat increased errors, in many commonly considered extensions. Assuming the baseΛCDM cosmology, the inferred (modeldependent) lateUniverse parameters are: Hubble constant H_{0} = (67.4 ± 0.5) km s^{1} Mpc^{1}; matter density parameter Ω_{m} = 0.315 ± 0.007; and matter fluctuation amplitude σ_{8} = 0.811 ± 0.006. We find no compelling evidence for extensions to the baseΛCDM model. Combining with baryon acoustic oscillation (BAO) measurements (and considering singleparameter extensions) we constrain the effective extra relativistic degrees of freedom to be N_{eff} = 2.99 ± 0.17, in agreement with the Standard Model prediction N_{eff} = 3.046, and find that the neutrino mass is tightly constrained to ∑m_{ν} < 0.12 eV. The CMB spectra continue to prefer higher lensing amplitudes than predicted in base ΛCDM at over 2σ, which pulls some parameters that affect the lensing amplitude away from the ΛCDM model; however, this is not supported by the lensing reconstruction or (in models that also change the background geometry) BAO data. The joint constraint with BAO measurements on spatial curvature is consistent with a flat universe, Ω_{K} = 0.001 ± 0.002. Also combining with Type Ia supernovae (SNe), the darkenergy equation of state parameter is measured to be w_{0} = 1.03 ± 0.03, consistent with a cosmological constant. We find no evidence for deviations from a purely powerlaw primordial spectrum, and combining with data from BAO, BICEP2, and Keck Array data, we place a limit on the tensortoscalar ratio r_{0.002} < 0.06. Standard bigbang nucleosynthesis predictions for the helium and deuterium abundances for the baseΛCDM cosmology are in excellent agreement with observations. The Planck baseΛCDM results are in good agreement with BAO, SNe, and some galaxy lensing observations, but in slight tension with the Dark Energy Survey's combinedprobe results including galaxy clustering (which prefers lower fluctuation amplitudes or matter density parameters), and in significant, 3.6σ, tension with local measurements of the Hubble constant (which prefer a higher value). Simple model extensions that can partially resolve these tensions are not favoured by the Planck data.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 September 2020
 DOI:
 10.1051/00046361/201833910
 arXiv:
 arXiv:1807.06209
 Bibcode:
 2020A&A...641A...6P
 Keywords:

 cosmic background radiation;
 cosmological parameters;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 73 pages