Planck 2018 results. VI. Cosmological parameters

Abstract

We present cosmological parameter results from the final full-mission Planck\nmeasurements of the CMB anisotropies. We find good consistency with the\nstandard spatially-flat 6-parameter $\\Lambda$CDM cosmology having a power-law\nspectrum of adiabatic scalar perturbations (denoted "base $\\Lambda$CDM" in this\npaper), from polarization, temperature, and lensing, separately and in\ncombination. A combined analysis gives dark matter density $\\Omega_c h^2 =\n0.120\\pm 0.001$, baryon density $\\Omega_b h^2 = 0.0224\\pm 0.0001$, scalar\nspectral index $n_s = 0.965\\pm 0.004$, and optical depth $\\tau = 0.054\\pm\n0.007$ (in this abstract we quote $68\\,\\%$ confidence regions on measured\nparameters and $95\\,\\%$ on upper limits). The angular acoustic scale is\nmeasured to $0.03\\,\\%$ precision, with $100\\theta_*=1.0411\\pm 0.0003$. These\nresults are only weakly dependent on the cosmological model and remain stable,\nwith somewhat increased errors, in many commonly considered extensions.\nAssuming the base-$\\Lambda$CDM cosmology, the inferred late-Universe parameters\nare: Hubble constant $H_0 = (67.4\\pm 0.5)$km/s/Mpc; matter density parameter\n$\\Omega_m = 0.315\\pm 0.007$; and matter fluctuation amplitude $\\sigma_8 =\n0.811\\pm 0.006$. We find no compelling evidence for extensions to the\nbase-$\\Lambda$CDM model. Combining with BAO we constrain the effective extra\nrelativistic degrees of freedom to be $N_{\\rm eff} = 2.99\\pm 0.17$, and the\nneutrino mass is tightly constrained to $\\sum m_\\nu< 0.12$eV. The CMB spectra\ncontinue to prefer higher lensing amplitudes than predicted in base\n-$\\Lambda$CDM at over $2\\,\\sigma$, which pulls some parameters that affect the\nlensing amplitude away from the base-$\\Lambda$CDM model; however, this is not\nsupported by the lensing reconstruction or (in models that also change the\nbackground geometry) BAO data. (Abridged)\n