Planck 2018 results. VI. Cosmological parameters

Kavli Affiliate: E. P. S. Shellard

| First 5 Authors: Planck Collaboration, N. Aghanim, Y. Akrami, M. Ashdown, J. Aumont

| Summary:

We present cosmological parameter results from the final full-mission Planck
measurements of the CMB anisotropies. We find good consistency with the
standard spatially-flat 6-parameter $Lambda$CDM cosmology having a power-law
spectrum of adiabatic scalar perturbations (denoted "base $Lambda$CDM" in this
paper), from polarization, temperature, and lensing, separately and in
combination. A combined analysis gives dark matter density $Omega_c h^2 =
0.120pm 0.001$, baryon density $Omega_b h^2 = 0.0224pm 0.0001$, scalar
spectral index $n_s = 0.965pm 0.004$, and optical depth $tau = 0.054pm
0.007$ (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 $100theta_*=1.0411pm 0.0003$. These
results are only weakly dependent on the cosmological model and remain stable,
with somewhat increased errors, in many commonly considered extensions.
Assuming the base-$Lambda$CDM cosmology, the inferred late-Universe parameters
are: Hubble constant $H_0 = (67.4pm 0.5)$km/s/Mpc; matter density parameter
$Omega_m = 0.315pm 0.007$; and matter fluctuation amplitude $sigma_8 =
0.811pm 0.006$. We find no compelling evidence for extensions to the
base-$Lambda$CDM model. Combining with BAO we constrain the effective extra
relativistic degrees of freedom to be $N_{rm eff} = 2.99pm 0.17$, and the
neutrino mass is tightly constrained to $sum m_nu< 0.12$eV. The CMB spectra
continue to prefer higher lensing amplitudes than predicted in base
-$Lambda$CDM at over $2,sigma$, which pulls some parameters that affect the
lensing amplitude away from the base-$Lambda$CDM model; however, this is not
supported by the lensing reconstruction or (in models that also change the
background geometry) BAO data. (Abridged)

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