<i>Planck</i> 2018 results

Abstract

We present cosmological parameter results from the final full-mission 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 large-scale 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 small-scale polarization leads to more robust constraints on many parameters, with residual modelling uncertainties estimated to affect them only at the 0.5 σ level. We find good consistency with the standard spatially-flat 6-parameter ΛCDM cosmology having a power-law 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 100 θ * = 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 base-ΛCDM cosmology, the inferred (model-dependent) late-Universe 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 base-ΛCDM model. Combining with baryon acoustic oscillation (BAO) measurements (and considering single-parameter 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 &lt; 0.12 eV. The CMB spectra continue to prefer higher lensing amplitudes than predicted in base ΛCDM at over 2 σ , 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 dark-energy 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 power-law primordial spectrum, and combining with data from BAO, BICEP2, and Keck Array data, we place a limit on the tensor-to-scalar ratio r 0.002 &lt; 0.06. Standard big-bang nucleosynthesis predictions for the helium and deuterium abundances for the base-ΛCDM cosmology are in excellent agreement with observations. The Planck base-ΛCDM results are in good agreement with BAO, SNe, and some galaxy lensing observations, but in slight tension with the Dark Energy Survey’s combined-probe results including galaxy clustering (which prefers lower fluctuation amplitudes or matter density parameters), and in significant, 3.6 σ , 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.

Keywords

Affiliated Institutions

• University of California, Berkeley US
• Université Paris Cité FR
• Jet Propulsion Laboratory US
• Institut National de Physique Nucléaire et de Physique des Particules FR
• Scuola Internazionale Superiore di Studi Avanzati IT
• University of Manchester GB
• Sorbonne Université FR
• University of Padua IT
• California Institute of Technology US
• AlbaNova SE
• Aix-Marseille Université FR
• University of Toronto CA
• Roche (France) FR
• Universidad de La Laguna ES
• Istituto Nazionale di Fisica Nucleare, Sezione di Bologna IT
• University of California, Davis US
• University of Oslo
• Laboratory for Ocean Physics and Satellite Remote Sensing FR
• European Space Astronomy Centre ES
• Sorbonne Paris Cité FR
• UNSW Sydney AU
• Indian Institute of Science Education and Research Thiruvananthapuram IN
• African Institute for Mathematical Sciences ZA
• Stellenbosch University ZA
• Centre National de la Recherche Scientifique FR
• Universidad de Oviedo ES
• Université de Bretagne Occidentale FR
• Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères FR
• Institut de Recherche pour le Développement FR
• Instituto de Física de Cantabria ES
• Helsinki Institute of Physics FI
• Institut d'Astrophysique Spatiale FR
• Istituto di Radioastronomia di Bologna IT
• Osservatorio Astronomico di Padova IT
• Ifremer FR
• National Institute of Science Education and Research IN
• Imperial College London GB
• Universidad de Cantabria ES
• University of Helsinki FI
• Istituto Nazionale di Fisica Nucleare, Sezione di Padova IT
• University of Sussex GB
• Université Paris-Saclay FR
• Cardiff University GB
• Trieste Astronomical Observatory IT
• Université Paris Sciences et Lettres FR
• École Normale Supérieure - PSL FR
• Commissariat à l'Énergie Atomique et aux Énergies Alternatives FR
• University of Ferrara IT
• Université Toulouse III - Paul Sabatier FR
• University of Milan IT
• Argonne National Laboratory US
• Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna IT
• Lawrence Berkeley National Laboratory US
• University of Cambridge GB
• Université Paris-Sud FR
• University of Geneva CH
• Shahid Beheshti University IR
• University of British Columbia CA
• Sun Yat-sen University CN
• University of KwaZulu-Natal ZA
• Leiden University NL
• Stockholm University SE
• Kavli Institute for the Physics and Mathematics of the Universe JP
• RWTH Aachen University DE
• University of the Western Cape ZA
• Simon Fraser University CA
• Université Grenoble Alpes FR
• Instituto de Astrofísica de Canarias ES
• Osservatorio di Astrofisica e Scienza dello Spazio
• Max Planck Institute for Astrophysics DE
• Institut d'Astrophysique de Paris FR
• National Centre for Nuclear Research PL
• Princeton University US
• Sapienza University of Rome IT
• Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara IT
• University of Warsaw PL
• The University of Tokyo JP
• Université Fédérale de Toulouse Midi-Pyrénées FR
• National Institute for Astrophysics IT

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