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Planck 2018 results: IX. Constraints on primordial non-Gaussianity

Akrami, Y; Arroja, F; Ashdown, M; Aumont, J; Baccigalupi, C; Ballardini, M; Banday, AJ; ... at alia, .; + view all (2020) Planck 2018 results: IX. Constraints on primordial non-Gaussianity. Astronomy & Astrophysics , 641 , Article A9. 10.1051/0004-6361/201935891. Green open access

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Abstract

We analyse the Planck full-mission cosmic microwave background (CMB) temperature and E-mode polarization maps to obtain constraints on primordial non-Gaussianity (NG). We compare estimates obtained from separable template-fitting, binned, and optimal modal bispectrum estimators, finding consistent values for the local, equilateral, and orthogonal bispectrum amplitudes. Our combined temperature and polarization analysis produces the following final results: : f^{local}_{NL} = −0.9 ± 5.1; f^{equil}_{NL} = −26 ± 47; and f^{ortho}_{NL} = −38 ± 24 (68% CL, statistical). These results include low-multipole (4 ≤ lambda < 40) polarization data that are not included in our previous analysis. The results also pass an extensive battery of tests (with additional tests regarding foreground residuals compared to 2015), and they are stable with respect to our 2015 measurements (with small fluctuations, at the level of a fraction of a standard deviation, which is consistent with changes in data processing). Polarizationonly bispectra display a significant improvement in robustness; they can now be used independently to set primordial NG constraints with a sensitivity comparable to WMAP temperature-based results and they give excellent agreement. In addition to the analysis of the standard local, equilateral, and orthogonal bispectrum shapes, we consider a large number of additional cases, such as scale-dependent feature and resonance bispectra, isocurvature primordial NG, and parity-breaking models, where we also place tight constraints but do not detect any signal. The nonprimordial lensing bispectrum is, however, detected with an improved significance compared to 2015, excluding the null hypothesis at 3.5σ. Beyond estimates of individual shape amplitudes, we also present model-independent reconstructions and analyses of the Planck CMB bispectrum. Our final constraint on the local primordial trispectrum shape is g^{local}_{NL} = (−5.8 ± 6.5) × 10^{4} (68% CL, statistical), while constraints for other trispectrum shapes are also determined. Exploiting the tight limits on various bispectrum and trispectrum shapes, we constrain the parameter space of different early-Universe scenarios that generate primordial NG, including general single-field models of inflation, multi-field models (e.g. curvaton models), models of inflation with axion fields producing parity-violation bispectra in the tensor sector, and inflationary models involving vector-like fields with directionally-dependent bispectra. Our results provide a high-precision test for structure-formation scenarios, showing complete agreement with the basic picture of the ΛCDM cosmology regarding the statistics of the initial conditions, with cosmic structures arising from adiabatic, passive, Gaussian, and primordial seed perturbations.

Type: Article
Title: Planck 2018 results: IX. Constraints on primordial non-Gaussianity
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/201935891
Publisher version: https://doi.org/10.1051/0004-6361/201935891
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.
Keywords: cosmic background radiation, cosmology: observations, cosmology: theory, early Universe, inflation, methods: data analysis
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10110649
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