Planck 2015 results. XVII. Constraints on primordial nonGaussianity
Abstract
The Planck full mission cosmic microwave background (CMB) temperature and Emode polarization maps are analysed to obtain constraints on primordial nonGaussianity (NG). Using three classes of optimal bispectrum estimators  separable templatefitting (KSW), binned, and modal  we obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result from temperature alone ƒ^{local}_{NL} = 2.5 ± 5.7, ƒ^{equil}_{NL}= 16 ± 70, , and ƒ^{ortho}_{NL} = 34 ± 32 (68% CL, statistical). Combining temperature and polarization data we obtain ƒ^{local}_{NL} = 0.8 ± 5.0, ƒ^{equil}_{NL}= 4 ± 43, and ƒ^{ortho}_{NL} = 26 ± 21 (68% CL, statistical). The results are based on comprehensive crossvalidation of these estimators on Gaussian and nonGaussian simulations, are stable across component separation techniques, pass an extensive suite of tests, and are consistent with estimators based on measuring the Minkowski functionals of the CMB. The effect of timedomain deglitching systematics on the bispectrum is negligible. In spite of these test outcomes we conservatively label the results including polarization data as preliminary, owing to a known mismatch of the noise model in simulations and the data. Beyond estimates of individual shape amplitudes, we present modelindependent, threedimensional reconstructions of the Planck CMB bispectrum and derive constraints on early universe scenarios that generate primordial NG, including general singlefield models of inflation, axion inflation, initial state modifications, models producing parityviolating tensor bispectra, and directionally dependent vector models. We present a wide survey of scaledependent feature and resonance models, accounting for the "look elsewhere" effect in estimating the statistical significance of features. We also look for isocurvature NG, and find no signal, but we obtain constraints that improve significantly with the inclusion of polarization. The primordial trispectrum amplitude in the local model is constrained to be 𝓰^{local}_{NL} = (0.9 ± 7.7 ) X 10^{4}(68% CL statistical), and we perform an analysis of trispectrum shapes beyond the local case. The global picture that emerges is one of consistency with the premises of the ΛCDM cosmology, namely that the structure we observe today was sourced by adiabatic, passive, Gaussian, and primordial seed perturbations.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 September 2016
 DOI:
 10.1051/00046361/201525836
 arXiv:
 arXiv:1502.01592
 Bibcode:
 2016A&A...594A..17P
 Keywords:

 cosmic background radiation;
 cosmology: observations;
 cosmology: theory;
 early Universe;
 inflation;
 methods: data analysis;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 68 pages, 32 figures, 31 tables. Subsection 6.3 on "Primordial curvature reconstruction" added