Planck 2013 results. XXIV. Constraints on primordial non-Gaussianity

Abstract

The Planck nominal mission cosmic microwave background (CMB) maps yield unprecedented constraints on primordial non-Gaussianity (NG). Using three optimal bispectrum estimators, separable template-fitting (KSW), binned, and modal, we obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result f(NL)(local) = 2.7 +/- 5.8, f(NL)(equil) = -42 +/- 75, and f(NL)(ortho) = 25 +/- 39 (68% CL statistical). Non-Gaussianity is detected in the data; using skew-C 'statistics we find a nonzero bispectrum from residual point sources, and the integrated-Sachs-Wolfe-lensing bispectrum at a level expected in the CDM scenario. The results are based on comprehensive crossvalidation of these estimators on Gaussian and non-Gaussian simulations, are stable across component separation techniques, pass an extensive suite of tests, and are confirmed by skew-C `, wavelet bispectrum and Minkowski functional estimators. Beyond estimates of individual shape amplitudes, we present model-independent, three-dimensional reconstructions of the Planck CMB bispectrum and thus derive constraints on early-Universe scenarios that generate primordial NG, including general single-field models of inflation, excited initial states (non-Bunch-Davies vacua), and directionally-dependent vector models. We provide an initial survey of scale-dependent feature and resonance models. These results bound both general single-field and multi-field model parameter ranges, such as the speed of sound, cs 0 : 02 (95% CL), in an effective field theory parametrization, and the curvaton decay fraction rD 0 : 15 (95% CL). The Planck data significantly limit the viable parameter space of the ekpyrotic / cyclic scenarios. The amplitude of the four-point function in the local model NL < 2800 (95% CL). Taken together, these constraints represent the highest precision tests to date of physical mechanisms for the origin of cosmic structure.