Planck2013 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 local NL = 2.7 ± 5.8, f equil NL = −42 ± 75, and f ortho NL = −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 ΛCDM 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, c s ≥ 0.02 (95% CL), in an effective field theory parametrization, and the curvaton decay fraction r D ≥ 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 τ NL < 2800 (95% CL). Taken together, these constraints represent the highest precision tests to date of physical mechanisms for the origin of cosmic structure.

Neglecting primordial non-Gaussianity threatens future cosmological experiment accuracy

“…The other two sets of spectra are for f loc NL ¼ 3.51 and 9.3 (short-and long-dashed curves, respectively). The former has been chosen because it is the Planck best-fit value (LSS convention) [12], while the latter better shows the PNG departure from the Gaussian prediction still lying within the Planck 1σ bound.…”

“…[5][6][7][8][9][10][11] and references therein). Recently, analyses of Planck satellite data managed to severely constrain the allowed parameter space of PNG [12]. Henceforth, according to a number of studies, only certain future LSS experiments will be able to provide comparable constraints on f NL , such as those using galaxy redshift surveys [11,[13][14][15] or that are conducted in the radio continuum [16,17], or those using newborn techniques such as neutral hydrogen intensity mapping [18] or crosscorrelation with other observables [19][20][21].…”

Effects of the speed of sound at largeN

“…is 1 [11]. This type of non-Gaussianity results from models where the speed of the inflation perturbations can differ from unity.…”

Test for the zero mean hypothesis in cosmology

“…Among these features, the Gaussianity and approximate scale invariance have been intensively tested by a number of observations and verified with high significance [2][3][4][5], while the statistical homogeneity and isotropy have been less tested and often assumed implicitly in cosmological analyses [6]. Recently, the test of statistical isotropy has attracted much attention [7][8][9][10][11], after the authors of Ref.…”