A general analysis of non-gaussianity from isocurvature perturbations

Kawasaki, Masahiro; Nakayama, Kazunori; Sekiguchi, Toyokazu; Suyama, Teruaki; Takahashi, Fuminobu

doi:10.1088/1475-7516/2009/01/042

Cited by 67 publications

(67 citation statements)

References 84 publications

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“…Isocurvature modes are usually investigated by considering their contribution to the power spectrum. However, if present, they would also contribute to the bispectrum, producing in general both a pure isocurvature bispectrum and mixed bispectra because of the cross-correlation between isocurvature and adiabatic perturbations (Komatsu 2002;Bartolo et al 2002;Komatsu et al 2005;Kawasaki et al 2008Kawasaki et al , 2009Langlois et al 2008;Hikage et al 2009;Langlois & Lepidi 2011;Langlois & van Tent 2011, 2012Kawakami et al 2012). While one might expect isocurvature NG to be negligible, since both (linear) isocurvature modes and (adiabatic) NG appear to be very small, and searches for isocurvature NG using WMAP data did not lead to any detections (Hikage et al 2013a,b), this expectation can be tested at significantly higher precision by Planck.…”

Section: Isocurvature Non-gaussianitymentioning

confidence: 99%

Planck2015 results

Ade

Aghanim

Arnaud

et al. 2016

A&A

477

256

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The Planck full mission cosmic microwave background (CMB) temperature and E-mode polarization maps are analysed to obtain constraints on primordial non-Gaussianity (NG). Using three classes of optimal bispectrum estimators -separable template-fitting (KSW), binned, and modalwe obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result from temperature alone f local NL = 2.5 ± 5.7, f equil NL = −16 ± 70, and f ortho NL = −34 ± 33 (68% CL, statistical). Combining temperature and polarization data we obtain f local NL = 0.8 ± 5.0, f equil NL = −4 ± 43, and f ortho NL = −26 ± 21 (68% CL, statistical). The results are based on comprehensive cross-validation of these estimators on Gaussian and non-Gaussian 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 time-domain de-glitching 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 model-independent, three-dimensional reconstructions of the Planck CMB bispectrum and derive constraints on early universe scenarios that generate primordial NG, including general single-field models of inflation, axion inflation, initial state modifications, models producing parityviolating tensor bispectra, and directionally dependent vector models. We present a wide survey of scale-dependent 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 = (−9.0 ± 7.7) × 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.

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Section: Isocurvature Non-gaussianitymentioning

confidence: 99%

Planck2015 results

Ade

Aghanim

Arnaud

et al. 2016

A&A

477

256

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“…The bispectrum thus contains the four terms: ζ k1 ζ k2 ζ k3 , ζ k1 ζ k2 S k3 , ζ k1 S k2 S k3 , and S k1 S k2 S k3 [48,56,57]. In order to make contact with the parameter f N L that is constrained in contemporary analyses, we define…”

Section: Non-gaussianitymentioning

confidence: 99%

Optimizing future experimental probes of inflation

Easson

Powell

2011

Phys. Rev. D

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The discovery of many novel realizations of the inflationary universe paradigm has led to a degeneracy problem: many different inflationary Lagrangians generate the same perturbation spectra. Resolving this problem requires the future discovery of additional observables, beyond the scalar adiabatic and tensor two-point functions on CMB scales. One important source of degeneracy arises in models where the density perturbation is generated by a non-inflationary degree of freedom, for example, through curvatons or modulated reheating. We consider the curvaton scenario as representative of this class, and analyze the degeneracy with single field, canonical inflation that results if the curvaton goes undetected by future observations. We perform Monte Carlo potential reconstructions in the absence of distinguishing observables, such as non-Gaussiantities or isocurvature modes. The resulting degeneracy is considerable and the improved measurements of spectral parameters from future probes like CMBPol, offer little to better the situation. Given a degeneracy-breaking observation, the observables must still be inverted to obtain the inflationary potential, with different observations resulting in reconstructions of varying quality. We find that a future detection of isocurvature modes or a precision measurement of the tensor spectral index will enable the most successful reconstructions in the presence of curvatons.

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“…In contrast, in Refs. [49,74,75] the fermions are produced from the on shell inflatons and/or curvatons (the latter has the closest identification in our model with σ) after the end of inflation. A sharp observable contrast of our model with these other models is that our scenario predicts an uncorrelated type of isocurvature (i.e.…”

Section: Fermion Isocurvature Modelmentioning

confidence: 78%

“…[49,74,75]). We explicitly predict the amplitudes of fermion density perturbations from a joint effect of the gravitational particle production and σ modulation on m ψ via the matter loop diagrams.…”

Section: Fermion Isocurvature Modelmentioning

confidence: 99%

Fermionic isocurvature perturbations

2015

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Isocurvature perturbations in the inflationary literature typically involve quantum fluctuations of bosonic field degrees of freedom. In this work, we consider isocurvature perturbations from fermionic quantum fluctuations during inflation. When a stable massive fermion is coupled to a non-conformal sector different from the scalar metric perturbations, observably large amplitude scale invariant isocurvature perturbations can be generated. In addition to the computation of the isocurvature two-point function, an estimate of the local non-Gaussianities is also given and found to be promising for observations in a corner of the parameter space. The results provide a new class of cosmological probes for theories with stable massive fermions. On the technical side, we explicitly renormalize the composite operator in curved spacetime and show that gravitational Ward identities play an important role in suppressing certain contributions to the fermionic isocurvature perturbations.

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A general analysis of non-gaussianity from isocurvature perturbations

Cited by 67 publications

References 84 publications

Planck2015 results

Planck2015 results

Optimizing future experimental probes of inflation

Fermionic isocurvature perturbations

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