Signatures of Initial State Modifications on Bispectrum Statistics

By P. Meerburg, J. Schaar, Pier Stefano Corasaniti. 2009

205 citations recorded by the source corpus.

Modifications of the initial-state of the inflaton field can induce a departure from Gaussianity and leave a testable imprint on the higher order correlations of the CMB and large scale structures in the Universe. We focus on the bispectrum statistics of the primordial curvature perturbation and its projection on the CMB. For a canonical single-field action the three-point correlator enhancement is localized, maximizing in the collinear limit, corresponding to enfolded or squashed triangles in comoving momentum space. We show that the available local and equilateral template are very insensitive to this localized enhancement and do not generate noteworthy constraints on initial-state modifications. On the other hand, when considering the addition of a dimension 8 higher order derivative term, we find a dominant rapidly oscillating contribution, which had previously been overlooked and whose significantly enhanced amplitude is independent of the triangle under consideration. Nevertheless, the oscillatory nature of (the sign of) the correlation function implies the signal is nearly orthogonal to currently available observational templates, strongly reducing the sensitivity to the enhancement. Constraints on departures from the standard Bunch-Davies vacuum state can be derived, but also depend on the next-to-leading terms. We emphasize that the construction and application of especially adapted templates could lead to CMB bispectrum constraints on modified initial states already competing with those derived from the power spectrum.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/563606c3e44e4dd74bcc1907cea478802fb7708d

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Citations in the corpus

The DESI Experiment Part I: Science,Targeting, and Survey Design (2016, background): “Recently, a number of inflationary models have been proposed which predict a potentially observable level of non-Gaussianity, these include those from fast-roll inflation [130, 131, 132, 133, 134], quasi-single field inflation [135, 136], warm inflation [137, 138], and non-Bunch-Davies or excited in”
Oscillations in the CMB from axion monodromy inflation (2009, background): “No complete analysis of the observational constraints on resonant non-Gaussianity has been performed to date (however, see [26]), and such an analysis is beyond the scope of the present work.”
Primordial non-Gaussianity from the large-scale structure (2010, background): “[28] P.”
Primordial Non-Gaussianity and Bispectrum Measurements in the Cosmic Microwave Background and Large-Scale Structure (2010, background): “It is possible to consider inflationary vacuum states which are more general than the Bunch-Davies vacuum, such as an excited Gaussian (and Hadamard) state (see [50], and also discussions in [19, 23]).”
Planck 2015 results. XVII. Constraints on primordial non-Gaussianity (2015, unknown): “Inflationary perturbations generated by “excited” initial states (non-Bunch-Davies vacuum states) generically create nonGaussianities with a distinct enfolded shape (see e.g., Chen et al. 2007b; Holman & Tolley 2008; Meerburg et al. 2009), that is, where the bispectrum signal is dominated by flatten”
Primordial Non-Gaussianities from Inflation Models (2010, methodology): “In order to facilitate the data analyses, a simple ansatz has been proposed in [123],”
Planck 2018 results. IX. Constraints on primordial non-Gaussianity (2019, background): “Inflationary perturbations generated by “excited” initial states (non-Bunch-Davies vacuum states) generically create nonGaussianities with a distinct enfolded shape (see e.g., Chen et al. 2007b; Holman & Tolley 2008; Meerburg et al. 2009), that is, where the bispectrum signal is dominated by flatten”
Cosmology and Fundamental Physics with the Euclid Satellite (2012, background): “Indeed, considering excited states over it, as done in [303, 600, 863], leads to a shape which is maximized in the collinear limit, corresponding to enfolded or squashed triangles in momentum space, although one can show that this shape can be written as a combination of the equilateral and orthogon”
Planck2018 results (2018, background): “Oscillatory features can appear in multiple correlation functions (Chen et al. 2008; Meerburg et al. 2009; Flauger et al. 2010; Flauger & Pajer 2011; Achúcarro et al. 2011; Adshead et al. 2012; Achúcarro et al. 2014; Flauger et al. 2017a,b) (see, e.g., Chluba et al. (2015) for a recent review).”
Trans-Planckian issues for inflationary cosmology (2012, background): “This is a highly non trivial procedure [98, 100].”
Sachs-Wolfe at second order: the CMB bispectrum on large angular scales (2009, background): “It is important to stress that the shape associated with lensing, with an angle dependent squeezed limit, represents another interesting template for the bispectrum besides the local, the equilateral and the ones studied in [44, 45].”
Non-Gaussianities in single field inflation and their optimal limits from the WMAP 5-year data (2009, methodology): “NL ∆ 2 Φ to be the coefficient that multiplies the enfolded shape presented in [31].”