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Bispectrum signatures of a modified vacuum in single field inflation with a small speed of sound

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arxiv 0910.4986 v2 pith:Z53DO5JJ submitted 2009-10-27 hep-th astro-ph.CO

Bispectrum signatures of a modified vacuum in single field inflation with a small speed of sound

classification hep-th astro-ph.CO
keywords soundspeedbogolyubovparametersmallbispectruminflationvacuum
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Deviations from the Bunch-Davies vacuum during an inflationary period can leave a testable imprint on the higher-order correlations of the CMB and large scale structures in the Universe. The effect is particularly pronounced if the statistical non-Gaussianity is inherently large, such as in models of inflation with a small speed of sound, e.g. DBI. First reviewing the motivations for a modified vacuum, we calculate the non-Gaussianity for a general action with a small speed of sound. The shape of its bispectrum is found to most resemble the 'orthogonal' or 'local' templates depending on the phase of the Bogolyubov parameter. In particular, for DBI models of inflation the bispectrum can have a profound 'local' template feature, in contrast to previous results. Determining the projection into the observational templates allows us to derive constraints on the absolute value of the Bogolyubov parameter. In the small sound speed limit, the derived constraints are generally stronger than the existing constraint derived from the power spectrum. The bound on the absolute value of the Bogolyubov parameter ranges from the 10^-6 to the 10^-3 level for H/\Lambda_c = 10^-3, depending on the specific details of the model, the sound speed and the phase of the Bogolyubov parameter.

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Cited by 1 Pith paper

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  1. Searching for Folded Primordial Non-Gaussianity with Galaxy Surveys

    astro-ph.CO 2026-07 conditional novelty 7.0

    The galaxy bispectrum, not the power spectrum, is the main probe of folded primordial non-Gaussianity; narrow folded signals are washed out by Fourier-space binning.