Implications of the Planck bispectrum constraints for the primordial trispectrum

Byrnes, Christian T, Nurmi, Sami, Tasinato, Gianmassimo and Wands, David (2013) Implications of the Planck bispectrum constraints for the primordial trispectrum. Europhysics Letters, 103 (1). 19001-p1-19001-p-8. ISSN 0295-5075

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The new Planck constraints on the local bispectrum parameter fnl are about 10^5 times tighter than the current constraints on the trispectrum parameter gnl, which means that the allowed numerical values of the second and third order terms in the perturbative expansion of the curvature perturbation are comparable. We show that a consequence of this is that if gnl is large enough to be detectable, then it will induce a large variation between the observable value of fnl and its value in a larger inflated volume. Even if there were only a few extra efoldings between the beginning of inflation and horizon crossing of our Hubble horizon, an observably large gnl means that fnl is unlikely to be as small as its current constraint, regardless of its true background value. This result is very general, it holds regardless of how many fields contributed to the curvature perturbation. We also generalise this result to other shapes of non-Gaussianity, beyond the local model. We show that the variance of the 3-point function in the squeezed limit is bounded from below by the square of the squeezed limit of the 4-point function.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy > QB0980 Cosmogony. Cosmology
Depositing User: Christian Byrnes
Date Deposited: 27 May 2014 11:14
Last Modified: 02 Jul 2019 20:07

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