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Mild non-Gaussianities under perturbative control from rapid-turn inflation models
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Number of Authors: 32019 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 12, article id 036Article in journal (Refereed) Published
Abstract [en]

Inflation can be supported in very steep potentials if it is generated by rapidly turning fields, which can be natural in negatively curved field spaces. The curvature perturbation, zeta, of these models undergoes an exponential, transient amplification around the time of horizon crossing, but can still be compatible with observations at the level of the power spectrum. However, a recent analysis (based on a proposed single-field effective theory with an imaginary speed of sound) found that the trispectrum and other higher-order, non-Gaussian correlators also undergo similar exponential enhancements. This arguably leads to 'hyper-large' non-Gaussianities in stark conflict with observations, and even to the loss of perturbative control of the calculations. In this paper, we provide the first analytic solution of the growth of the perturbations in two-field rapid-turn models, and find it in good agreement with previous numerical and single-field EFT estimates. We also show that the nested structure of commutators of the in-in formalism has subtle and crucial consequences: accounting for these commutators, we show analytically that the naively leading-order piece (which indeed is exponentially large) cancels exactly in all relevant correlators. The remaining non-Gaussianities of these models are modest, and there is no problem with perturbative control from the exponential enhancement of zeta. Thus, rapid-turn inflation with negatively curved field spaces remains a viable and interesting class of candidate theories of the early universe.

Place, publisher, year, edition, pages
2019. no 12, article id 036
Keywords [en]
cosmological perturbation theory, inflation, non-gaussianity
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-178780DOI: 10.1088/1475-7516/2019/12/036ISI: 000507261900033OAI: oai:DiVA.org:su-178780DiVA, id: diva2:1396197
Available from: 2020-02-25 Created: 2020-02-25 Last updated: 2020-02-25Bibliographically approved

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Ferreira, Ricardo Z.Marsh, M. C. David
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