Non-Gaussianities from ekpyrotic collapse with multiple fields

Kazuya Koyama, Shuntaro Mizuno, F. Vernizzi, David Wands

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We compute the non-Gaussianity of the curvature perturbation generated by ekpyrotic collapse with multiple fields. The transition from the multi-field scaling solution to a single-field dominated regime converts initial isocurvature field perturbations to an almost scale invariant comoving curvature perturbation. In the specific model of two fields, 1 and 2, with exponential potentials, −Viexp(−cii), we calculate the bispectrum of the resulting curvature perturbation. We find that the non-Gaussianity is dominated by non-linear evolution on super-Hubble scales and hence is of the local form. The non-linear parameter of the curvature perturbation is given by fNL = 5cj2/12, where cj is the exponent of the potential for the field which becomes subdominant at late times. Since cj2 must be large, in order to generate an almost scale invariant spectrum, the non-Gaussianity is inevitably large. Thus, the model is strongly constrained by observational bounds on the spectral index and non-Gaussianity
Original languageEnglish
Pages (from-to)024
Number of pages1
JournalJournal of Cosmology and Astroparticle Physics
Issue number11
Publication statusPublished - Nov 2007


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