Mixed non-Gaussianity in multiple-DBI inflation

Jon Emery, Gianmassimo Tasinato, David Wands

Research output: Contribution to journalArticlepeer-review


We study a model of multiple-field DBI inflation leading to mixed form of primordial non-Gaussianity, including equilateral and local bispectrum shapes. We present a general formalism based on the Hamilton-Jacobi approach, allowing us to go beyond slow-roll, combining the three-point function for the fields at Hubble-exit with the non-linear evolution of super-Hubble scales. We are able to obtain analytic results by taking a separable Ansatz for the Hubble rate. We find general expressions for both the equilateral and local type non-Gaussianity parameter fNL. The equilateral non-Gaussianity includes the usual enhancement for small sound speeds, but multiplied by an analytic factor which can lead to a suppression. We illustrate our results with two scenarios. In the first model, previously found to have detectable local non-Gaussianity, we find that the equilateral signal is not sufficiently suppressed to evade current observational bounds. In our second scenario we construct a model which exhibits both a detectable equilateral fNL and a negative local fNL.
Original languageEnglish
JournalJournal of Cosmology and Astroparticle Physics
Issue number5
Publication statusPublished - May 2013


  • inflation
  • string theory and cosmology
  • physics of the early universe
  • cosmological perturbation theory


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