Mixed non-Gaussianity in multiple-DBI inflation
Abstract
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.
Cite
@article{arxiv.1303.3975,
title = {Mixed non-Gaussianity in multiple-DBI inflation},
author = {Jon Emery and Gianmassimo Tasinato and David Wands},
journal= {arXiv preprint arXiv:1303.3975},
year = {2013}
}
Comments
29 pages, 2 figures; typos corrected, references added, accepted for publication in JCAP. arXiv admin note: text overlap with arXiv:1203.6625