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.
- Publication:
-
Journal of Cosmology and Astroparticle Physics
- Pub Date:
- May 2013
- DOI:
- 10.1088/1475-7516/2013/05/021
- arXiv:
- arXiv:1303.3975
- Bibcode:
- 2013JCAP...05..021E
- Keywords:
-
- Astrophysics - Cosmology and Extragalactic Astrophysics;
- High Energy Physics - Theory
- E-Print:
- 29 pages, 2 figures