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.

29 pages, 2 figures; typos corrected, references added, accepted for publication in JCAP. arXiv admin note: text overlap with arXiv:1203.6625

References in corpus (21)

• Observational Signatures and Non-Gaussianities of General Single Field Inflation
• Primordial Non-Gaussianities from Inflation Models
• Non-Gaussianities in two-field inflation
• Primordial perturbations and non-Gaussianities in DBI and general multi-field inflation
• Primordial trispectrum from inflation
• Primordial fluctuations and non-Gaussianities in multi-field DBI inflation
• Multi-brid inflation and non-Gaussianity
• Scale-dependent non-Gaussianity probes inflationary physics
• Spinflation
• Primordial Non-Gaussianity in Multi-Scalar Slow-Roll Inflation
• Lorentz boost and non-Gaussianity in multi-field DBI-inflation
• Non-standard primordial fluctuations and nongaussianity in string inflation
• Primordial Trispectrum from Entropy Perturbations in Multifield DBI Model
• N-flation from multiple DBI type actions
• Non-Gaussianities in Multifield Inflation: Superhorizon Evolution, Adiabaticity, and the Fate of fnl
• Primordial Non-Gaussianities from the Trispectra in Multiple Field Inflationary Models
• On the Unlikeliness of Multi-Field Inflation: Bounded Random Potentials and our Vacuum
• Note on Non-Gaussianities in Two-field Inflation
• Separable and non-separable multi-field inflation and large non-Gaussianity
• Local non-Gaussianity from rapidly varying sound speeds
• Non-Gaussianities in multi-field DBI inflation with a waterfall phase transition

Cited by in corpus (9)

• Mechanisms for Primordial Black Hole Production in String Theory
• CMB Power Asymmetry from Primordial Sound Speed Parameter
• D-brane Potentials in the Warped Resolved Conifold and Natural Inflation
• Hubble multi-scalar inflation
• Scale-dependent CMB power asymmetry from primordial speed of sound and a generalized $\delta$N formalism
• Non-Gaussianity in multi-sound-speed disformally coupled inflation
• Covariant second-order perturbations in generalized two-field inflation
• Bouncing cosmologies in the presence of a Dirac-Born-Infeld field
• Multi-brid DBI Inflation