Large Nonlocal Non-Gaussianity from a Curvaton Brane

TL;DR

This paper investigates how the decay mechanism of a curvaton brane influences the non-Gaussian features of primordial curvature perturbations, revealing different non-Gaussian shapes depending on the brane's relativistic motion.

Contribution

It introduces a generalized delta N formalism to analyze non-Gaussianity in a string-inspired curvaton brane model, highlighting the impact of decay mechanisms and brane motion on non-Gaussian shapes.

Findings

Non-Gaussianity shape is local when brane moves nonrelativistically.

Non-Gaussianity shape becomes equilateral when brane moves relativistically.

Decay mechanism significantly affects the size and shape of non-Gaussianity.

Abstract

We use a generalized delta N formalism to study the generation of the primordial curvature perturbation in the curvaton brane scenario inspired by stringy compactifications. We note that the non-Gaussian features, especially the trispectra, crucially depend on the decay mechanism in a general curvaton scenario. Specifically, we study the bispectra and trispectra of the curvaton brane model in detail to illustrate the importance of curvaton decay in generating nonlinear fluctuations. When the curvaton brane moves nonrelativistically during inflation, the shape of non-Gaussianity is local, but the corresponding size is different from that in the standard curvaton scenario. When the curvaton brane moves relativistically in inflationary stage, the shape of non-Gaussianity is of equilateral type.