Non-standard primordial fluctuations and nongaussianity in string inflation

TL;DR

This paper explores how string theory inflation models with multiple light scalar fields can produce observable non-Gaussian features in primordial fluctuations, especially in the context of the LARGE Volume scenario.

Contribution

It provides an explicit string-inflationary example showing how multiple light fields can generate detectable non-Gaussianity, highlighting a potential observational signature of string cosmology.

Findings

Predicted non-Gaussianity level f_NL ~ O(10)

Bi-spectrum maximized by squeezed triangles

Multi-field dynamics favored by potential observations

Abstract

Inflationary scenarios in string theory often involve a large number of light scalar fields, whose presence can enrich the post-inflationary evolution of primordial fluctuations generated during the inflationary epoch. We provide a simple example of such post-inflationary processing within an explicit string-inflationary construction, using a Kahler modulus as the inflaton within the framework of LARGE Volume Type-IIB string flux compactifications. We argue that inflationary models within this broad category often have a selection of scalars that are light enough to be cosmologically relevant, whose contributions to the primordial fluctuation spectrum can compete with those generated in the standard way by the inflaton. These models consequently often predict nongaussianity at a level, f_NL ~ O(10), potentially observable by the Planck satellite, with a bi-spectrum maximized by triangles with squeezed shape in a string realisation of the curvaton scenario. We argue that the observation of such a signal would robustly prefer string cosmologies such as these that predict a multi-field dynamics during the very early universe.