Observing Brane Inflation

TL;DR

This paper investigates brane inflation models, demonstrating their robustness and exploring observational signatures, including tensor-to-scalar ratios and non-Gaussianities, within the Dirac-Born-Infeld framework.

Contribution

It links slow-roll and ultra-relativistic brane inflation scenarios, showing the robustness of the KKLMMT model and analyzing observational constraints and predictions.

Findings

Inflation is generic in the model's parameter space.

Intermediate relativistic regime can produce observable signatures.

The model can saturate current bounds on tensor/scalar ratio or non-Gaussianity.

Abstract

Linking the slow-roll scenario and the Dirac-Born-Infeld scenario of ultra-relativistic roll (where, thanks to the warp factor, the inflaton moves slowly even with an ultra-relativistic Lorentz factor), we find that the KKLMMT D3/anti-D3 brane inflation is robust, that is, enough e-folds of inflation is quite generic in the parameter space of the model. We show that the intermediate regime of relativistic roll can be quite interesting observationally. Introducing appropriate inflationary parameters, we explore the parameter space and give the constraints and predictions for the cosmological observables in this scenario. Among other properties, this scenario allows the saturation of the present observational bound of either the tensor/scalar ratio r (in the intermediate regime) or the non-Gaussianity f_NL (in the ultra-relativistic regime), but not both.