DBI Inflation in the Tip Region of a Warped Throat

TL;DR

This paper investigates DBI inflation near the tip of a warped throat, highlighting the potential for sufficient inflation but also the challenge of large non-gaussianities, with implications for observable cosmological signatures.

Contribution

It extends DBI inflation models to the near-tip region of warped throats, analyzing inflation duration and non-gaussianity constraints in this specific setting.

Findings

60 or more e-folds possible near the throat tip

Large non-gaussianities are typically produced due to small sound speed

Inflation near the tip may be generic in some throat solutions like Klebanov-Strassler

Abstract

Previous work on DBI inflation, which achieves inflation through the motion of a $D3$ brane as it moves through a warped throat compactification, has focused on the region far from the tip of the throat. Since reheating and other observable effects typically occur near the tip, a more detailed study of this region is required. To investigate these effects we consider a generalized warp throat where the warp factor becomes nearly constant near the tip. We find that it is possible to obtain 60 or more e-folds in the constant region, however large non-gaussianities are typically produced due to the small sound speed of fluctuations. For a particular well-studied throat, the Klebanov-Strassler solution, we find that inflation near the tip may be generic and it is difficult to satisfy current bounds on non-gaussianity, but other throat solutions may evade these difficulties.