Warp Features in DBI Inflation

TL;DR

This paper develops a generalized slow roll approximation for DBI inflation, enabling accurate modeling of features in the power spectrum caused by transient sound speed changes, and applies it to explain observed CMB features.

Contribution

It introduces an extended slow roll method for order unity features in DBI inflation, linking potential constraints to observable power spectrum features.

Findings

The approximation accurately models oscillatory features in the CMB spectrum.

A sharp horizon scale step can explain observed CMB oscillations.

Small power suppression on horizon scales is predicted.

Abstract

In Dirac-Born-Infeld inflation, changes in the sound speed that transiently break the slow roll approximation lead to features in the power spectrum. We develop and test the generalized slow roll approximation for calculating such effects and show that it can be extended to treat order unity features. As in slow-roll, model independent constraints on the potential of canonical inflation can be directly reinterpreted in the DBI context through this approximation. In particular, a sharp horizon scale step in the warped brane tension can explain oscillatory features in the WMAP7 CMB power spectrum as well as features in the potential. Differences appear only as a small suppression of power on horizon scales and larger.