Duality cascade in brane inflation

Abstract

We show that brane inflation is very sensitive to tiny sharp features in extra dimensions,including those in the potential and in the warp factor. This can show up as observationalsignatures in the power spectrum and/or non-Gaussianities of the cosmic microwavebackground radiation (CMBR). One general example of such sharp features is a successionof small steps in a warped throat, caused by Seiberg duality cascade using gauge/gravityduality. We study the cosmological observational consequences of these steps in braneinflation. Since the steps come in a series, the prediction of other steps and their propertiescan be tested by future data and analysis. It is also possible that the steps are tooclose to be resolved in the power spectrum, in which case they may show uponly in the non-Gaussianity of the CMB temperature fluctuations and/or EEpolarization. We study two cases. In the slow-roll scenario, where steps appear in theinflaton potential, the sensitivity of brane inflation to the height and width of thesteps is increased by several orders of magnitude compared to that in previouslystudied large field models. In the IR DBI scenario, where steps appear in thewarp factor, we find that the glitches in the power spectrum caused by thesesharp features are generally small or even unobservable, but associated distinctivenon-Gaussianity can be large. Together with its large negative running of the powerspectrum index, this scenario clearly illustrates how rich and different a braneinflationary scenario can be when compared to generic slow-roll inflation. Suchdistinctive stringy features may provide a powerful probe of superstring theory.