Confronting brane inflation with Planck and pre-Planck data

Abstract

In this paper, we compare brane inflation models with the Planck data and the pre-Planck data (which combines WAMP, ACT, SPT, BAO and H₀ data). The Planck data prefer a spectral index less than unity at more than 5σ confidence level, and a running of the spectral index at around 2σ confidence level. We find that the KKLMMT model can survive at the level of 2σ only if the parameter β (the conformal coupling between the Hubble parameter and the inflaton) is less than O(10^-3), which indicates a certain level of fine-tuning. The IR DBI model can provide a slightly larger negative running of spectral index and red tilt, but in order to be consistent with the non-Gaussianity constraints from Planck, its parameter also needs fine-tuning at some level.