Confronting brane inflation with Planck and pre-Planck data

Understand

In this paper, we compare brane inflation models with the Planck data and the pre-Planck data (which combines WMAP, ACT, SPT, BAO and H0 data).

• The Planck data prefer a spectral index less than unity at more than 5\sigma confidence level, and a running of the spectral index at around 2\sigma confidence level.
• We find that the KKLMMT model can survive at the level of 2\sigma only if the parameter $\beta$ (the conformal coupling between the Hubble parameter and the inflaton) is less than $\mathcal{O}(10^{-3})$, 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.