While dust contamination now appears as a likely explanation of the apparent tension between the recent BICEP2 data and the Planck data, we will here explore the consequences of a large running in the spectral index as suggested by the BICEP2 collaboration as an alternative explanation of the apparent tension, but which would be in conflict with prediction of the simplest model of chaotic inflation. The large field chaotic model is sensitive to UV physics, and the nontrivial running of the spectral index suggested by the BICEP2 collaboration could therefore, if true, be telling us some additional new information about the UV completion of inflation. However, before we would be able to draw such strong conclusions with confidence, we would first have to also carefully exclude all the alternatives. Assuming monomial chaotic inflation is the right theory of inflation, we therefore explore the possibility that the running could be due to some other less UV sensitive degree of freedom. As an example, we ask if it is possible that the curvature perturbation spectrum has a contribution from a curvaton, which makes up for the large running in the spectrum. We find that this effect could mask the information we can extract about the UV physics. We also study different different models, which might lead to a large negative intrinsic running of the curvaton.
Physical Review D (particles, Fields, Gravitation and Cosmology), 2014