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.Comment: V2: Extended version to appear in PR
