Running of the spectral index and violation of the consistency relation between tensor and scalar spectra from trans-Planckian physics

One of the firm predictions of inflationary cosmology is the consistency relation between scalar and tensor spectra. It has been argued that such a relation-if experimentally confirmed-would offer strong support for the idea of inflation. We examine the possibility that trans-Planckian physics violates the consistency relation in the framework of inflation with a cut-off proposed in [astro-ph/0009209]. We find that despite the ambiguity that exists in choosing the action, Planck scale physics modifies the consistency relation considerably. It also leads to the running of the spectral index. For modes that are larger than our current horizon, the tensor spectral index is positive. For a window of k values with amplitudes of the same order of the modes which are the precursor to structure formation, the behavior of tensor spectral index is oscillatory about the standard quantum field theory result, taking both positive and negative values. There is a hope that in the light of future experiments, one can verify this scenario of short distance physics.