Ruling out the power-law form of the scalar primordial spectrum

Abstract

Combining Planck CMB temperature [1] and BICEP2 B-mode polarization data\n[2,3] we show qualitatively that, assuming inflationary consistency relation,\nthe power-law form of the scalar primordial spectrum is ruled out at more than\n$3\\sigma$ CL. This is an important finding, since the power-law form of the\nscalar primordial spectrum is one of the main assumptions of concordance model\nof cosmology and also a direct prediction of many inflationary scenarios. We\nshow that a break or step in the form of the primordial scalar perturbation\nspectrum, similar to what we studied recently analyzing Planck data [4] can\naddress both Planck and BICEP2 results simultaneously. Our findings also\nindicate that the data may require more flexibilities than what running of\nscalar spectral index can provide. Finally we show that an inflaton potential,\noriginally appeared in [5] can generate both the step and the break model of\nscalar primordial spectrum in two different limits. The discussed potential is\nfound to be favored by Planck data but marginally disfavored by BICEP2 results\nas it produces slightly lower amplitude of tensor primordial spectrum. Hence,\nif the tensor-to-scalar ratio ($r$) quoted by BICEP2 persists, it is of\nimportance that we generate inflationary models with large $r$ and at the same\ntime provide suppression in scalar primordial spectrum at large scales.\n