Consistency of Planck Data With Power-Law Primordial Scalar Power Spectrum

Abstract

In this work we explore the possibility of variations in the primordial scalar power spectrum around the power-law shape, as predicted by single-field slow-roll inflationary scenarios. We search for the trace of these fluctuations in a semi-blind, model-independent way in the observations of the Cosmic Microwave Background (CMB) sky. In particular we use two sets of perturbation patterns, specific patterns with typical features such as oscillations, bumps and transitions, as well as perturbation modes, constructed from the eigenanalysis of the forecasted or measured covariance of perturbation parameters. These modes, in principle, span the parameter space of all possible perturbations to the primordial spectrum, and when rank-ordered, the ones with the highest detectability would suffice to explore the constrainable features around the power-law spectrum in a data-driven (and not theoretically-biased) manner. With Planck measurements of CMB anisotropies, the amplitudes of all perturbation patterns considered in this work are found to be consistent with zero. This finding confirms, in the absence of theoretical biases, the consistency of the Planck data with the assumption of power-law inflationary pattern for the primordial spectrum.