Post-WMAP Assessment of Infrared Cutoff in the Primordial Spectrum from Inflation

Abstract

The recent Cosmic Microwave Background (CMB) measurements indicate that there is power deficiency of the CMB anisotropies at large scales compared with the $Λ$CDM model. We have investigated the possibility of explaining such effects by a class of primordial power spectra which have infrared cutoffs close to the horizon scale. The primordial power spectrum recovered by direct deconvolution of the observed CMB angular spectrum indicates that the data prefers a sharp infrared cutoff with a localized excess (bump) just above the cutoff. We have been motivated to assess plausible extensions of simplest inflationary scenarios which readily accommodate similar form of infrared cutoff. We carry out a complete Bayesian analysis of the parameter space using {\it Markov Chain Monte Carlo} technique with such a class of primordial power spectra. We show that primordial power spectrum that have features such as an infrared cutoff followed by a subsequent excess in power give better fit to the observed data compared to a nearly scale-invariant power law or power spectrum with just a monotonic infrared cutoff. However, there is substantial room for improvement in the match to data and calls for exploration of other mechanisms that may lead to infrared cutoff even closer to that recovered by direct deconvolution approach.