Deviations from slow roll inflation and features in the primordial spectrum

by Rajeev Jain (Harish-Chandra Research Institute)

Friday 12 Dec 2008, 11:30 → 12:30 Europe/Zurich

Universite de Geneve, Auditoire 234

In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius and therefore, these scenarios predict a nearly scale invariant spectrum of perturbations. However, it has been realized that deviations from slow roll inflation lead to features in the scalar power spectrum which can possibly provide a better fit to the CMB data. We find that a class of potentials that are similar in form to those that arise in certain minimal supersymmetric extensions of the standard model allow a brief period of departure from inflation sandwiched between two stages of slow roll inflation. This background behavior results in a step like feature in the scalar power spectrum. We set the scales such that the drop in the power occurs at a length scale that corresponds to the Hubble radius today--a feature that seems necessary to explain the lower power observed in the quadrupole moment of the CMB anisotropies. We perform a Markov Chain Monte Carlo analysis to determine the values of the model parameters that provide the best fit to the recent WMAP 5-year data for the CMB angular power spectrum. We find that such a spectrum with a suppression of power at large scales leads to a much better fit (with just one extra parameter, $\chi_{\rm eff}^{2}$ improves by 6.62) of the observed data when compared to the best fit reference $\Lambda$CDM model with a featureless, power law, primordial spectrum.