Changes in the halo formation rates due to features in the primordial spectrum

Abstract

Features in the primordial scalar power spectrum provide a possible roadway to describe the outliers at the low multipoles in the WMAP data. Apart from the CMB angular power spectrum, these features can also alter the matter power spectrum and, thereby, the formation of the large scale structure. Carrying out a complete numerical analysis, we investigate the effects of primordial features on the formation rates of the halos. We consider a few different inflationary models that lead to features in the scalar power spectrum and an improved fit to the CMB data, and analyze the corresponding imprints on the formation of halos. Performing a Markov Chain Monte Carlo analysis with the WMAP seven year data and the SDSS halo power spectrum from LRG DR7 for the models of our interest, we arrive at the parameter space of the models allowed by the data. We illustrate that, inflationary potentials, such as the quadratic potential with sinusoidal modulations and the axion monodromy model, which generate certain repeated, oscillatory features in the inflationary perturbation spectrum, do not induce a substantial difference in the number density of halos at their best fit values, when compared with, say, a nearly scale invariant spectrum as is generated by the standard quadratic potential. However, we find that the number density and the formation rates of halos change by about 13-22% for halo masses ranging over 10^4-10^14 solar mass, for potential parameters that lie within 2-sigma around the best fit values arrived at from the aforesaid joint constraints. We briefly discuss the implications of our results.