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