Estimation of Primordial Spectrum with post-WMAP 3 year data

TL;DR

This study uses an improved deconvolution algorithm on WMAP 3-year data to reconstruct the primordial power spectrum, revealing features like a horizon-scale cutoff and bump, and shows data's ability to discriminate cosmological parameters even with a free spectrum.

Contribution

It introduces an error-sensitive Richardson-Lucy deconvolution method for primordial spectrum estimation and explores its implications across various cosmological parameters.

Findings

Reconstructed spectra show a horizon-scale cutoff and bump.

Likelihood improves significantly over power-law spectra.

Data favors different matter densities when spectrum is free.

Abstract

In this paper we implement an improved (error sensitive) Richardson-Lucy deconvolution algorithm on the measured angular power spectrum from the WMAP 3 year data to determine the primordial power spectrum assuming different points in the cosmological parameter space for a flat LCDM cosmological model. We also present the preliminary results of the cosmological parameter estimation by assuming a free form of the primordial spectrum, for a reasonably large volume of the parameter space. The recovered spectrum for a considerably large number of the points in the cosmological parameter space has a likelihood far better than a `best fit' power law spectrum up to \Delta \chi^2_{eff} \approx -30. We use Discrete Wavelet Transform (DWT) for smoothing the raw recovered spectrum from the binned data. The results obtained here reconfirm and sharpen the conclusion drawn from our previous analysis of the WMAP 1st year data. A sharp cut off around the horizon scale and a bump after the horizon scale seem to be a common feature for all of these reconstructed primordial spectra. We have shown that although the WMAP 3 year data prefers a lower value of matter density for a power law form of the primordial spectrum, for a free form of the spectrum, we can get a very good likelihood to the data for higher values of matter density. We have also shown that even a flat CDM model, allowing a free form of the primordial spectrum, can give a very high likelihood fit to the data. Theoretical interpretation of the results is open to the cosmology community. However, this work provides strong evidence that the data retains discriminatory power in the cosmological parameter space even when there is full freedom in choosing the primordial spectrum.