Cosmological parameter estimation with free-form primordial power spectrum

TL;DR

This paper introduces a novel approach to estimate cosmological parameters by reconstructing the primordial power spectrum without assuming a specific form, revealing strong evidence against a flat universe without dark energy.

Contribution

It is the first to perform cosmological parameter estimation with a free-form primordial spectrum, avoiding biases from power-law assumptions.

Findings

Flat universe without cosmological constant is ruled out at >4σ confidence.

Higher baryonic and matter densities are favored with free-form PPS.

Estimated parameters overlap with power-law assumptions at 1σ confidence.

Abstract

Constraints on the main cosmological parameters using CMB or large scale structure data are usually based on power-law assumption of the primordial power spectrum (PPS). However, in the absence of a preferred model for the early universe, this raises a concern that current cosmological parameter estimates are strongly prejudiced by the assumed power-law form of PPS. In this paper, for the first time, we perform cosmological parameter estimation allowing the free form of the primordial spectrum. This is in fact the most general approach to estimate cosmological parameters without assuming any particular form for the primordial spectrum. We use direct reconstruction of the PPS for any point in the cosmological parameter space using recently modified Richardson-Lucy algorithm however other alternative reconstruction methods could be used for this purpose as well. We use WMAP 9 year data in our analysis considering CMB lensing effect and we report, for the first time, that the flat spatial universe with no cosmological constant is ruled out by more than 4\sigma confidence limit without assuming any particular form of the primordial spectrum. This would be probably the most robust indication for dark energy using CMB data alone. Our results on the estimated cosmological parameters show that higher values of baryonic and matter density and lower value of Hubble parameter (in comparison to the estimated values by assuming power-law PPS) is preferred by the data. However, the estimated cosmological parameters by assuming free form of the PPS have overlap at 1\sigma confidence level with the estimated values assuming power-law form of PPS.