Cosmological Parameters from a re-analysis of the WMAP-7 low resolution maps

TL;DR

This paper introduces a pixel-based likelihood estimator for WMAP 7-year data that jointly handles temperature and polarization, providing a refined analysis of cosmological parameters with minimal shifts from previous results.

Contribution

The authors develop and test a new pixel-based likelihood method for WMAP data, improving the treatment of polarization and monopole/dipole marginalization compared to the standard approach.

Findings

Parameter shifts are below 1 sigma compared to the original WMAP analysis.

The new method results in a smaller scalar spectral index n_S.

The approach enhances the joint analysis of temperature and polarization data.

Abstract

Cosmological parameters from WMAP 7 year data are re-analyzed by substituting a pixel-based likelihood estimator to the one delivered publicly by the WMAP team. Our pixel based estimator handles exactly intensity and polarization in a joint manner, allowing to use low-resolution maps and noise covariance matrices in $T,Q,U$ at the same resolution, which in this work is 3.6$^\circ$. We describe the features and the performances of the code implementing our pixel-based likelihood estimator. We perform a battery of tests on the application of our pixel based likelihood routine to WMAP publicly available low resolution foreground cleaned products, in combination with the WMAP high-$\ell$ likelihood, reporting the differences on cosmological parameters evaluated by the full WMAP likelihood public package. The differences are not only due to the treatment of polarization, but also to the marginalization over monopole and dipole uncertainties implemented in the WMAP 7 year pixel likelihood code for temperature. The credible central value for the cosmological parameters change below the 1 $\sigma$ level with respect to the evaluation by the full WMAP 7 year likelihood code, with the largest difference in a shift to smaller values of the scalar spectral index $n_S$.