Large-Angle Correlations in the Cosmic Microwave Background

TL;DR

This paper investigates the large-angle correlations in the CMB, demonstrating that the observed low correlations do not necessarily contradict the standard LambdaCDM model, and introduces methods to reconstruct these correlations independently of statistical isotropy assumptions.

Contribution

The study compares estimators of the CMB temperature correlation function and shows how to reconstruct large-scale features without assuming statistical isotropy, challenging previous claims.

Findings

Reconstructed large-scale correlations are consistent with full-sky data.

Bayesian analysis shows data cannot exclude LambdaCDM.

Methods work reliably with sky cuts and data outside them.

Abstract

It has been argued recently by Copi etal (2009) that the lack of large angular correlations of the CMB temperature field provides strong evidence against the standard, statistically isotropic, inflationary LambdaCDM cosmology. We compare various estimators of the temperature correlation function showing how they depend on assumptions of statistical isotropy and how they perform on the WMAP 5 year ILC maps with and without a sky cut. We show that the low multipole harmonics that determine the large-scale features of the temperature correlation function can be reconstructed accurately, independent of any assumptions concerning statistical isotropy, from the data that lie outside the sky cuts. The temperature correlation functions computed from our reconstructions are in good agreement with those computed from the whole sky. A Bayesian analysis of the large-scale correlations is presented which shows that the data cannot exclude the standard LambdaCDM model. We discuss the differences between our conclusions and those of Copi et al.