Large-Angle Anomalies in the Microwave Background

TL;DR

This paper reviews claims of large-scale anomalies in the cosmic microwave background measured by WMAP, emphasizing the importance of new data to objectively assess their statistical significance and potential implications for new physics.

Contribution

It critically examines the claims of large-angle anomalies in the CMB and discusses strategies for obtaining new data to evaluate their significance objectively.

Findings

Current anomalies lack definitive statistical significance

A new data set is needed to confirm or refute anomalies

Examines three specific anomalies: lack of large-angle power, north-south asymmetry, multipole alignments

Abstract

Several claims have been made of anomalies in the large-angle properties of the cosmic microwave background anisotropy as measured by WMAP. In most cases, the statistical significance of these anomalies is hard or even impossible to assess, due to the fact that the statistics used to quantify the anomalies were chosen a posteriori. On the other hand, the possibility of detecting new physics on the largest observable scales is so exciting that, in my opinion, it is worthwhile to examine the claims carefully. I will focus on three particular claims: the lack of large-angle power, the north-south power asymmetry, and multipole alignments. In all cases, the problem of a posteriori statistics can best be solved by finding a new data set that probes similar physical scales to the large-angle CMB. This is a difficult task, but there are some possible routes to achieving it.