Isotropy in the two-point angular correlation function of the CMB

TL;DR

This paper investigates the directional dependence of the CMB's two-point correlation function, introducing new statistics to analyze anisotropies and low power at large scales, revealing significant contributions from specific sky directions.

Contribution

The paper introduces two novel statistics for analyzing the directional dependence of the CMB correlation function, enhancing understanding of anisotropies and large-scale power deficits.

Findings

Most low power in WMAP cut-sky maps originates from specific sky directions.

Unusually low contributions from quadrupole and octupole lobes explain large-scale power suppression.

New statistics help identify anisotropic features in the CMB correlation function.

Abstract

We study the directional dependence of the angular two-point correlation function in maps of the cosmic microwave background (CMB). We propose two new statistics, one which measures the correlation of each point in the sky with a ring of points separated angle theta away, and a second that measures the missing angular correlation above 60 degrees as a function of direction. Using these statistics, we find that most of the low power in cut-sky maps measured by the WMAP experiment comes from unusually low contributions from the directions of the lobes of the quadrupole and the octupole. These findings may aid a future explanation of why the CMB exhibits low power at large angular scales.