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

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.