Anomalous parity asymmetry of WMAP power spectrum data at low multpoles: is it cosmological or systematics?

TL;DR

This paper investigates the anomalous odd-parity preference in WMAP 7-year data at low multipoles, ruling out some systematics and suggesting a possible primordial or common origin with other CMB anomalies.

Contribution

It identifies the odd-parity preference as highly anomalous and explores its potential cosmological or systematic origins, linking it to other CMB anomalies.

Findings

Odd-parity preference is anomalous at 4-in-1000 level.

Systematic effects like beams and noise are ruled out as causes.

Low quadrupole power may be part of the same anomaly.

Abstract

We have investigated the odd-parity preference of the WMAP 7 year power spectrum. Comparison with simulation shows the odd-parity preference of WMAP data (2<= l <=22) is anomalous at 4-in-1000 level. We have investigated its origins, and ruled out some of non-cosmological origins such as asymmetric beams, noise and cut-sky effect. We also find primordial origin requires |Re[\Phi(\mathbf k)]|\ll|Im[\Phi(\mathbf k)]| for k\lesssim 22/\eta_0, where \eta_0 is the present conformal time. Multipoles associated with the odd-parity preference happen to coincide with some of other CMB anomalies. Therefore, there may exist a common origin, whether cosmological or not. Besides, we find it likely that low quadrupole power is the part of this odd-parity preference anomaly rather than an isolated one. The Planck surveyor, which possesses wide frequency coverage and systematics distinct from the WMAP, may allow us to resolve the mystery of the anomalous odd-parity preference.