Anomalous parity asymmetry of WMAP 7-year power spectrum data at low multipoles: Is it cosmological or systematics?

It is natural to assume a parity-neutral Universe and accordingly no particular parity preference in the cosmic microwave background sky. However, our investigation based on the WMAP 7-year power spectrum shows there exists a large-scale odd-parity preference with high statistical significance. We also find that the odd-parity preference in WMAP7 data is slightly higher than earlier releases. We have investigated possible origins, and ruled out various noncosmological origins. We also find that the primordial origin requires |Re[Φ(k)]||Im[Φ(k)]| for k22/η₀, where η₀ is the present conformal time. In other words, it requires translational invariance in the primordial Universe to be violated on scales larger than 4 Gpc. 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. Furthermore, polarization maps of large-sky coverage will reduce degeneracy in cosmological origins.