Needlet Bispectrum Asymmetries in the WMAP 5-year Data

TL;DR

This paper uses needlet formalism to analyze WMAP 5-year data, confirming asymmetries in non-Gaussianity between hemispheres and identifying specific scales and configurations with anomalies, without affecting the non-linear parameter estimate.

Contribution

It introduces the application of needlet bispectrum analysis to WMAP data to detect and characterize non-Gaussianity asymmetries across scales and configurations.

Findings

Asymmetry in non-Gaussianity between hemispheres

Anomalies most significant on large scales and in squeezed configurations

No significant difference in $nl$ between hemispheres

Abstract

We apply the needlet formalism to the Wilkinson Microwave Anisotropy Probe 5-year data, looking for evidence of non-Gaussianity in the bispectrum of the needlet amplitudes. We confirm earlier findings of an asymmetry in the non-Gaussianity between the northern and southern galactic hemispheres. We attempt to isolate which scales and geometrical configurations are most anomalous, and find the bispectrum is most significant on large scales and in the more co-linear configurations, and also in the `squeezed' configurations. However, these anomalies do not appear to affect the estimate of the non-linear parameter $\fnl$, and we see no significant difference between its value measured in the two hemispheres.