Unveiling Hidden Patterns in CMB Anisotropy Maps

Bianchi VIIh models have been recently proposed to explain potential anomalies in the CMB anisotropy as observed by WMAP. We investigate the statistical isotropy of embedded Bianchi VIIh templates in the CMB anisotropy maps to determine whether the existence of a hidden Bianchi template in the WMAP data is consistent with the previous null detection of the bipolar power spectrum in the WMAP first year maps. We compute the bipolar power spectrum for low density Bianchi VIIh models embedded in the background CMB anisotropy maps with the power spectrum that best fits the first year WMAP data. By examining statistical isotropy of these maps, we put a limit of ( σ H )0 ≥ 2.55×10−10(99.9%CL) on the shear parameter in Bianchi VIIh models which is (marginally) consistent with Jaffe et al. (2005) but not with the enhanced Bianchi templates of Cayon et al. (2006). In this paper we also present a detailed review of Bianchi models and their properties.