Evidence of vorticity and shear at large angular scales in the WMAP data:: A violation of cosmological isotropy?

Motivated by the large-scale asymmetry observed in the cosmic microwave background sky, we consider a specific class of anisotropic cosmological models - Bianchi type VIIh - and compare them to the WMAP first-year data on large angular scales. Remarkably, we find evidence of a correlation that is ruled out as a chance alignment at the 3 sigma level. The best-fit Bianchi model corresponds to x = 0.55, Omega(o) = 0.5, a rotation axis in the direction ( l, b) = (222 degrees, -62 degrees), shear (sigma/H)(o) = 2.4 x 10(-10), and a right-handed vorticity (omega/H)(o) = 4.3 x 10(-10). Correcting for this component greatly reduces the significance of the large-scale power asymmetry, resolves several anomalies detected on large angular scales (i.e., the low quadrupole amplitude and quadrupole/octopole planarity and alignment), and can account for a non-Gaussian "cold spot" on the sky. Despite the apparent inconsistency with the best-fit parameters required in inflationary models to account for the acoustic peaks, we consider the results sufficiently provocative to merit further consideration.