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 σ level. The best-fit Bianchi model corresponds to x = 0.55, Ω0 = 0.5, a rotation axis in the direction (l, b) = (222°, -62°), shear 0 = 2.4 × 10-10, and a right-handed vorticity 0 = 4.3 × 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.