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

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

2005-03-09

arxiv.org/abs/astro-ph/0503213v2

Astrophys.J.629:L1-L4,2005

Astronomy and Astrophysics

Astrophysics

4 pages, 3 figures; emulateapj.cls; ApJL accepted version plus fixed error in vorticity calculation (sqrt(2) off in Table 1, a

Scientific paper

10.1086/444454

Motivated by the large-scale asymmetry observed in the cosmic microwave background sky, we consider a specific class of anisotropic cosmological models -- Bianchi type VII_h -- and compare them to the WMAP first-year data on large angular scales. Remarkably, we find evidence of a correlation which is ruled out as a chance alignment at the 3sigma level. The best fit Bianchi model corresponds to x=0.55, Omega_0=0.5, a rotation axis in the direction (l,b)=(222degr,-62degr), shear (sigma/H)_0=2.4e-10 and a right--handed vorticity (omega/H)_0=6.1e-10. Correcting for this component greatly reduces the significance of the large-scale power asymmetry, resolves several anomalies detected on large angular scales (ie. 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.

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