Statistical Isotropy violation of the CMB brightness fluctuations

Understand

Certain anomalies at large angular scales in the cosmic microwave background measured by WMAP have been suggested as possible evidence of breakdown of statistical isotropy(SI).

• Most CMB photons free-stream to the present from the surface of last scattering.
• It is thus reasonable to expect statistical isotropy violation in the CMB photon distribution observed now to have originated from SI violation in the baryon-photon fluid at last scattering, in addition to anisotropy of the primordial power spectrum studied earlier in literature.
• We consider the generalized anisotropic brightness distribution fluctuations, $\Delta(\vec{k}, \hat{n}, \tau)$ (at conformal time $\tau$) in contrast to the SI case where it is simply a function of $|\vec{k}|$ and $\hat{k} \cdot \hat{n}$.