Statistical isotropy of the Cosmic Microwave Background

The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra large scale structure of the cosmos, in particular, of non trivial cosmic topology. The statistical isotropy (SI) of the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even beyond the cosmic horizon. We propose a set of measures, $\kappa_\ell$ ($\ell=1,2,3, ...$) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. We numerically compute the predicted $\kappa_\ell$ spectra for CMB anisotropy in flat torus universe models. Characteristic signature of different models in the $\kappa_\ell$ spectrum are noted.