Intriguing aspects of the Cosmic Hemispherical Asymmetry

The standard model of cosmology predicts a statistically isotropic distribution of fluctuations in the measured Cosmic Microwave Background (CMB) temperature and polarisation maps. Enigmatic anomalies claimed in the WMAP and Planck CMB sky maps could challenge the standard model. However, these claims need to be cast in an objective mathematical framework and established with statistical rigour. We present a general method for Bayesian inference of the underlying covariance structure of random fields on a sphere. We employ the Bipolar Spherical Harmonic (BipoSH) representation of general covariance structure on the sphere. We illustrate the efficacy of the method with a principled approach to assess violation of statistical isotropy (SI) in the sky maps of CMB fluctuations. We pay particular attention to quantifying the nature and significance of the tentative evidence for a Cosmic Hemispherical asymmetry.