Orthogonal bipolar spherical harmonics measures: Scrutinizing sources of isotropy violation

Abstract

The two-point correlation function of the cosmic microwave background temperature anisotropies is generally assumed to be statistically isotropic (SI). Deviations from this assumption could be traced to physical or observational artifacts and systematic effects. Measurement of nonvanishing power in the bipolar spherical harmonic spectra is a standard statistical technique to search for isotropy violations. Although this is a neat tool allowing a blind search for SI violations in the cosmic microwave background sky, it is not easy to discern the cause of isotropy violation by using this measure. In this article, we propose a novel technique of constructing orthogonal bipolar spherical harmonic estimators, which can be used to discern between models of isotropy violation.