Statistical isotropy violation in WMAP CMB maps resulting from
  non-circular beams
  Statistical isotropy (SI) of Cosmic Microwave Background (CMB) fluctuations
is a key observational test to validate the cosmological principle underlying
the standard model of cosmology. While a detection of SI violation would have
immense cosmological ramification, it is important to recognise their possible
origin in systematic effects of observations. WMAP seven year (WMAP-7) release
claimed significant deviation from SI in the bipolar spherical harmonic
(BipoSH) coefficients $A_{ll}^{20}$ and $A_{l-2l}^{20}$. Here we present the
first explicit reproduction of the measurements reported in WMAP-7, confirming
that beam systematics alone can completely account for the measured SI
violation. The possibility of such a systematic origin was alluded to in WMAP-7
paper itself and other authors but not as explicitly so as to account for it
accurately. We simulate CMB maps using the actual WMAP non-circular beams and
scanning strategy. Our estimated BipoSH spectra from these maps match the
WMAP-7 results very well. It is also evident that only a very careful and
adequately detailed modelling, as carried out here, can conclusively establish
that the entire signal arises from non-circular beam effect. This is important
since cosmic SI violation signals are expected to be subtle and dismissing a
large SI violation signal as observational artefact based on simplistic
plausibility arguments run the serious risk of "throwing the baby out with the
bathwater".
