Aditya Rotti, Moumita Aich, Tarun Souradeep
Statistical isotropy (SI) has been one of the simplifying assumptions in
cosmological model building. Experiments like WMAP and PLANCK are attempting to
test this assumption by searching for specific signals in the Cosmic Microwave
Background (CMB) two point correlation function. Modifications to this
correlation function due to gravitational lensing by the large scale structure
(LSS) surrounding us have been ignored in this context. Gravitational lensing
will induce signals which mimic isotropy violation even in an isotropic
universe. The signal detected in the Bipolar Spherical Harmonic (BipoSH)
coefficients $A^{20}_{ll}$ by the WMAP team may be explained by accounting for
the lensing modifications to these coefficients. Further the difference in the
amplitude of the signal detected in the V-band and W-band maps can be explained
by accounting for the differences in the designed angular sensitivity of the
instrumental beams. The arguments presented in this article have crucial
implications for SI violation studies. Constraining SI violation will only be
possible by complementing CMB data sets with all sky measurements of the large
scale dark matter distribution. Till that time, the signal detected in the
BipoSH coefficients from WMAP-7 could also be yet another suggested evidence of
strong deviations from the standard $\Lambda$CDM cosmology based on homogeneous
and isotropic FRW models.
View original:
http://arxiv.org/abs/1111.3357
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