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Abstract: We derive the CMB radiative transfer equation in the form of a multipolehierarchy in the nearly-Friedmann-Robertson-Walker limit of homogeneous, butanisotropic, universes classified via their Bianchi type. Compared withprevious calculations, this allows a more sophisticated treatment ofrecombination, produces predictions for the polarization of the radiation, andallows for reionization. Our derivation is independent of any assumptions aboutthe dynamical behaviour of the field equations, except that it requiresanisotropies to be small back to recombination; this is already demanded byobservations.We calculate the polarization signal in the Bianchi VIIh case, with theparameters recently advocated to mimic the several large-angle anomalousfeatures observed in the CMB. We find that the peak polarization signal is ~1.2 micro K for the best-fit model to the temperature anisotropies, and ismostly confined to multipoles l<10. Remarkably, the predicted large-angle EEand TE power spectra in the Bianchi model are consistent with WMAP observationsthat are usually interpreted as evidence of early reionization. However, thepower in B-mode polarisation is predicted to be similar to the E-mode power andparity-violating correlations are also predicted by the model; the WMAPnon-detection of either of these signals casts further strong doubts on theveracity of attempts to explain the large-angle anomalies with globalanisotropy. On the other hand, given that there exist further dynamical degreesof freedom in the VIIh universes that are yet to be compared with CMBobservations, we cannot at this time definitively reject the anisotropyexplanation.

Autor: Andrew Pontzen 1, Anthony Challinor 1,2 1 IoA Cambridge, 2 DAMTP Cambridge


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