Bianchi Model CMB Polarization and its Implications for CMB Anomalies

Understand

We derive the CMB radiative transfer equation in the form of a multipole hierarchy in the nearly-Friedmann-Robertson-Walker limit of homogeneous, but anisotropic, universes classified via their Bianchi type.

• Compared with previous calculations, this allows a more sophisticated treatment of recombination, produces predictions for the polarization of the radiation, and allows for reionization.
• Our derivation is independent of any assumptions about the dynamical behaviour of the field equations, except that it requires anisotropies to be small back to recombination; this is already demanded by observations.
• We calculate the polarization signal in the Bianchi VIIh case, with the parameters recently advocated to mimic the several large-angle anomalous features observed in the CMB.