Abstract

Anomalies in the large-scale CMB temperature sky measured by WMAP have been suggested as possible evidence for a violation of statistical isotropy. In any physical model for broken isotropy, there are testable consequences for the CMB polarization field. I will discuss the predictions for the polarization field in models that break statistical isotropy locally through a modulation field. I will consider two different models: dipolar modulation, invoked to explain the asymmetry in power between the northern and southern ecliptic hemispheres, and quadrupolar modulation, proposed to explain the alignments between the quadrupole and octopole. I will show that the addition of polarization information substantially improves the ability to test for modulation models and to discriminate among possible explanations. Finally, I will briefly discuss a polarization test of a possible anomaly at multipoles \ell ~ 20-40 in the observed temperature angular power spectrum, which utilises fortuitous properties of the polarization transfer function at these scales. As predictions of anomaly models, polarization statistics move beyond the a posteriori inferences that currently dominate the field.