"Second Order" Polarization of the CMB


Lensing by large scale structure between last scattering and us distorts the polarization pattern...
mixes E into B to a small extent.
Called "Lensing B-modes"

Gravity waves propagating through the primordial plasma add to all spectra...
based on existing T data we know contribution small.
Called "Gravity Wave B-modes"

When Universe re-ionizes additional scattering occurs
generates extra large scale anisotropy.
Called "Re-ionization Signature"