On the Local Separation of E and B Polarization Patterns in CMBR

Abstract

The work examines the small-scale E and B patterns of the CMBR polarization anisotropy. Particularly we address the topological natures and spatial symmetries of the E and B modes, and how one may make use of the local measurements of Stokes parameters to separate these two modes. The analysis of a local map in the Fourier space for separating the E and B modes can be an ill-defined problem, due to the non-periodic boundary condition in the map for each mode. A strategy for the E-B separation in a local map can be through an appropriate projection of the polarization tensor field into a unique vector field, which naturally contains a curl-free E component and a divergence-free B component. An integral method, equivalent to the real-space, top-hat filtering, is proposed for extracting the smoothed "charge" and "current" of the E and B modes separately. The top-hat filter function exhibits, in its power spectrum, an oscillation of a well-defined frequency comparable to the filter size. It is pointed out that when the inverse filter size is chosen properly, matching the oscillation period in the E-mode power spectrum, the sensitivity for the E-mode detection can be made to be significantly improved.