LARGE-ANGLE POLARIZATION AND ANISOTROPY OF THE COSMIC MICROWAVE BACKGROUND-RADIATION AND REIONIZATION

We discuss the effect of matter reionization on the large angular scal e anisotropy and polarization of the cosmic microwave background radia tion (CMBR) in the standard cold dark matter model. We examine three c ases, in which the anisotropy is induced by pure-scalar, pure-tenser, and mixed metric perturbations. It is found that, if reionization occu rs early enough, the polarization can reach a detectable level of, res pectively, 6%, 9%, and 6.9% of the anisotropy. In general, a higher de gree of polarization implies a dominant contribution from the tensor m ode or reionization at high redshift. Since early reionization will su ppress small-scale CMBR anisotropies and polarizations significantly, measurement of the polarization on few-degree scales can be a direct p robe of the reionization history of the early universe.