Large-scale polarization of the cosmic microwave background radiation

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Abstract
The anisotropy and polarization of the cosmic microwave background radiation (CMBR) induced by the scalar and tensor metric perturbations are computed in the long-wavelength limit. It is found that the large-scale polarization of the CMBR induced by the decaying tensor mode can reach a few percent. This is different from the scalar or inflation-induced tensor mode, where the polarization is at least two orders of magnitude lower. The effect of matter reionization on the CMBR is also considered. We conclude that measuring the polarization of the CMBR on large-angular scales can probe the ionization history of the early Universe, and test different cosmological models.