Late reionizations of the Universe and their manifestation in the WMAP and future Planck data

We investigate two sets of two-epoched reionization models and their manifestation in the CMB anisotropy and polarization data of the recent WMAP project and make some predictions for the future Planck missions. In the first set of models, the universe was reionized twice, first at z ≃ 15 by population III stars and then at z ≃ 6 by stars in large galaxies. In the second set of models, the extra peak-like reionization at high redshifts z > 100 is induced by the decay of unstable particles, followed by the standard picture of reionization at z ≃ 6. We examine the general properties of these two-epoched reionization models and their implication in the WMAP CMB temperature anisotropy-polarization cross-correlation. We have shown that these models have comparable likelihood values for the WMAP data and distinct characters which can be tested with the Planck high sensitivities.