GRAVITY WAVE-INDUCED POLARIZATION OF THE COSMIC MICROWAVE BACKGROUND-RADIATION

We discuss the contribution of pure gravitational waves to the cosmic microwave background radiation (CMBR) anisotropy and polarization. It is found that the large-scale polarization of the CMBR is less than 1% of the anisotropy for an universe with standard recombination. The ef fect of early matter reionization will enhance the CMBR polarization t o a 10% level. We have also computed the CMBR polarization for a unive rse having high baryon density and gravitational waves with a tilted s pectrum and found that further enhancement of the polarization is poss ible. We conclude that measuring the polarization of the CMBR on large angular scares can probe the ionization history of the early universe and set constraints on cosmological models.