Generation of Circular Polarization of CMB via Polarized Compton Scattering

Abstract

The standard scenario of cosmology predicts a measurable amount for linear polarization of the Cosmic Microwave Background radiation (CMB) via Thomson scattering, while through this scenario, the generation of circular polarization is excluded. On the another hand, the circular polarization of CMB has not been excluded in observational evidence. The generation of CMB photons circular polarization via their Compton scattering with polarized cosmic electrons is considered in this paper. Our motivation for considering polarized Compton scattering comes from the effects of the external magnetic field in large scale, the chiral magnetic instability and new physics interactions of the cosmic electrons. It is shown that damping term of polarized Compton scattering in the presence of scalar perturbation can generate circular polarization in CMB radiation, so that the power spectrum of circular polarization of CMB $C_l^{V(S)}$ is proportional to the power spectrum of temperature anisotropy of CMB $C_l^{I(S)}$ and also $\delta^2$ which is a fraction of polarized electron number density to the total one with net Left- or Right-handed polarizations. We have discussed that at least we need $\delta<10^{-4}$ to find consistency with a reported upper limit of CMB circular polarization.