Abstract
Standard models describing the radiation transfer of the cosmic microwave background (CMB) through Compton scattering predict that cosmological scalar perturbations at linear order are not able to source V and B polarization modes. In this work, we investigate the possibility that such CMB polarization modes are generated even in the presence of linear scalar perturbations only. We provide a general parametrization of the photon-fermion forward-scattering amplitude and compute mixing terms between different CMB polarization modes. We discuss different general extensions of Standard Model interactions which violate discrete symmetries, while preserving the combination of charge conjugation, parity and time reversal. We show that it is possible to source CMB circular polarization by violating parity and charge conjugation symmetries. Instead, B-mode generation is associated to the violation of symmetry for time-reversal. Our results provide a useful tool to constrain new physics using CMB data.
Highlights
cosmic microwave background (CMB) radiation represents a crucial observational tool of modern cosmology
Standard models describing the radiation transfer of the cosmic microwave background (CMB) through Compton scattering predict that cosmological scalar perturbations at linear order are not able to source V and B polarization modes
We investigate the possibility that such CMB polarization modes are generated even in the presence of linear scalar perturbations only
Summary
CMB radiation represents a crucial observational tool of modern cosmology. The standard models describing the radiation transfer of the CMB from the recombination epoch until today predict the presence of some level of linear polarization, the so-called E- and B-modes, which have been widely studied and reviewed in the literature (see e.g., Refs. [1,2,3,4,5,6,7,8]). Together with the anisotropies in the fermionic stress tensor, we need the fermion to interact with the photon only in the L- or R-handed helicity state, like the Lhanded neutrino in the Standard Model interactions This last case confirms and generalizes the results found in Ref. In the case of a generic interaction which violates P, T symmetries, it is possible to generate B-modes with no conditions on the fermions the photons interact with, while in the case in which C, T are violated we need the fermion to be in the L- or R-handed helicity state
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