Cosmic Birefringence: Cross-Spectra and Cross-Bispectra with CMB Anisotropies

Understand

Parity-violating extensions of Maxwell electromagnetism induce a rotation of the linear polarization plane of photons during propagation.

• This effect, known as cosmic birefringence, impacts on the Cosmic Microwave Background (CMB) observations producing a mixing of $E$ and $B$ polarization modes which is otherwise null in the standard scenario.
• Such an effect is naturally parametrized by a rotation angle which can be written as the sum of an isotropic component $\alpha_0$ and an anisotropic one $\delta\alpha(\hat{\mathbf{n}})$.
• In this paper we compute angular power spectra and bispectra involving $\delta\alpha$ and the CMB temperature and polarization maps.