Probing Axions through Tomography of Anisotropic Cosmic Birefringence

Understand

Cosmic birefringence is the in-vacuo rotation of the linear polarization plane experienced by photons of the Cosmic Microwave Background (CMB) radiation when theoretically well-motivated parity-violating extensions of Maxwell electromagnetism are considered.

• If the angle, parametrizing such a rotation is dependent on the photon's direction, then this phenomenon is called Anisotropic Cosmic Birefringence (ACB).
• In this paper, we perform for the first time a tomographic treatment of the ACB, by considering photons emitted both at the recombination and reionization epoch.
• This allows one to extract additional and complementary information about the physical source of cosmic birefringence with respect to the isotropic case.