CMB Mode Coupling with Isotropic Polarization Rotation

Understand

We provide a new analysis technique to measure the effect of the isotropic polarization rotation, induced by e.g.

• the isotropic cosmic birefringence from axion-like particles and a miscalibration of CMB polarization angle, via mode coupling in the cosmic microwave background (CMB).
• Several secondary effects such as gravitational lensing and CMB optical-depth anisotropies lead to mode coupling in observed CMB anisotropies, i.e., non-zero off-diagonal elements in the observed CMB covariance.
• To derive the mode coupling, however, we usually assume no parity violation in the observed CMB anisotropies.