Computing Microwave Background Polarization Power Spectra from Cosmic Birefringence

Understand

We present a new publicly available code, $\texttt{class_rot}$, which modifies $\texttt{class}$ to enable fast non-perturbative calculation of cosmic microwave background polarization power spectra due to both isotropic and anisotropic polarization rotation from cosmic birefringence.

• Cosmic birefringence can arise from new parity-violating physics such as axion dark matter with a Chern-Simons coupling to photons or Faraday rotation due to a primordial magnetic field.
• Constraints on these effects can be obtained by comparing measurements to precise numerical calculations of the polarization power spectra.
• We describe the implementation of $\texttt{class_rot}$ in terms of both mathematical formalism and coding architecture.