Computing Microwave Background Polarization Power Spectra from Cosmic Birefringence

TL;DR

This paper introduces a new code, class_rot, for rapid and accurate computation of CMB polarization spectra affected by cosmic birefringence, aiding in testing new physics like axion dark matter and primordial magnetic fields.

Contribution

The paper presents a novel publicly available code, class_rot, that enables non-perturbative calculations of polarization spectra due to cosmic birefringence, improving analysis of related cosmological effects.

Findings

Code accurately reproduces simulations

Enables fast analysis of birefringence effects

Facilitates constraints on new physics models

Abstract

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. We also provide usage examples and demonstrate the accuracy of the code by comparing with simulations.