HET Seminar | Birefringence and Axiogenesis

Recent analyses of Planck and ACT CMB data report a 2–4σ hint of isotropic cosmic birefringence of β ≈ 0.3°. This corresponds to a parity-violating rotation of CMB photon polarization and points to new physics beyond the Standard Model. We demonstrate that cosmic birefringence and the baryon asymmetry can be simultaneously explained by the rotation of an axion in field space. In this axiogenesis framework, the axion rotation generates the baryon asymmetry through electroweak sphalerons, while such a rotation can arise in the early universe from explicit U(1) symmetry breaking expected from quantum gravity. The minimal models predict the correct sign of β based on the observed baryon asymmetry, as well as a period of matter and kination domination ending around a temperature of 3-50 MeV that makes the models falsifiable through future astrophysical probes and can lead to unique gravitational-wave signatures.