Improving cosmic birefringence constraints via delensing

Abstract We present a study on using delensing to enhance cosmic birefringence measurements based on full-sky, map-based simulations. In our analysis, we neglect foreground contamination and instrumental systematics to isolate the intrinsic impact of delensing on both isotropic and anisotropic birefringence. For the isotropic case, assuming a constant rotation angle of β = 0.35°, delensing reduces the lensing-induced variance in the EB power spectrum, yielding an improvement in sensitivity of approximately 10% at 6 μ K-arcmin noise for ℓ < 200 and 25–40% at lower noise levels for ℓ < 1000. For the anisotropic case, using simulations at 1 μ K-arcmin noise, we reconstruct the birefringence angle for a scale-invariant spectrum and mitigate lensing bias by delensing, achieving a 50% reduction in the leading N (0) bias and a 30% improvement in the constraints on the amplitude A CB . Our results demonstrate that delensing is an effective tool for enhancing the detectability of subtle parity-violating signals in the CMB with forthcoming experiments such as the Simons Observatory, CMB-S4, and LiteBIRD.