Beschreibung
Large-scale B-mode polarization of the cosmic microwave background (CMB) is a prime target for current and future experiments in search of primordial gravitational waves (PGW). With increasingly sensitive instruments being deployed, secondary B-modes induced by the weak gravitational lensing of CMB photons are becoming an important limitation and need to be mitigated. My talk will cover the construction and validation of a lensing B-mode template using data from the Atacama Cosmology Telescope (ACT), the unWISE galaxy survey, and Planck. Our template achieves the highest delensing efficiency demonstrated on real observations, removing 47% of the lensing B-mode power on large scales. I will then outline prospects for further improvements with data from the Simons Observatory (SO) and upcoming cosmological surveys, leading to forecasts for new constraints on the tensor-to-scalar ratio. Subject to data availability, I will finally discuss first steps towards the delensing of early SO polarization maps.