Optimal Cosmic Microwave Background Gravitational Lensing Reconstruction, Delensing, and Parameter Estimation with SPT-3G Polarization Data*

I will present simultaneous Bayesian estimates of gravitational-lensing potential bandpowers and unlensed cosmic microwave background (CMB) bandpowers derived from South Pole Telescope (SPT) observations in 2019 and 2020, as well as cosmological parameter estimates enabled by these spectra. These observations produce the deepest-ever high-angular-resolution CMB polarization maps at 90, 150, and 220 GHz. At these depths the standard Quadratic Estimation (QE) lensing reconstruction method is suboptimal. We use the Marginal Unbiased Score Expansion (MUSE) method to perform optimal map-level Bayesian inference of lensing potential bandpowers and unlensed CMB EE bandpowers, effectively using all N-point statistics of the CMB polarization maps. With CMB polarization maps from SPT-3G 2019/20 observations, the MUSE lensing reconstruction noise is ~2 times smaller than the QE estimation. Unlensed (or de-lensed) power spectra have lower sample variance and sharper features, in principle allowing for tighter constraints on cosmological parameters.