Delensing CMB Polarization with External Datasets

One of the primary scientific targets of current and future CMB polarization experiments is the search for a stochastic background of gravity waves in the early universe. As instrumental sensitivity improves, the limiting factor will eventually be B-mode power generated by gravitational lensing, which can be removed through use of so-called “delensing” algorithms. We forecast prospects for delensing using lensing maps which are obtained externally to CMB polarization: either from largescale structure observations, or from high-resolution maps of CMB temperature. We conclude that the forecasts in either case are not encouraging, and that significantly delensing large-scale CMB polarization requires high-resolution polarization maps with sufficient sensitivity to measure the lensing B-mode. We also present a simple formalism for including delensing in CMB forecasts which is computationally fast and agrees well with Monte Carlos. ar X iv :1 01 0. 00 48 v2 [ as tr oph .C O ] 5 O ct 2 01 0