CMB-S4: Iterative Internal Delensing and $r$ Constraints

Understand

The tightest constraints on the tensor-to-scalar ratio $r$ can only be obtained after removing a substantial fraction of the lensing $B$-mode sample variance.

• The planned CMB-S4 experiment will remove the lensing $B$-mode signal internally by reconstructing the gravitational lenses from high-resolution observations.
• We document here a first lensing reconstruction pipeline able to achieve this optimally for arbitrary sky coverage.
• We make it part of a map-based framework to test CMB-S4 delensing performance and its constraining power on $r$, including inhomogeneous noise and two non-Gaussian Galactic polarized foreground models.