Delensing CMB Polarization with External Datasets

TL;DR

This paper evaluates the potential of external datasets for delensing CMB polarization to improve the detection of primordial gravitational waves, finding current external methods insufficient without high-resolution polarization maps.

Contribution

It introduces a formalism for incorporating delensing with external datasets into CMB forecasts and assesses the effectiveness of these datasets for delensing.

Findings

External datasets alone are insufficient for significant delensing.

High-resolution polarization maps are necessary for effective delensing.

The proposed formalism is fast and aligns well with Monte Carlo simulations.

Abstract

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 large-scale 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.