The Benefits of CMB Delensing

TL;DR

CMB delensing improves the precision of cosmological measurements, enhances the detection of primordial gravitational waves, and simplifies data analysis by reversing lensing effects without requiring changes in survey design.

Contribution

We develop a comprehensive, iterative all-orders method for CMB delensing on the curved sky and demonstrate its benefits for future surveys.

Findings

Sharper acoustic peaks and damping tails in delensed spectra.

Reduced B-mode power enhances gravitational wave searches.

Lower covariance improves constraints on non-Gaussianities.

Abstract

The effects of gravitational lensing of the cosmic microwave background (CMB) have been measured at high significance with existing data and will be measured even more precisely in future surveys. Reversing the effects of lensing on the observed CMB temperature and polarization maps provides a variety of benefits. Delensed CMB spectra have sharper acoustic peaks and more prominent damping tails, allowing for improved inferences of cosmological parameters that impact those features. Delensing reduces $B$-mode power, aiding the search for primordial gravitational waves and allowing for lower variance reconstruction of lensing and other sources of secondary CMB anisotropies. Lensing-induced power spectrum covariances are reduced by delensing, simplifying analyses and improving constraints on primordial non-Gaussianities. Biases that result from incorrectly modeling nonlinear and baryonic feedback effects on the lensing power spectrum are mitigated by delensing. All of these benefits are possible without any changes to experimental or survey design. We develop a self-consistent, iterative, all-orders treatment of CMB delensing on the curved sky and demonstrate the impact that delensing will have with future surveys.