Internal Delensing of Cosmic Microwave Background Acoustic Peaks

TL;DR

This paper introduces an internal delensing method for CMB acoustic peaks using reconstructed lensing maps, identifies a bias caused by correlated noise, and proposes a technique to mitigate this bias, aiding future CMB analyses.

Contribution

The paper presents a novel internal delensing approach for CMB acoustic peaks and addresses the bias caused by correlated noise in lensing potential reconstructions.

Findings

Bias in delensed power spectrum due to correlated noise

Method to remove bias using scale-specific reconstructions

Improved potential for tighter cosmological parameter constraints

Abstract

We present a method to delens the acoustic peaks of the CMB temperature and polarization power spectra internally, using lensing maps reconstructed from the CMB itself. We find that when delensing CMB acoustic peaks with a lensing potential map derived from the same CMB sky, a large bias arises in the delensed power spectrum. The cause of this bias is that the noise in the reconstructed potential map is derived from, and hence correlated with, the CMB map when delensing. This bias is more significant relative to the signal than an analogous bias found when delensing CMB B modes. We calculate the leading term of this bias, which is present even in the absence of lensing. We also demonstrate one method to remove this bias, using reconstructions from CMB angular scales within given ranges to delens CMB scales outside of those ranges. Some details relevant for a realistic analysis are also discussed, such as the importance of removing mask-induced effects for successful delensing, and a useful null test, obtained from randomizing the phases of the reconstructed potential. Our findings should help current and next-generation CMB experiments obtain tighter parameter constraints via the internal removal of lensing-induced smoothing from temperature and E-mode acoustic peaks.