Characterizing CMB noise anisotropies from CMB delensing

Abstract

Un-doing the effect of gravitational lensing on the Cosmic Microwave Background (`de-lensing') is essential in shaping constraints on weak signals limited by lensing effects on the CMB, for example on a background of primordial gravitational waves. Removing these anisotropies induced by large-scale structures from the CMB maps also generally helps our view of the primordial Universe by sharpening the acoustic peaks and the damping tail. However, practical implementations of delensing transfer parts of these anisotropies to the noise maps. This will induce a new large scale `mean-field' bias to any anisotropy estimator applied to the delensed CMB, and this bias directly traces large-scale structures. This paper analytically quantifies this delensed noise mean-field and its impact on quadratic (QE) and likelihood-based lensing estimators. We show that for Simons-Observatory-like surveys, this mean-field bias can reach 15\% in cross-correlation with large-scale structures if unaccounted for. We further demonstrate that this delensed noise mean-field can be safely neglected in likelihood-based estimators without compromising the quality of lensing reconstruction or $B$-mode delensing, provided the resulting lensing map is properly renormalized.

12 pages, 7 figures, version accepted for publication

References in corpus (29)

• Weak Gravitational Lensing of the CMB
• BICEP / Keck XIII: Improved Constraints on Primordial Gravitational Waves using Planck, WMAP, and BICEP/Keck Observations through the 2018 Observing Season
• Planck 2018 results. VIII. Gravitational lensing
• CMB Lensing Reconstruction on the Full Sky
• Planck 2018 results. IV. Diffuse component separation
• Reconstruction of lensing from the cosmic microwave background polarization
• Improved limits on the tensor-to-scalar ratio using BICEP and Planck
• The shape of the CMB lensing bispectrum
• Bias-Hardened CMB Lensing
• Reconstructing Patchy Reionization from the Cosmic Microwave Background
• Maximum a posteriori CMB lensing reconstruction
• CMB Delensing Beyond the B Modes
• Cosmology From CMB Lensing and Delensed EE Power Spectra Using 2019-2020 SPT-3G Polarization Data
• Internal delensing of Planck CMB temperature and polarization
• Quadratic estimators for CMB weak lensing
• Demonstration of cosmic microwave background delensing using the cosmic infrared background
• Bayesian delensing of CMB temperature and polarization
• Full-sky CMB lensing reconstruction in presence of sky-cuts
• The Atacama Cosmology Telescope: Cosmology from cross-correlations of unWISE galaxies and ACT DR6 CMB lensing
• CMB Lensing Reconstruction in Real Space
• The Simons Observatory: Constraining inflationary gravitational waves with multi-tracer B-mode delensing
• CMB-S4: Iterative Internal Delensing and $r$ Constraints
• MUSE: Marginal Unbiased Score Expansion and Application to CMB Lensing
• BICEP / Keck XVII: Line of Sight Distortion Analysis: Estimates of Gravitational Lensing, Anisotropic Cosmic Birefringence, Patchy Reionization, and Systematic Errors
• Lensing power spectrum of the Cosmic Microwave Background with deep polarization experiments
• Limitations of CMB B-mode template delensing
• CMB Mode Coupling with Isotropic Polarization Rotation
• Robust and efficient CMB lensing power spectrum from polarization surveys
• Real-world CMB lensing quadratic estimator power spectrum response