An iterative CMB lensing estimator minimizing instrumental noise bias

TL;DR

This paper presents a new CMB lensing estimator that minimizes instrumental noise bias by using split-map correlations, enabling unbiased and nearly optimal lensing measurements for future surveys.

Contribution

The authors introduce a MAP-based lensing estimator that reduces sensitivity to complex noise anisotropies by relying on independent noise realizations, improving bias control.

Findings

Estimator effectively removes noise bias in simulations.

Method maintains high signal-to-noise ratio.

Suitable for next-generation CMB surveys.

Abstract

Noise maps from CMB experiments are generally statistically anisotropic, due to scanning strategies, atmospheric conditions, or instrumental effects. Any mis-modeling of this complex noise can bias the reconstruction of the lensing potential and the measurement of the lensing power spectrum from the observed CMB maps. We introduce a new CMB lensing estimator based on the maximum a posteriori (MAP) reconstruction that is minimally sensitive to these instrumental noise biases. By modifying the likelihood to rely exclusively on correlations between CMB map splits with independent noise realizations, we minimize auto-correlations that contribute to biases. In the regime of many independent splits, this maximum closely approximates the optimal MAP reconstruction of the lensing potential. In simulations, we demonstrate that this method is able to determine lensing observables that are immune to any noise mis-modeling with a negligible cost in signal-to-noise ratio. Our estimator enables unbiased and nearly optimal lensing reconstruction for next-generation CMB surveys.