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  • Open Access

An iterative CMB lensing estimator minimizing instrumental noise bias

Louis Legrand1,2,*, Blake Sherwin1,2, Anthony Challinor3,1,2, Julien Carron4, and Gerrit S. Farren5,6

  • 1Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
  • 2Kavli Institute for Cosmology, Cambridge, Madingley Road, Cambridge CB3 OHA, United Kingdom
  • 3Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, United Kingdom
  • 4Université de Genève, Département de Physique Théorique et CAP, 24 Quai Ansermet, CH-1211 Genève 4, Switzerland
  • 5Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
  • 6Berkeley Center for Cosmological Physics, University of California, Berkeley, California 94720, USA

  • *Contact author: ll783@cam.ac.uk
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Phys. Rev. D 112, 103530 – Published 17 November, 2025

DOI: https://doi.org/10.1103/8kt3-d8z6

Abstract

Noise maps from cosmic microwave background (CMB) experiments are generally statistically anisotropic, due to scanning strategies, atmospheric conditions, or instrumental effects. Any mismodeling 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 autocorrelations 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 mismodeling with a negligible cost in signal-to-noise ratio. Our estimator enables unbiased and nearly optimal lensing reconstruction for next-generation CMB surveys.

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Phys. Rev. D 112, 103530– Published 17 November, 2025
  • Received 18 July 2025
  • Accepted 29 October 2025
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