Cosmic Microwave Background Lensing Techniques
Summary
Cosmic microwave background (CMB) lensing refers to the subtle deflection of primordial photons by the gravitational influence of intervening matter as they travel from the surface of last scattering to our telescopes. These deflections imprint coherent distortions on the CMB temperature and polarisation patterns, offering a direct probe of the large-scale distribution of dark matter, neutrinos and cosmic structure evolution. Techniques for reconstructing the lensing signal range from quadratic estimators—where pairs of CMB Fourier modes are combined to infer the lensing potential—to fully Bayesian and likelihood-based approaches that iterate remapping operations for improved accuracy. Delensing methods then subtract the reconstructed lensing contribution to isolate primordial B-mode polarisation, a key target for probing inflationary gravitational waves. Recent advances span fast spherical harmonic transform algorithms, end-to-end machine-learning pipelines and high-resolution mass mapping from millimetre-wave surveys. Together, these approaches refine cosmological parameter estimation, test the ΛCDM paradigm on multiple redshift slices and establish vital cross-correlations with galaxy and quasar surveys worldwide.
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Cosmic Microwave Background Lensing Techniques publication trend
The graph below shows the total number of articles in cosmic microwave background lensing techniques across all publications each year (not limited to Nature Index journals).
Technical terms
Gravitational lensing: Deflection of CMB photons by large-scale matter potentials, producing coherent distortions in observed temperature and polarisation fields.
Delensing: Process of removing reconstructed lensing distortions from CMB maps to reveal underlying primordial signals, especially B-mode polarisation.
E-mode and B-mode polarisation: Even-parity (curl-free) and odd-parity (divergence-free) components of the CMB polarisation field, with B-modes sensitive to tensor perturbations and lensing effects.
Lensing potential: Projected gravitational potential integrated along the line of sight, which encodes the deflection field applied to the CMB.
Quadratic estimator: Statistical algorithm combining pairs of CMB Fourier (or spherical harmonic) coefficients to reconstruct the lensing potential under the assumption of nearly Gaussian primordial fluctuations.
References
- Delensing of Cosmic Microwave Background Polarization with Machine Learning. The Astrophysical Journal Supplement Series (2023).
- Improved cosmic microwave background (de-)lensing using general spherical harmonic transforms. Astronomy & Astrophysics (2023).
- The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters. The Astrophysical Journal (2024).
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