The impact of galaxies and clusters on delensing of CMB B-mode polarization

Jun 06, 2022 - 11:00 am to 12:00 pm


Campus, Varian 355

Antón Baleato Lizancos (UC Berkeley) zoom

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Measurements of the B-mode polarization of the CMB are uniquely poised to elucidate the physics of cosmic inflation. However, the search for a primordial signal is limited by the sample variance of B-modes produced at later times by gravitational lensing. Constraints can be improved by `delensing': using some proxy of the matter distribution to partially remove the lensing-induced B-modes. Current and soon-upcoming experiments will infer a matter map -- at least in part -- from the temperature anisotropies of the CMB. These reconstructions are contaminated by foreground emission from galaxies and clusters: AGN, the cosmic infrared background, or the Sunyaev--Zel'dovich effects. In this talk, I report that foreground non-Gaussianity causes spurious B-mode power after delensing; this will need to be taken into account by Stage-3 CMB experiments to avoid biasing constraints on the tensor-to-scalar ratio, r. I will explain how these effects can be modelled using a simple-yet-accurate analytic prescription calibrated to observations, and demonstrate that alternative lensing estimators exist which can not only mitigate the biases to acceptable levels, but also lead to lower power after delensing than the standard Hu & Okamoto estimator. Finally, I will discuss the (non-trivial) generalization of these effects to the more realistic case where the temperature-based reconstructions are coadded with ones derived from polarization, or with external tracers of the matter distribution. Thanks to these considerations, temperature-based reconstructions remain powerful tools in the quest to measure r.