Understanding biases to CMB lensing and delensing on the road to precision science

20.11.2020 11:30 – 12:30

For cosmologists, CMB lensing can be both a blessing and a nuisance. It's a nuisance because it generates spurious B-mode polarisation which obscures the highly-sought-after signal from inflationary gravitational waves, but it's a blessing because it can be used to reconstruct maps of the projected matter distribution of the Universe, from which any physics affecting the growth of cosmic structure can be constrained. In this talk, I will focus on systematics that needs to be addressed in order to harness the full statistical power of upcoming CMB experiments and make progress in both of these exciting areas. In the first part of my talk, I will briefly review the ways in which extragalactic emission from galaxies and clusters can bias CMB lensing reconstruction power spectra and cross-correlations with other tracers of the matter distribution. I will then present ongoing work on a novel approach where we model these biases analytically as a function of experimental characteristics, enabling improved physical insight, a quantification of theoretical uncertainties and potentially opening the door to improved mitigation methods. In the second part of the talk, I will explain how the lensing contamination to CMB B-modes can be removed — what is known as delensing — in order to facilitate searches for inflationary gravitational waves, and describe limitations of the commonly-used "template" approach to delensing. I will then briefly summarize preparatory efforts to delens data from the upcoming Simons Observatory. Finally, I will conclude by discussing biases affecting the procedure (and how to mitigate them) when lensing is reconstructed internally from the CMB itself, and in the alternative scenario where the CIB is used as a tracer of the matter.

Lieu

Bâtiment: Ecole de Physique

entrée libre