Speaker: Anton Baleato Lizancos (Cambridge)

Title: “Understanding biases to CMB lensing and delensing on the road to precision science”

Abstract: 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 need 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.

Speaker: Utkarsh Giri (Perimeter Institute of Theoretical Physics) 

Title: “Exploring kSZ velocity reconstruction with N-body simulations and the halo model”

Abstract:

KSZ velocity reconstruction is a recently proposed method for mapping the largest-scale modes of the universe, by applying a quadratic estimator v̂ to the small-scale CMB and a galaxy catalog. We implement kSZ velocity reconstruction in an N-body simulation pipeline and explore its properties. We find that the reconstruction noise can be larger than the analytic prediction which is usually assumed. We revisit the analytic prediction and find additional noise terms that explain the discrepancy. The new terms are obtained from a six-point halo model calculation, and are analogous to the N(1) and N(3/2) biases in CMB lensing. We implement an MCMC pipeline which estimates fNL from N-body kSZ simulations and show that it recovers unbiased estimates of fNL, with statistical errors consistent with a Fisher matrix forecast. Overall, these results confirm that kSZ velocity reconstruction will be a powerful probe of cosmology in the near future, but new terms should be included in the noise power spectrum.

Join Zoom Meeting: https://lbnl.zoom.us/j/97706913102?pwd=QVl4M0xScklRbUwyVXNVbkF2R0tDUT09

Meeting ID: 977 0691 3102

Passcode: 505782 505782

Abstract: https://inpa.lbl.gov/event/special-double-f…tkarsh-giri-pitp/