Speaker
Description
Quadratic estimators (used notably for current most precise CMB lensing measurements) are a wide class of estimators efficient in capturing small signals of anisotropies. They will provide sub-percent contraints on the growth structure in the near future. After discussing how these estimators relate to bispectra, I will describe a general expansion of spherical (full-sky) bispectra into a set of orthogonal modes, with the aim to separate physically-distinct signals. The expansion uses a new set of discrete polynomials that are pairwise orthogonal with respect to the relevant Wigner 3j symbol, and reduce as desired to Chebyshev polynomials (i.e. Fourier series) in the flat-sky limit for both parity-even and parity-odd cases. We use the full-sky expansion to construct a tower of orthogonal CMB lensing quadratic estimators and construct estimators that are immune to foregrounds like point sources or noise inhomogeneities. In parity-even combinations (such as the lensing gradient mode from TT, or the lensing curl mode from EB) the leading two modes can be identified with information from the magnification and shear respectively, whereas the parity-odd combinations are shear-only.
