Speaker
Description
First-order gravitational lensing is a pure gradient, and hence only gives image magnification and shear. But post-Born corrections give rise to an additional small image rotation. I discuss the impact of this rotation on galaxies and the CMB temperature and polarization, and explain the challenges in trying to measure it. The rotation is somewhat enhanced for CMB lensing due to the large source path length, but remains small and very challenging to detect directly by CMB lensing reconstruction alone. I show the rotation may be detectable at high significance as a cross-correlation signal between the curl reconstructed with Simons Observatory (SO) or CMB-S4 data, and a template constructed from quadratic combinations of large-scale structure (LSS) tracers. I’ll give forecasts showing that in idealized cases this should be a new signal detectable at over 5 sigma with forthcoming data, and describe some of the theoretical complications. There is a follow-up talk by Mathew Robertson discussing more realistic cases and simulation results.
