Abstract

In the standard theory of weak gravitational lensing, beams of light are assumed to be infinitesimal, i.e., very narrow compared to any relevant length scale of the problem at hand. However, this hypothesis is violated whenever light propagates through matter. Thus, one must wonder about the domain of validity of the standard lensing results, and about the magnitude of the possible corrections to it. In this talk, I will present the first theory of weak lensing with finite beams. I will start by discussing its interest regarding fundamental questions, and then turn to observational aspects; finite-beam corrections to current weak-lensing surveys will be considered, as well as novel observables.