Weak lensing distortions beyond shear

TL;DR

This paper develops a complex analysis formalism to describe and predict higher-order weak lensing distortions beyond shear, revealing new observables sensitive to small-scale matter distribution in the universe.

Contribution

It extends the finite-beam approach to include cosmic correlations of distortions beyond shear and introduces a method for noncircular sources, enhancing weak lensing analysis.

Findings

Predicted cosmic correlations of distortions beyond shear for the first time

Identified new weak-lensing observables sensitive to small-scale matter features

Extended the formalism to noncircular, elliptic sources

Abstract

When a luminous source is extended, its distortions by weak gravitational lensing are richer than a mere combination of magnification and shear. In a recent work, we proposed an elegant formalism based on complex analysis to describe and calculate such distortions. The present article further elaborates this finite-beam approach, and applies it to a realistic cosmological model. In particular, the cosmic correlations of image distortions beyond shear are predicted for the first time. These constitute new weak-lensing observables, sensitive to very-small-scale features of the distribution of matter in the Universe. While the major part of the analysis is performed in the approximation of circular sources, a general method for extending it to noncircular sources is presented and applied to the astrophysically relevant case of elliptic sources.