Weak lensing distortions beyond shear
  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.
