Cosmic Flexion
  Cosmic flexion, like cosmic shear, is a correlation function whose signal
originates from the large-scale structure of the universe. Building on the
observational success of cosmic shear, along with the unprecedented quality of
large-scale cosmological datasets, the time is ripe to explore the practical
constraints from cosmic flexion. Unlike cosmic shear, which has a broad window
function for power, cosmic flexion is only measurable on small scales and
therefore can uniquely place constraints on the small-scale matter power
spectrum. Here, we present a full theoretical formalism for cosmic flexion,
including both flexion-flexion and shear-flexion two-point correlations. We
present forecasts for measuring cosmic flexion in the Dark Energy Survey (DES),
a Stage III cosmological survey, and comment on the future prospects of
measuring these cosmological flexion signals in the upcoming era of Stage IV
experiments.
