Weak gravitational flexion in various spacetimes: Exotic lenses and modified gravity

TL;DR

This paper explores how weak gravitational flexion can reveal unique signatures of exotic lenses like Ellis wormholes and serve as a probe for scale-dependent modified gravity models, offering insights beyond traditional shear analysis.

Contribution

It demonstrates the potential of directional flexion to distinguish exotic lens types and highlights flexion's role in testing parametric modified gravity models.

Findings

Directional flexion distinguishes positive and negative convergence.

Flexion provides unique signatures for Ellis wormhole lenses.

Flexion is a sensitive probe for scale-dependent modified gravity.

Abstract

Exotic objects such as the Ellis wormhole are expected to act as gravitational lenses. Much like their nonexotic counterparts, information about these lenses can be found by considering the strong and weak lensing fields they induce. In this work, we consider how weak gravitational lensing flexion can provide information beyond that of shear. We find that directional flexion can distinguish between the case of a positive or negative convergence where directional shear cannot, and therefore can provide a unique lensing signature for objects with an Ellis wormhole-type metric. We also consider cosmic flexion, the flexion correlation function whose signal originates from the large-scale structure of the Universe, in the context of modified gravity. We find flexion to be a unique probe of parametric models of modified gravity, particularly in the case of scale-dependent phenomenological post-general relativity functions.