Degeneracy in exotic gravitational lensing

TL;DR

This paper explores three distinct astrophysical scenarios where gravitational lens equations become degenerate, highlighting the challenges in distinguishing between different lensing causes and proposing methods to resolve this ambiguity.

Contribution

It identifies and analyzes three different physical situations causing degeneracy in gravitational lens equations, and discusses strategies to break this degeneracy.

Findings

Degeneracy occurs in exotic matter, scalar fields, and closed universe lensing scenarios.

The paper discusses how to distinguish between these degenerate cases.

Potential real-world implications for interpreting gravitational lensing observations.

Abstract

We present three different theoretically foreseen, but unusual, astrophysical situations where the gravitational lens equation ends up being the same, thus producing a degeneracy problem. These situations are (a) the case of gravitational lensing by exotic stresses (matter violating the weak energy condition and thus having a negative mass, particular cases of wormholes solutions can be used as an example), (b) scalar field gravitational lensing (i.e. when considering the appearance of a scalar charge in the lensing scenario), and (c) gravitational lensing in closed universes (with antipodes).The reasons that lead to this degeneracy in the lens equations, the possibility of actually encountering it in the real universe, and eventually the ways to break it, are discussed.