Gravitational lensing shear by an exotic lens object with negative convergence or negative mass

TL;DR

This paper investigates gravitational lensing effects caused by exotic objects with negative convergence or mass, revealing distinctive image distortions that could help detect or constrain such exotic matter or energy.

Contribution

It analyzes shear patterns in gravitational lensing by exotic matter models with negative convergence, highlighting unique radial or tangential image distortions.

Findings

Repulsive lens models cause radially elongated images.

Attractive models produce tangentially elongated images.

Potential to identify exotic matter through lensing surveys.

Abstract

Gravitational lens models with negative convergence(surface mass density projected onto the lens plane) inspired by modified gravity theories, exotic matter and energy have been recently discussed in such a way that a static and spherically-symmetric modified spacetime metric depends on the inverse distance to the power of positive $n$(n=1 for Schwarzschild metric, n=2 for Ellis wormhole) in the weak-field approximation [Kitamura, Nakajima and Asada, PRD 87, 027501 (2013)], and it has been shown that demagnification of images could occur for $n>1$ lens models associated with exotic matter (and energy), though they cause the gravitational pull on light rays. The present paper considers gravitational lensing shear by the demagnifying lens models and other models such as negative-mass compact objects causing the gravitational repulsion on light rays like a concave lens. It is shown that images by the lens models for the gravitational pull are tangentially elongated, whereas those by the repulsive ones are radially distorted. This feature of lensed image shapes may be used for searching(or constraining) localized exotic matter or energy with gravitational lensing surveys. It is suggested also that an underdense region such as a cosmic void might produce radially elongated images of background galaxies rather than tangential ones.