Influence of the cosmological constant on gravitational lensing in small systems

The cosmological constant $\ensuremath{\Lambda}$ affects gravitational lensing phenomena. The contribution of $\ensuremath{\Lambda}$ to the observable angular positions of multiple images and to their amplification and time delay is here computed through a study of the weak deflection limit of the equations of motion in the Schwarzschild--de Sitter metric. Because of $\ensuremath{\Lambda}$ the unresolved images are slightly demagnified, the radius of the Einstein ring decreases, and the time delay increases. The effect is however negligible for near lenses. In the case of a null cosmological constant, we provide some updated results on lensing by a Schwarzschild black hole.

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