Strong field gravitational lensing in scalar tensor theories

TL;DR

This paper investigates strong field gravitational lensing within Brans-Dicke scalar-tensor theory, analyzing photon deflection and relativistic images, and finds minimal scalar field effects on observable lensing parameters, questioning their discriminative power.

Contribution

It provides the first detailed analysis of strong field lensing in Brans-Dicke theory, including numerical estimates of observable effects and their comparison with general relativity.

Findings

No significant scalar field effect on lensing observables.

Relativistic image positions and magnifications are similar to those in general relativity.

Strong lensing parameters may not effectively distinguish scalar-tensor theories.

Abstract

Strong field gravitational lensing in the Brans-Dicke theory has been studied. The deflection angle for photons passing very close to the photon sphere is estimated for the static spherically symmetric space-time of the theory and the position and magnification of the relativistic images are obtained. Modeling the super massive central object of the galaxy by the Brans-Dicke space-time, numerical values of different strong lensing observable are estimated. It is found that against the expectation there is no significant scalar field effect in the strong field observable lensing parameters. This observation raises question on the potentiality of the strong field lensing to discriminate different gravitational theories.