Effect of the dilaton field and plasma medium on deflection angle by black holes in Einstein-Maxwell-dilaton-axion theory

TL;DR

This paper calculates the weak deflection angle of light around Einstein-Maxwell-Dilaton-Axion black holes using the Gauss-Bonnet theorem, considering plasma effects and implications for dark matter detection.

Contribution

It introduces a method to compute light deflection in this black hole background and explores plasma and dark matter effects on the deflection angle.

Findings

Plasma medium influences the deflection angle significantly.

Dark matter candidates like dilaton and axion affect light bending.

Method supports observational studies of dark matter via black hole lensing.

Abstract

In this paper, we argue that one can calculate the weak deflection angle of light in the background of Einstein-Maxwell-Dilaton-Axion black hole using the Gauss-Bonnet theorem. To support this, the optical geometry of the black hole with the Gibbons-Werner method are used to obtain the deflection angle of light in the weak field limits. Moreover, we investigate the effect of a plasma medium on deflection of light for a given black hole. Because of dilaton and axion are one of the candidate of the dark matter, it can give us a hint on observation of dark matter which is supported by the black hole. Hence we demonstrate the observational viability via showing the effect of the dark matter on the weak deflection angle of light.