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

Understand

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.