Optical Aspect of Cosmological Black Holes in Einstein-Maxwell-Dilaton Theory

Abstract: Motivated by string theory scenarios, we study the optical aspect of AdS black holes in Einstein-Maxwell-dilaton theory. Concretely, we investigate and examine the shadows and the deflection angle of light rays by such cosmological black holes. Concerning the shadows, we first deal with the non-rotating solutions. As expected, we obtain perfect circular shadows where their sizes are controlled by the involved parameter including the charge and the cosmological constant. Combining the Newman-Janis formalism and the Hamilton-Jacobi algorithm, we approach the rotating black hole shadows using one dimensional real curves. Among others, we observe that the size and the shape shadows depend on certain parameters including the rotating one. To make contact with Event Horizon Telescope observational data, we show that certain constrains should be imposed on such parameters. Then, we study the behaviors of the light rays near such cosmological black holes by computing the deflection angle in terms of Einstein-Maxwell-dilaton theory parameters. Specifically, we reveal that the effect of the cosmological constant on the deflection angle depends on the coupling between the black hole parameters. Introducing the rotating parameter, we observe this effect becomes similar to that of the cosmological constant in ordinary AdS black holes.