Constrained Deflection Angle and Shadows of Rotating Black Holes in Einstein-Maxwell-scalar Theory

Abstract

Motivated by recent Event Horizon Telescope findings, we investigate constrained optics of rotating black holes in Einstein-Maxwell-scalar gravity theory. Precisely, we mainly study the parameter effects on two relevant optical concepts being the shadow and deflection angle. Using the Hamilton-Jacobi algorithm, we find certain shadow geometries being corroborated by observational data once appropriate constraints on a stringy coupling parameter $\beta$ are imposed. For such constrained regions of the black hole moduli space, we compute the deflection angle of light rays near to such black holes. Concretely, we show that this optical quantity can be split into two contributions describing the absence and the presence of the coupling parameter $\beta$. Then, we discuss and analyse such an optical quantity in terms of $\beta$ contributions.