Periapsis shift and deflection of light by hairy black holes

Abstract

We investigate the orbit equations and the eikonal equation for light respectively, under influence of the hairy black holes (asymptotically flat) in four dimensions. We consider two hairy black hole solutions with non-trivial potentials, and one of these solutions has Schwarzschild case as a smooth limit. Following to Landau and Lifshitz, we use the Hamilton-Jacobi method, and we show hairy corrections for periapsis shift, where the effect of the hair is to increase it. In the same way, using the eikonal equation we show the deflection of the light and the relevant scalar hair corrections. Interestingly we find that the hair screening the gravitational field, decreasing the angle of deflection as the hair increases.