No-Go Theorems for Hairy Black Holes in Scalar- or Vector-Tensor-Gauss-Bonnet Theory

Abstract: In this paper, we show a no-go theorem for static spherically symmetric black holes with vector hair in Einstein-$\Lambda$-Vector-Tensor-Gauss-Bonnet theory where a complex vector field non-minimally couples with Gauss-Bonnet invariant. For this purpose, we expand metric functions and radial functions of a vector field around the event horizon, and substitute the expansions into equations of motion. Demanding that the equations of motion are satisfied in each order, we show that the complex vector field vanishes on the event horizon. Moreover, when the event horizon is degenerated, it is also implied that the complex vector field vanishes on and outside the horizon.