Motion of a rotating black hole in a homogeneous scalar field
In the present paper, we consider a rotating black hole moving in a homogeneous massless scalar field. We assume that the field is weak and neglect its backreaction, so that the metric at far distance from the black hole is practically flat. In this domain one can introduce two reference frames, $K$ and $\tilde{K}$. The frame $\tilde{K}$ is associated with the homogeneous scalar field, in which its constant gradient has only time component. The other frame, $K$, is the frame in which the black hole is at rest. To describe the Kerr metric of the black hole we use its Kerr-Schild form $g_{\mu\nu}=\eta_{\mu\nu}+\Phi l_{\mu}l_{\mu}$, where $\eta_{\mu\nu}$ is the (asymptotic) flat metric in $K$ frame. We find an explicit solution of the scalar field equation which is regular at the horizon and properly reproduce the asymptotic form of the scalar field at the infinity. Using this solution we calculate the fluxes of the energy, momentum and the angular momentum of the scalar field into the black hole. This allows us to derive the equation of motion of the rotating black hole. We discuss main general properties of solutions of these equations and obtain explicit solutions for special type of the motion of the black hole.