  Black holes threaded by massive vector fields can be subject to a
superradiant instability, growing a cloud of massive vector particles around
it. In this work, we consider what happens if such a dark matter candidate
field mimicking a dark photon interacts with an accretion flow onto the black
hole. By including a kinetic mixing term with the standard model photon, we
extend the commonly used equations of general-relativistic magnetohydrodynamics
to a dark photon constituent. The coupling to the dark photon then appears as
an effective dynamo term together with a dark Lorentz force acting on the
accreting matter. We numerically study the interactions between the
superradiant dark photon cloud and the inner accretion flow by solving the
coupled system in full numerical relativity. By parameterically varying the
mixing parameter between dark and standard model sector, we provide a first
investigation of how the accretion flow could be modified. Depending on the
coupling strength, our solutions exhibit increased wind launching, as well as
oscillation modes in the disk.
