Bar-halo angular-momentum transfer

Exchange of angular momentum between a stellar bar and a dark matter halo through orbital resonances. If the unperturbed halo distribution function depends only on energy and decreases with it, the resonant torque from a rotating perturbation is nonnegative for positive pattern angular velocity. Strict transfer requires nonzero resonant overlap. The reaction torque slows a rigid bar of constant positive moment of inertia; evolving bar structure and halo redistribution require updating the response.