Self-force on a particle in orbit around a black hole

We study the self-force acting on a scalar charge in uniform circular motio n around a Schwarzschild black hole. The analysis is based on a direct calc ulation of the self-force via mode decomposition, and on a regularization p rocedure based on Ori's mode-sum regularization prescription. We find the f our self-forces at arbitrary radii and angular velocities (both geodesic an d nongeodesic), in particular near the black hole, where general-relativist ic effects are strongest, and for fast motion. We find the radial component of the self-force to be repulsive or attractive, depending on the orbit.