Self-force of a scalar field for circular orbits about a Schwarzschild black hole

The foundations are laid for the numerical computation of the actual worldline for a particle orbiting a black hole and emitting gravitational waves. The essential practicalities of this computation are illustrated here for a scalar particle of infinitesimal size and small but finite scalar charge. This particle deviates from a geodesic because it interacts with its own retarded field psi(ret). A recently introduced Green's function G(S) precisely determines the singular part psi(S) of the retarded field. This part exerts no force on the particle. The remainder of the field psi(R)=psi(ret)-psi(S) is a vacuum solution of the field equation and is entirely responsible for the self-force. A particular, locally inertial coordinate system is used to determine an expansion of psi(S) in the vicinity of the particle. For a particle in a circular orbit in the Schwarzschild geometry, the mode-sum decomposition of the difference between psi(ret) and the dominant terms in the expansion of psi(S) provide a mode-sum decomposition of an approximation for psi(R) from which the self-force is obtained. When more terms are included in the expansion, the approximation for psi(R) is increasingly differentiable, and the mode sum for the self-force converges more rapidly.