Spin-curvature interaction for particles of rest mass zero

Using a WKB approximation, equations of motion are derived for integral spin particles of zero rest mass. The equations are similar to Papapetrou's equations. A modified, extended WKB approximation is used to derive the equations for half-integral spin particles. The equations are applied to particles travelling down the axis of a spinning black hole, and to particles in a stationary, weak-field spacetime. The results agree with frequency cut-offs and linear polarization rotation results found by various other methods. Some previously known polarization results for electromagnetic waves are extended to other spins