Spin-geodesic deviations in the Schwarzschild spacetime

TL;DR

This paper investigates how the spin of a particle causes deviations from geodesic paths in Schwarzschild spacetime, revealing oscillatory and drifting behaviors influenced by spin orientation.

Contribution

It extends geodesic deviation theory to include spin effects using the Mathisson-Papapetrou-Dixon model with linearized spin, providing new insights into spinning particle trajectories.

Findings

Spin causes oscillations in particle position perpendicular to motion.

Azimuthal motion exhibits oscillations plus secular drift.

Deviations depend on initial conditions and spin orientation.

Abstract

The deviation of the path of a spinning particle from a circular geodesic in the Schwarzschild spacetime is studied by an extension of the idea of geodesic deviation. Within the Mathisson-Papapetrou-Dixon model and assuming the spin parameter to be sufficiently small so that it makes sense to linearize the equations of motion in the spin variables as well as in the geodesic deviation, the spin-curvature force adds an additional driving term to the second order system of linear ordinary differential equations satisfied by nearby geodesics. Choosing initial conditions for geodesic motion leads to solutions for which the deviations are entirely due to the spin-curvature force, and one finds that the spinning particle position for a given fixed total spin oscillates roughly within an ellipse in the plane perpendicular to the motion, while the azimuthal motion undergoes similar oscillations plus an additional secular drift which varies with spin orientation.