On the Possibility of Non-Geodesic Motion of the Massless Spinning Top

Understand

The motion of spinning massless particles in gravitationally curved backgrounds is revisited by considering new types of constraints.

• Those constraints guarantee zero mass ($P_\mu P^\mu=0$) and they allow for the possibility of trajectories which are not simply null geodesics.
• To exemplify this previously unknown possibility, the equations of motion are solved for radial motion in Schwarzschild background.
• It is found that the particle experiences a spin-induced energy shift, which is proportional to the Hawking temperature of the black hole background.