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

TL;DR

This paper explores the potential for massless spinning particles to follow non-geodesic paths in curved spacetime, revealing new dynamics influenced by spin and black hole temperature effects.

Contribution

It introduces new constraints allowing massless particles to deviate from null geodesics and demonstrates this with solutions in Schwarzschild spacetime.

Findings

Massless spinning particles can follow non-geodesic trajectories.

Spin induces an energy shift proportional to Hawking temperature.

New constraints enable alternative motion paths for massless particles.

Abstract

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.