Can Schwarzschild Black Holes Be Accelerators of Spinning Massive Particles?

It is known that the center-of-mass energy of the collision of two massive particles following geodesics around a black hole presents a maximum. The maximum energy increases when the black hole is endowed with spin, and for a maximally rotating hole this energy blows up, offering, in principle, a unique probe of fundamental physics. This work extends the latter studies by considering that the colliding particles possess intrinsic angular momentum (spin), described by the Hanson-Regge-Hojman theory of spinning particles. By analyzing planar trajectories of spinning particles around non-rotating black holes, a significant increase of the invariant collision energy is found. Radial turning points, causality constraints, and limitations of the theory are discussed.