From topological quantum mechanics to the physics of spin-one particles
  We give an example of topological theory whose Hilbert space contains physical objects: the N=2 supersymmetric Lagrangian of spin-one particles moving in D-dimensional space-time equals the Lagrangian of a topological sigma model in a (D+2)-dimensional target. The equivalence is valid for a curved space-time. As an application, we calculate the deviation of spin-one particles in a Schwarzschild background (gravitational Stern-Gerlach effect). 
Romain Attal and Laurent Baulieu