Motion of Spin 1/2 Massless Particle in a Curved Spacetime. I.   Lagrangian Approach
  Quasi-classical picture of motion of spin 1/2 massless particle in a curved spacetime is built on base of simple Lagrangian model. The one is constructed due to analogy with Lagrangian of massive spin 1/2 particle. Equations of motion and spin propagation coincide with Papapetrou equations describing dynamic of photon in a curved spacetime. 
A.T. Muminov