Topological spin transport of relativistic electron
  We derive the semiclassical (with accuracy of $\hbar$) motion equation for relativistic electron, which follow from the Dirac equation. We determine both the evolution equation for electron polarization, which takes the non-Abelian Berry phase into account, and Hamiltonian equations for trajectories of the particle (wave packet) center in the phase space. The equations have covariant form with respect to U(2) gauge transformations and contain topological spin terms that are connected to the Berry gauge field arising during the diagonalization of the Dirac equation. The trajectory equations obtained are substantially different from the traditional ones (for instance, those that follow from the Pauli Hamiltonian) and correspond to contemporary ideas of topological spin transport of particles. 
K.Yu. Bliokh