Candidate entanglement invariants for two Dirac spinors

We consider two spacelike separated Dirac particles and construct five invariants under the spinor representations of local proper orthochronous Lorentz groups. All constructed are identically zero for product states. The behaviour unitary evolutions that act unitarily on any subspace with fixed particle momenta is studied. have invariant absolute values such subspaces if generated by zero-mass Hamiltonians. Some them also case nonzero-mass. Therefore, they considered potential candidates describing entanglement particles, either or arbitrary mass. Furthermore, their relations to Wootters concurrence investigated in Foldy-Wouthuysen picture given.