Relativistic invariant projectors on a complex spinor space and a rule   of polarizations summation in a complex bispinor space
  Relativistic invariant projectors of states in a complex bispinor space on a complex spinor space are constructed. An expression for sections of bundle with connection on group SU(4) in an explicit form has been obtained. Within the framework of the proposed geometrical approach the rule of summation over polarizations of states in a complex bispinor space has been derived. It has been shown that states in a complex bispinor space always describe a pair of Dirac's particles. 
H. V. Grushevskaya