Spin 1/2 and Invariant Coefficients
  Massive spin 1/2 particles require 2-spinors for rotations, 4-spinors for rotations and boosts with parity. Including translations requires 8-spinors. Adapting 4-spinor field theory to 8-spinor fields with translation symmetry is discussed here. It is shown that four of these spin components act like conventional 4-spinors, satisfying the conventional free-particle Dirac equation. The remaining four components have unconventional coordinate dependence due to translation symmetry. One finds that the 4-vector current of the 8-spinor is proportional to the electromagnetic 4-vector potential of the conventional 4-spinor, with arbitrary charge. Thus translation symmetry in field theory unites a conventional 4-spinor field and its electromagnetic vector potential. 
Richard Shurtleff