Electromagnetic Waves in the Vacuum with Torsion and Spin
  Exact radiative wave solutions to the classical homogeneous Maxwell equations in the vacuum have been found that are not transverse, exhibit both torsion and spin, and for which the second Poincare invariant, E.B, is not zero. Two four component rank 3 tensors of spin current and torsion are constructed on topological grounds. The divergence of each pseudo vector generates the Poincare invariants of the electromagnetic system. 
R. M. Kiehn