where the bottom line commutator of two boosts is often referred to as a "Wigner rotation". The simplification [ J m + i K m , J n − − i K n ] = 0 permits reduction of the Lorentz subalgebra to s u ( 2 ) ⊕ ⊕ s u ( 2 ) and efficient treatment of its associated representations. In terms of the physical parameters, we have