Spin and the Symplectic Flag Manifold
  A theory for the transitive action of a group on the configuration space of a system of particles is shown to lead to the conclusion that interactions can be represented by the action of cosets of the group. By application of this principle to Pauli spinors, the symplectic group Sp(n) is shown to be the largest group of isometries of the space. Interactions between particles are represented by the complete quaternionic flag variety Sp(n)/Sp(1)^n. 
Bruce E. Eichinger
math-ph math.MP quant-ph