G parity and the breaking of exchange degeneracy

Exact exchange degeneracy, a property of the planar S matrix, is not a feature of the physical world. G parity, an exact symmetry of strong interactions, fails to be maintained by the discontinuities of the planar S matrix. This paper examines the connection between these two conflicting concepts and shows how calculations of exchange-degeneracy breaking may be based on G parity. The relation of G parity to the cylinder and torus components of the topological expansion is a central feature. We apply our arguments to ρ-A2 splitting and justify the use of an unsubtracted dispersion relation for αA2-αρ. Our analysis of the dispersion relation reveals a dominant role for the ππ channel.