Spin and Isospin in S-Matrix Theory

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Abstract
The Gunson‐Olive technique for exploiting physical region poles and the unitarity equations to derive the analytic properties of S‐matrix elements is applied to particles which belong to isospin multiplets and to particles with spin. In the former case it is shown that, in the framework of S‐matrix theory, crossing symmetry leads to the requirement that particles and antiparticles transform according to complex conjugate representations; and it is possible to clarify the origin of the familiar isospin crossing matrices. In the case of particles with spin the construction of appropriate ``spinor'' basic states is discussed and the analytic properties of the corresponding spinor S‐matrix elements or ``M‐functions'' are derived.