We prove a new theorem on the impossibility of combining space-time and internal symmetries in any but a trivial way. The theorem is an improvement on known results in that it is applicable to infinite-parameter groups, instead of just to Lie groups. This improvement is gained by using information about the matrix; previous investigations used only information about the single-particle spectrum. We define a symmetry group of the matrix as a group of unitary operators which turn one-particle states into one-particle states, transform many-particle states as if they were tensor products, and commute with the matrix. Let be a connected symmetry group of the matrix, and let the following five conditions hold: (1) contains a subgroup locally isomorphic to the Poincaré group. (2) For any , there are only a finite number of one-particle states with mass less than . (3) Elastic scattering amplitudes are analytic functions of and , in some neighborhood of the physical region. (4) The matrix is nontrivial in the sense that any two one-particle momentum eigenstates scatter (into something), except perhaps at isolated values of . (5) The generators of , written as integral operators in momentum space, have distributions for their kernels. Then, we show that is necessarily locally isomorphic to the direct product of an internal symmetry group and the Poincaré group.
- Received 16 March 1967
- Published in the issue dated July 1967
© 1967 The American Physical Society