1. T. D. Lee andG. C. Wick:Nucl. Phys.,9 B, 209 (1969);10 B, 1 (1969). The relativistic model with the propagator (1.2) has been discussed inb)T. D. Lee:A relativistic complex pole model with indefinite metric, Columbia University preprint (1969).
2. The complex conjugate poles on the physical sheet have been discussed in earlier literature, for example ina)|W. Pauli:Proceedings of the International Conference on High-Energy Physics at CERN (1958), p, 127; b)M. Froissart:Suppl. Nuovo Cimento,14, 197 (1959);c)H. Kita andY. Kawai:Progr. Theor. Phys..,31, 269 (1964);d)J. Lukierski:Nuovo Cimento,47 A, 326 (1967). Only, however, in (1a,b) a scheme was proposed, introducing the complex poles on the first Riemann sheet as allowed by general physical principles.
3. See (1b),, formula (2.15), where the propagator (2) is introduced witha=0. The case with arbitrary complex conjugate residues represents the most general way of introducing a pair of comlex-mass particles. Seea)R. E. Cutkosky, P. V. Landhoff, D. I. Olive andJ. C. Polkinghorne:A nonanalytic S-matrix, Cambridge preprint (1969).
4. J. Lukierski andL. Turko: CERN preprint TH. 1095 (1969);
5. Nuovo Cimento,66 A, 409 (1970).