See for example:E. M. Friedländer:Phys. Rev. Lett.,5, 212 (1960)
L. G. Hyman, R. Ely, D. H. Frisch andM. A. Wahlig:Phys. Rev. Lett.,3, 93 (1959).
J. J. Sakurai:Nuovo Cimento,20, 1212 (1961).
G. F. Chew andF. E. Low:Phys. Rev.,113, 1640 (1959).
C. Goebel:Phys. Rev. Lett.,1, 337 (1958).
F. Bonsignori andF. Selleri:Nuovo Cimento,15, 465 (1960).
S. D. Drell:Phys. Rev. Lett.,5, 278, 342 (1960).
J. G. Rushbrooke andD. Radojicic:Phys. Rev. Lett.,5, 567 (1960)
T. Kobayashi:Prog. Theor. Phys.,18, 318 (1957).
E. Ferrari andF. Selleri:Phys. Rev. Lett.,7, 387 (1961).
E. Ferrari:Nuovo Cimento,15, 652 (1960).
D. Boccaletti andC. Gualdi:Nuovo Cimento,18, 895 (1960);D. Boccaletti, G. De Franceschi andC. Gualdi:Nuovo Cimento,20, 375 (1961);D. Boccaletti andF. Selleri:Nuovo Cimento,22, 1099 (1961).
E. Ferrari andF. Selleri:Nuovo Cimento,21, 1028 (1961); see also:J. Iizuka andA. Klein:Prog. Theor. Phys.,25, 1017 (1961).
S. D. Drell:Phys. Rev. Lett.,5, 278 (1960).
S. D. Drell andK. Hiida:Phys. Rev. Lett.,7, 199 (1961).
G. Cocconi, A. W. Diddens, E. Lillethun andA. M. Wetherell:Phys. Rev. Lett.,6, 231 (1961).
D. Amati, S. Fubini, A. Stanghellini andM. Tonin:Nuovo Cimento,22, 569 (1961).
M. Nauenberg andA. Pais:Phys. Rev.,123, 1958 (1961), Sect.2.
ref. (11). Here the smallness of such terms is inferred by phase-space considerations, without referring to the presence of a resonance inσ 1.
G. Cocconi:Phys. Rev.,111, 1699 (1958).
F. Salzman andG. Salzman:Phys. Rev.,121, 1541 (1961).
V. B. Berestetski andI. Ya. Pomeranchuk:Soviet Physics, JETP,12, 752 (1961); andNucl. Phys.,22, 629 (1961).
W. J. Fickinger, E. Pickup D. K. Robinson andE. O. Salant:Phys. Rev. Lett.,7, 196 (1961).
