The following remarks are made on the applicability of the double dispersion approach to the Beth-Salpeter equation introduced previously. 1) Any invariant solution of the Bethe-Salpeter equation in ladder approximation satisfies the double dispersion representation when the total energy-momentum is space-lake. 2) There are some exceptional invariant solutions which are not given by the previous method in the equal-mass case, but the existence of such solutions is very unlikely in the unequal-mass case. 3) In the case of the general separated kernel the previous results give the correct solutions even if the kernel does not reproduce the double dispersion representation.

During the past year notable progress was made in several laboratories on design for linear accelerators in the energy range up to and above 1 Bev. Interest in linacs for this energy centers on two possible applications: first, as injectors for 300 to 1000 Bev synchrotrons, and second, as sources of intense meson beams. To review this progress, a conference jointly sponsored by the Brookhaven National Laboratory and Yale University was held at Brookhaven during the week of August 20, 1962.

This note describes some results of the study of single pion production in π⁻-p interactions at 4.65 Bev/c, using the BNL 20" Hydrogen Bubble Chamber. It is well known that the observability of some of the particle resonances (e.g. 33 Isobar and η) varies markedly with the energy of the incident particle. The ρ meson has been observed in π⁻-p interactions at 1.25 Bev/c and 1.9 Bev/c incident pion energies. Evidence will be shown that this resonance persists with the much higher incident pion energy used in the present experiment.

Using requirements of analyticity and the unitarity of the S-matrix we obtain the dependence of a transition amplitude on the invariant mass of two particles strongly coupled to other two particle channels. As an example, we consider the production of a Σπ state near the Y*₀ resonance assuming it is coupled to a KN state in an s 1/2 state.