Long-Range Forces in Meson-Baryon Systems

We have evaluated single-particle-exchange forces at low energies for all two-particle meson-baryon states with angular momentum from S1/2 to H11/2. Using real masses and SU(3) coupling constants normalized to experiment, we considered the exchange of the following SU(3) multiplets: baryon octet, P3/2 decuplet, Y₀^_*(1520) singlet, vector-meson octet (vector and tensor coupling), and D3/2 octet. The forces were classified in the direct channel according to SU(3) irreducible representations, an association which is inexact owing to mass splitting but which nevertheless allows us to relate resonant states thereby generated in various isospin and hypercharge channels. We found strong attractive forces in the P1/2, F5/2 octet, P3/2, F7/2 decuplet, and D3/2 singlet states. In particular, the exchange of vector mesons was observed to play a significant role in all these channels. Our analysis suggests that the D5/2 Y₁^_*(1765) be assigned to an octet, the other members of which are relatively inhibited by mass-splitting effects to the extent that they may not be observable experimentally as resonances. No forces likely to generate resonances in the multiplet 27 were found.