Resonances and the Weinberg-Tomozawa 56-baryon-35-meson interaction

Vector meson degrees of freedom are incorporated into the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian by using a scheme which relies on spin-flavor SU(6) symmetry. The corresponding Bethe-Salpeter approximation successfully reproduces previous SU(3)-flavor WT results for the lowest-lying s-wave negative-parity baryon resonances, and it also provides some information on the dynamics of the heavier ones. Moreover, it also predicts the existence of an isoscalar spin-parity ^- K^*N bound state (strangeness +1) with a mass around 1.7-1.8GeV, unstable through K^* decay. Neglecting d-wave KN decays, this state turns out to be quite narrow ( Γ≤15MeV) and it might provide clear signals in reactions like γp→ˉ⁰ pK ⁺ π ^- by looking at the three-body pK ⁺ π ^- invariant mass.