
It is shown that in the 70 and 700 SU(6) irreducible spaces, the SU(6) extension of the WeinbergTomozawa (WT) swave mesonbaryon interaction incorporating vector mesons (hepph/0505233) scales as O(Nc(0)), instead of the wellknown O(Nc(1)) behavior for its SU(3) counterpart. However, the WT interaction behaves as order O(Nc(1)) within the 56 and 1134 mesonbaryon spaces. Explicit expressions for the WT couplings (eigenvalues) in the irreducible SU(2N(F)) spaces, for arbitrary NF and Nc, are given. This extended interaction is used as a kernel of the Bethe Salpeter equation, to study the large Nc scaling of masses and widths of the lowestlying negative parity swave baryon resonances. Analytical expressions are found in the Nc >infinity limit, from which it can be deduced that resonance widths and excitation energies (MRM) behave as order O(Nc(0)), in agreement with model independent arguments, and moreover they fall in the 70plet, as expected in constituent quark models for an orbital excitation. For the 56 and 1134 spaces, excitation energies and widths grow O(Nc(1/2)) indicating that such resonances do not survive in the large Nc limit. The relation of this latter Nc behavior with the existence of exotic components in these resonances is discussed. The interaction comes out repulsive in the 700.
