Analysis of 56-plet positive parity baryon decays in the 1/Nc expansion

The partial decay widths of positive parity baryons belonging to 56-plets of SU(6) are analyzed in the framework of the 1/Nc expansion. The channels considered are those with emission of a single pion, K or K-bar mesons, and the analysis is carried out to subleading order in 1/Nc and to first order in SU(3) symmetry breaking. The results for the multiplet [56,0+], to which the Roper resonance belongs, indicate a poor description at leading order, requiring important next to leading order corrections. For the multiplet [56,2+], the P-wave decays in the non-strange sector are well described at leading order, while the F-wave decays require the next to leading order corrections, which turn out to be of natural magnitude. SU(3) breaking effects are poorly determined, because only few decays with K meson in final state are established, and their widths are not known with sufficient accuracy.