SU(3)-subsector approach to hadron properties and the classification problem

I review the essential features and main applications of the SU(3)-subsector approach to hadron properties, developed in the last two years by Dattoli, Prosperi, Camiz, and myself. Such a formalism is based on the three-quark sectors of SU(N), which are obtained by picking out three of the N quarks in all possible ways. The sectors can be divided in four classes, according to the charges of the quarks constituting them, and an SU(3) algebra can be defined for any class of sectors, by introducing generalized operators (like hypercharge and isospin) induced by the SU(N) generators. General formulae are derived for baryon magnetic moments, both in the case of an exact symmetry and of a partially broken one. Mass sum rules for hadrons are discussed by means of a generalized Gell-Mann-Okubo mass formula. Lastly, it is stressed that the effectiveness of the formalism is better understood if one looks on SU(N) as a classification group for hadrons, rather than concerning hadron structure. In this connection, a till open legacy of Heisenberg about quark hypothesis is singled out