Delta isobar masses, large N-c relations, and the quark model - art. no. 014032.

Motivated by recent remarks on the Delta(+) mass and comparisons between th e quark model and relations based on large-iri, with perturbative flavor br eaking, two sets of Delta masses consistent with these constraints are cons tructed. These two sets, based either on an experimentally determined mass splitting or a quark model of isospin symmetry breaking, are shown to be in consistent. The model dependence of this inconsistency is examined, and sug gestions for improved experiments are made. An explicit quark model calcula tion and mass relations based on the large-N-c limit with perturbative flav or breaking are compared. The expected level of accuracy of such relations is realized in the quark model, except for mass relations derived by combin ing others which correspond to different SU(6) representations. It is shown that the Delta(0) and Delta(++) pole masses and Delta(0) - Delta(+) = (Del ta(-) - Delta(++))/3 similar or equal to 1.5 MeV are more consistent with m odel expectations than the analogous Breit-Wigner masses and their splittin gs. [S0556-2821(99)02301-2].