Hadron electromagnetic mass differences

Mass differences between members of isotopic-spin multiplets of hadrons are calculated in the MIT bag model. All low-mass SU(4) multiplets of spin 0, 1/2, 1, and 3/2 particles are considered. Both Coulomb and magnetic contributions to mass differences are evaluated without the assumption of SU(6) -degenerate intermediate states. The mass difference between the ''up'' and the ''down'' quarks inside the bag is not (necessarily) taken to be a constant; we propose a parameterization for it that works well for its contribution to known hadron electromagnetic mass differences. Based on the parametrization we present a class of sum rules for charmed-particle electromagnetic mass differences