STRONG SU(2) BREAKING AND MASS SPLITTINGS IN PSEUDOSCALAR MESONS

The mass splittings within the SU(2) multiplets of pseudoscalar mesons (pi, K, D, B) are used as a laboratory to determine the mass differen ce between d and u quarks (current), through the simplest (two-point) quark-loop diagrams for the self-energies of the corresponding hadrons , together with the associated quark-condensate diagrams within the lo ops. The second-order e.m. correction is also calculated with a photon line joining the two opposite quark lines in the self-energy loop. Th e basic ingredient is a hadron-quark-vertex function generated from a vector-exchange-like (chirally invariant) four-fermion Lagrangian (wit h current quarks) under dynamical symmetry breaking (D chi SB), precal ibrated to spectroscopy and other important low-energy amplitudes. The results which are expressed as proportional to the u-d mass differenc e delta(c), but are otherwise free from any adjustable parameters, rep roduce in a rather accurate way all the SU(2) mass differences (from k aon to bottom) with delta(c) = 4.0 MeV, when all the three self-energy diagrams are included. The pion receives only e.m. contributions with a value 5.24 MeV.