LIGHT-QUARK MASSES AND ISOSPIN VIOLATION

Isospin-violating effects arising from a nonvanishing quark mass difference md-mu are discussed, in particular for the +-0 mass-difference question and for 3 and +e+ decays. The role of the strong anomaly is emphasized, and exploited to bring out certain relations among heavy-quark, light-quark, and gluon operator matrix elements. The anomaly suppresses isospin-violating effects that might otherwise be substantial for the Bjorken electroproduction sum rule. © 1979 The American Physical Society.