VENEZIANO GHOST VERSUS ISOSPIN BREAKING

It is argued that an account for the Veneziano ghost pole, appearing in the resolution of the U(1) problem, is necessary for understanding isospin violation in the pi-eta-eta' system. By virtue of a perturbative expansion around the SU(2)v (m(u) = m(d)) symmetric Veneziano solution, we find that the ghost considerably suppresses isospin-breaking gluon and s-quark matrix elements. We further speculate on a few cases where the proposed mechanism can play an essential role. We discuss the isospin violation in meson-nucleon couplings and its relevance to the problem of charge asymmetric nuclear forces and the possible breaking of the Bjorken sum rule. It is shown that the ghost pole could yield an isospin violation of the order of 2% for the piN couplings and 20% for the Bjorken sum rule.