QCD Sum Rules and Chiral Symmetry Breaking

We investigate, in the context of QCD sum rules, the role of Goldstone bosons arising from chiral symmetry breaking, especially on the need of matching the world of hadrons to that of some effective chiral quark theory. We show that the proposal yields predictions on induced condensates which are just needed to reproduce the observed value of the strong $\pi NN$ coupling constant. The result indicate that the observed large $\pi NN$ coupling comes primarily from the nonperturbative induced-condensate effect. On the other hand, the prediction on the parity-violating weak $\pi NN$ coupling, $\mid f_{\pi NN}\mid \sim 2.6 \times 10^{-7}$ (at $M_B \sim 1.0 \, GeV$), is in good agreement with the value ($\sim 2 \times 10^{-7}$) obtained by Adelberger and Haxton from an overall fit to the existing data, but may appear to be slightly too large (but not yet of statistical significance) as compared to the most recent null experiment. Altogether, it is clear that the proposal of matching onto a chirally broken effective theory should enable us to treat, in a quantitative and consistent manner, the various nonleptonic strong and weak processes involving Goldstone bosons.