QCD-duality aproach to non-leptonic weak transitions: Towards an understanding of the vertical strokeΔIvertical stroke=1/2 rule

The progress done in the QCD-duality analysis of strangeness changing nonleptonic weak transitions is reviewed. The method combines the information provided by the effective chiral realization of QCD at long distances with its perturbative short-distance behaviour, via a duality approach. Special attention is given to the failure of the earlier leading-logarithm calculations in explaining the observed vertical strokeΔIvertical stroke=1/2 K→ππ amplitude. It is shown that the next-to-leading αs corrections to the vertical strokeΔIvertical stroke=1/2 correlator are enormous, and with the appropriate sign to produce the required enhancement. (orig.)