Towards a quantitative understanding of the Delta I=1/2 rule
  A recently proposed strategy to quantify the role of the charm quark mass in the $\Delta I=1/2$ rule is reviewed. Results for the low-energy couplings of the $\Delta S=1$ chiral effective Hamiltonian in a theory with a light charm quark (GIM limit) are obtained through a matching of three-point correlation functions computed in Chiral Perturbation Theory and in quenched lattice QCD. We observe a large $\Delta I=1/2$ enhancement, which is not large enough to explain the experimental result, but suggests significant long-distance contributions to the physical $\Delta I=1/2$ which are unrelated to penguin contractions or operators. 
P. Hernandez