Unfactorizing Polychromatic Penguins

Firstly, I report on a recent work -carried out with T. Hambye and E. de Rafael- on how to use the large- N c expansion to calculate unfactorized contributions from the strong penguin operators, and their impact on observables such as e′/e and the Δ I = 1/2 rule. Secondly, based on work done with M. Golterman, I explain how this calculation allows one to predict some rather dramatic consequences for quenched QCD. This may help explain the present discrepancy between lattice and experimental results for e′/e . The emphasis of this article is put on the explanation of the method of calculation used, which is fully analytic. This allows one to build some intuition and understand the role played by the different hadronic scales in determining the size of the different contributions.