Rescattering Effects, Isospin Relations and Electroweak Penguins in B -> pi K Decays

It is argued that, in the presence of soft final-state interactions, the diagrammatic amplitude approach adopted in many analyses of hadronic B decays into light mesons can be misleading when used to deduce the unimportance of certain decay topologies. With the example of B -> pi K decays, it is shown that the neglect of so-called annihilation and colour-suppressed amplitudes (including electroweak penguins), as well as penguin contributions involving an up-quark loop, is not justified. The implications for the Fleischer-Mannel bound on the angle gamma of the unitarity triangle, and for the CP asymmetry in the decays B^± -> pi^± K^0, are pointed out.