Trojan penguins and isospin violation in hadronic B decays

Some rare hadronic decays of B mesons, such as B → πK, are sensitive to isospin-violating contributions from physics beyond the Standard Model. Although commonly referred to as electroweak penguins, such contributions can often arise through tree-level exchanges of heavy particles, or through strong-interaction loop diagrams. The Wilson coefficients of the corresponding electroweak penguin operators are calculated in a large class of New Physics models, and in many cases are found not to be suppressed with respect to the QCD penguin coefficients. Several tests for these effects using observables in B^± →πK decays are discussed, and nontrivial bounds on the couplings of the various New Physics models are derived.