the small charged-current contribution and through the electroweak penguin operators in the low-energy effective weak Hamiltonian [@Heff]. In the SM, these operators are induced by penguin and box diagrams involving the exchange of weakly interacting $W$ and $Z$ bosons, or of a photon. Here we point out that in a large class of New Physics models such effects can be mediated by “trojan” electroweak penguins, which are neither (pure) penguins nor of electroweak origin. Nevertheless, at low energies their effects are parameterized by an extension of the usual basis of electroweak penguin operators. We will explore examples where trojan penguins are induced by tree-level couplings, e.g., models with an extra $Z'$ boson, or pure strong-interaction processes, e.g., gluino box diagrams in SUSY models.

In the present work we calculate the Wilson coefficients of the hadronic electroweak penguin operators in the effective weak Hamiltonian in an extended operator basis and for a large class of New Physics models. We then explore the phenomenological consequences of these new, isospin-violating contributions for weak-interaction observables. This serves two purposes: first, it allows us to derive bounds on New Physics parameters, which in some cases improve upon existing bounds derived from other processes; secondly, it 