Electromagnetism in nonleptonic weak interactions

We construct a low-energy effective field theory that permits the complete treatment of isospin-breaking effects in nonleptonic weak interactions to n ext-to-leading order. To this end, we enlarge the chiral Lagrangian describ ing strong and DeltaS = 1 weak interactions by including electromagnetic te rms with the photon as additional dynamical degree of freedom. The complete and minimal list of local terms at next-to-leading order is given. We perf orm the one-loop renormalization at the level of the generating functional and specialize to K --> pi pi decays. (C) 2000 Elsevier Science B.V. All ri ghts reserved.