Resonance Contributions to the Electromagnetic Low Energy Constants of   Chiral Perturbation Theory
  The effective chiral Lagrangian of the strong and electromagnetic interactions of the pseudoscalar mesons at low energies depends on a set of low energy constants. We determine the contributions to the electromagnetic coupling constants at order $O(e^2 p^2)$, which arise from resonances within a photon loop. We give some implications of our results, in particular we discuss in detail the effects on the corrections to Dashen's theorem. 
Robert Baur and Res Urech