A sum rule approach to the violation of Dashenʹs theorem Original Research Article

A classic sum rule by Das et al. is extended to seven of the low-energy constants K1, introduced by Urech, which parametrize electromagnetic corrections at chiral order O(e2p2). Using the spurion formalism, a simple convolution representation is shown to hold and the structure in terms of the chiral renormalization scale, the QCD renormalization scale and the QED gauge parameter is displayed. The role of the resonances is studied as providing rational interpolants to relevant QCD n-point functions in the Euclidean domain. A variety of asymptotic constraints must be implemented which have phenomenological consequences. A current assumption concerning the dominance of the lowest-lying resonances is shown clearly to fail in some cases.