Chiral Lagrangian with vector and axial vector meson for π+ - π0 mass difference

It is shown that the simple expression for the forward virtual Compton scattering on a soft pion for the π+ - π0 electromagnetic mass difference calculation usually obtained from Current Algebra and Weinberg sum rules can be derived in a simple manner from a chiral Lagrangian with vector and axial vector mesons. We also discuss the relation between the chiral Lagrangian approach and the dispersion relation for the Compton amplitude.