Chiral perturbation theory and vector mesons in e⁺e^-→π⁰γ and π⁰ℓ⁺ℓ^-

The low-energy cross-section for e+e-→π0γ is predicted in χPT at next-to-leading order and the saturation of its counter-terms by vector-meson resonances is confirmed. Further details on this saturation by vector mesons are discussed for e+e-→π0μ+μ -. Cross-sections are predicted from threshold up to the ω-mass region for different choices of the relevant parameters in the lagrangian. It is suggested that measurements of these cross-sections at low-energy high luminosity e+e- machines, like DAPHNE, will allow to distinguish between different sets of parameters. © 1992.