Vector meson dominance and ρ-ω mixing

The scale of a phenomenologically successful charge-symmetry-violating nucleon-nucleon interaction, that attributed to meson exchange with a $\Delta I=1\mathrm{}$ ρ-ω transition, is set by the Coleman-Glashow SU(2)-breaking tadpole mechanism. A single tadpole scale has been obtained from symmetry arguments, electromagnetic meson and baryon measured mass splittings, and the observed isospin-violating $(\Delta I=1)$ decay $\overrightarrow{\omega }{\pi }^{+}{\pi }^{-}$. The hadronic realization of this tadpole mechanism lies in the $I=1\mathrm{}$ $a_0$ scalar meson. We show that measured hadronic and two-photon widths of the $a_0$ meson, with the aid of the vector meson dominance model, recover the universal Coleman-Glashow tadpole scale.