Vector meson dominance

In physics, vector meson dominance was a model developed by J. J. Sakurai in the 1960s before the advent of QCD in order to describe interactions between photons and hadronic matter. In particular the hadronic components of the photon polarization tensor consist of the lightest vector mesons $\rho ,\omega$ and $\phi$. Therefore interactions between photons and hadronic matter occur by the exchange of a hadron between the dressed photon and the hadronic target.

Hadronic contribution to the photon propagator in the VMD model