VERTEX CORRECTIONS TO VACUUM POLARIZATION IN HADRONIC FIELD-THEORIES

Vacuum polarization is studied in a model with neutral vector mesons and Dirac baryons. The lowest-order polarization is known to produce a ghost pole when it is summed to all orders in the vector meson propagator. It is also known that the infrared structure of the meson-baryon (NN-omega) vertex in this model produces a proper vertex function that is strongly damped at large spacelike momentum transfer; this is analogous to the result first derived by Sudakov in quantum electrodynamics. When the model vertex function is approximated by its on-shell form and combined with the lowest-order polarization, the vacuum contributions are significantly reduced. The resulting random-phase approximation meson propagator has no ghost pole and is finite at large spacelike momenta. Implications and perspectives of this result and necessary extensions of this calculation are also discussed.