MEDIUM MODIFICATIONS TO THE OMEGA-MESON MASS IN THE WALECKA MODEL

We calculate the effective mass of the omega meson in nuclear matter i n a relativistic random-phase approximation to the Walecka model. The dressing of the meson propagator is driven by its coupling to particle -hole pairs and nucleon-antinucleon (N NBAR) excitations. We report a reduction in the omega-meson mass of about 170 MeV at nuclear-matter s aturation density. This reduction arises from a competition between th e density-dependent (particle-hole) dressing of the propagator and vac uum polarization (N NBAR pairs). While density-dependent effects lead to an increase in the mass proportional to the classical plasma freque ncy, vacuum polarization leads to an even larger reduction caused by t he reduced effective nucleon mass in the medium.