Vector Mesons in Nuclear Medium – an Effective Lagrangian Approach –

Effective masses of ρ and ω mesons in nuclear medium are studied in a hadronic effective theory. Both the pole position and the screening mass decrease in nuclear matter due to the polarization of the nucleon Dirac sea. The physical origin of the decrease is a reduction of the wave function renormalization constant induced by the tensor (vector) interaction of the ρ (ω) with the nucleon. Relation to the results of the QCD sum rules is also discussed. 1 1. INTRODUCTION. Effective masses of the vector mesons (ρ, ω, φ) in nuclear medium [1, 2] have recently attracted wide interests. The decrease of the masses in nuclei is interpreted as an evidence of the partial restoration of chiral symmetry [3]. Direct experiments using the e + e − production in γ − A and p − A processes are also proposed to check the mass shift [4].