COMPOSITE NUCLEONS AND THE DIRAC SEA

Effects associated with the Dirac sea of nucleons have been proposed as important to several nuclear physics problems. The simplest interpretation of these effects is in terms of virtual NNBAR pairs. Here it is argued that the composite nature of the nucleon probably suppresses the contribution of NNBAR pairs compared to what is expected in naive Dirac hole theory. This is made plausible by studying tractable systems of interacting composite fermions. These systems include general topological soliton models in 1 + 1 dimensions, the exactly solvable massive Thirring model and large-N(c) QCD. It is convenient to discuss these models in terms of a compositeness parameter c = MR, where M and R are the mass and intrinsic size of the composite fermion. It is found on general theoretical grounds that for these systems in the limit c --> infinity the NNBAR pairs contributions are smaller than any power law in c. The successful Dirac phenomenology of intermediate energy proton-nucleus scattering can be reconciled with this suppression of virtual NNBAR. The "z graphs' in the phenomenology, however, should not be interpreted as arising from virtual NNBAR pairs. One-nucleon-loop contributions in quantum hadrodynamics do appear to be suppressed.