MEDIUM DEPENDENCE OF THE VECTOR-MESON MASS - DYNAMICAL AND OR BROWN-RHO SCALING/

We discuss the similarities and differences for the theories of Rapp, Wambach and collaborators (called R/W in short) and those based on Bro wn-Rho scaling (called B/R), as applied to reproduce the dileptons mea sured by the CERES collaboration in the CERN experiments. In both theo ries the large number of dileptons at invariant masses similar to m(rh o)/2 are shown to be chiefly produced by a density-dependent p-meson m ass. In R/W the medium dependence is dynamically calculated using hadr onic variables defined in the matter-free vacuum. In B/R scaling it fo llows from movement towards chiral symmetry restoration due to medium- induced vacuum change, and is described in terms of constituent (or qu asiparticle) quarks. We argue that the R/W description should he relia ble up to densities somewhat beyond nuclear density, where hadrons are the effective variables. At higher density there should be a crossove r to constituent quarks as effective variables scaling according to B/ R. In the crossover region, the two descriptions must be ''dual.'' For the moment there is a factor greater than or similar to 2 difference between the predicted number of dileptons from the two theories, B/R s caling giving the larger number. We show that a substantial. factor re sults because in B/R, fluctuation is made about the ''vacuum'' modifie d by density, so that a different mass m(rho) appears in the Lagrangi an for each density, thereby rendering residual interactions between h adrons weaker, whereas R/W calculate a mass m(rho) for each density w ith an effective Lagrangian defined in the zero-density vacuum, which has the free m(rho) in the Lagrangian and hence the coupling is strong . Thus more diagrams need to be incorporated in R/W to reduce the disc repancy. On the other hand, R/W include processes which may be additio nal to these of B/R.. These constitute several (smaller) corrections. It is argued that the N-hole state [N*(1520) N-1](1-) is almost compl etely rho-meson like in content; i.e., it is, to a good approximation, just the state rho\0] that would be produced by the rho-meson field a cting on time nuclear ground state (finite temperatures are not expect ed to disturb this picture by much).