NUCLEAR-MATTER STUDIES WITH DENSITY-DEPENDENT MESON-NUCLEON COUPLING-CONSTANTS

Due to the internal structure of the nucleon, we should expect, in gen eral, that the effective meson nucleon parameters may change in nuclea r medium. We study such changes by using a chiral confining model of t he nucleon. We use density-dependent masses for all mesons except the pion. Within a Dirac-Brueckner analysis, based on the relativistic cov ariant structure of the NN amplitude, we show that the effect of such a density dependence in the NN interaction on the saturation propertie s of nuclear matter, while not large, is quite significant. Due to the density dependence of the g(sigma NN), as predicted by the chiral con fining model, we find, in particular, a looping behavior of the bindin g energy at saturation as a function of the saturation density. A simp le model is described, which exhibits looping and which is shown to be mainly caused by the presence of a peak in the density dependence of the medium modified sigma N coupling constant at low density. The effe ct of density dependence of the coupling constants and the meson masse s tends to improve-the results for EIA and density of nuclear matter a t saturation. From the present study we see that the relationship betw een binding energy and saturation density may not be as universal as f ound in nonrelativistic studies and that more model dependence is exhi bited once medium modifications of the basic nuclear interactions are considered.