Density fluctuations in nuclear matter

Abstract

Variational computations of the binding energy per particle for various models of nuclear matter are reported. The main purpose is to compare the results corresponding to a «semi-crystallic» structure characterized by correlated density fluctuations of the four spin-isospin nucleon types, with those corresponding to the standard «Fermi gas» homogeneous and isotropic nuclear-matter structure. It is found that, in some cases, the semicrystallic configuration yields more overall attraction (actually less overall repulsion) than the Fermi-gas case, already at (mean) nuclear densities equal to the central density of ordinary (heavy) nuclei. This effect becomes more pronounced at higher (mean) nuclear densities; it can, in most cases, be attributed, at least in part, to the tensor component of the nuclear interaction, that averages to zero in the Fermi-gas case, and yields instead an attractive contribution in configurations with appropriately correlated density fluctuations of the four spin-isospin nucleon states. All computations are based on realistic one-boson exchange nucleon-nucleon potentials. The correlations associated with the strongly repulsive character of the nucleon-nucleon interaction at short range have not been properly accounted for. The results of this paper have therefore no immediate phenomenological implications; whether the effect displayed here is preserved when the repulsive core of the nucleon-nucleon interaction is properly taken into account (both in the computations with and without density fluctuations) remains an open question.