Recovering relativistic nuclear phenomenology from the quark-meson coupling model

Abstract

The quark-meson coupling (QMC) model for nuclear matter, which describes nuclear matter as non-overlapping MIT bags bound by the self-consistent exchange of scalar and vector mesons is modified by the introduction of a density dependent bag constant. It is found that when the bag constant is significantly reduced in nuclear medium with respect to its free space value, large canceling isoscalar Lorentz scalar and vector potentials for the nucleon in nuclear matter emerge naturally. Such potentials are comparable to those suggested by relativistic nuclear phenomenology. This suggests that the modification of the bag constant in the nuclear medium may play an important role in low-and medium-energy nuclear physics.

Change of MIT bag constant in nuclear medium and implication for the EMC effect

“…B/B 0 ∼ 35 − 40% at the nuclear matter saturation density, the predictions for the rescaling parameter are in good agreement with those required to explain the depletion of the structure function observed in a range of nuclei. Such a large reduction of the bag constant, as shown in previous works [11,12], also implies large and canceling Lorentz scalar and vector potentials for the nucleon in nuclear matter which are comparable to those suggested by the relativistic nuclear phenomenology and finite-density QCD sum rules. This indicates that the reduction of bag constant and hence the increase of confinement size in nuclei may play important role in low-and medium-energy nuclear physics and the modified QMC model provides a useful framework to accommodate both the change of confinement size and the quark structure of the nucleon in describing nuclear phenomena.…”

“…[11][12][13]. This modification can lead to the recovery of relativistic nuclear phenomenology, in particular the large canceling isoscalar Lorentz scalar and vector potentials and hence the strong spin-orbit force for the nucleon in nuclear matter.…”

Modified quark-meson coupling model for nuclear matter

“…In a recent paper [15], the present authors have pointed out that the resulting small nucleon potentials in the QMC model stem from the assumption of fixing the bag constant at its free-space value, and that this assumption is questionable. We then included a density dependent bag constant and found that when the bag constant drops significantly in nuclear matter relative to its free-space value, the large potentials for nucleons in nuclear matter, as seen in the relativistic nuclear phenomenology and finite-density QCD sum rules, can be recovered.…”

Consistent thermodynamic treatment for a quark-mass density-dependent model

“…To illustrate the medium effects more transparently in theory, instead of first principle calculation, many authors introduced different hypothesis to represent the medium contributions, for example, supposed the density-dependent vacuum energy B(ρ) to modify QMC model [5,6], suggested the density-dependent NNρ coupling to address liquid-gas phase transition [7], and etc.. Employing these hypothesis, many physical properties of nuclear matter, quark matter, nucleon system and hyperon system had been discussed.…”