Nucleon structure effect on the longitudinal response function

Using the quark-meson coupling model, we study the longitudinal response function for quasielastic electron scattering from nuclear matter within relativistic RPA. In QMC the coupling constant between the scalar meson and the nucleon is expected to decrease with increasing nuclear density. Furthermore, since the electromagnetic form factors of the in-medium nucleon are modified at the same time, the longitudinal response function and the Coulomb sum are reduced by a total of about 20% in comparison with the Hartree contribution.Comment: 4 pages with 2 ps files, talk at "Int. Conference on Quark Nuclear Physics", Adelaide, Australia, 21 - 25 Feb. 2000, to be published in Nucl. Phys. A (2000

Quark-Meson Coupling Model for a Nucleon

The quark-meson coupling model for a nucleon is considered. The model describes a nucleon as an MIT bag, in which quarks are coupled to scalar and vector mesons. A set of coupled equations for the quark and the meson fields are obtained and are solved in a self-consistent way. It is shown that the mass of a nucleon as a dressed MIT bag interacting with sigma- and omega-meson fields significantly differs from the mass of a free MIT bag. A few sets of model parameters are obtained so that the mass of a dressed MIT bag becomes the nucleon mass. The results of our calculations imply that the self-energy of the bag in the quark-meson coupling model is significant and needs to be considered in doing the nuclear matter calculations.Comment: 3 figure

Hyperons in nuclear matter

The chiral version of the QMC model, in which the effect of gluon and pion exchanges is included self-consistently, is applied to the hyperons in a nuclear medium. The hyperfine interaction due to the gluon exchange plays an important role in the in-medium baryon spectra, while the pion-cloud effect is relatively small. At the quark mean-field level, the $\Lambda$ feels more attractive force than the \Sigma or \Xi in matter.Comment: 9 pages, 6 figure

Effect of nucleon structure variation on the longitudinal response function

Using the quark-meson coupling (QMC) model, we study the longitudinal response function for quasielastic electron scattering from nuclear matter. In QMC the coupling constant between the scalar ($\sigma$) meson and the nucleon is expected to decrease with increasing nuclear density, because of the self-consistent modification of the structure of the nucleon. The reduction of the coupling constant then leads to a smaller contribution from relativistic RPA than in the Walecka model. However, since the electromagnetic form factors of the in-medium nucleon are modified at the same time, the longitudinal response function and the Coulomb sum are reduced by a total of about 20% in comparison with the Hartree contribution. We find that the relativistic RPA and the nucleon structure variation both contribute about fifty-fifty to the reduction of the longitudinal response.Comment: 14 pages, including 3 ps file

Spectral change of sigma and omega mesons in a dense nuclear medium

The spectra of the scalar ($\sigma$) and vector ($\omega$) mesons in nuclear matter are studied in detail using the quark-meson coupling (QMC) model. It is shown that above normal nuclear matter density the effects of $\sigma$-$\omega$ mixing and the decay of the $\sigma$ into $2\pi$ change the spectra of $\sigma$ and $\omega$ mesons considerably. As in Quantum Hadrodynamics we find a remarkable spectral change in the $\sigma$ meson and the longitudinal mode of the $\omega$ meson, namely a two-peak structure.Comment: 14 pages + 9 ps files for 4 figs. The paper was revised, and accepted for publication in Physics Letters

Charge Symmetry Violation in Nuclear Physics

The study of charge symmetry violation in nuclear physics is a potentially enormous subject. Through a few topical examples we aim to show that it is not a subject of peripheral interest but rather goes to the heart of our understanding of hadronic systems.Comment: Invited talk at the Int. Conference on Weak and Electromagnetic Interactions in Nuclei, Osaka, June 12-16 199

Pseudospin and Deformation-induced Gauge Field in Graphene

The basic properties of $\pi$-electrons near the Fermi level in graphene are reviewed from a point of view of the pseudospin and a gauge field coupling to the pseudospin. The applications of the gauge field to the electron-phonon interaction and to the edge states are reported.Comment: 27 pages, 7 figure