36,180 research outputs found
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
Spectral change of sigma and omega mesons in a dense nuclear medium
The spectra of the scalar () and vector () 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 -
mixing and the decay of the into change the spectra of
and mesons considerably. As in Quantum Hadrodynamics we find a
remarkable spectral change in the meson and the longitudinal mode of
the 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
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 feels more
attractive force than the \Sigma or \Xi in matter.Comment: 9 pages, 6 figure
Pseudospin and Deformation-induced Gauge Field in Graphene
The basic properties of -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
Naturalness in the quark-meson coupling model
The quark-meson coupling (QMC) model is examined using Georgi's ``naive
dimensional analysis''. We argue that the QMC model is quite natural as an
effective field theory for nuclei.Comment: 11pages, no fig., submitted to Phys. Lett.
HST/FOS Eclipse mapping of IP Pegasi in outburst
We report the results of a time-resolved eclipse mapping of the dwarf nova IP
Pegasi during the decline of its May 1993 outburst from HST/FOS fast
spectroscopy covering 3 eclipses in the ultraviolet spectral range.Comment: 1 page 0 figure
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