30,226 research outputs found

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

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    The spectra of the scalar (σ\sigma) and vector (ω\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 σ\sigma-ω\omega mixing and the decay of the σ\sigma into 2π2\pi change the spectra of σ\sigma and ω\omega mesons considerably. As in Quantum Hadrodynamics we find a remarkable spectral change in the σ\sigma meson and the longitudinal mode of the ω\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

    Hyperons in nuclear matter

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    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 Λ\Lambda feels more attractive force than the \Sigma or \Xi in matter.Comment: 9 pages, 6 figure

    Naturalness in the quark-meson coupling model

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    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

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    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

    Effect of nucleon structure variation on the longitudinal response function

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    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 (σ\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