| Co-Investigator(Kenkyū-buntansha) |
TOKI Hiroshi Osaka University, RCNP,professor, 核物理研究センター, 教授 (70163962)
MATSUI Tetsuo Kyoto University, Yukawa Institute, Professor, 基礎物理学研究所, 教授 (00252528)
SAITO Sakae Nagoya University, Physics, Professor, 理学部, 教授 (40022694)
FUJITA Takehisa Nihon University, Physics, Professor, 理工学部, 教授 (80147694)
YAZAKI Koichi University of Tokyo, Physics, Professor, 大学院・理学系研究科, 教授 (60012382)
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| Research Abstract |
Conventionally a nucleus is assumed to be composed of nucleons, which interact with each other trough phenomenological strong interactions. The fundamental theory of hadorons, however, is quantum chromodynamics (QCD). The purpose of our project is to investigate the relationship between the conventional nuclear models and QCD.
The conventional nuclear models assume the strong interactions coming from meson exchanges between nucleons. Then, as the first step to QCD,we have studied a relativistic model (QHD) where both nucleon and meson degrees of freedom are explicitly taken into account. QHD has been shown to work very well for understanding low to intermediate energy phenomena.
In QHD,nucleons are described as an elementary particle. QMC assumes nucleons composed of three quarks which exchange mesons each other. The quark degrees of freedom have been found to explain the density-dependence of nucleon-meson interactions required in QHD.
Both QHD and QMC assume Lorentz scalar sigma meson to reproduce nuclear density and binding energy. It was a longstanding problem whether the sigma meson was fictitious or not. It has been shown that the QCD effective theory predicts the sigma meson. The meson mass in nuclear medium and the possibility to observe it experimentally have been also discussed. Moreover, according to the QCD effective theory, we have investigated other meson masses, baryon interactions and nucleon structure itself, and shown the usefulness of the effective theory. The confinement of quarks and the chiral symmetry breaking, which are not contained in most of the QCD effective theories, have been also explored extensively.
For our purpose it is very important to observe QCD phenomena directly in nuclear medium. As candidates of those phenomena, nuclear transparency and quark-gluon plasma have been studied in detail.
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