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Restoration of Chiral Symmetry in Nuclear medium

核介质中手性对称性的恢复

基本信息

批准号：
12640263
负责人：
HATSUDA Tetsuo
金额：
$ 2.5万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

Dynamical breaking of chiral symmetry is one of the most characteristic pheno mena of quantum chromodynamics (QCD) which is the fundamental theory of strong interactions. Because of this phenomenon, the pion behaves as a pseudo Nambu-Goldstone boson and it leads to the long range part of the nuclear force as well as the nuclear bindings from multi-pion exchange. In this sense, even the nuclear stability is deeply related to chiral symmetry.For past few years, we have focused on the properties of the pion and other mesons in nuclei and studied the role of chiral symmetry in nuclei.We had two major findings ;* The pion pair in I=J=0 channel has a broad resonance called the sigma-meson. Due to the partial restoration of chiral symmetry, the mass and the width of the sigma meson tend to decrease in nuclear medium. This leads to a possible long-lived bound state of the sigma with medium-heavy nuclei. We have studied the reactions such as (d,t) and (d,He3) and have shown that there arises a characteristic structure in the reaction cross section near 2-pion threshold.* The relation between the sigma-meson and the rho-meson, which are both resonances in the pi-pi scattering, has not been known before. We have treated both mesons in a same footing using the N/D method combined with the chiral perturbation theory. By generalizing this approach to the pion pair in the nuclear medium, we found that the sigma and the rho have simultaneous softening in nuclear medium. Furthermore, their behavior is dictated by a single function : namely we found a universality of the softening of hadronic spectra in matter.

手性对称性的动力学破缺是强相互作用的基础理论——量子色动力学（QCD）最典型的现象之一。由于这种现象，π介子表现为伪南部-戈德斯通玻色子，并导致核力的长程部分以及多π介子交换的核结合。从这个意义上说，即使是核稳定性也与手性对称性密切相关。在过去的几年里，我们一直关注原子核中π介子和其他介子的性质，研究手性对称性在原子核中的作用。我们有两个主要发现；* I=J=0通道中的π介子对具有广泛的共振，称为西格玛介子。由于手性对称性部分恢复，西格玛介子的质量和宽度在核介质中趋于减小。这导致西格玛与中重原子核可能存在长寿命束缚态。我们研究了 (d,t) 和 (d,He3) 等反应，并表明在 2-p 介子阈值附近的反应截面中出现了特征结构。* sigma-介子和 rho-介子（两者都是 pi-pi 散射中的共振）之间的关系以前未知。我们使用 N/D 方法结合手性微扰理论以相同的基础对待两个介子。通过将此方法推广到核介质中的 π 介子对，我们发现 sigma 和 rho 在核介质中同时软化。此外，它们的行为由单一函数决定：即我们发现物质中强子光谱软化的普遍性。