Study of Hadron Properties in QCD with Finite Temperature and/or Density.

量子色动力学(QCD)是在低温低密度条件下的禁色，真空处于手征对称性破缺阶段。人们认为，当温度和/或密度变高时，真空将经历到一个新的基态的相变，在那里色度被解除限制，手征对称性必须恢复。阐明相变性质的非微扰方法。在这个研究项目的第一阶段，一个全新的奇异强子--五夸克被发现，并引起了人们对这种新情况的极大兴趣。从这次事件开始，奇异强子及其结构和产生机制，以及普通强子的奇异多夸克成分的主题成为热门。我们从有限温度和有限密度QCD的角度研究了奇异强子。主要研究结果如下：(1)QCD求和规则方法中的奇异强子的五夸克和谱：我们首次在QCD的基础上利用QCD求和规则技术对五夸克的质量和量子数进行了分析。我们发现，正宇称五夸克不太可能位于低质量区域。我们还提出了一种区分强子中不同夸克数目的分量的方法。我们将该方法应用于标量介子和Lambda^*重子，它们含有主要的奇异分量。(2)五夸克和奇异强子的晶格QCD分析：我们分析了猝灭晶格QCD中的五夸克谱。为了区分共振和连续体，我们提出了扭曲边界公式，并验证了其有效性。

Quantum Chromodynamics (QCD) is confining color in low-temperature and low density and the vacuum is in the chiral-symmetry breaking phase. It is believed that when the temperature and/or density get higher, the vacuum goes through a phase transition to a new ground state where color is de-confined and chiral symmetry must be restored. Non-perturbative approaches to clarify the properties of the phase transition. At the first stage of this research project, a totally new exotic hadron, pentaquark, was discovered and much interest was paid in this new situation. Starting with this event, the subjects of exotic hadrons, their structure and production mechanism, as well as exotic multi-quark components of ordinary hadrons become hot. We have studied the exotic hadrons from the viewpoints of finite temperature and density QCD.The main results of the research were itemized.(1)Pentaquark and spectrum of the exotic hadrons in the QCD sum rule approach :We performed the first analysis of the pentaquark mass and quantum numbers based on the QCD, using the QCD sum rule technique. We found that the positive-parity pentaquarks are not likely to be in the low-mass region. We also proposed a method which distinguish the components of different number of quarks in a hadron. We applied the method to scalar mesons as well as Lambda^* baryon and they contain major exotic components.(2)Lattice QCD analysis of pentaquarks and exotic hadrons :We have analyzed pentaquark spectrum in the quenched lattice QCD. In order to distinguish a resonance from continuum, we proposed a twisted-boundary prescription and confirmed its effectiveness.