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

量子色动力学（QCD）是指在低温低密度下，真空处于手征对称性破缺阶段的禁闭色。据信，当温度和/或密度变得更高时，真空经历相变到新的基态，其中颜色被解除限制并且手征对称性必须恢复。用非微扰方法阐明相变的性质。在这个研究计划的第一阶段，一个全新的奇异强子--五夸克态被发现，引起了人们极大的兴趣。从这一事件开始，奇异强子、奇异强子的结构和产生机制，以及奇异强子的多夸克成分成为研究热点。本文从有限温度和有限密度QCD的观点出发，对奇异强子进行了研究，并列举了主要的研究结果。（1）QCD求和规则方法中的五夸克态和奇异强子谱：我们首次利用QCD求和规则方法对五夸克态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在低质量区。我们还提出了一种区分强子中不同夸克数的组分的方法。我们把这个方法应用于标量介子和λ ^* 重子，它们都含有主要的奇异成分。（2）五夸克态和奇异强子的格点QCD分析：我们分析了淬灭格点QCD中的五夸克态谱。为了区分共振和连续，我们提出了扭曲边界的规定，并证实了它的有效性。

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.