QCD Chiral Phase Transition and Its Microscopic Origin  

量子色动力学手征相变及其微观起源

作　　者：DING Hengtong 丁亨通(华中师范大学夸克与轻子物理教育部重点实验室和粒子物理研究所,武汉430079)

机构地区：[1]Key Laboratory of Quark and Lepton Physics(MOE)and Institute of Particle Physics,Central China Normal University,Wuhan 430079,China

出　　处：《原子核物理评论》2024年第1期109-116,共8页Nuclear Physics Review

基　　金：国家重点研发计划项目(2022YFA1604900);国家自然科学基金资助项目(12293064,12293060,12325508)。

摘　　要：The transition of strong-interaction matter from the hadronic phase to the quark-gluon plasma phase is a rapid crossover but not a true phase transition in nature.The true phase transition of strong-interaction matter is expected to exist only in certain limits,e.g.chiral limit of massless quarks and etc.In this contribution to CNPC2023 Special Issue we present our recent studies on the true phase transition of strong-interaction matter in the chiral limit of massless quarks as well as its microscopic origin.The study is based on(2+1)-flavor lattice QCD simulations using highly improved staggered fermions,with pion masses ranging from 160 MeV down to 55 MeV.Utilizing a newly proposed method to compute the quark mass derivatives of the Dirac eigenvalue spectrum on the lattice,it is found that the axial U(1)anomaly is still manifested at 1.6T_(c),with a microscopic origin consistent with the dilute instanton gas approximation.Furthermore,based on lattice QCD results and a generalized Banks-Casher relation,it is found that the macroscopic singularity of the chiral phase transition is encoded in the correlation of the Dirac eigenvalue spectrum.Future research directions along these findings are also discussed,including the investigation of the temperature range between T_(c) and 1.6 T_(c) to understand the breakdown of the dilute instanton gas approximation and its connection to the chiral phase transition.强相互作用主导的核物质从强子相到夸克-胶子等离子体相的转变是一个快速的平滑过渡,而不是真实意义上(即存在发散临界行为)的相变。量子色动力学真实意义上的相变只存在于某些特定的极限中,比如夸克质量为零的手征极限等极限条件。在本工作中将展示我们最近关于手征相变及其微观起源的研究。这些研究均基于(2+1)-味的、采用了高度改进的交错费米子的、π介子质量为160 MeV到55 MeV的格点量子色动力学模拟。基于新提出的方法计算格点上Dirac本征值谱的夸克质量导数,发现轴U(1)反常在1.6T_(c)时仍然存在,其微观起源与稀疏瞬子气体近似相一致。此外,基于格点QCD结果和提出的广义Banks-Casher关系,发现手征相变的宏观奇异性体现在Dirac本征值谱的关联之中。对未来相关研究方向做了展望,包括研究温度在T_(c)到1.6T_(c)之间的QCD相变行为来理解稀疏瞬子气体近似的失效及其与手征相变的联系。

关 键 词：QCD phase structure Dirac eigenvalue spectrum axial anomaly chiral symmetry CRITICALITY 

分 类 号：O571.6[理学—粒子物理与原子核物理]