强外磁场下QCD物质相结构及临界行为特征研究

In recent years, people found strong magnetic field could be produced in the non-central collisions, albeit for a very short time in the study of high-energy heavy-ion collisions experiments. While on the surface of the compact star objects such as the neutron star, there also exist strong magnetic field. Under these backgroud, this project prepared to study the phase structures and critical behaviors of QCD matter in the strong external magnetic field by the method of model theory. First, we consider to introduce the chiral chemical potential and the isospin chemical potential and to investigate the effect of strong external magnetic field, temperature and corresponding chemical potential to QCD characters such as the chirality and deconfinement and so on. We will deeply discuss the chiral magnetic effect on the superfluidity and confinement, and then analyse about the meson mix and BEC-BCS superfluidity. Second, we will take the method of the phase transition analyse which are used in the condensed matter physics to study the symmetry of thermal and dense QCD matter system in a strong magnetic field. We will try to investigate the phase transition types, the transitin of critical behaviors at different critical points and the character of critical exponents in the view of universal.

近年来在高能重离子碰撞实验研究中发现，在非对心碰撞中能产生强的瞬时性磁场。而在致密星体如中子星表面，也存在强磁场。在此背景下，本项目旨在利用理论模型方法研究强外磁场下QCD物质相结构及临界行为特征。首先，考虑引入手征化学势和同位旋化学势，考察强外磁场、温度及相关化学势对QCD物质特性如手征性和禁闭性的影响，探讨手征磁效应对超流和禁闭的作用，分析介子混合及BEC-BCS超流等问题。然后，借鉴凝聚态物理中的相变分析方法，对强外磁场下的热密QCD物质系统进行对称性分析，从普适角度考察其相变类型，不同临界点处的临界行为过渡及临界指数特征等行为。

研究强外磁场对热密QCD物质超流性质的影响是本项目的主要内容。基于热平衡统计物理和虚时温度场论计算方法，我们得到有强外磁场和同位旋化学势存在时两味Nambu-Jona--Lasinio (NJL)和Polyakov-NJL (PNJL)模型的基本巨热力学势，讨论了序参量的相互耦合和对QCD物质相结构的影响，为实验学家进行能量扫描寻找QCD物质临界点提供了理论基础。结果表明：强外磁场对手征对称破缺有催化作用，van Alfen-de Hass振荡效应在热密QCD物质中也有体现，QCD物质相变临界点的位置朝高温低密区移动。研究难点在于：拉式量中的协变导数既包含电磁场分量，又包含规范场分量。有同位旋化学势时，传播子的逆矩阵出现非对角元，同时夸克味自由度分开；而外磁场的引入使得夸克三动量部分出现磁场，沿垂直于磁场方向准粒子能量量子化。研究结果已总结成三篇代表性论文，一篇投往Phys.Rev.D，另两篇在修改中。