发表机构
University of Utah（犹他大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过泰勒展开至四阶，扩展了晶格QCD对外磁场中夸克-胶子等离子体的响应测定，证实了顺磁行为，并发现四阶系数在交叉附近增强，且存在有限体积效应。
AI 中文摘要
我们利用在零磁场下压力的泰勒展开，扩展了晶格QCD对夸克-胶子等离子体对外部磁场响应的测定。一种零净通量的“半半”磁场构型允许在B=0处生成规范系综时，对场振幅进行连续微分。电磁矢量势被选择为最小化泰勒算子中的随机噪声。先前通过O(B^2)的结果被扩展到O(B^4)，使用了具有m_l/m_s=0.05和N_t=8的2+1味HISQ/tree系综。重整化的二次系数证实了在QCD交叉上方的顺磁行为。四阶系数C_4在高温下较小，在交叉附近增强。在T=167 MeV时，48^3×8上的C_4结果比相应的32^3×8结果高出约两个标准差，表明可能存在有限体积效应。对于eB=0.2 GeV^2（这是与重离子现象学相关的磁场特征值），在中等和高温下，四阶贡献相对于主要磁修正较小，但在交叉附近，在真空压力扣除后，大体积结果约为二次项中心值的一半。我们还将该方法置于其他磁化率晶格测定的背景下，并阐明了有限体积效应对热扣除的相关性。这项工作于2014年完成，初步结果已在Lattice 2014会议上报告。
英文摘要
We extend a lattice-QCD determination of the response of the quark-gluon plasma to an external magnetic field using a Taylor expansion of the pressure at zero field. A zero-net-flux ``half-and-half'' magnetic-field configuration permits continuous differentiation with respect to the field amplitude on gauge ensembles generated at $B=0$. The electromagnetic vector potential is chosen to minimize stochastic noise in the Taylor operators. Previous results through $O(B^2)$ are extended to $O(B^4)$ using $2+1$-flavor HISQ/tree ensembles with $m_l/m_s=0.05$ and $N_t=8$. The renormalized quadratic coefficient confirms paramagnetic behavior above the QCD crossover. The fourth-order coefficient $C_4$ is small at high temperature and is enhanced near the crossover. At $T=167$ MeV the $C_4$ result at $48^3\times 8$ lies about two standard deviations above the corresponding $32^3\times8$ one, indicating likely finite- volume effects. For $eB = 0.2$ GeV$^2$, characteristic of magnetic fields relevant to heavy-ion phenomenology, the fourth-order contribution is small compared with the leading magnetic correction at moderate and high temperatures, but near the crossover the large-volume result is about half of the central value of the quadratic term, after the vacuum-pressure subtraction. We also place the method in the context of other lattice determinations of magnetic susceptibility and clarify the relevance of finite-volume effects for the thermal subtraction. This work was completed in 2014 and preliminary results were reported at Lattice 2014.
Comments11 pages, 4 figures, preliminary results reported at Lattice 2014
