标题： QCD在磁场背景下的Roberge-Weiss相变 显示英文标题

标题： The Roberge-Weiss transition for QCD in a magnetic background

摘要： 我们研究磁性背景场如何影响物理夸克质量下$N_f = 2+1$QCD 的 Roberge-Weiss (RW) 有限温度相变的位置和性质。 为此，我们对有限温度理论进行了数值模拟，通过 stout 非相对论格点夸克和树级改进的 Symanzik 纯规范作用量离散化，考虑了格点单位中两个不同的欧几里得时间扩展值，$N_t = 6, 8$。 临界温度$T_{RW}$随$eB$的增加而减小，特别是它紧密跟随赝临界 QCD 交叉温度$T_{pc}$的行为，因此在误差范围内，对于磁场高达$eB \sim 1$GeV$^2$的情况，$T_{RW} (eB) - T_{pc}(eB)$几乎是恒定的；从手征凝聚的下降中也得到了一致的结果，这表明手征对称性恢复，导致在转变之上出现逆磁催化现象。 此外，我们发现磁场将 RW 转变从二阶转变为一阶，在 1 到 2.4 GeV$^2$之间存在三重临界磁场，即比标准 QCD 转变变为一阶的磁场要低得多。 显示英文摘要

摘要： We investigate how a magnetic background field influences the location and the nature of the Roberge-Weiss (RW) finite temperature transition for $N_f = 2+1$ QCD with physical quark masses. To that purpose, we perform numerical simulations of the finite temperature theory, discretized through stout staggered quarks and the tree-level improved Symanzik pure gauge action, considering two different values of the Euclidean temporal extent in lattice units, $N_t = 6, 8$. The RW transition temperature $T_{RW}$ decreases with $eB$, in particular it follows closely the behavior of the pseudo-critical QCD crossover temperature $T_{pc}$, so that $T_{RW} (eB) - T_{pc}(eB)$ is practically constant, within errors, for magnetic fields up to $eB \sim 1$ GeV$^2$; consistent results are found from the drop of the chiral condensate, which signals chiral symmetry restoration, leading also to the phenomenon of inverse magnetic catalysis above the transition. Moreover, we find that the magnetic field turns the RW transition from second order to first order, with a tri-critical magnetic field in-between 1 and 2.4 GeV$^2$, i.e. for magnetic fields substantially lower than those for which the standard QCD transition turns to first order.