AI 中文总结
研究Nf=2+1+1 QCD在罗伯格-魏斯相变附近的拓扑性质，采用特定离散化方式，发现其拓扑 susceptibility和四阶累积量的相变特征与纯规范理论相似，且与Nf=2+1 QCD结果一致。
AI 中文摘要
我们研究了量子色动力学（QCD）在有限温度罗伯格-魏斯（Roberge-Weiss）相变过程中的拓扑性质，该相变发生在虚重子化学势取特定值时。本研究针对具有物理夸克质量的Nf=2+1+1 QCD展开，采用stout改进的交错费米子进行离散化处理，主要考虑紧致化维度的两个不同取值：Nt=8和Nt=10。T_RW及相关普适类的结果与采用略有不同离散化方式的Nf=2+1 QCD的结果一致。拓扑 susceptibility在T≤T_RW时几乎保持恒定，在更高温度下则快速衰减。对拓扑电荷分布的四阶累积量b2的分析表明，其在T_RW后与稀瞬子气体近似（Dilute Instanton Gas Approximation）的预测相符，显示出明显的相变特征，这与纯规范理论中观测到的结果更为相似，而与标准热路径上全QCD的情况不同——此前研究中观测到后者的相变更为缓慢。
英文摘要
We investigate the topological properties of QCD across the finite temperature Roberge-Weiss transition, which is found for particular values of the imaginary baryon chemical potential. Our study is conducted for $N_f = 2+1+1$ QCD with physical quark masses, discretized via stout improved staggered fermions and considering mostly two different values of the compactifed dimension, $N_t = 8$ and $N_t = 10$. Results for $T_{RW}$ and for the associated universality class are consistent with those found in the $N_f = 2 + 1$ case with a slightly different discretization. The topological susceptibility appears to be practically constant for $T \lesssim T_{RW}$, then rapidly decaying for higher temperatures. The analysis of the fourth order cumulant of the topological charge distribution, $b_2$, reveals that it is compatible with the prediction of the Dilute Instanton Gas Approximation right after $T_{RW}$, showing thus a sharp transition, which is more similar to what observed in pure gauge theories rather than to full QCD along the standard thermal line, where instead a slower transition was observed in previous studies.
Comments14 pages, 12 figures
