We present results on the second-order fluctuations of and correlations among net baryon number, electric charge and strangeness in (2 + 1)-flavor lattice QCD in the presence of a background magnetic field. Simulations are performed using the tree-level improved gauge action and the highly improved staggered quark (HISQ) action with a fixed scale approach (\(a\simeq \) 0.117 fm). The light quark mass is set to be 1/10 of the physical strange quark mass and the corresponding pion mass is about 220 MeV at vanishing magnetic field. Simulations are performed on \(32^3\times N_\tau \) lattices with 9 values of \(N_\tau \) varying from 96 to 6 corresponding to temperatures ranging from zero up to 281 MeV. The magnetic field strength eB is simulated with 15 different values up to \(\sim \)2.5 GeV\(^2\) at each nonzero temperature. We find that quadratic fluctuations and correlations do not show any singular behavior at zero temperature in the current window of eB while they develop peaked structures at nonzero temperatures as eB grows. By comparing the electric charge-related fluctuations and correlations with hadron resonance gas model calculations and ideal gas limits we find that the changes in degrees of freedom start at lower temperatures in stronger magnetic fields. Significant effects induced by magnetic fields on the isospin symmetry and ratios of net baryon number and baryon-strangeness correlation to strangeness fluctuation are observed, which could be useful for probing the existence of a magnetic field in heavy-ion collision experiments.

我们展示了在背景磁场存在下 (2 + 1) 风味晶格 QCD 中净重子数、电荷和奇异性的二阶波动和相关性的结果。使用树级改进规范作用和高度改进的交错夸克 (HISQ) 作用和固定尺度方法 ( \(a\simeq \) 0.117 fm)进行模拟。轻夸克质量设置为物理奇夸克质量的 1/10，相应的介子质量在磁场消失时约为 220 MeV。模拟在\(32^3\times N_\tau \)格子上进行，其中\(N_\tau \) 的9 个值从 96 到 6 不等，对应于从零到 281 MeV 的温度。磁场强度eB在每个非零温度下用 15 个不同的值进行模拟，最高为\(\sim \) 2.5 GeV \(^2\)。我们发现二次波动和相关性在eB的当前窗口中在零温度下没有表现出任何奇异行为，而它们在非零温度下形成峰值结构作为eB成长。通过将与电荷相关的波动和相关性与强子共振气体模型计算和理想气体极限进行比较，我们发现自由度的变化始于更强磁场中的较低温度。观察到磁场对同位旋对称性和净重子数的比值和重子奇异度相关性与奇异度波动的显着影响，这对于探索重离子碰撞实验中磁场的存在是有用的。