AI 中文总结
该研究利用晶格量子色动力学，在背景磁场中研究量子色动力学的手征和单重态U(1)_A对称性，确定相关磁化率差，通过数值计算得出在特定系综上的结果，首次对背景磁场中手征和单重态U(1)_A伙伴磁化率分裂进行晶格量子色动力学研究。
AI 中文摘要
我们使用晶格量子色动力学研究背景磁场中量子色动力学的手征对称性和单重态U(1)_A对称性。首先阐明纯磁背景下的中性扇区对称结构，其中轻夸克不等电荷明确降低非单重味对称性。确定中性π介子-西格玛磁化率差χ_π^0 - χ_σ为与幸存中性非单重轴矢对称性相关的手征伙伴分裂，中性π介子-德尔塔磁化率差χ_π^0 - χ_δ^0为单重态U(1)_A伙伴分裂。还讨论了对中性π介子磁化率的非连接贡献及其连续统约束。在固定尺度(2 + 1)味HISQ系综上获得数值结果，发现中性手征伙伴分裂在低温下随磁场强度eB增加，在交叉点附近足够大的eB时减小，单重态U(1)_A伙伴分裂也有类似表现。这些结果首次通过晶格量子色动力学研究了背景磁场中手征和单重态U(1)_A伙伴磁化率分裂的中性扇区探针。
英文摘要
We study chiral symmetry and singlet $U(1)_A$ symmetry in QCD in a background magnetic field using lattice QCD. We first clarify the neutral-sector symmetry structure in a pure magnetic background, where the unequal electric charges of the light quarks explicitly reduce the non-singlet flavor symmetry. We identify the neutral-pion--sigma susceptibility difference, $χ_{π^0}-χ_σ$, as the chiral-partner splitting associated with the surviving neutral non-singlet axial symmetry, and the neutral-pion--delta susceptibility difference, $χ_{π^0}-χ_{δ^0}$, as the singlet $U(1)_A$ partner splitting. We also discuss the disconnected contribution to the neutral-pion susceptibility and its continuum constraint. Numerical results are obtained on fixed-scale $(2+1)$-flavor HISQ ensembles with $m_l=m_s^{\rm phys}/10$, corresponding to a pion mass of about $220~{\rm MeV}$ at vanishing magnetic field. We find that the neutral chiral-partner splitting increases with the magnetic field strength $eB$ at low temperature and decreases at sufficiently large $eB$ near the crossover, providing susceptibility-splitting counterparts of magnetic catalysis and inverse magnetic catalysis, respectively. The singlet $U(1)_A$ partner splitting shows an analogous low-temperature enhancement and large-field suppression near the crossover, with the suppression setting in at larger $eB$ and remaining milder than in the chiral channel. These results provide a first lattice-QCD study of neutral-sector probes of chiral and singlet $U(1)_A$ partner susceptibility splittings in background magnetic fields.
Comments12 pages, 4 figures
