发表机构
Fudan University; Nagoya University; Osaka University（复旦大学; 名古屋大学; 大阪大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究采用含Kobayashi-Maskawa-'t Hooft型耦合的$N_f=2+1$夸克-介子模型，分析有限温密下同位旋QCD的π凝聚相变、介子质量谱及声速特征，为格点模拟提供对称性视角的参考。
AI 中文摘要
我们研究了具有同位旋化学势（$μ_I$）的QCD在有限温度和密度下的相结构、介子质量谱和声速。我们采用$N_f=2+1$的夸克-介子模型，纳入Kobayashi-Maskawa-'t Hooft型耦合以捕捉$U(1)_A$轴反常的动力学效应。在夸克单圈平均场近似下，我们分析了π凝聚的起始，在该近似下，它在低温下表现为二级相变，在更高温度下可能呈现一级行为。我们研究了标量和赝标量单态-八重态介子的相应质量谱，其中$π_+$质量在超流相由于其Nambu-Goldstone玻色子性质而严格为零质量。同时，我们发现中性π介子质量在π凝聚相中随$μ_I$呈严格线性增长。我们还研究了等温平方声速，并识别出与相变相关的特征结构。此外，我们强调了增强的$U(1)_A$反常效应如何促使π凝聚体在冷介质中产生更不显著的声速峰。我们的研究结果有望为未来的格点模拟提供来自对称性方面的介子质量谱有用信息。
英文摘要
We study phase structures, meson mass spectra, and sound velocities at finite temperature and density in QCD with isospin chemical potential ($μ_I$). We employ the quark-meson model with $N_f=2+1$, incorporating the Kobayashi-Maskawa-'t Hooft type coupling to capture dynamical effects of the $U(1)_A$ axial anomaly. Within the mean-field approximation at quark one-loop, we analyze the onset of pion condensation, which manifests as a second-order phase transition at low temperatures and may exhibit a first-order behavior at higher temperatures within this approximation. We examine the corresponding mass spectra of scalar and pseudoscalar singlet-octet mesons, in which the $π_+$ mass is exactly massless in the superfluid phase due to its Nambu-Goldstone boson nature. The neutral pion mass is, meanwhile, found to exhibit a strictly linear growth with $μ_I$ in the pion condensed phase. We also investigate the isothermal squared sound velocity and identify characteristic structures associated with the phase transitions. Furthermore, we highlight how enhanced $U(1)_A$ anomaly effects facilitate the pion condensate to generate a less-pronounced sound velocity peak in cold medium. Our findings are expected to provide future lattice simulations with useful information on meson mass spectra from symmetry aspects.
