Equation of state and electric (isospin) charge fluctuations are studied for matter composed of interacting pions. The pion matter is described by self interacting scalar fields via a ${\varphi }^4\text{−}{\varphi }^6$-type Lagrangian. The mean-field approximation is used, and interaction parameters are fixed by fitting lattice QCD results on the isospin density as a function of the isospin chemical potential at zero temperature. Two scenarios for fixing the model parameters—with and without the first-order phase transition—are considered, both yielding a satisfactory description of the lattice data. Thermodynamic functions and isospin charge fluctuations are studied and systematically compared for these two scenarios, yielding qualitative differences in the behavior of isospin charge susceptibilities. These differences can be probed by lattice simulations at temperatures $T\lesssim 100$ MeV.

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相互作用的 pion 物质和同位旋电荷波动的相图

研究了由相互作用的介子组成的物质的状态方程和电（同位旋）电荷波动。π 物质是通过自相互作用标量场来描述的${\phi }^4\text{-}{\phi }^6$型拉格朗日。使用平均场近似，并且相互作用参数通过在同位旋密度上拟合晶格 QCD 结果来固定，作为零温度下同位旋化学势的函数。考虑了固定模型参数的两种情况——有和没有一阶相变——都产生了对晶格数据的令人满意的描述。研究并系统地比较了这两种情况的热力学函数和同位旋电荷波动，从而产生了同位旋电荷磁化率行为的质的差异。这些差异可以通过温度下的晶格模拟来探测$吨\lesssim 100$ 兆伏。