标题： 任意维FRW宇宙的热力学：焦耳-汤姆逊膨胀 显示英文标题

标题： Thermodynamics of the arbitrary dimensional FRW universe: Joule-Thomson expansion

摘要： 在本文中，我们研究了$n$维 FRW（弗里德曼-罗伯逊-沃尔克）宇宙的热力学，特别是焦耳-汤姆逊膨胀。我们推导了$P=P(V, T)$的$n$维 FRW 宇宙在爱因斯坦引力和爱因斯坦-高斯-博内特引力中的热力学状态方程，其中热力学压力$P$由完美流体的工作密度$W$定义，$i.e.$ $P\equiv W$ 。 此外，我们将焦耳-汤姆逊膨胀作为这些状态方程的应用，以阐明$n$维弗里德曼-勒梅特-罗伯逊-沃尔克 (FRW) 宇宙的冷却-加热特性。我们首次确定了任意维数 FRW 宇宙中的反转温度和反转压力，并在$T$-$P$平面上展示了反转曲线和等焓曲线的特性。这项研究有助于加深我们对 FRW 宇宙中冷却和加热区域的理解，从而揭示其膨胀机制。 显示英文摘要

摘要： In this paper, we investigate the thermodynamics especially the Joule-Thomson expansion of the $n$-dimensional FRW (Friedmann-Robertson-Walker) universe with a perfect fluid. We derive the thermodynamic equations of state $P=P(V, T)$ for the $n$-dimensional FRW universe in Einstein gravity and Einstein-Gauss-Bonnet gravity, where the thermodynamic pressure $P$ defined by the work density $W$ of the perfect fluid, $i.e.$ $P\equiv W$. Furthermore, we present the Joule-Thomson expansion as an application of these equations of state to elucidate the cooling-heating properties of the $n$-dimensional FRW universe. We determine the inversion temperature and inversion pressure in the FRW universe with arbitrary dimensions for the first time, and illustrate the characteristics of inversion curves and isenthalpic curves in the $T$-$P$ plane. This study offers insights into deepening our comprehension of cooling and heating regions in the FRW universe, thereby revealing its expansion mechanisms.