发表机构
Universidad de Valparaíso; Universidad Veracruzana; Pontificia Universidad Católica de Valparaíso（瓦尔帕莱索大学; 韦拉克鲁斯大学; 瓦尔帕莱索天主教 Pontifical 大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文在单模引力宇宙学中研究物质创生，推导出创生压强、创生率与扩散项为独立熵产生源的一般恒等式，并指出即使创生绝热，扩散项非恒定仍导致非绝热演化。
AI 中文摘要
我们研究了单模引力宇宙学框架下的物质创生。我们将能量密度 $\rho$、压强 $p$、粒子数密度 $n$ 以及粒子数 $N=nV$ 作为物质部门的热力学物理变量，并通过平衡方程 $N^{\mu}{}_{;\mu}=n\Gamma$ 直接引入粒子创生。将该开放系统表述与单模扩散项 $Q$ 相结合，我们推导出精确恒等式 $nT\dot\sigma=-3Hp_c-(\rho+p)\Gamma-\dot Q$，该式表明创生压强 $p_c$、创生率 $\Gamma$ 和扩散项 $Q$ 通常是每个粒子熵产生的三个独立来源。采用粒子创生本身是绝热的标准假设，前两项恒等抵消，该关系简化为特殊情况 $nT\dot\sigma=-\dot Q$，因此每个粒子的熵仅在 $Q$ 为常数时才是常数。由此，即使与 $\Gamma$ 相关的创生过程在通常的普里戈金意义上是绝热的，只要 $\dot Q\neq0$，单模引力中的完整物质演化就是非绝热的。然而，该一般恒等式仍可作为未来工作中放宽这一假设的出发点。
英文摘要
We investigate matter creation in the cosmological framework of unimodular gravity. We keep the energy density $ρ$, pressure $p$, particle number density $n$, and particle number $N=nV$ as the physical thermodynamic variables of the matter sector, and introduce particle creation directly through the balance equation $N^μ{}_{;μ}=nΓ$. Combining this open-system formulation with the unimodular diffusion term $Q$, we derive the exact identity $nT\dotσ=-3Hp_c-(ρ+p)Γ-\dot Q$, which shows that the creation pressure $p_c$, the creation rate $Γ$, and the diffusion term $Q$ are, in general, three independent sources of entropy production per particle. Adopting the standard postulate that particle creation is itself adiabatic, the first two terms cancel identically and the relation reduces to the particular case $nT\dotσ=-\dot Q$, so that the entropy per particle is constant only when $Q$ is constant. Thus, even when the creation process associated with $Γ$ is adiabatic in the usual Prigogine sense, the full matter evolution in unimodular gravity is non-adiabatic whenever $\dot Q\neq0$. The general identity, however, remains available as a starting point for relaxing this postulate in future work.
CommentsPublished version in PLB. 7 pages, 1 figure
Journal refPhys. Lett. B 881, 140955 (2026)
DOI：10.1016/j.physletb.2026.140955
