AI 中文总结
本研究基于可变物质扩散唯象框架构建晚期宇宙学模型，结合多类晚期观测数据约束发现，纳入SH0ES校准数据时单参数常数扩散模型统计表现显著优于ΛCDM与CPL参数化，非线性扩散形式未获明显统计支持。
AI 中文摘要
我们研究了一类源自可变物质扩散唯象框架的晚期宇宙学模型。在这类情形中，能量-动量守恒要求物质与有效标量场暗能量组分$\phi$之间存在持续的能量交换。我们考虑了一个基准的常数扩散情形，以及四种非线性幂律参数化形式，其中扩散系数分别随尺度因子、物质密度、标量场密度或哈勃膨胀率的函数演化。为评估它们的宇宙学可行性，我们在\texttt{SimpleMC}中实现了这些模型，并利用晚期观测数据对其进行约束，观测数据包括宇宙计时钟、重子声学振荡测量、经局部SH0ES校准及未经该校准的Ia型超新星。在无局部校准的情况下，扩散模型仅带来适度的拟合提升（$\Delta\chi^2 \approx -4$），表现与CPL参数化相当，同时相对于$\Lambda$CDM模型呈现负的贝叶斯对数证据差。相比之下，纳入SH0ES数据后，最小$\chi^2$大幅降低（$\Delta\chi^2 \approx -22$），且贝叶斯证据明确支持扩散框架（$\Delta\ln\mathcal{Z} \approx 9$）。值得注意的是，单参数的常数扩散模型几乎贡献了全部的统计提升，其$\chi^2$表现比CPL参数化优10个单位以上，$\Delta\ln\mathcal{Z}$则优8个单位以上。四种非线性扩展带来的额外提升可忽略不计（$\Delta\chi^2 \approx -1$），这表明当前的晚期背景观测更支持存在非零的物质扩散相互作用，而非$\Lambda$CDM模型，但并未提供具有统计显著性的证据表明扩散系数存在特定的时间依赖函数形式。
英文摘要
We investigate a class of late-time cosmological models derived from the phenomenological framework of variable matter diffusion. In these scenarios, energy-momentum conservation requires a continuous energy exchange between matter and an effective scalar-field dark-energy component, $ϕ$. We consider a baseline constant-diffusion scenario alongside four non-linear power-law parametrizations, in which the diffusion coefficient evolves as a function of the scale factor, matter density, scalar-field density, or Hubble expansion rate. To assess their cosmological viability, we implement these models within \texttt{SimpleMC} and constrain them using late-time observations, including cosmic chronometers, baryon acoustic oscillation measurements, Type Ia supernovae with and without the local SH0ES calibration. In the absence of the local calibration, the diffusion models yield only modest improvements in the fit ($Δχ^2 \approx -4$), performing comparably to the CPL parametrization while exhibiting negative Bayesian log-evidence differences relative to $Λ$CDM. In contrast, including SH0ES leads to a dramatic reduction in the minimum $χ^2$ ($Δχ^2 \approx -22$) and decisive Bayesian evidence in favor of the diffusion framework ($Δ\ln\mathcal{Z} \approx 9$). Remarkably, the single-parameter constant-diffusion model accounts for virtually all the statistical improvement, outperforming the CPL parametrization by more than 10 units in $χ^2$ and more than 8 units in $Δ\ln\mathcal{Z}$. The four non-linear extensions provide only negligible additional improvements ($Δχ^2 \approx -1$), indicating that current late-time background observations favor the presence of a non-vanishing matter-diffusion interaction over $Λ$CDM, while providing no statistically significant evidence for a specific time-dependent functional form of the diffusion coefficient.
Comments20 pages, 9 figures
