AI 中文总结
研究通过考虑三种近似\(\Lambda\)CDM宇宙学闭合，利用马尔可夫链蒙特卡罗分析多种观测数据，在不假设暗能量状态方程参数化的情况下，直接从观测重建宇宙膨胀历史，结果表明这些模型与标准暗能量模型有竞争力，证明了模型无关宇宙学的作用。
AI 中文摘要
宇宙学条件\(j(z)=1\)提供了空间平坦\(\Lambda\)CDM模型的运动学特征，与任何特定暗能量或修正引力理论无关。我们通过考虑三种现象学的“近似\(\Lambda\)CDM”宇宙学闭合来研究当前观测允许偏离此条件的程度，其中宇宙急动通过小变形参数\(\epsilon\)与1略有不同。使用马尔可夫链蒙特卡罗分析对近期DESI重子声学振荡测量、压缩的普朗克宇宙微波背景似然以及Union3、Pantheon +和DESY5 Ia型超新星汇编对模型进行约束。我们的宇宙学框架直接从观测重建膨胀历史，有效暗能量状态方程作为导出量出现。发现所有三种闭合都被紧密约束在\(\Lambda\)CDM宇宙学不动点附近，普朗克数据推动向\(j_0\simeq1\)和\(w_{\rm DE,0}\simeq - 1\)的首选演化。尽管运动学结构不同，但重建的暗能量演化在接近\(w = - 1\)时始终表现出平滑的冻结行为，未穿过幻像分界线。模型比较表明近似\(\Lambda\)CDM模型在统计上与标准暗能量参数化具有竞争力，同时对\(w(z)\)的函数形式假设更少。这些结果证明了模型无关宇宙学在约束宇宙膨胀历史方面的能力，并为未来宇宙学微扰和结构形成研究提供了自然框架。
英文摘要
The cosmographic condition $j(z)=1$ provides the kinematical signature of the spatially flat $Λ$CDM model independently of any specific dark-energy or modified-gravity theory. We investigate the extent to which current observations permit departures from this condition by considering three phenomenological ``almost-$Λ$CDM'' cosmographic closures, in which the cosmic jerk differs slightly from unity through a small deformation parameter $ε$. The models are constrained using Markov Chain Monte Carlo analyses of recent DESI baryon acoustic oscillation measurements together with compressed Planck cosmic microwave background likelihoods and the Union3, Pantheon+, and DESY5 Type Ia supernova compilations. Rather than assuming a parameterized dark-energy equation of state, our cosmographic framework reconstructs the expansion history directly from observations, with the effective dark-energy equation of state emerging as a derived quantity. We find that all three closures are tightly constrained to the vicinity of the $Λ$CDM cosmographic fixed point, with Planck data driving the preferred evolution toward $j_0\simeq1$ and $w_{\rm DE,0}\simeq-1$. Despite their distinct kinematical constructions, the reconstructed dark-energy evolution consistently exhibits smooth freezing behaviour close to $w=-1$, without crossing the phantom divide. Model comparison using the Akaike and Bayesian information criteria shows that the almost-$Λ$CDM models remain statistically competitive with standard dark-energy parameterizations while requiring fewer assumptions about the functional form of $w(z)$. These results demonstrate the power of model-independent cosmography for constraining the cosmic expansion history and provide a natural framework for future studies of cosmological perturbations and structure formation.
Comments7 figures, 5 tables
