What is flat ΛCDM, and may we choose it?
What is flat ΛCDM, and may we choose it?
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DOI：
10.1088/1475-7516/2023/02/049
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发表时间：
2022-07
影响因子：
6.4
通讯作者：
S. Anselmi;M. Carney;J. Giblin;Saurabh Kumar;J. Mertens;M. O'Dwyer;G. Starkman;C. Tian
中科院分区：
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作者：
S. Anselmi;M. Carney;J. Giblin;Saurabh Kumar;J. Mertens;M. O'Dwyer;G. Starkman;C. Tian
宇宙既不是均匀的，也不是各向同性的，但它足够接近，我们可以在适当的大尺度上合理地近似它。暴胀的-Λ-Cold暗物质（ΛCDM）和谐宇宙学建立在这些假设的基础上，用来描述涨落的起源和演化。在关于应力-能量源的标准假设下，该系统仅由七个现象学参数指定，这些参数与潜在基本理论的精确关系是复杂的，并且可能取决于这些领域的细节。然而，通常的做法是将表征空间曲率的参数Ω K精确地设置为零。这个参数固定的ΛCDM被授予特殊的地位，作为单独的模型，“平坦ΛCDM”。事实上，这使得“弯曲ΛCDM”的支持者有责任提供足够的证据来证明Ω K≠0，并且需要作为参数。虽然某些膨胀模型拉格朗日量，具有特定的参数值和特定的初始条件，将导致今天的宇宙被很好地描述为包含零曲率，但这并不能证明将拉格朗日量，参数和初始条件的子集区分为一个单独的模型。在没有任何理论论据的情况下，我们不能使用表明Ω K较小的观察结果来强制执行Ω K = 0。我们在选择暴胀模型及其先验参数方面的记录使这种选择变得可疑，而对宇宙参数和大角度宇宙微波背景异常的紧张关系的关注加强了反对这种选择的论点。我们认为Ω K不能设为零，并且ΛCDM仍然是至少有7个参数的现象学模型。
The Universe is neither homogeneous nor isotropic, but it is close enough that we can reasonably approximate it as such on suitably large scales. The inflationary-Λ-Cold Dark Matter (ΛCDM) concordance cosmology builds on these assumptions to describe the origin and evolution of fluctuations. With standard assumptions about stress-energy sources, this system is specified by just seven phenomenological parameters, whose precise relations to underlying fundamental theories are complicated and may depend on details of those fields. Nevertheless, it is common practice to set the parameter that characterizes the spatial curvature, Ω K , exactly to zero. This parameter-fixed ΛCDM is awarded distinguished status as separate model, “flat ΛCDM.” Ipso facto this places the onus on proponents of “curved ΛCDM” to present sufficient evidence that Ω K ≠ 0, and is needed as a parameter. While certain inflationary model Lagrangians, with certain values of their parameters, and certain initial conditions, will lead to a present-day universe well-described as containing zero curvature, this does not justify distinguishing that subset of Lagrangians, parameters and initial conditions into a separate model. Absent any theoretical arguments, we cannot use observations that suggest small Ω K to enforce Ω K = 0. Our track record in picking inflationary models and their parameters a priori makes such a choice dubious, and concerns about tensions in cosmological parameters and large-angle cosmic-microwave-background anomalies strengthens arguments against this choice. We argue that Ω K must not be set to zero, and that ΛCDM remains a phenomenological model with at least 7 parameters.