额外辐射的证据？剖面似然与贝叶斯后验
Evidence for extra radiation? Profile likelihood versus Bayesian posterior
摘要：
最近对宇宙学数据的一些分析报告了一些线索，表明存在超出标准模型预期的额外辐射。为了测试这些索赔的鲁棒性，根据不同的方法构建参数约束，我们进行了贝叶斯后验和基于似然配置文件的分析当前的数据。我们确认后和配置文件为基础的约束之间存在轻微的差异，与边缘化的后更喜欢较高的值的中微子种类N_eff的有效数量。这可以追溯到体积效应发生在边缘化过程中，我们证明了这种效果是相关的事实，即宇宙微波背景（CMB）数据约束N_eff只有间接通过红移的物质辐射平等。一旦CMB数据与外部信息相结合，例如，哈勃参数，方法之间的差异变得很小相比，N_eff的不确定性。我们的结论是，偏好的精密宇宙学数据过量辐射是“真实的”，而不是一个特定的选择可信/置信区间建设的神器。
英文摘要：
A number of recent analyses of cosmological data have reported hints for the presence of extra radiation beyond the standard model expectation. In order to test the robustness of these claims under different methods of constructing parameter constraints, we perform a Bayesian posterior-based and a likelihood profile-based analysis of current data. We confirm the presence of a slight discrepancy between posterior- and profile-based constraints, with the marginalised posterior preferring higher values of the effective number of neutrino species N_eff. This can be traced back to a volume effect occurring during the marginalisation process, and we demonstrate that the effect is related to the fact that cosmic microwave background (CMB) data constrain N_eff only indirectly via the redshift of matter-radiation equality. Once present CMB data are combined with external information about, e.g., the Hubble parameter, the difference between the methods becomes small compared to the uncertainty of N_eff. We conclude that the preference of precision cosmological data for excess radiation is "real" and not an artifact of a specific choice of credible/confidence interval construction.
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