Challenging the standard cosmological model

宇宙学的标准模型成功地解释了一组广泛的精确数据，只需要几个简化的假设和七个自由参数。大约25年来，它基本上保持不变。然而，它纯粹是现象学的，包含了几个无法解释的方面，例如，对于暗物质或暗能量的性质，或者对于初始密度扰动的起源，没有任何解释。这个模型远远谈不上优雅，此外，也没有人期望它是完整的。此外，尽管取得了成功，但标准宇宙学模型的盔甲上仍存在一些明显的缺陷，有不同的名称，如“反常”、“好奇”或“张力”--目前尚不清楚哪些缺陷可能会为新物理学指明方向，这些缺陷是由不明的系统效应引起的，而这些缺陷只是统计上的波动。当然，取得进展的明显方式是从未来的实验中获得更敏感的数据，目的是发现可能需要新的参数(例如原始引力波的一个分量，一种不平凡的暗能量，或者来自大质量中微子的可观察到的效应)。我参与了这样雄心勃勃的宇宙微波背景(CMB)实验，但结果不会很快出现。在这里提出的五年研究中，我将探索四种不同的方法来扩展宇宙学模型，每一种方法都涉及到学生试图更直接地挑战标准宇宙学。首先，一些现有的异常可以直接用新的数据进行调查，例如使用CMB偏振或透镜数据探测大尺度的奇点。其次，参数张力可以在修正重力思想或在模型中添加其他新的物理成分的背景下进行探索。第三，我们可以利用CMB“二次”信号和其他天体物理测量数据之间的相互关系，从现有数据中提取额外的宇宙学信息，并与标准模型的预测相对抗。最后，我们可以搜索在标准图像中难以解释的结构，特别是高红移的原始星系团。通过这些相互关联的研究推力的组合，这项提议将检查标准宇宙学模型需要如何演变才能完全描述未来的宇宙学数据。

The standard model of cosmology successfully explains a wide set of precise data, with a few simplifying assumptions and just seven free parameters. It has remained essentially unchanged for about 25 years. However, it is purely phenomenological and contains several unexplained aspects, e.g. there is no explanation for the nature of the dark matter or dark energy, or for the origin of the initial density perturbations. The model is far from being elegant, and additionally there is no expectation that it can be complete. Moreover, despite its successes, there are some apparent chinks in the armour of the standard cosmological model, variously called "anomalies", "curiosities" or "tensions" - it is currently unclear which of them may point the way towards new physics, which are caused by unidentified systematic effects, and which are just statistical fluctuations. Of course the obvious way to make progress is through obtaining much more sensitive data from future experiments with the goal of discovering that new parameters may be needed (such as a component of primordial gravitational waves, a non-trivial kind of dark energy, or observable effects from massive neutrinos). I am involved in such ambitious cosmic microwave background (CMB) experiments, but the results are not expected soon. For the 5 years of research proposed here, I will explore 4 separate ways to extend the cosmological model, each involving students in attempts to more immediately challenge the standard cosmology. First, some existing anomalies can be directly investigated with new data, e.g. probing large-scale curiosities using CMB polarization or lensing data. Second, parameter tensions can be explored in the context of modified-gravity ideas or adding other novel physics ingredients to the model. Third, we can use cross-correlations between CMB "secondary" signals and other astrophysical survey data to extract additional cosmological information from existing data and confront this with the predictions of the standard model. Last, we can search for structures that would be difficult to explain within the standard picture, particularly proto-clusters of galaxies at high redshift. Through a combination of these interrelated research thrusts, this proposal will examine how the standard cosmological model needs to evolve to fully describe future cosmological data.