We use the Om statistic and the Genetic Algorithms (GA) in order to derive a null test on the spatially flat cosmological constant model $Λ$CDM. This is done in two steps: first, we apply the GA to the Constitution SNIa data in order to acquire a model independent reconstruction of the expansion history of the Universe $H(z)$ and second, we use the reconstructed $H(z)$ in conjunction with the Om statistic, which is constant only for the $Λ$CDM model, to derive our constraints. We find that while $Λ$CDM is consistent with the data at the $2σ$ level, some deviations from $Λ$CDM model at low redshifts can be accommodated.
Cosmic shear nulling as a geometrical cosmological probe: Methodology and sensitivity to cosmological parameters and systematics
Université Paris-Saclay, IPHT, DRF-INP, UMR 3681, CEA（巴黎萨克雷大学）；Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris（索邦大学）；Université Paris-Cité, DAP, UMR 7158, CEA（巴黎西岱大学）
The assumption of a Friedmann-Lemaître-Roberton-Walker (FLRW) Universe is one of the fundamental pillars of modern Cosmology. It is crucial to confront it against cosmological observations in order to confirm (or rule out) the validity of the $Λ$CDM paradigm. We perform a consistency test of the FLRW metric using measurements of both radial and transversal modes of Baryonic Acoustic Oscillations in a model-independent fashion using Gaussian Processes. The impact of different prior assumptions for the sound horizon scale and the Hubble Constant is also explored. We find a mild deviation of the …
The prospect of nonparametric reconstructions of cosmological parameters from observational data sets has been a popular topic in the literature for a number of years. This has mainly taken the form of a technique based on Gaussian processes but this approach is exposed to several foundational issues ranging from overfitting to kernel consistency problems. In this work, we explore the possibility of using artificial neural networks (ANN) to reconstruct late-time expansion and large scale structure cosmological parameters. We first show how mock data can be used to design an optimal ANN for bot…
The weak equivalence principle is one of the cornerstone of general relativity. Its validity has been tested with impressive precision in the Solar System, with experiments involving baryonic matter and light. However, on cosmological scales and when dark matter is concerned, the validity of this principle is still unknown. In this paper we construct a null test that probes the validity of the equivalence principle for dark matter. Our test has the strong advantage that it can be applied on data without relying on any modelling of the theory of gravity. It involves a combination of redshift-sp…
National Technical University of Athens（雅典国立技术大学）；Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens（雅典国家天文台天体物理学、空间应用与遥感研究所）；Universidad Católica del Norte（北天主教学会大学）；CAS Key Laboratory for Researches in Galaxies and Cosmology, School of Astronomy and Space Science, University of Science and Technology of China（中国科学院星系与宇宙学重点实验室，中国科学技术大学天文与空间科学学院）
Observational constraints on the non-flat $ΛCDM$ model and a null test using the transition redshift
标准宇宙学模型的一个自然延伸是包含曲率作为自由参数的模型。在这项工作中，我们详细研究的观测约束的非平坦$ΛCDM$模型使用两个主要的几何测试：SNIa和哈勃参数测量。在一般情况下，我们表明，观测约束的参数的$ΛCDM$模型强烈依赖于曲率参数。特别地，我们研究了由物质支配的宇宙的跃迁红移（$z_{t}$）的约束条件下的宇宙学常数占主导地位的宇宙。使用这个可观察的，我们构造了一个新的零测试定义$ζ= z_{t, flat}-z_{t, non flat}$。该检验仅依赖于哈勃参数、哈勃常数和物质密度参数的数据。然而，它并不像文献中的许多测试那样依赖于可观察量的导数。为了重建这个测试，我们使用高斯过程方法。当我们使用$PLANCK/2018$的最佳拟合参数值时，我们没有发现数据和标准模型（平面$ΛCDM$）之间存在不一致的证据，但如果我们使用来自$RIESS/2018$的$H_{0}$值，我们发现在标准模型中存在不一致。然而，重要的是要注意，哈勃参数数据对于可靠的统计分析有很大的误差。
