标题： 附近距离偶极子的理论预测 显示英文标题

标题： A theoretical prediction for the dipole in nearby distances using cosmography

摘要： 宇宙学测绘是一种广泛应用于推断小宇宙尺度下宇宙运动学的方法，同时对所涉及的引力理论保持中立。通常，宇宙学家在宇宙学测绘分析中会使用弗里德曼-勒梅特-罗伯逊-沃尔克（FLRW）度规，但广义方法允许在不假设任何几何模型的情况下进行分析。这些方法有望能够独立于模型地绘制宇宙邻域，其中宇宙尚未趋于各向同性。在这个区域内，如果未考虑各向异性，可能会导致参数推断的偏差，因此即使主要目的是推断背景宇宙学，也必须将其包括在内以进行精确的宇宙学分析。在本文中，我们开发了一种方法来预测由于附近不均匀性引起的光度距离二极管。这是标准各向同性距离-红移定律的一阶修正。在非常广泛的广义相对论宇宙模型中，我们提供了一种解释，即通过膨胀率和密度的梯度来解释二极管，这种解释不受任何基础背景宇宙学的影响。我们使用数值相对论模拟，结合改进的初始数据方法，并辅以完全相对论的光线追踪来测试我们预测的效力。我们发现，在合理平滑的模拟中，我们的预测在红移$z\lesssim 0.07$的范围内准确捕捉到了二极管特征，误差约为10%。在存在更多非线性密度场的情况下，我们发现这会降低到$z\lesssim 0.02$。与基于简单局部宇宙学测绘的预测相比，这代表了数量级的提升。因此，本文解决了关于各向异性宇宙学测绘级数展开收敛性质的重要问题，这些问题原本会限制其在非常狭窄的红移范围内的应用。 显示英文摘要

摘要： Cosmography is a widely applied method to infer kinematics of the Universe at small cosmological scales while remaining agnostic about the theory of gravity at play. Usually cosmologists invoke the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric in cosmographic analyses, however generalised approaches allow for analyses outside of any assumed geometrical model. These methods have great promise to be able to model-independently map the cosmic neighborhood where the Universe has not yet converged to isotropy. In this regime, anisotropies can bias parameter inferences if they are not accounted for, and thus must be included for precision cosmology analyses, even when the principle aim is to infer the background cosmology. In this paper, we develop a method to predict the dipole in luminosity distances that arises due to nearby inhomogeneities. This is the leading-order correction to the standard isotropic distance-redshift law. Within a very broad class of general-relativistic universe models, we provide an interpretation of the dipole in terms of the gradients in expansion rate and density which is free from any underlying background cosmology. We use numerical relativity simulations, with improved initial data methods, alongside fully relativistic ray tracing to test the power of our prediction. We find our prediction accurately captures the dipole signature in our simulations to within ~10% for redshifts $z\lesssim 0.07$ in reasonably smooth simulations. In the presence of more non-linear density fields, we find this reduces to $z\lesssim 0.02$. This represents up to an order of magnitude improvement with respect to what is achieved by naive, local cosmography-based predictions. Our paper thus addresses important issues regarding convergence properties of anisotropic cosmographic series expansions that would otherwise limit their applicability to very narrow redshift ranges.