The long-wavelength coherent overdensity and tidal force, which are not direct observables for a finite-volume survey, affect time evolution of cosmic structure formation and therefore clustering observables through the mode coupling. In this paper we develop an "anisotropic" separate universe (SU) simulation technique to simulate large-scale structure formation taking into account the effect of large-scale tidal force into the anisotropic expansion of local background. We modify the TreePM N-body simulation code to implement the anisotropic SU simulations, and then study the "response" function of matter power spectrum that describes how the matter power spectrum responds to the large-scale tidal effect as a function of wavenumber and redshift for a given global cosmology. We test and validate the SU simulation results from the comparison with the perturbation theory predictions and the results from high-resolution PM simulations. We find that the response function displays characteristic scale dependences over the range of scales down to nonlinear scales, up to k ~ 6 h/Mpc.

中文翻译：

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各向异性分离宇宙模拟

长波长相干超密度和潮汐力不是有限体积测量的直接可观测物，它们影响宇宙结构形成的时间演化，因此通过模式耦合对可观测物进行聚类。在本文中，我们开发了一种“各向异性”分离宇宙 (SU) 模拟技术，以模拟大尺度结构形成，同时考虑到大尺度潮汐力对局部背景各向异性膨胀的影响。我们修改TreePM N体模拟代码以实现各向异性SU模拟，然后研究物质功率谱的“响应”函数，该函数描述了物质功率谱如何响应大尺度潮汐效应作为波数和红移的函数对于给定的全球宇宙学。我们通过与扰动理论预测和高分辨率 PM 模拟结果的比较来测试和验证 SU 模拟结果。我们发现响应函数在向下到非线性尺度的尺度范围内显示特征尺度依赖性，高达 k ~ 6 h/Mpc。