约束模拟和偏移集：了解“转基因”晕圈的风险和益处
Constrained simulations and excursion sets: understanding the risks and benefits of `genetically modified' haloes
摘要：
高斯随机场的约束实现在宇宙学中被用来设计数值模拟的特殊初始条件。我们回顾这种方法及其应用密度峰值提供了几个工作的例子。然后，我们批判性地讨论了最近的建议，使用约束实现修改内和周围的拉格朗日补丁，形成暗物质晕的线性密度场。这一雄心勃勃的概念是在非线性进化之后打造具有某些理想特性的“转基因”晕圈。我们证明，这种方法的原始实现是不准确的，但近似的，因为它默认的假设，原生晕采样一组随机点与一个固定的平均超密度。我们表明，进行全面的基因改造是一项艰巨而艰巨的任务，需要一个数学上的理解是什么决定了在线性密度场的原晕的偏置位置。我们讨论近似的解决方案的基础上受过教育的猜测有关的性质的原晕。我们说明了如何可以适应的非线性演化的修改补丁，从而微调的约束条件，是必要的，以获得预选晕属性的预测集的方法。这项技术使我们能够探索遗传修饰原始算法的自由度。我们发现，这是最敏感的量的变化是晕质量吸积率在质量尺度上的约束设置。最后讨论了基于原晕角动量的约束条件。
英文摘要：
Constrained realisations of Gaussian random fields are used in cosmology to design special initial conditions for numerical simulations. We review this approach and its application to density peaks providing several worked-out examples. We then critically discuss the recent proposal to use constrained realisations to modify the linear density field within and around the Lagrangian patches that form dark-matter haloes. The ambitious concept is to forge `genetically modified' haloes with some desired properties after the non-linear evolution. We demonstrate that the original implementation of this method is not exact but approximate because it tacitly assumes that protohaloes sample a set of random points with a fixed mean overdensity. We show that carrying out a full genetic modification is a formidable and daunting task requiring a mathematical understanding of what determines the biased locations of protohaloes in the linear density field. We discuss approximate solutions based on educated guesses regarding the nature of protohaloes. We illustrate how the excursion-set method can be adapted to predict the non-linear evolution of the modified patches and thus fine tune the constraints that are necessary to obtain preselected halo properties. This technique allows us to explore the freedom around the original algorithm for genetic modification. We find that the quantity which is most sensitive to changes is the halo mass-accretion rate at the mass scale on which the constraints are set. Finally we discuss constraints based on the protohalo angular momenta.
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