Initial conditions for cold dark matter particles and General Relativity
Initial conditions for cold dark matter particles and General Relativity
复制标题
冷暗物质粒子的初始条件和广义相对论
DOI：
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发表时间：
2013
期刊：
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通讯作者：
G. Rigopoulos
中科院分区：
文献类型：
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作者：
Cornelius Rampf;G. Rigopoulos
我们用相对论梯度展开来描述宇宙的无旋尘埃成分，并将所得的同步度量转换为牛顿坐标系。这两个度量通过类空间位移场和类时间扰动连接，提供从拉格朗日坐标到欧拉坐标变换的相对论概括。位移场的相对论部分已经在初始时间产生二阶非局部密度扰动。这是纯粹的相对论效应，因为它源于时空混合。对于如何在 N 体模拟中包含相对论修正，我们提供了两种选择：被动方法和主动方法。在被动方法中，我们将校正视为初始高斯场的非高斯修改（也可以合并原始非高斯性）。引起的非高斯性取决于设定初始条件的尺度和红移，对于足够小的尺度和红移，f_NL ~ 很少。在主动方法中，我们展示了如何使用相对论轨迹来获取用于 N 体模拟的粒子的初始位移和速度，而不修改初始高斯场。
We describe the irrotational dust component of the universe in terms of a relativistic gradient expansion and transform the resulting synchronous metric to a Newtonian coordinate system. The two metrics are connected via a space-like displacement field and a time-like perturbation, providing a relativistic generalization of the transformation from Lagrangian to Eulerian coordinates. The relativistic part of the displacement field generates already at initial time a non-local density perturbation at second order. This is a purely relativistic effect since it originates from space-time mixing. We give two options, the passive and the active approach, on how to include the relativistic corrections for example in N-body simulations. In the passive approach we treat the corrections as a non-Gaussian modification of the initial Gaussian field (primordial non-Gaussianity could be incorporated as well). The induced non-Gaussianity depends on scale and the redshift at which initial conditions are set, with f_NL ~ few for small enough scales and redshifts. In the active approach we show how to use the relativistic trajectory to obtain the initial displacement and velocity of particles for N-body simulations without modifying the initial Gaussian field.