报告题目：An Accurate P3M Algorithm for Gravitational Lensing Studies in Simulations

　　报告人：徐坤 博士

　　报告人简介：徐坤，上海交通大学物理与天文学院天文系博士生。2019年本科毕业于上海交通大学物理系，后入选上海交通大学博士生致远荣誉计划，攻读天文学。目前已在《The Astrophysical Journal》等期刊上以第一作者身份发表论文三篇，主要研究方向为星系形成和宇宙大尺度结构。

　　摘要：We present a two-dimensional (2D) Particle-Particle-Particle-Mesh (P3M) algorithm with an optimized Green function and adaptive softening length for gravitational lensing studies in N-Body simulations. The analytical form of the optimized Green function G(k) is given. The softening schemes (S) are studied for both the PM and the PP calculations in order for accurate force calculation and suppression of the particle discreteness effect. Our method is two orders of magnitude more accurate than the simple PM algorithm with the poor man’s Green function (∝ 1/k2 ) at a scale of a few mesh cells or smaller. The force anisotropy is also much smaller than the conventional PM calculation. We can achieve a force accuracy better than 0.1 percent at all scales with our algorithm. When we apply the algorithm to computing lensing quantities in N-Body simulations, the errors are dominated by the Poisson noise caused by particle discreteness. The Poisson noise can be suppressed by smoothing out the particle distribution, which can be achieved by simply choosing an adaptive softening length in the PP calculation. We have presented a criterion to set the adaptive softening length. Our algorithm is also applicable to cosmological simulations. We provide a python implementation P3Mlens for this algorithm.

　　报告时间：2021年04月02日下午2点

　　报告地点：紫台5-516会议室

　　邀请团组：星系宇宙学与暗能量研究

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