标题： ΛCDM和修正引力宇宙学中完全非线性阶段的成对运动动力学 显示英文标题

标题： Dynamics of pairwise motions in the fully non-linear regime in LCDM and Modified Gravity cosmologies

摘要： 与我们对密度场示踪物的理解相比，关于宇宙速度场的直接统计建模仍存在显著改进的机会。 非线性区域中双流速的准确建模缺乏限制了我们充分利用这一可观测信息的能力。 我们提出了一种稳健的方法来建模平均吸积速度 $v_{12}(r,a)$，该方法具有广泛的适用性，涵盖了亚兆秒差距尺度和超出标准LCDM范式的宇宙学。 我们的方法涉及使用精确的非线性功率谱描述来求解完整的双粒子守恒方程。 为了评估模型的稳健性，我们将其扩展到超出标准LCDM的宇宙学，特别是Hu-Sawicki的 $f(R)$-引力和Dvali-Gabadadze-Porrati (DGP) 修改的引力模型。 值得注意的是，我们在千秒差距尺度上对暗物质粒子双流速的预测在整个动力学范围内（$0.1 \lesssim \xi \lesssim 1000$，或 $r\geq0.4$ Mpc/h）与N体模拟结果表现出极好的一致性。 此外，我们表明不同的引力模型会在平均双流速的形状和动力学中留下独特的特征，为宇宙引力定律提供了强有力的检验。 显示英文摘要

摘要： In contrast to our understanding of density field tracers, the modelling of direct statistics pertaining to the cosmic velocity field remains open to significant opportunities for improvement. The lack of accurate modelling for the non-linear domain of pairwise velocities restricts our capacity to fully exploit the information encoded in this observable. We present a robust approach for modelling the mean infall velocities, $v_{12}(r,a)$, with broad applicability spanning sub-megaparsec scales and cosmologies extending beyond the standard LCDM paradigm. Our approach involves solving the full pair-conservation equation using accurate non-linear power spectrum descriptions. To assess the robustness of our model, we extend it to cosmologies beyond the standard LCDM, in particular, the Hu-Sawicki $f(R)$-gravity and Dvali-Gabadadze-Porrati (DGP) modified gravity models. Remarkably, our predictions for pairwise velocities of dark matter particles at kilo-parsec scales exhibit excellent agreement with N-body simulations throughout the entire dynamical range ($0.1 \lesssim \xi \lesssim 1000$, or $r\geq0.4$Mpc/h). Furthermore, we show that different gravity models leave distinct signatures in the shape and dynamics of the mean pairwise velocities, providing a potent test of cosmological gravity laws.