preprint Nicolas Borghini author Marc Borrell author Hendrik Roch author 27 department PC2: Computing Resources Provided by the Paderborn Center for Parallel Computing project We investigate the early time development of the anisotropic transverse flow and spatial eccentricities of a fireball with various particle-based transport approaches using a fixed initial condition. In numerical simulations ranging from the quasi-collisionless case to the hydrodynamic regime, we find that the onset of $v_n$ and of related measures of anisotropic flow can be described with a simple power-law ansatz, with an exponent that depends on the amount of rescatterings in the system. In the few-rescatterings regime we perform semi-analytical calculations, based on a systematic expansion in powers of time and the cross section, which can reproduce the numerical findings. 2022 eng 2201.13294 Borghini N, Borrell M, Roch H. Early time behavior of spatial and momentum anisotropies in kinetic  theory across different Knudsen numbers. <i>arXiv:220113294</i>. Published online 2022. N. Borghini, M. Borrell, and H. Roch, “Early time behavior of spatial and momentum anisotropies in kinetic  theory across different Knudsen numbers,” <i>arXiv:2201.13294</i>. 2022. Borghini, Nicolas, Marc Borrell, and Hendrik Roch. “Early Time Behavior of Spatial and Momentum Anisotropies in Kinetic  Theory across Different Knudsen Numbers.” <i>ArXiv:2201.13294</i>, 2022. @article{Borghini_Borrell_Roch_2022, title={Early time behavior of spatial and momentum anisotropies in kinetic  theory across different Knudsen numbers}, journal={arXiv:2201.13294}, author={Borghini, Nicolas and Borrell, Marc and Roch, Hendrik}, year={2022} } N. Borghini, M. Borrell, H. Roch, ArXiv:2201.13294 (2022). Borghini, Nicolas, et al. “Early Time Behavior of Spatial and Momentum Anisotropies in Kinetic  Theory across Different Knudsen Numbers.” <i>ArXiv:2201.13294</i>, 2022. Borghini, N., Borrell, M., &#38; Roch, H. (2022). Early time behavior of spatial and momentum anisotropies in kinetic  theory across different Knudsen numbers. In <i>arXiv:2201.13294</i>. 321772022-06-27T09:08:04Z2022-06-27T09:35:53Z