Kurkela Aleksi, van der Schee Wilke, Wiedemann Urs Achim, Wu Bin
Theoretical Physics Department, CERN, CH-1211 Genève 23, Switzerland.
Faculty of Science and Technology, University of Stavanger, 4036 Stavanger, Norway.
Phys Rev Lett. 2020 Mar 13;124(10):102301. doi: 10.1103/PhysRevLett.124.102301.
Whether, how, and to what extent solutions of Bjorken-expanding systems become insensitive to aspects of their initial conditions is of importance for heavy-ion collisions. Here we study 1+1D and phenomenologically relevant boost-invariant 3+1D systems in which initial conditions approach a universal attractor. In Israel-Stewart theory (IS) and kinetic theory where the universal attractor extends to arbitrarily early times, we show that all initial conditions approach the attractor at early times by a power law while their approach is exponential at late times. In these theories, the physical mechanisms of hydrodynamization operational at late times do not drive the approach to the attractor at early times, and the early-time attractor is reached prior to hydrodynamization. In marked contrast, the attractor in strongly coupled systems is realized concurrent with hydrodynamization. This qualitative difference may offer a basis for discriminating weakly and strongly coupled scenarios of heavy-ion collisions.
对于重离子碰撞而言， Bjorken 膨胀系统的解是否、如何以及在何种程度上对其初始条件的各个方面变得不敏感是很重要的。在此，我们研究 1 + 1 维以及现象学上相关的具有快度不变性的 3 + 1 维系统，其中初始条件趋近于一个普适吸引子。在以色列 - 斯图尔特理论（IS）和动力学理论中，普适吸引子延伸到任意早的时刻，我们表明所有初始条件在早期通过幂律趋近吸引子，而在晚期其趋近是指数型的。在这些理论中，晚期起作用的流体动力学形成的物理机制在早期并不会驱动向吸引子的趋近，并且在流体动力学形成之前就已达到早期吸引子。与之形成鲜明对比的是，强耦合系统中的吸引子是与流体动力学形成同时实现的。这种定性差异可能为区分重离子碰撞的弱耦合和强耦合情形提供一个基础。
