Collective dynamics in heavy and light-ion collisions -- I) Kinetic Theory vs. Hydrodynamics

High-energy nuclear collisions exhibit collective flow, which emerges as a dynamical response of the Quark-Gluon Plasma (QGP) to the initial state geometry of the collision. Collective flow in heavy-ion collisions is usually described within multi-stage evolution models, which employ a viscous relativistic hydrodynamic description of the space-time evolution of the QGP. By comparing event-by-event simulations in kinetic theory and viscous hydrodynamics in OO, AuAu and PbPb collisions at RHIC and LHC energies, we quantify to what extent a macroscopic hydrodynamic description can accurately describe the development of collective flow and to what extent collective flow in small systems, such as OO, is sensitive to the non-equilibrium evolution of the QGP beyond hydrodynamics.