Holography under extreme conditions

ended

Understanding the properties of extreme phases of nuclear matter is one of the major challenges in theoretical physics today. Matter at high temperatures dominated the first microsecond of the early universe and is nowadays produced in relativistic heavy ion collisions in the form of the Quark-Gluon Plasma (QGP). Systematic experimental studies at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC) support the picture of the QGP as an almost perfect fluid but the mechanism for its fast emergence from collisions of hadronic matter remains a puzzle to this day. Another surprising observation was the liquid-like behavior of small systems emerging from proton-proton or proton-lead collisions and the absence of jet quenching which is considered to be a crucial probe characterizing the strongly-coupled QGP. In this proposal I aim at finding a dynamical picture of the thermalisation of out-of-equilibrium matter into hydrodynamic fields by making use of a powerful new framework for studying strongly-coupled dynamical systems: the gauge/gravity duality. It allows to map the strongly-coupled gauge theory dynamics of colliding ions to the collision of gravitational shockwaves which is amenable to numerical general relativity. This offers a unique real-time approach to study the dynamics of hot matter out-of-equilibrium, which I will exploit to tackle two essential problems: i) out-of-equilibrium emergence of collectivity and the fast thermalization of the QGP; ii) system-size dependence of the momentum broadening by jets; This project is inter-disciplinary as it involves applying numerical gravity via holography to the physics of matter at extreme conditions, using the most advanced High-Performance-Computing techniques which I am an expert in. The understanding of the thermalisation scale, of jet quenching and the description of pre-flow, is essential for a determination of the QGP properties of heavy-ion collisions.