The early and late time attractors in nuclear collisions
The high-energy heavy ion collisions (illustrated above) produce matter far from equilibrium. It is astounding that within yoctoseconds, the QCD matter can be successfully described by fluid dynamics. The leading explanation of such rapid QCD thermalisation is the attractor phenomena . It can be shown that far-from-equilbrium quantum systems rapidly approach a simple trajectory in phase-space (attractor) that does not depend on the details of initial conditions. Such attractor behaviour is universal and can be found in systems ranging from non-relativistic scalar theories to strongly-correlated QFTs described by gauge/gravity duality (Berges et al., 2021).
A system near a non-thermal attractor exhibit a self-similar behaviour. For example, the time evolution of particle distribution at early stages of heavy-ion collisions can be described by rescaling the initial conditions with a few scaling exponents (left subplot above). I have generalised the scaling behaviour to time-dependent scaling exponents—pre-scaling (Mazeliauskas & Berges, 2019). We have also made analytical prediction for pre-scaling that has been confirmed in a cold-atom experiment (Heller et al., 2024). At later stages of heavy- ion collision the system approaches equilibrium and exhibits hydrodynamic behaviour much earlier than naive estimates would suggest (right subplot above). Such behaviour is called a hydrodynamic attractor. I have extensively studied hydrodynamic attractors in QCD kinetic theory and their phenomenological implications in heavy-ion collisions (Giacalone et al., 2019; Berges et al., 2021). I am also researching hydrodynamic attractor behaviour in cold-atom systems.
@article{Heller:2023mah,author={Heller, Michal P. and Mazeliauskas, Aleksas and Preis, Thimo},title={{Prescaling Relaxation to Nonthermal Attractors}},archiveprefix={arXiv},primaryclass={hep-th},doi={10.1103/PhysRevLett.132.071602},journal={Phys. Rev. Lett.},volume={132},number={7},pages={071602},year={2024},}
@article{Garcia-Montero:2023lrd,author={Garcia-Montero, Oscar and Mazeliauskas, Aleksas and Plaschke, Philip and Schlichting, S\"oren},title={{Pre-equilibrium photons from the early stages of heavy-ion collisions}},archiveprefix={arXiv},primaryclass={hep-ph},doi={10.1007/JHEP03(2024)053},journal={JHEP},volume={03},pages={053},year={2024}}
@article{Mikheev:2022fdl,author={Mikheev, Aleksandr N. and Mazeliauskas, Aleksas and Berges, J\"urgen},title={{Stability analysis of nonthermal fixed points in longitudinally expanding kinetic theory}},archiveprefix={arXiv},primaryclass={hep-ph},reportnumber={CERN-TH-2022-030},doi={10.1103/PhysRevD.105.116025},journal={Phys. Rev. D},volume={105},number={11},pages={116025},year={2022}}
2021
Rev. Mod. Phys.
QCD thermalization: Ab initio approaches and interdisciplinary connections
Jürgen Berges, Michal P. Heller, Aleksas Mazeliauskas, and 1 more author
Heavy-ion collisions at BNL’s Relativistic Heavy Ion Collider and CERN’s Large Hadron Collider provide strong evidence for the formation of a quark-gluon plasma, with temperatures extracted from relativistic viscous hydrodynamic simulations shown to be well above the transition temperature from hadron matter. Outstanding problems in QCD include how the strongly correlated quark-gluon matter forms in a heavy-ion collision, its properties off equilibrium, and the thermalization process in the plasma. The theoretical progress in this field in weak-coupling QCD effective field theories and in strong-coupling holographic approaches based on gauge-gravity duality is reviewed. The interdisciplinary connections of different stages of the thermalization process to nonequilibrium dynamics in other systems across energy scales ranging from inflationary cosmology to strong-field QED to ultracold atomic gases are outlined, with emphasis placed on the universal dynamics of nonthermal and hydrodynamic attractors. Measurements in heavy-ion collisions are surveyed that are sensitive to the early nonequilibrium stages of the collision and the potential for future measurements is discussed. The current state of the art in thermalization studies is summarized and promising avenues for further progress are identified.
@article{Berges:2020fwq,author={Berges, J\"urgen and Heller, Michal P. and Mazeliauskas, Aleksas and Venugopalan, Raju},title={{QCD thermalization: Ab initio approaches and interdisciplinary connections}},archiveprefix={arXiv},primaryclass={hep-th},reportnumber={CERN-TH-2020-080},doi={10.1103/RevModPhys.93.035003},journal={Rev. Mod. Phys.},volume={93},number={3},pages={035003},year={2021},}
@article{Mazeliauskas:2018yef,author={Mazeliauskas, Aleksas and Berges, J\"urgen},title={{Prescaling and far-from-equilibrium hydrodynamics in the quark-gluon plasma}},archiveprefix={arXiv},primaryclass={hep-ph},doi={10.1103/PhysRevLett.122.122301},journal={Phys. Rev. Lett.},volume={122},number={12},pages={122301},year={2019}}
@article{Giacalone:2019ldn,author={Giacalone, Giuliano and Mazeliauskas, Aleksas and Schlichting, S\"oren},title={{Hydrodynamic attractors, initial state energy and particle production in relativistic nuclear collisions}},archiveprefix={arXiv},primaryclass={hep-ph},reportnumber={INT-PUB-19-036},doi={10.1103/PhysRevLett.123.262301},journal={Phys. Rev. Lett.},volume={123},number={26},pages={262301},year={2019}}
@article{Kurkela:2018vqr,author={Kurkela, Aleksi and Mazeliauskas, Aleksas and Paquet, Jean-Fran\c{c}ois and Schlichting, S\"oren and Teaney, Derek},title={{Effective kinetic description of event-by-event pre-equilibrium dynamics in high-energy heavy-ion collisions}},archiveprefix={arXiv},primaryclass={hep-ph},doi={10.1103/PhysRevC.99.034910},journal={Phys. Rev. C},volume={99},number={3},pages={034910},year={2019}}
@article{Kurkela:2018wud,author={Kurkela, Aleksi and Mazeliauskas, Aleksas and Paquet, Jean-Fran\c{c}ois and Schlichting, S\"oren and Teaney, Derek},title={{Matching the Nonequilibrium Initial Stage of Heavy Ion Collisions to Hydrodynamics with QCD Kinetic Theory}},archiveprefix={arXiv},primaryclass={hep-ph},doi={10.1103/PhysRevLett.122.122302},journal={Phys. Rev. Lett.},volume={122},number={12},pages={122302},year={2019}}
