Quantum-to-classical transition of initial fluctuations in strongly interacting systems

Ascertain the mechanism by which initial quantum fluctuations in closed, strongly interacting many-body systems—such as the quark–gluon plasma produced in relativistic heavy-ion collisions—evolve into classical collective behavior that can be effectively described by hydrodynamic equations and attractor dynamics.

Background

The paper investigates hydrodynamic attractors in relativistic heavy-ion collisions and demonstrates that attractors from higher-order hydrodynamic theories converge to the same late-time behavior as second-order theories when the second-order transport coefficients are matched. This suggests that properly formulated second-order hydrodynamics can effectively approximate higher-order descriptions from intermediate times onward.

From the perspective of thermalization, the authors highlight the dominance of collective motion over microscopic quantum interactions at late times. Despite these insights, the fundamental question of how quantum fluctuations in the early, far-from-equilibrium stage give rise to classical collective behavior remains unresolved and is identified as an open problem.