Abstract
High-energy nuclear collisions produce a nonequilibrium plasma of quarks and gluons which thermalizes and exhibits hydrodynamic flow. There are currently no practical frameworks to connect the early particle production in classical field simulations to the subsequent hydrodynamic evolution. We build such a framework using nonequilibrium Green's functions, calculated in QCD kinetic theory, to propagate the initial energy-momentum tensor to the hydrodynamic phase. We demonstrate that this approach can be easily incorporated into existing hydrodynamic simulations, leading to stronger constraints on the energy density at early times and the transport properties of the QCD medium. Based on (conformal) scaling properties of the Green's functions, we further obtain pragmatic bounds for the applicability of hydrodynamics in nuclear collisions.
Highlights
Theoretical Physics Department, CERN, Geneva, Switzerland and Faculty of Science and Technology, University of Stavanger, 4036 Stavanger, Norway
In this Letter, we address this challenge by showing how an effective kinetic theory (EKT) of weakly coupled quantum chromodynamics (QCD) [10] can be used to smoothly describe the evolution of a general out-of-equilibrium energy-momentum tensor specified at very early time τEKT ≪ τhydro to its late time hydrodynamic form
While the underlying kinetic approach can be justified rigorously for the collision of large nuclei only in the limit of very weak coupling, we show that the kinetic response to a variety of initial conditions can be smoothly extrapolated to physically relevant couplings by using an appropriate scaling variable
Summary
Theoretical Physics Department, CERN, Geneva, Switzerland and Faculty of Science and Technology, University of Stavanger, 4036 Stavanger, Norway. There are currently no practical frameworks to connect the early particle production in classical field simulations to the subsequent hydrodynamic evolution We build such a framework using nonequilibrium Green’s functions, calculated in QCD kinetic theory, to propagate the initial energy-momentum tensor to the hydrodynamic phase. Collisions of heavy nuclei at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) heat up nuclear matter sufficiently to produce a plasma of deconfined colored degrees of freedom—the quark-gluon plasma (QGP) [1,2,3,4] The properties of this deconfined plasma can only be constrained indirectly from the mass and momentum distribution of the final shower of colorneutral particles reaching the detectors. The deconfined matter is not amenable to a coarse-grained description in terms of macroscopic hydrodynamics fields, and a microscopic
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