Abstract
We perform real-time lattice simulations of nonequilibrium quark production in the longitudinally expanding QCD plasma. Starting from a highly occupied gluonic state with vacuum quark sector, we extract the time evolution of quark and gluon number densities per unit transverse area and rapidity. The total quark number shows after an initial rapid increase an almost linear growth with time. Remarkably, this growth rate appears to be consistent with a simple kinetic theory estimate involving only two-to-two scattering processes in small-angle approximation. This extends previous findings about the role of two-to-two scatterings for purely gluonic dynamics in accordance with the early stages of the bottom-up thermalization scenario.
Highlights
AND OUTLINERecently, much progress has been achieved in understanding the spatio-temporal evolution of the QCD plasma for relativistic heavy-ion collisions at sufficiently high energies
Perturbative descriptions are not expected to apply. In this regime the nonequilibrium quantum dynamics can be mapped onto a classical-statistical field theory description with quantum initial conditions, which can be solved with lattice simulation techniques
We find that the total quark number shows after an initial rapid increase an almost linear growth with time
Summary
Much progress has been achieved in understanding the spatio-temporal evolution of the QCD plasma for relativistic heavy-ion collisions at sufficiently high energies. They diminish the problem of our insufficient knowledge about the system’s details at the time of collisional impact Attractors imply another aspect of great practical importance: they reflect the presence of a large number of irrelevant operators in the renormalization group sense, such that rather simple effective descriptions of the relevant dynamics may be expected.. Previous lattice simulation results of the longitudinally expanding pure gauge theory identified, after a short period of highly complex dynamics with gluon number changing processes, a number conserving regime that is consistently described by two-to-two scattering processes [3,4] in agreement with the earlier stages of the bottom-up thermalization scenario [18]. II we describe the framework of real-time lattice simulations with dynamical quarks in the longitudinally expanding geometry This includes a detailed discussion of the initial conditions for the nonequilibrium evolution and how observables are extracted from the lattice data. V, we provide two appendices on details about the treatment of fermion doublers on a real-time lattice in Appendix A and a discussion on lattice cutoff dependencies in Appendix B
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