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We study the evolution of quantum fluctuations in the glasma, created immediately after the collision of heavy nuclei. We show how the presence of instabilities leads to an enhancement of nonlinear interactions among initially small fluctuations. The nonlinear dynamics leads to an enhanced growth of fluctuations in a large momentum region, exceeding by far the originally unstable band. We investigate the dependence on the coupling constant at weak coupling using classical statistical lattice simulations for SU(2) gauge theory and show how these nonlinearities can be analytically understood within the framework of two-particle irreducible effective action techniques. The dependence on the coupling constant is only logarithmic, in accordance with analytic expectations. Concerning the isotropization of bulk quantities, our results indicate that the system exhibits an order-one anisotropy on parametrically large time scales. Despite this fact, we find that gauge invariant pressure correlation functions seem to exhibit a power law behavior characteristic for wave turbulence. [ABSTRACT FROM AUTHOR]

We study nonequilibrium dynamics of SU(2) pure gauge theory starting from initial overpopulation, where intense classical gauge fields are characterized by a single momentum scale Qs. Classical-statistical lattice simulations indicate a quick evolution towards an approximate scaling behavior with exponent 3/2 at intermediate times. Remarkably, the value for the scaling exponent may be understood as arising from the leading O(g²) contribution in the presence of a time-dependent background field. The phenomenon is associated to weak wave turbulence describing an energy cascade towards higher momenta. This particular aspect is very similar to what is observed for scalar theories, where an effective cubic interaction arises because of the presence of a time-dependent Bose condensate. [ABSTRACT FROM AUTHOR]

We study the dynamics of weakly coupled non-Abelian plasmas within the frameworks of classical-statistical lattice gauge theory and kinetic theory. We focus on a class of systems which are highly occupied, isotropic at all times and initially characterized by a single momentum scale. These represent an idealized version of the situation in relativistic heavy-ion collisions in the color glass condensate picture, where on a time scale 1/Qs, after the collision of heavy nuclei a longitudinally expanding plasma characterized by the saturation scale Qs is formed. Our results indicate that the system evolves according to a turbulent Kolmogorov cascade in the classical regime. Taking this into account, the kinetic description is able to reproduce characteristic features of the evolution correctly. [ABSTRACT FROM AUTHOR]

We employ a nonequilibrium quantum chromodynamics kinetic description to study the kinetic and chemical equilibration of the quark-gluon plasma at weak coupling. Based on our numerical framework, which explicitly includes all leading order processes involving light flavor degrees of freedom, we investigate the thermalization process of homogeneous and isotropic plasmas far-from equilibrium and determine the relevant timescales for kinetic and chemical equilibration. We further simulate the longitudinally expanding preequilibrium plasma created in ultrarelativistic heavy-ion collisions at zero and nonzero density of the conserved charges and study its microscopic and macroscopic evolution toward equilibrium. [ABSTRACT FROM AUTHOR]

We discuss baryon stopping in the color glass condensate description of high energy scattering. We consider the scattering of a distribution of valence quarks on an ultrarelativistic sheet of colored charge. We compute the distribution of scattered quarks from a composite projectile, and calculate the baryon currents before and after the collisions and on an event by event basis. We obtain simple analytic estimates of the baryon number compression and rapidity shifts, which in the idealized case of plane wave scattering, produce results that agree with considerations of Anishetty-Koehler-McLerran [Phys. Rev. D 22, 2793 (1980)]. [ABSTRACT FROM AUTHOR]

We calculate the one- and two-point correlation functions of the energy density and the divergence of the Chern-Simons current in the nonequilibrium glasma state formed in a high-energy nuclear collision. We show that the latter depends on the difference of the total and linearly polarized gluon transverse momentum distributions. Since the divergence of the Chern-Simons current provides the source of axial charge, we infer information about the statistical properties of axial charge production at early times. We further develop a simple phenomenological model to characterize axial charge distributions in terms of distributions of the energy density. [ABSTRACT FROM AUTHOR]

We study the dynamics of nonequilibrium instabilities in anisotropically expanding systems. The most prominent example of such a system is the "glasma" in the context of relativistic heavy-ion collision experiments, where the expansion is a consequence of approximately boost-invariant initial conditions. Here we consider the problem of parametric resonance in scalar TV-component quantum field theories with boost-invariant initial conditions, which is similar in spirit. We find that many aspects of the dynamics can be treated analytically by introducing a generalized conformai time. Primary instabilities, which are described by the linearized evolution equations, are seen to lead to a secondary regime of amplifications with strongly enhanced growth rates due to nonlinear corrections. For the secondary instabilities we present a power-counting scheme for weak coupling, and discuss their role for the question of isotropization and the establishment of an equation of state. [ABSTRACT FROM AUTHOR]

We present a real-time lattice approach to study the nonequilibrium dynamics of vector and axial charges in SU(N)×U(1) gauge theories. Based on a classical description of the non-Abelian and Abelian gauge fields, we include dynamical fermions and develop operator definitions for (improved) Wilson and overlap fermions that allow us to study real-time manifestations of the axial anomaly from first principles. We present a first application of this approach to anomalous transport phenomena such as the chiral magnetic effect (CME) and the chiral separation effect (CSE) by studying the dynamics of fermions during and after a SU(N) sphaleron transition in the presence of a U(1) magnetic field. We investigate the fermion mass and magnetic field dependence of the suggested signatures of the CME and the CSE and point out some important aspects which need to be accounted for in the macroscopic description of anomalous transport phenomena. [ABSTRACT FROM AUTHOR]

Following an explicit example, we present the chain of steps required for an event-by-event description of hadron production in high energy hadronic and nuclear collisions. We start from incoming nuclei, described in the color glass condensate effective theory, whose collision creates the gluon fields of the glasma. Individual gluons are then sampled from the gluon fields' Husimi (smeared Wigner) distributions and clustered using a new spacetime based algorithm. Clusters are fed into the Herwig event generator, which performs the hadronization, conserving energy and momentum. We discuss the physical implications of smearing and problems with the quasiparticle picture for the studied processes. We compute spectra of charged hadrons and identified particles and their azimuthal momentum anisotropies, and address systematic uncertainties on observables, resulting from the general lack of detailed knowledge of the hadronization mechanism. [ABSTRACT FROM AUTHOR]

Nonequilibrium Green's functions provide an efficient way to describe the evolution of the energy-momentum tensor during the early-time preequilibrium stage of high-energy heavy-ion collisions. Besides their practical relevance they also provide a meaningful way to address the question when and to what extent a hydrodynamic description of the system becomes applicable. Within the kinetic theory framework we derive a new method to calculate time-dependent nonequilibrium Green's functions describing the evolution of energy and momentum perturbations on top of an evolving far-from-equilibrium background. We discuss the approach toward viscous hydrodynamics along with the emergence of various scaling phenomena for conformal systems. By comparing our results obtained in the relaxation time approximation to previous calculations in Yang-Mills kinetic theory, we further address the question which macroscopic features of the energy-momentum tensor are sensitive to the underlying microscopic dynamics. [ABSTRACT FROM AUTHOR]

We investigate the relative importance of initial and final state effects on azimuthal correlations of gluons in low and high multiplicity p + Pb collisions. To achieve this, we couple Yang-Mills dynamics of pre-equilibrium gluon fields (IP-GLASMA) to a perturbative QCD based parton cascade for the final state evolution (BAMPS) on an event-by-event basis. We find that signatures of both the initial state correlations and final state interactions are seen in azimuthal correlation observables, such as v2{2PC} (pT), their strength depending on the event multiplicity and transverse momentum. Initial state correlations dominate v2{2PC} (pT) in low multiplicity events for transverse momenta pT > 2 GeV. While final state interactions are dominant in high multiplicity events, initial state correlations affect v2{2PC} (pT) for pT > 2 GeV as well as the pT integrated v2{2PC}. [ABSTRACT FROM AUTHOR]