0000000000313269
AUTHOR
Jarkko Peuron
Broad excitations in a 2+1D overoccupied gluon plasma
Motivated by the initial stages of high-energy heavy-ion collisions, we study excitations of far-from-equilibrium 2+1 dimensional gauge theories using classical-statistical lattice simulations. We evolve field perturbations over a strongly overoccupied background undergoing self-similar evolution. While in 3+1D the excitations are described by hard-thermal loop theory, their structure in 2+1D is nontrivial and nonperturbative. These nonperturbative interactions lead to broad excitation peaks in spectral and statistical correlation functions. Their width is comparable to the frequency of soft excitations, demonstrating the absence of soft quasiparticles in these theories. Our results also su…
Heavy quark diffusion in an overoccupied gluon plasma
We extract the heavy-quark diffusion coefficient \kappa and the resulting momentum broadening in a far-from-equilibrium non-Abelian plasma. We find several features in the time dependence of the momentum broadening: a short initial rapid growth of , followed by linear growth with time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency. We show that these novel oscillations are not easily explained using perturbative techniques but result from an excess of gluons at low momenta. These oscillation are therefore a gauge invariant confirmation of the infrared enhancement we had previously observed in gauge-fixed correlation functions. We argue that…
Plasmon mass scale in two dimensional classical nonequilibrium gauge theory
We study the plasmon mass scale in weakly coupled strongly interacting nonabelian gauge theory in a two dimensional configuration that mimics the boost invariant initial color fields in a heavy ion collision. We numerically measure the plasmon mass scale using three different methods: a Hard Thermal Loop (HTL) expression involving the quasiparticle spectrum constructed from Coulomb gauge field correlators, an effective dispersion relation and the measurement of oscillations between electric and magnetic energies after introducing a spatially uniform perturbation to the electric field. We find that the hard thermal loop expression and the uniform electric field measurement are in rough agree…
Spectral function for overoccupied gluodynamics from real-time lattice simulations
We study the spectral properties of a highly occupied non-Abelian non-equilibrium plasma appearing ubiquitously in weak coupling descriptions of QCD matter. The spectral function of this far-from-equilibrium plasma is measured by employing linear response theory in classical-statistical real-time lattice Yang-Mills simulations. We establish the existence of transversely and longitudinally polarized quasiparticles and obtain their dispersion relations, effective mass, plasmon frequency, damping rate and further structures in the spectral and statistical functions. Our new method can be interpreted as a non-perturbative generalization of hard thermal loop (HTL) effective theory. We see indica…
Plasmon mass scale in classical nonequilibrium gauge theory
Classical lattice Yang-Mills calculations provide a good way to understand different nonequilibrium phenomena in nonperturbatively overoccupied systems. Above the Debye scale the classical theory can be matched smoothly to kinetic theory. The aim of this work is to study the limits of this quasiparticle picture by determining the plasmon mass in classical real time Yang-Mills theory on a lattice in 3 spatial dimensions. We compare three methods to determine the plasmon mass: a hard thermal loop expression in terms of the particle distribution, an effective dispersion relation constructed from fields and their time derivatives, and by measuring oscillations between electric and magnetic fiel…
Determination of the non-abelian Debye screening mass using classical chromodynamics
Tässä työssä tutkitaan gluonin Debye-massaa, ja sen aika- ja miehityslukudis- tribuutioriippuvuutta käyttäen klassista väridynamiikkaa kahdessa paikkaulot- tuvuudessa. Työssä tutkitaan myös ominaista liikemääräskaalaa ja miehitys- lukudistribuutioita. Gluonin Debye-massa määritetään sovittamalla suora glu- onien dispersiorelaatioon pienellä liikemäärällä. Tuloksia verrataan termisestä kenttäteoriasta johdetun kaavan ennusteisiin. Aluksi tutustutaan raskasionifysiikkaan liittyvään viitekehykseen. Tämän jälkeen kerrataan nopeasti klassinen Yang-Mills teoria jatkumossa ja hilalla. Käydään läpi Fourier kiihdytetty Coulombin mitan kiinnitysmenetelmä yk- sityiskohtaisesti jatkumossa ja hilalla. T…
Time evolution of linearized gauge field fluctuations on a real-time lattice
Classical real-time lattice simulations play an important role in understanding non-equilibrium phenomena in gauge theories and are used in particular to model the prethermal evolution of heavy-ion collisions. Due to instabilities, small quantum fluctuations on top of the classical background may significantly affect the dynamics of the system. In this paper we argue for the need for a numerical calculation of a system of classical gauge fields and small linearized fluctuations in a way that keeps the separation between the two manifest. We derive and test an explicit algorithm to solve these equations on the lattice, maintaining gauge invariance and Gauss's law.
Jet momentum broadening during initial stages in heavy-ion collisions
We study the jet quenching parameter $\hat q$ in the initial pre-equilibrium stages of heavy-ion collisions using the QCD kinetic theory description of the anisotropic quark-gluon plasma. This allows us to smoothly close the gap in the literature between the early glasma stage of the collision and the onset of hydrodynamics. We find that the pre-hydrodynamic evolution of $\hat q$ during the bottom-up kinetic scenario shows little sensitivity to the initial conditions, jet energies and models of the transverse momentum cutoff. We also observe that, similarly to the glasma case, the jet quenching parameter is enhanced along the beam axis as compared to the transverse direction during most of …
Plasmon mass scale and quantum fluctuations of classical fields on a real time lattice
Classical real-time lattice simulations play an important role in understanding non-equilibrium phenomena in gauge theories and are used in particular to model the prethermal evolution of heavy-ion collisions. Above the Debye scale the classical Yang-Mills (CYM) theory can be matched smoothly to kinetic theory. First we study the limits of the quasiparticle picture of the CYM fields by determining the plasmon mass of the system using 3 different methods. Then we argue that one needs a numerical calculation of a system of classical gauge fields and small linearized fluctuations which correspond to quantum fluctuations, in a way that keeps the separation between the two manifest. We demonstra…
Probing spectral properties of the QGP with real-time lattice simulations
We present a new method to obtain spectral properties of a non-Abelian gauge theory in the region where occupation numbers are high. The method to measure the (single-particle) spectral function is based on linear response theory and classical-statistical lattice simulations. Although we apply it to a system far from equilibrium in a self-similar regime, the extracted spectral function can be understood within the hard thermal loop (HTL) formalism and can thus be connected to thermal equilibrium at high temperatures. This allows us to obtain quantities like the lifetime of quasiparticles that are beyond the leading order and difficult to compute within HTL. The approach has the potential to…
Spectral function for overoccupied gluodynamics from classical lattice simulations
We study the spectral properties of an overoccupied gluonic system far from equilibrium. Using classical Yang-Mills simulations and linear response theory, we determine the statistical and spectral functions. We measure dispersion relations and damping rates of transversally and longitudinally polarized excitations in the gluonic plasma, and also study further structures in the spectral function.
Quasiparticle properties of nonequilibrium gluon plasma
We apply classical gluodynamics to early stages of ultrarelativistic heavy-ion collisions. We start by giving a brief overview of QCD. Then we proceed to the space-time evolution of ultrarelativistic heavy-ion collisions in the color glass condensate framework and go through the basics of real-time gluodynamics on the lattice in the temporal gauge. We study the plasmon mass scale in three- and two-dimensional systems by comparing three different methods to measure the mass scale. The methods are a formula which can be derived from Hard Thermal Loop effective theory at leading order (HTL), the effective dispersion relation (DR) and measurement of the plasma oscillation frequency triggered by th…