Chromodynamic Weibel instabilities in relativistic nuclear collisions

Employing a previously derived formulation, and extending the treatment from purely transverse modes to wave vectors having a longitudinal component, we discuss the prospects for the occurrence of Weibel-type color-current filamentation in high-energy nuclear collisions. Numerical solutions of the dispersion equation for a number of scenarios relevant to RHIC and LHC suggest that modes with (predominantly transverse) wave numbers of several hundred MeV may become moderately agitated during the early collision stage. The emergence of filamentation helps to speed up the equilibration of the parton plasma and it may lead to non-statistical azimuthal patterns in the hadron final state.Comment: 11 pages, RevTex, 13 (e)ps files (revised for PRC

Quasiquarks in two stream system

We study the collective quark excitations in an extremely anisotropic system of two interpenetrating streams of the quark-gluon plasma. In contrast to the gluon modes, all quark ones appear to be stable in such a system. Even more, the quark modes in the two-stream system are very similar to those in the isotropic plasma.Comment: 4 pages, 2 figures, minor corrections, to appear in Phys. Rev.

Density Fluctuations in the Quark-Gluon Plasma

Using the kinetic theory we discuss how the particle and energy densities of the quark-gluon plasma fluctuate in a space-time cell. The fluctuations in the equilibrium plasma and in that one from the early stage of ultrarelativistic heavy-ion collisions are estimated. Within the physically interesting values of the parameters involved the fluctuations appear sizeable in both cases.Comment: 8 pages, no macro

Chromodynamic Fluctuations in Quark-Gluon Plasma

Fluctuations of chromodynamic fields in the collisionless quark-gluon plasma are found as a solution of the initial value linearized problem. The plasma initial state is on average colorless, stationary and homogeneous. When the state is stable, the initial fluctuations decay exponentially and in the long-time limit a stationary spectrum of fluctuations is established. For the equilibrium plasma it reproduces the spectrum which is provided by the fluctuation-dissipation relation. Fluctuations in the unstable plasma, where the memory of initial fluctuations is not lost, are also discussed.Comment: 19 pages, numerous but minor corrections, to appear in Phys. Rev.

Momentum Broadening of a Fast Parton in a Perturbative Quark-Gluon Plasma

The average transverse momentum transfer per unit path length to a fast parton scattering elastically in a perturbative quark-gluon plasma is related to the radiative energy loss of the parton. We first calculate the momentum transfer coefficient $\hat q$ in terms of a classical Langevin problem and then define it quantum-mechanically through scattering matrix element. After treating the well known case of a quark-gluon plasma in equilibrium we consider an off-equilibrium unstable plasma. As a specific example, we treat the two-stream plasma with unstable modes of longitudinal chromoelectric field. In the presence of the instabilities, $\hat q$ is shown to exponentially grow in time.Comment: Updated version containing an analysis of insufficiencies in previous calculations of momentum broadening in unstable plasma

p_T-fluctuations in high-energy p-p and A-A collisions

The event-by-event p_T-fluctuations in proton-proton and central Pb-Pb collisions, which have been experimentally studied by means of the so-called Phi-measure, are analyzed. The contribution due to the correlation which couples the average p_T to the event multiplicity is computed. The correlation appears to be far too weak to explain the preliminary experimental value of Phi (p_T) in p-p interactions. The significance of the result is discussed.Comment: 5 pages, 2 figures, minor improvement

Deciphering Azimuthal Correlations in Relativistic Heavy-Ion Collisions

We discuss various sources of azimuthal correlations in relativistic heavy-ion collisions. The integral measure Phi is applied to quantify the correlations. We first consider separately the correlations caused by the elliptic flow, resonance decays, jets and transverse momentum conservation. An effect of randomly lost particles is also discussed. Using the PYTHIA and HIJING event generators we produce a sample of events which mimic experimental data. By means of kinematic cuts and particle's selection criteria, the data are analyzed to identify a dominant source of correlations.Comment: 8 pages, minor corrections, to appear in Phys. Rev.

Whitening of the Quark-Gluon Plasma

Parton-parton collisions do not neutralize local color charges in the quark-gluon plasma as they only redistribute the charges among momentum modes. We discuss color diffusion and color conductivity as the processes responsible for the neutralization of the plasma. For this purpose, we first compute the conductivity and diffusion coefficients in the plasma that is significantly colorful. Then, the time evolution of the color density due to the conductivity and diffusion is studied. The conductivity is shown to be much more efficient than the diffusion in neutralizing the plasma at the scale longer than the screening length. Estimates of the characteristic time scales, which are based on close to global equilibrium computations, suggest that first the plasma becomes white and then the momentum degrees of freedom thermalize.Comment: 9 pages, revised, to appear in Phys. Rev.

Hard Loop Approach to Anisotropic Systems

Anisotropic systems of quarks and gluons, which at least for sufficiently short space-time intervals can be treated as homogeneous and static, are considered. The gluon polarization tensor of such a system is explicitly computed within the semiclassical kinetic and Hard Loop diagrammatic theories. The equivalence of the two approaches is demonstrated. The quark self energy is computed as well, and finally, the dispersion relations of quarks and gluons in the anisotropic medium are discussed.Comment: 10 pages, revised to appear in Phys. Rev.