Plasmons of quark-gluon plasma, or gluon collective modes, are systematically studied. The plasma is, in general, nonequilibrium but homogeneous. We consider anisotropic momentum distributions of plasma constituents which are obtained from the isotropic one by stretching or squeezing in one direction. This leads to prolate or oblate distributions, respectively. We study all possible degrees of one-dimensional deformation from the extremely prolate case, when the momentum distribution is infinitely elongated in one direction to the extremely oblate distribution, which is infinitely squeezed in the same direction. In between these extremes we discuss arbitrarily prolate, weakly prolate, isotropic, weakly oblate, and arbitrarily oblate distributions. For each case, the number of modes is determined using a Nyquist analysis and the complete spectrum of plasmons is found analytically if possible and numerically when not. Unstable modes are shown to exist in all cases except that of isotropic plasma. We derive conditions on the wave vectors for the existence of these instabilities. We also discuss stable modes which are not limited to small domains of wave vectors and therefore have an important influence on the system's dynamics.

The momentum distribution of quark-gluon plasma at the early stage of a relativistic heavyion collision is anisotropic and consequently the system, which is assumed to be weakly coupled, is unstable due to chromomagnetic plasma modes. We consider a high-energy parton which flies across such an unstable plasma, and the energy transfer between the parton and the medium is studied as an initial value problem. In the case of equilibrium plasmas, the well-known formula of collisional energy loss is reproduced. The unstable plasma case is much more complex, and the parton can lose or gain energy depending on the initial conditions. The extremely prolate and extremely oblate systems are considered as examples of unstable plasmas, and two classes of initial conditions are discussed. When the initial chromodynamic field is uncorrelated with the color state of the parton, it typically looses energy, and the magnitude of the energy loss is comparable to that in an equilibrium plasma of the same density. When the initial chromodynamic field is induced by the parton, it can be either accelerated or decelerated depending on the relative phase factor. With a correlated initial condition, the energy transfer grows exponentially in time and its magnitude can much exceed the absolute value of energy loss in an equilibrium plasma. The energy transfer is also strongly directionally dependent. Consequences of our findings for the phenomenology of jet quenching in relativistic heavy-ion collisions are briefly discussed.

Bulk and shear viscosity coefficients for systems composed of quasiparticles with medium-modified dispersion relations are determined within an effective kinetic theory approach of Boltzmann-Vlasov type. Local conservation of energy and momentum, which is self-consistently embedded in the kinetic theory, implies in thermal equilibrium thermodynamic consistency in quasiparticle approaches.

We investigate production of φ mesons and Ξ baryons in nucleusnucleus collisions. Reactions on strange particles acting as a catalyser are proposed to interpret the high observed φ yields in HADES experiments as well as the energy dependence of the widths of φ rapidity spectra in collisions at the SPS energies. It is argued that the enhancement of Ξ − yield observed by HADES is even higher than originally reported, if effects of the experimental centrality trigger are taken into account. Cross sections for new hadronic processes that could produce Ξ − are reviewed.

Abstract. The energy loss of a highly energetic parton in a weakly coupled quark-gluon plasma is studied as an initial value problem. An extremely prolate plasma, where the momentum distribution is infinitely elongated along one direction, is considered. The energy loss is strongly time and direction dependent and its magnitude can much exceed the equilibrium value. It is logarithmically ultraviolet divergent. We argue that a good approximation to the energy loss can be obtained if this divergence is cut off with the parton energy.