The wake potential in the viscous quark–gluon plasma

Based on the dielectric function derived from the viscous chromohydrodynamic approach, we investigate the wake potential induced by a fast parton traveling through the viscous quark–gluon plasma. An oscillatory wake potential and a Lennard-Jones potential are found in the backward direction for the fast parton speeds v=0.99c$v=0.99c$ and v=0.55c$v=0.55c$, respectively. In the forward direction, there is a modified Coulomb screening potential for both two speeds. When v=0.99c$v=0.99c$, shear viscosity makes the oscillation of potential more remarkable with the increase of η/s$\eta /s$. While v=0.55c$v=0.55c$, the viscous effects on the wake potential are very trivial in both the forward and backward directions. Finally, we give some explanations for the speed-dependent viscous effects on the wake properties.     

Role of glueballs in non-perturbative quark–gluon plasma

Discussed is how non-perturbative properties of quark gluon plasma, recently discovered in RHIC experiment, can be related to the change of properties of scalar and pseudoscalar glueballs. We set up a model with the Cornwall–Soni's glueball–gluon interaction, which shows that the pseudoscalar glueball becomes massless above the critical temperature of deconfinement phase transition. This change of properties gives rise to the change of sign of the gluon condensate at T>Tc$T>T_c$. We discuss the other physical consequences resulting from the drastic change of the pseudoscalar glueball mass above the critical temperature.     

Non-abelian effects on wake potential in quark–gluon plasma

In this paper, based on the dielectric function calculated with the hard thermal loop (HTL) resummation approach, we study the wake potential induced by a fast parton traveling through quark–gluon plasma (QGP). In contrast to the wake potential calculated in the HTL approximation, our results show that non-abelian effects from the resummation calculation enhance the anisotropy of the wake potential. By investigating the relation between the anisotropic properties of the wake potential and the imaginary part of the dielectric function, we give some explanations for the enhancement of the anisotropy.     

The thermal width of heavy quarkonia moving in quark–gluon plasma

The velocity dependence of the thermal width of heavy quarkonia traveling with respect to the quark–gluon plasma is calculated up to the NLO in perturbative QCD. At the LO, the width decreases with increasing speed, whereas at the NLO it increases with a magnitude approximately proportional to the expectation value of the relative velocity between the quarkonium and a parton in thermal equilibrium. Such an asymptotic behavior is due to the NLO dissociation cross section converging to a nonvanishing value in the high energy limit.     

Suppression of forward dilepton production from an anisotropic quark–gluon plasma

We calculate the rapidity dependence of leading-order medium dilepton yields resulting from a quark–gluon plasma which has a local time-dependent anisotropy in momentum space. We present a phenomenological model which includes the temporal evolution of the plasma anisotropy parameter, ξ, and the hard momentum scale, p _hard. Our model interpolates between a 1+1 dimensional collisionally broadened expansion at early times and a 1+1 dimensional ideal hydrodynamic expansion at late times. Using our model, we find that at LHC energies, forward high-energy medium dilepton production would be suppressed by a factor of up to 3 if one assumes an isotropization/thermalization time of 2 fm/c. Therefore, it may be possible to use forward dilepton yields to experimentally determine the time of the onset of locally isotropic hydrodynamic expansion of the quark–gluon plasma as produced in ultrarelativistic heavy-ion collisions.     

Charmonium suppression in the presence of dissipative forces in a strongly-coupled quark–gluon plasma

We study the survival of charmonium states in a strongly-coupled quark–gluon plasma in the presence of dissipative forces. We consider first-order dissipative corrections to the plasma equation of motion in the Bjorken boost-invariant expansion with a strongly-coupled equation of state for QGP and study the survival of these states with the dissociation temperatures obtained by correcting the full Cornell potential not its Coulomb part alone with a dielectric function encoding the effects of deconfined medium. We further explore the sensitivity of prompt and sequential suppression of these states to the shear viscosity-to-entropy density ratio, η/s from perturbative QCD and AdS/CFT predictions. Our results show nice agreement with the recent experimental results at RHIC.     

Photon polarization as a probe for quark–gluon plasma dynamics

Prospects of measuring polarized photons emitted from a quark–gluon plasma (QGP) are discussed. In particular, the detection of a possible quark spin polarization in a QGP using circularly polarized photons emitted from the plasma is studied. Photons leave the QGP without further interaction and thus provide a primary probe for quark polarization within the QGP. We find that photon polarization cannot solely arise due to a possible QGP momentum space anisotropy, but may be enhanced due to it. In particular, for oblate momentum distributions and high photon energies, quark polarization is efficiently transfered to photon polarization. The role of competing sources of polarized photons in heavy-ion collisions is discussed.     

Synchrotron contribution to photon emission from a quark–gluon plasma

The influence of the magnetic field on the photon emission from the quark–gluon plasma created in AA collisions is studied. It is found that the effect of magnetic field is very small even for very optimistic assumption on the magnitude of the magnetic field for noncentral AA collisions.     

Quark potential in a quark–meson plasma

We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly coupled in the temperature region 1≤T/T _c≤3, with T _c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase transition point.     

Towards tomography of quark–gluon plasma using double inclusive forward-central jets in Pb–Pb collision

We propose a new framework, merging High Energy Factorization with final-state jet quenching effects due to interactions in a quark–gluon plasma, to compute di-jet rates at mid-rapidity and forward rapidity. It allows one to consistently study the interplay of initial-state effects with medium interactions, opening the possibility for understanding the dynamics of hard probes in heavy-ion collisions and the QGP evolution in rapidity.     

Colormagnetic confinement in the quark–gluon thermodynamics

Nonperturbative effects in the quark–gluon thermodynamics are studied in the framework of vacuum correlator method. It is shown, that for T > T ₀ = 175 MeV two correlators: colorelectric D ₁ ^E (x) and colormagnetic D ^H (x), provide the Polyakov line and the colormagnetic confinement in the spatial planes respectively. As a result, both effects produce the realistic behavior of p(T) and I(T), being in good agreement with numerical lattice data.     

Quark–gluon plasma as a strongly coupled color-Coulombic plasma

We show that the extensively studied equation of state (EOS) of strongly coupled QED plasma fits the recent lattice EOS data of gluon plasma remarkably well, with appropriate modifications to take account of color degrees of freedom and the running coupling constant. Hence we conclude that the quark–gluon plasma near the critical temperature is a strongly coupled color-Coulombic plasma. Received: 13 January 1999 / Revised version: 22 March 1999 / Published online: 14 October 1999     

Quasi-particle model for lattice QCD: quark–gluon plasma in?heavy ion collisions

We propose a quasi-particle model to describe the lattice QCD equation of state for pure SU(3) gauge theory in its deconfined state, for T≥1.5T _c. The method involves mapping the interaction part of the equation of state to an effective fugacity of otherwise non-interacting quasi-gluons. We find that this mapping is exact. Using the quasi-gluon distribution function, we determine the energy density and the modified dispersion relation for the single particle energy, in which the trace anomaly is manifest. As an application, we first determine the Debye mass, and then the important transport parameters, viz., the shear viscosity, η, and the shear viscosity to entropy density ratio, h/S\eta/{\mathcal{S}}. We find that both η and h/S\eta/{\mathcal{S}} are sensitive to the interactions, and that the interactions significantly lower both η and h/S\eta/\mathcal{S}.     

HQET quark–gluon vertex at one loop

We calculate the HQET quark–gluon vertex at one loop, for arbitrary external momenta, in an arbitrary covariant gauge and space-time dimension. Relevant results and algorithms for the three-point HQET integrals are presented. We also show how one can obtain the HQET limit directly from QCD results for the quark–gluon vertex. Received: 8 March 2001 / Published online: 18 May 2001     

Nucleon electromagnetic form factors in a quark–gluon core model

We study the nucleon electromagnetic form factors in a quark–gluon core model framework, which can be viewed as an extension of the Isgur–Karl model of baryons. Using this picture we derive nucleon electromagnetic dipole form factors at low Q ² and the deviation from the dipole form at high Q ², that are consistent with the existing experimental data.     

Do chemically saturated antihyperon abundancies signal the quark gluon plasma?

We first review the production and the possible chemical equilibration of strange particles at CERN-SPS energies within a microscopic hadronic transport calculation. It is shown in particular that the strange quarks are produced initially via string excitations in the primary, secondary and ternary interactions. We then further elaborate on a recent idea of antihyperon production by multi-mesonic reactions like $n_1 \pi + n_2 K \to \bar Y + p$ corresponding to the inverse of the strong binary baryon-antibaryon annihilation process. It is argued that by these reactions the (rare) antihyperons are driven towards local chemical equilibrium with pions, nucleons and kaons on a timescale of 1–3 fm/c in the still moderately baryon-dense initial hadronic environment after the termination of the prehadronic string phase. Accordingly this mechanism can provide a convenient explanation for the antihyperon yields at CERN-SPS energies without any need of a deconfined quark gluon plasma phase.