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.     

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.     

AdS-QCD quark–antiquark potential,meson spectrum and tetraquarks

The AdS/QCD correspondence predicts the structure of the quark–antiquark potential in the static limit. We use this piece of information together with the Salpeter equation (Schrödinger equation with relativistic kinematics) and a short range hyperfine splitting potential to determine quark masses and the quark potential parameters from the meson spectrum. The agreement between theory and experimental data is satisfactory, provided one considers only mesons comprising at least one heavy quark. We use the same potential (in the one-gluon-exchange approximation) and these data to estimate the constituent diquark masses. Using these results as input we compute tetraquark masses using a diquark–antidiquark model. The masses of the states X(3872) or Y(3940) are predicted rather accurately. We also compute tetraquark masses with open charm and strangeness. Our result is that tetraquark candidates such as D _s (2317), D _s (2457) or X(2632) can hardly be interpreted as diquark–antidiquark states within the present approach.     

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     

Suppression of elliptic flow in a minimally viscous quark–gluon plasma

We compute the time evolution of elliptic flow in non-central relativistic heavy-ion collisions, using a (2+1$2+1$)-dimensional code with longitudinal boost-invariance to simulate viscous fluid dynamics in the causal Israel–Stewart formulation. We show that even “minimal” shear viscosity η/s=?/(4π)$\eta /s=?/(4\pi )$ leads to a large reduction of elliptic flow compared to ideal fluid dynamics, raising questions about the interpretation of recent experimental data from the Relativistic Heavy Ion Collider.     

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.     

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.     

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.     

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.     

Magnetic moment of hyperons in nuclear matter by using quark–meson coupling models

We calculate the magnetic moments of hyperons in dense nuclear matter by using relativistic quark models. Hyperons are treated as MIT bags, and the interactions are considered to be mediated by the exchange of scalar and vector mesons which are approximated as mean fields. Model dependence is investigated by using the quark–meson coupling model and the modified quark–meson coupling model; in the former the bag constant is independent of density and in the latter it depends on density. Both models give us the magnitudes of the magnetic moments increasing with density for most octet baryons. But there is a considerable model dependence in the values of the magnetic moments in dense medium. The magnetic moments at the nuclear saturation density calculated by the quark–meson coupling model are only a few percents larger than those in free space, but the magnetic moments from the modified quark–meson coupling model increase more than 10% for most hyperons. The correlations between the bag radius of hyperons and the magnetic moments of hyperons in dense matter are discussed.     

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.     

A quark model of the meson fragmentation region in πp collisions

A model is explored in which the fragmentation region is populated by the hadronization of a string which stretches from a fast forward quark to a quark in the backward hemisphere of the p collision. This model is a part of more complicated models which have been studied elsewhere. It successfully fits observed inclusive production of ⁰-mesons, ⁰-mesons and -mesons, and agrees with the result that their production in p collisions is harder than in electron-position annihilation if: (a) the forward quark has an initial momentum which is at least 0·9 of that of the ⁰-mesons (b) gluon radiation is weaker than in electron-positron annihilation.     

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.     

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}.