Heavy quarks and QCD matter

I present recent results on the theory of QCD matter production in high energy heavy ion collisions and on the interactions of heavy quarks in such environment. The centrality and rapidity dependence of hadron production is evaluated in semi--classical approach. The energy loss of heavy quarks in matter is computed. The heavy--to--light meson ratio (e.g., D/pion) at moderate transverse momenta is demonstrated to be both sensitive to the density of color charges in the medium and infrared stable.Comment: 10 pages, 3 figures; invited talk at the international conference on "Statistical QCD", August 26-30, 2001, Bielefel

QCD and Heavy Ions

This short paper is an attempt to describe a theorist's view of the goals of relativistic heavy ion program which has just entered the collider era. These goals are centered around understanding the properties and the critical behavior of Quantum Chromo-Dynamics (QCD) in the non-linear regime of high color field strength and high parton density. Some of the current theoretical challenges are highlighted, and the place of heavy ion research in the broader context of modern particle and nuclear physics is discussed.Comment: 8 pages, 2 figures, invited talk at the Third International Conference on Perspectives in Hadronic Physics, Trieste, Italy, 7-11 May 200

Broken scale invariance, massless dilaton and confinement in QCD

Classical conformal invariance of QCD in the chiral limit is broken explicitly by scale anomaly. As a result, the lightest scalar particle (scalar glueball, or dilaton) in QCD is not light, and cannot be described as a Goldstone boson. Nevertheless basing on an effective low-energy theory of broken scale invariance we argue that inside the hadrons the non-perturbative interactions of gluon fields result in the emergence of a massless dilaton excitation (which we call the "scalaron"). We demonstrate that our effective theory of broken scale invariance leads to confinement. This theory allows a dual formulation as a classical Yang-Mills theory on a curved conformal space-time background. Possible applications are discussed, including the description of strongly coupled quark-gluon plasma and the spin structure of hadrons.Comment: 18 pages, 2 figures; v2: fixed numerous typo

Topologically induced local P and CP violation in hot QCD

Very stringent experimental bounds exist on the amount of P and CP violation in strong interactions. Nevertheless, the presence of non-Abelian topological solutions and the axial anomaly make the issue of CP invariance in QCD non-trivial ("the strong CP problem"). Even in the absence of a global P and CP violation the fluctuations of topological charge in the QCD vacuum are expected to play an important role in the breaking of chiral symmetry, and in the mass spectrum and other properties of hadrons. Here I argue that topological fluctuations in hot QCD matter can become directly observable in the presence of a very intense external magnetic field by inducing local P- and CP- odd effects. These local parity-violating phenomena can be described by using the Maxwell-Chern-Simons, or axion, electrodynamics as an effective theory. Local P and CP violation in hot QCD matter can be observed in experiment through the "chiral magnetic effect" - the separation of electric charge along the axis of magnetic field that is created by the colliding relativistic ions. There is a recent evidence for the electric charge separation relative to the reaction plane of heavy ion collisions from the STAR Collaboration at RHIC.Comment: 10 pages, 2 figures; presented at the 25th Winter Workshop on Nuclear Dynamics, Big Sky, Montana, February 1-8, 200

Bulk viscosity of QCD matter near the critical temperature

Kubo's formula relates bulk viscosity to the retarded Green's function of the trace of the energy-momentum tensor. Using low energy theorems of QCD for the latter we derive the formula which relates the bulk viscosity to the energy density and pressure of hot matter. We then employ the available lattice QCD data to extract the bulk viscosity as a function of temperature. We find that close to the deconfinement temperature bulk viscosity becomes large, with viscosity-to-entropy ratio zeta/s about 1.Comment: 8 pages, 1 figur

J/ψJ/\psi suppression in heavy ion collsions and the QCD phase transition

We suggest that the new regime of $J/\psi$ suppression in Pb-Pb collisions found by the NA50 experiment at CERN is the result of non-trivial space-time evolution due to specific behavior of the Equation of State (EOS) near the QCD phase transition. We also study another suppression channel, the conversion of $J/\psi$ into $\eta_c$ during the late cool hadronic stage, and find it rather inefficient.Comment: 10 pages, 3 figure