Quark stars: features and findings

Under extreme conditions of temperature and/or density, quarks and gluons are expected to undergo a deconfinement phase transition. While this is an ephemeral phenomenon at the ultra-relativistic heavy-ion collider (BNL-RHIC), quark matter may exist naturally in the dense interior of neutron stars. Here, we present an appraisal of the possible phase structure of dense quark matter inside neutron stars, and the likelihood of its existence given the current status of neutron star observations. We conclude that quark matter inside neutron stars cannot be dismissed as a possibility, although recent observational evidence rules out most soft equations of state. PACS 97.60.Jd; 26.60.+c     

Summary talk

An overview of some of major physics themes covered at this conference is presented.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.38.-t Quantum chromodynamics - 12.39.-x Phenomenological quark models - 11.15.-q Gauge field theories - 24.85. + p Quarks, gluons, and QCD in nuclei and nuclear processes - 12.38.Mh Quark-gluon plasma - 25.20.-x Photonuclear reactions - 25.30.-c Lepton-induced reactions - 21.80. + a Hypernuclei - 25.40.-h Nucleon-induced reactions - 25.75.-q Relativistic heavy-ion collisions     

Dihadron fragmentation: in vacuum and in matter

Two particle correlations within a single jet produced in deeply inelastic scattering (DIS) off a large nucleus as well as in heavy-ion collisions are explored. These are performed within the framework of the medium modified dihadron fragmentation functions. The modification occurs due to gluon bremsstrahlung induced by multiple scattering. The modified fragmentation functions for dihadrons are found to follow closely that of single hadrons leading to a weak nuclear suppression of their ratios as measured by HERMES in DIS experiments. Meanwhile, a moderate medium enhancement of the near-side correlation of two high p_T hadrons is found in central heavy-ion collisions, partially due to trigger bias caused by the competition between parton energy loss and the initial Cronin effect.Arrival of the final proofs: 21 March 2005PACS: 12.38.Mh, 11.10.Wx     

QGP and modified jet fragmentation

Recent progress in the study of jet modification in hot medium and its consequences in high-energy heavy-ion collisions is reviewed. In particular, I will discuss energy loss for propagating heavy quarks and the resulting modified fragmentation function. Medium modification of the parton fragmentation function due to quark recombination is formulated within finite temperature field theory and the implication for the search for a deconfined quark-gluon plasma is also discussed.Arrival of the final proofs: 20 July 2005PACS: 13.87.Fh, 12.38.Bx, 12.38.Mh, 11.80.La     

The realistic QCD equation of state in relativistic heavy-ion collisions and the early Universe

The realistic equation of state of strongly interacting matter, that has been successfully applied in the recent hydrodynamic studies of hadron production in relativistic heavy-ion collisions at RHIC, is used in the Friedmann equation to determine the precise time evolution of thermodynamic parameters in the early Universe. A comparison with the results obtained with simple ideal-gas equations of state is made. The realistic equation of state describes a crossover rather than the first-order phase transition between the quark–gluon plasma and hadronic matter. Our numerical calculations show that small inhomogeneities of strongly interacting matter in the early Universe are moderately damped during such crossover.     

Holographic prediction for the deconfinement temperature

We argue that deconfinement in anti-de Sitter space models of quantum chromodynamics (AdS/QCD models) occurs via a first order Hawking-Page type phase transition between low temperature thermal AdS and a high temperature black hole. Such a result is consistent with the expected temperature independence, to leading order in 1/Nc, of the meson spectrum and spatial Wilson loops below the deconfinement temperature. As a by-product, we obtain model dependent deconfinement temperatures Tc in the hard- and soft-wall models of AdS/QCD. Our result for Tc in the soft-wall model is close to a recent lattice prediction.     

Space-time evolution of hadronization

Beside its intrinsic interest for the insights it can give into color confinement, knowledge of the space-time evolution of hadronization is very important for correctly interpreting jet-quenching data in heavy-ion collisions and extracting the properties of the produced medium. On the experimental side, the cleanest environment to study the space-time evolution of hadronization is semi-inclusive deeply inelastic scattering on nuclear targets. On the theoretical side, two frameworks are presently competing to explain the observed attenuation of hadron production: quark energy loss (with hadron formation outside the nucleus) and nuclear absorption (with hadronization starting inside the nucleus). I will discuss recent observables and ideas which will help to distinguish these two mechanisms and to measure the time scales of the hadronization process. PACS 25.30.-c; 25.75.-q; 24.85.+p; 13.87.Fh     

Heavy quarkonia survival in potential model

We investigate the quarkonia correlators in QCD with no light quarks within a potential model with different screened potentials. Our results for the temperature dependence of the charmonium and bottomonium correlators are qualitatively consistent with existing and preliminary lattice results. We identify however, a much richer structure in the correlators than the one seen on the lattice.Arrival of the final proofs: 3 March 2005PACS: 11.15.Ha, 11.10.Wx, 12.38.Mh, 25.75.Nq     

UV–blue photoluminescence from ZrO2 nanopowders prepared via glycine nitrate process

This work is motivated by heavy-ion irradiation of materials exposed to high hydrostatic pressures in a diamond anvil cell (DAC). Those studies require the complete passage of ions through one of the two anvils consisting of natural diamond. Due to typical anvil lengths of about 2–3 mm, ion energies of a few hundred MeV/u, as provided by the SIS heavy-ion synchrotron of GSI, are needed. Data of energy loss and range of ions in this energy regime being scarce for diamond, a set of experiments was devoted to range measurements by irradiating a single DAC diamond and an immediately following stack of 100 polycarbonate foils (each 30-m thick) with ²³⁸U ions of 50.3 GeV (211.5 MeV/u). Ion range and range straggling in the stack were determined by etching the tracks and counting the pores. The experimentally determined ion range in the polymer foil stack is consistent with energy-loss values in diamond and polymer obtained with the SRIM and ATIMA computer codes and also confirms the reliability of these codes for diamond. Therefore, SRIM and ATIMA will be used in further experiments aimed at heavy-ion irradiation of materials pressurized in DACs. PACS 07.35.+k; 61.80.Jh; 61.85.+p; 81.05.Uw     

Heavy quark potentials and quarkonium binding

I review recent progress in studying in-medium modification of inter-quark forces at finite temperature in lattice QCD. Some applications to the problem of quarkonium binding in potential models are also discussed.Received: 16 February 2005, Published online: 31 May 2005PACS: 11.15.Ha, 11.10.Wx, 12.38.Mh, 25.75.Nq     

On the violation of the holographic viscosity versus entropy KSS bound in non-relativistic systems

A computation of the quotient of shear viscosity and entropy density, or the Kovtun, Son and Starinets (KSS) number η/s, is performed in the non-relativistic and classical regime, first in chiral perturbation theory, and then in the SO(g+1)/SO(g) non-linear sigma model in the large g limit. Both are field theories stemming from a renormalizable sigma model, but, in spite of that, we explicitly calculate how one avoids the KSS bound by increasing the number of degenerate pions sufficiently. However, we argue that particle production could still keep the validity of the KSS bound in the weak sense. We also show how a large number of molecular isomers (which we estimate in terms of simple molecular properties) could avoid the bound in the strong sense. This might be possible with carbon based molecules. We finally argue that a measurement of η/s in heavy-ion collisions might be turned into an upper bound on the number of hadron resonances. PACS  11.15.Pg; 12.38.Mh; 25.75.q; 51.20.+d     

Field-theoretical treatment of the liquid-vapor phase transition in nuclear systems

The liquid-vapor phase transition in hot nuclear matter is investigated in a field-theoretical approach employing euclidean-space (imaginary time) path-integral techniques. This approach allows us to study the nucleation due to both quantum and thermodynamic fluctuations. The bubbles of the new phase appear as instanton solutions of the euclidean-space field equations. The critical bubble sizes and associated transition probabilities are calculated. We examine the temperature and density values for which a phase transition may develop in hot nuclear matter produced in the course of a heavy-ion reaction.     

Charmonium and bottomonium in heavy-ion collisions

We review the present status in the theoretical and phenomenological understanding of charmonium and bottomonium production in heavy-ion collisions. We start by recapitulating the basic notion of “anomalous quarkonium suppression” in heavy-ion collisions and its recent amendments involving regeneration reactions. We then survey in some detail concepts and ingredients needed for a comprehensive approach to utilize heavy quarkonia as a probe of hot and dense matter. The theoretical discussion encompasses recent lattice QCD computations of quarkonium properties in the Quark-Gluon Plasma, their interpretations using effective potential models, inelastic rate calculations and insights from analyses of electromagnetic plasmas. We illustrate the powerful techniques of thermodynamic Green functions (T-matrices) to provide a general framework for implementing microscopic properties of heavy quarkonia into a kinetic theory of suppression and regeneration reactions. The theoretical concepts are tested in applications to heavy-ion reactions at SPS, RHIC and LHC. We outline perspectives for future experiments on charmonium and bottomonium production in heavy-ion collisions over a large range of energies (FAIR, RHIC-II and LHC). These are expected to provide key insights into hadronic matter under extreme conditions using quarkonium observables.     

Equilibrium between anisotropic normal and pion-condensed nuclear matter

The properties of the pion-condensed phase of nuclear matter are investigated at finite temperatures in the framework of a relativistic field theory. The solution of the field equations and the expectation value of the energy-momentum tensor are calculated in the mean-field approximation. It is observed that the self-consistent set of equations for the amplitudes of the mesonic fields obtained directly from the field equations are identical with the conditions of thermodynamical equilibrium. The pressure of the pion-condensed phase is found to be isotropic in thermodynamical equilibrium.

The possibility of phase equilibrium between pion-condensed and anisotropic normal nuclear matter is studied. The nuclear matter produced in heavy-ion collisions is anisotropic and it is far from thermodynamical equilibrium. During the collision process the anisotropy is decreasing and the system approaches thermodynamical equilibrium. It is shown that non-equilibrated pion- condensed nuclear matter may have the same anisotropy as the normal one and they may be in phase equilibrium during the whole collision process. This circumstance allows us to draw the following conclusion: if there is a chance at all for the phase transition from normal to pion- condensed phase then the anisotropy inevitably produced in heavy-ion collisions does not prevent this transition.     

Nucleon propagation through nuclear matter in chiral effective field theory

We treat the propagation of a nucleon in nuclear matter by evaluating the ensemble average of the two-point function of the nucleon currents in the framework of chiral effective field theory. We first derive the effective parameters of the nucleon to one loop. The resulting formula for the effective mass has been known since before and gives an absurd value at normal nuclear density. We then modify it following Weinberg’s method for the two-nucleon system in the effective theory. Our results for the effective mass and the width of the nucleon are compared with those in the literature. PACS 11.30.Rd; 12.38.Lg; 12.39.Fe; 24.85.+p     

Pion collectivity in relativistic heavy-ion collisions

The inelastic nucleon-nucleon cross section may be enhanced in the nuclear medium by pion collectivity. Empirical hamiltonians are on the borderline of strongly collective behavior, and the predicted enhancement factors range from 1–5 for various hamiltonians from the literature. An enhancement would have a substantial effect on the sideward flow in relativistic heavy-ion collisions. If this effect is present, the equation of state could be softer than in previous analyses.     

Modelization of the EOS

This paper summarizes theoretical predictions for the density and isospin dependence of the nuclear mean field and the corresponding nuclear equation of state. We compare predictions from microscopic and phenomenological approaches. An application to heavy-ion reactions requires to incorporate these forces into the framework of dynamical transport models. Constraints on the nuclear equation of state derived from finite nuclei and from heavy-ion reactions are discussed.