We study the correlations between quark-antiquark pairs in different quantum number channels in a deconfined plasma by using an effective model of QCD. Using the three flavour PNJL model, the finite temperature spectral functions for different mesonic states are studied at zero and nonzero quark chemical potentials. It is found that in the $η$ channel resonance structures survive above the chiral transition temperature $\tc$, while the kaonic states seem to get washed off just above $\tc$. The sensitivity of the structures to the anomaly term are carefully investigated.
The model for hybrid excitations of the QCD string with quarks is presented starting from the perturbation theory in the nonperturbative background. The propagation of a system containing $q \bar q$-pair and gluon is considered. The simplified version of the Hamiltonian, including both long-range nonperturbative interaction and Coulomb force, is derived. The masses of the lowest $q \bar q g$ hybrids are evaluated, and numerical results for the spectra are listed.
Various thermodynamic quantities and the phase diagram of strongly interacting hot and dense magnetized quark matter are obtained with the $ 2 $-flavour Nambu-Jona-Lasinio model with Polyakov loop considering finite values of the anomalous magnetic moment (AMM) of the quarks. Susceptibilities associated with constituent quark mass and traced Polyakov loop are used to evaluate chiral and deconfinement transition temperatures. It is found that, inclusion of the AMM of the quarks in presence of the background magnetic field results in a substantial decrease in the chiral as well as deconfinement …
The quark-gluon plasma (QGP) excitations, corresponding to the scalar and pseudoscalar meson quantum numbers, for different temperatures are calculated. Analysis is performed in the Hard Thermal Loop (HTL) Approximation and leads to a better understanding of the excitations of QGP in the deconfined phase and is also of relevance for lattice studies.
We study quark-hadron phase transition at finite temperature with zero net baryon density by the Nambu-Jona-Lasinio model for interacting quarks in uniform background temporal color gauge fields. At low temperatures, unphysical thermal quark-antiquark excitations which would appear in the mean field approximation, are eliminated by en- forcing vanishing expectation value of the Polyakov-loop of the background gauge field, while at high temperatures this expectation value is taken as unity allowing thermal excitations of free quarks and antiquarks. Mesonic excitations in the low temperature pha…
By extending the Bielefeld LGS (Lattice Gauge Simulation) color singlet interaction, we find that the masses of pi, sigma, rho and a_1 excitations, 32 degrees of freedom in all, go to zero (in the chiral limit) as T -> T_c. This result indicates a smooth phase transition at T_c, at which from above the masses and couplings of mesons vanish `a la Brown-Rho scaling. We discuss that our scenario successfully explains the STAR (STAR Collaboration) rho^0/pi^- ratio in Au-Au peripheral collisions at RHIC.
We develop a quantum kinetic theory of the chiral condensate and meson quasi-particle excitations using the O(N) linear sigma model which describe the chiral phase transition both in and out of equilibrium in a unified way. A mean field approximation is formulated in the presence of mesonic quasi-particle excitations which are described by generalized Wigner functions. It is shown that in equilibrium our kinetic equations reduce to the gap equations which determine the equilibrium condensate amplitude and the effective masses of the quasi-particle excitations, while linearization of transport …
We formulate a kinetic theory of self-interacting meson fields with an aim to describe the freezeout stage of the space-time evolution of matter in ultrarelativistic nuclear collisions. Kinetic equations are obtained from the Heisenberg equation of motion for a single component real scalar quantum field taking the mean field approximation for the non-linear interaction. The mesonic mean field obeys the classical non-linear Klein-Gordon equation with a modification due to the coupling to mesonic quasi-particle excitations which are expressed in terms of the Wigner functions of the quantum fluct…
We investigate colorless (mesonic) 3q-q qbar components in the nucleon and the Roper resonance N*(1440). Starting from constituent quarks and gluons we estimate the excitation of quark-antiquark pairs in a gluon exchange model with the strong coupling constant extracted from a comparison with a non-perturbative resonating group calculation of the pi, eta, rho and omega content of the nucleon. Applying the same model to the Roper resonance, we find as the most striking result a very strong scalar-isoscalar sigma content of the N*(1440) with a strength of the 3q-q qbar configurations comparable …
The excitation function of the in-plane directed flow of nucleons is studied within a non-equilibrium transport approach. It is demonstrated that a local minimum in the excitation function of the directed flow develops, which is not related to a transition into a quark-gluon plasma (QGP) phase. It is a consequence of the dynamical softening of the underlying equation of state, due to the onset of resonance matter and particle production. Thus, the interpretation of this minimum as a 'smoking gun' signature for the creation of a QGP is premature.
We consider the thermal production of dileptons and photons at temperatures above the critical temperature in QCD. We use a model where color excitations are suppressed by a small value of the Polyakov loop, the semi Quark-Gluon Plasma (QGP). Comparing the semi-QGP to the perturbative QGP, we find a mild enhancement of thermal dileptons. In contrast, to leading logarithmic order in weak coupling there are far fewer hard photons from the semi-QGP than the usual QGP. To illustrate the possible effects on photon and dileptons production in heavy ion collisions, we integrate the rate with a realis…
Collective excitations in the hot QCD medium and the propagation of Heavy Quarks
Key Laboratory of Quark and Lepton Physics (MOE) & Institute of Particle Physics, Central China Normal University（夸克与轻子物理教育部重点实验室及粒子物理研究所，华中师范大学）；School of Physical Sciences, National Institute of Science Education and Research, HBNI（物理科学学院，国家科学教育研究中心，HBNI）
Motivated by the observation that there may exist hadronic excitations even in the quark-gluon plasma (QGP) phase, we investigate how the properties of quarks, especially within the quasi-particle picture, are affected by the coupling with bosonic excitations at finite temperature (T), employing Yukawa models with a massive scalar (pseudoscalar) and vector (axial-vector) boson of mass m. The quark spectral function and the quasi-dispersion relations are calculated at one-loop order. We find that there appears a three-peak structure in the quark spectral function with a collective nature when T…
We study the response function which describes the evolution of energy density induced by an initial disturbance for a Bjorken-expanding quark-gluon plasma (QGP). We compare the results from solving linearized Boltzmann equation under the relaxation time approximation with those from viscous hydrodynamics. While in long time limit the response becomes hydrodynamics, the non-hydrodynamic response is important at intermediate times when excitations of wavelength larger than the inverse of the relaxation time $1/τ_{R}$ are not fully damped. Therefore observables sensitive to the jet-induced mediu…
Using a relativistic hadron transport model, we investigate the utility of the elliptic flow excitation function as a probe for the stiffness of nuclear matter and for the onset of a possible quark-gluon-plasma (QGP) phase-transition at AGS energies 1 < E_Beam < 11 AGeV. The excitation function shows a strong dependence on the nuclear equation of state, and exhibits characteristic signatures which could signal the onset of a phase transition to the QGP.
We first discuss, on a no-QGP basis, the two prominent indications of (a) enhanced strangeness production and of (b) anomalous $J/ψ$-suppression: We elaborate in particular on a recent idea of antihyperon production solely by multi-mesonic reactions. As a possible source for an enhanced dissociation of $c \bar{c}$ pairs we summarize the findings within the 'early'-comover absorption scenario of prehadronic string excitations. As an exotic candidate we then finally adress the stochastic formation of so called disoriented chiral condensates: An experimentally feasible DCC, if it does exist, has …
We calculate excitation functions for various dynamical quantities as well as experimental observables from SIS to RHIC energies within the HSD transport approach which is based on string, quark, diquark ($q, \bar{q}, qq, \bar{q}\bar{q}$) and hadronic degrees of freedom without including any explicit phase transition to a quark-gluon plasma (QGP). It is argued that the failure of this more 'conventional' approach in comparison to experimental data should indicate the presence of a different phase which might be either attributed to space-time regions of vanishing scalar quark condensate ($<q\b…
We compute the equation of state of hadronic matter at finite temperature with zero net baryon density by the Nambu-Jona-Lasinio model for interacting quarks in uniform background temporal color gauge fields. In the low temperature confining phase, unphysical thermal quark-antiquark excitations which would appear in the mean field approximation, are eliminated by enforcing vanishing expectation value of the "Polyakov-loop" of the background gauge field, while in the high temperature confining phase this expectation value is taken as close to unity allowing thermal excitations of free quarks an…
When the quark-gluon plasma (QGP) - a system of deconfined quarks and gluons - is in a nonequilibrium state, it is usually unstable with respect to color collective modes. The instabilities, which are expected to strongly influence dynamics of the QGP produced in relativistic heavy-ion collisions, are extensively discussed under the assumption that the plasma is weakly coupled. We begin by presenting the theoretical approaches to study the QGP, which include: field theory methods based on the Keldysh-Schwinger formalism, classical and kinetic theories, and fluid techniques. The dispersion equa…
Dynamical correlations across momentum scales in the quark-gluon plasma
Nuclear Science Division, Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室核科学部）；Department of Physics, University of California, Berkeley（加州大学伯克利分校物理系）
Sensitivity of Jet Observables to Molière Scattering Off Quasiparticles in Quark-Gluon Plasma
SLAC National Accelerator Laboratory（斯坦福直线加速器中心）；Center for Theoretical Physics — a Leinweber Institute, Massachusetts Institute of Technology（麻省理工学院莱因韦伯理论物理中心）；Departamento de Física, Universidad de Oviedo（奥维耶多大学物理系）；Instituto Universitario de Ciencias y Tecnologías Espaciales de Asturias (ICTEA)（阿斯图里亚斯宇宙科学与技术大学研究所）
We survey the non-locked color-flavor-spin channels for quark-quark (color superconducting) condensates in QCD, using an NJL model. We also study isotropic quark-antiquark (mesonic) condensates. We make mean-field estimates of the strength and sign of the self-interaction of each condensate, using four-fermion interaction vertices based on known QCD interactions. For the attractive quark pairing channels, we solve the mean-field gap equations to obtain the size of the gap as a function of quark density. We also calculate the dispersion relations for the quasiquarks, in order to see how fully g…
Probing the QCD Phase Structure with Dileptons from SIS to LHC Energies
Frankfurt Institute for Advanced Studies (FIAS)（法兰克福高等研究所）；Helmholtz Research Academy Hessen for FAIR (HFHF)（黑森亥姆霍兹FAIR研究院）；GSI Helmholtz Center for Heavy Ion Physics（重离子物理亥姆霍兹中心）；Institute for Theoretical Physics, Johann Wolfgang Goethe University（约翰·沃尔夫冈·歌德大学理论物理研究所）；GSI Helmholtzzentrum fur Schwerionenforschung GmbH（重离子研究亥姆霍兹中心有限公司）；State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究所核物理与技术国家重点实验室）
