38 research outputs found
Rethinking the Properties of the Quark-Gluon Plasma at
We argue that although at asymptotically high temperatures the QGP in bulk
behaves as a gas of weakly interacting quasiparticles (modulo long-range
magnetism), at temperatures up to few times the critical temperature it
displays different properties. If the running of the QCD coupling constant
continues in the Coulomb phase till the screening length scale, it reaches the
strong coupling treshold . As a result, the Coulomb phase
supports weakly bound Coulombic s-wave , light quark and even
states.
The existence of shallow bound states dramatically increases the
quasiparticle rescattering at low energies, reducing the viscosity and thereby
explaining why heavy ion collisions at RHIC exhibit robust collective
phenomena. In conformal gauge theories at finite temperature the Coulomb
binding persists further in the strong coupling regime, as found for SUSY YM in the Maldacena regime.Comment: v2 version have one more figure and one more reference, v3 is the
same as v2 except a double-page format (the v2 had corrupted last lines on
the page
Strongly Coupled Quark Gluon Plasma (SCQGP)
We propose that the reason for the non-ideal behavior seen in lattice
simulation of quark gluon plasma (QGP) and relativistic heavy ion collisions
(URHICs) experiments is that the QGP near T_c and above is strongly coupled
plasma (SCP), i.e., strongly coupled quark gluon plasma (SCQGP). It is
remarkable that the widely used equation of state (EoS) of SCP in QED (quantum
electrodynamics) very nicely fits lattice results on all QGP systems, with
proper modifications to include color degrees of freedom and running coupling
constant. Results on pressure in pure gauge, 2-flavors and 3-flavors QGP, are
all can be explained by treating QGP as SCQGP as demonstated here.Energy
density and speed of sound are also presented for all three systems. We further
extend the model to systems with finite quark mass and a reasonably good fit to
lattice results are obtained for (2+1)-flavors and 4-flavors QGP. Hence it is
the first unified model, namely SCQGP, to explain the non-ideal QGP seen in
lattice simulations with just two system dependent parameters.Comment: Revised with corrections and new results, Latex file (11 pages),
postscript file of 7 figure
Screening of the topological charge in a correlated instanton vacuum
Screening of the topological charge due to he fermion-induced interactions is
an important phenomenon, closely related with the resolution of the strong CP
and U(1) problems. We study the mechanism of such screening in a 'correlated
instanton vacuum', as opposed to the 'random' one. Both scalar and pseudoscalar
gluonic correlators are analyzed by means of an observable that minimizes
finite size effects. Screening of the topological charge is established. This
allows us to calculate the mass without having to invert the Dirac
operator. We suggest that this method might be used in lattice QCD calculations
as well. Our results for the screening of the topological charge are in
agreement with the chiral Ward identities, and the scalar gluonic correlator
satisfies a low energy theorem first derived by Novikov et al.
\cite{Novikov-etal}. We also propose to evaluate the topological susceptibility
in the Witten-Veneziano formula not in an infinite box in an world
fermions but in an infinitesimal box in a world fermions.Comment: 22 pages + 5 postscript figures, SUNY-NTG/94-25. Corrected LATEX
erro
The Instanton Molecule Liquid and "Sticky Molasses" Above T_c
The main objective of this work is to explore the evolution in the structure
of the quark-antiquark bound states in going down in the chirally restored
phase from the so-called "zero binding points" T_zb to the QCD critical
temperature T_c at which the Nambu-Goldstone and Wigner-Weyl modes meet. In
doing this, we adopt the idea recently introduced by Shuryak and Zahed for
charmed , light-quark mesons and
gluons that at T_zb, the quark-antiquark scattering length goes through
infinity at which conformal invariance is restored, thereby transforming the
matter into a near perfect fluid behaving hydrodynamically, as found at RHIC.
We show that the binding of these states is accomplished by the combination of
(i) the color Coulomb interaction, (ii) the relativistic effects, and (iii) the
interaction induced by the instanton-anti-instanton molecules. The spin-spin
forces turned out to be small. While near T_zb all mesons are large-size
nonrelativistic objects bound by Coulomb attraction, near T_c they get much
more tightly bound, with many-body collective interactions becoming important
and making the and masses approach zero (in the chiral limit).
The wave function at the origin grows strongly with binding, and the near-local
four-Fermi interactions induced by the instanton molecules play an increasingly
more important role as the temperature moves downward toward T_c.Comment: Contribution to QM2004 proceedings, 4 page
The instanton liquid in QCD at zero and finite temperature
In this paper we study the statistical mechanics of the instanton liquid in
QCD. After introducing the partition function as well as the gauge field and
quark induced interactions between instantons we describe a method to calculate
the free energy of the instanton system. We use this method to determine the
equilibrium density and the equation of state from numerical simulations of the
instanton ensemble in QCD for various numbers of flavors. We find that there is
a critical number of flavors above which chiral symmetry is restored in the
groundstate. In the physical case of two light and one intermediate mass flavor
the system undergoes a chiral phase transition at MeV. We show
that the mechanism for this transition is a rearrangement of the instanton
liquid, going from a disordered, random, phase at low temperatures to a
strongly correlated, molecular, phase at high temperature. We also study the
behavior of mesonic susceptibilities near the phase transition.Comment: 50 pages, revtex, 16 figures, uuencode
A Comment on Conical Flow Induced by Heavy-Quark Jets
The suppression of high transverse momentum particles, recently discovered at
RHIC, is commonly interpreted as due to parton energy loss. In high energy
nuclear collisions, QCD jets would deposit a large fraction of their energy and
into the produced matter. The question of how this energy is degraded and
whether we can use this phenomenon to probe the properties of the produced
matter is now under active discussion. It has been proposed that if this
matter, which is now being referred to as a {\em strongly coupled Quark-Gluon
Plasma} (sQGP), may behave as a liquid with a very small viscosity.
In this case, a very specific collective excitation should be produced,
called the ``conical flow'', similar e.g. to the sonic booms generated by the
shock waves produced by supersonic planes. The RHIC experiments seem indeed to
be obtaining some indication that the production of particles emitted opposite
to a high- jet may actually be peaked away from the quenched jet
direction, at an angle roughly consistent with the direction expected in case a
shock wave is produced (i.e. orthogonal to the Mach cone). In this note we
speculate that for tagged heavy-quark jets one may observe a shrinkage of the
Mach cone at moderate . The experimental observation of such an effect
would be a very good test for the validity of the whole picture currently
emerging from the study of partonic matter in nuclear collisions
Instanton-induced Effects in QCD High-Energy Scattering
We evaluate a number of new instanton-induced phenomena in QCD, starting with
static dipole-dipole potentials, and proceeding to quark-quark and
dipole-dipole scattering at high energy. We use a non-perturbative formulation
of the scattering amplitude in terms of a correlator of two Wilson-lines
(quarks) or Wilson-loops (dipoles) and analyze the Euclidean amplitudes with
both perturbative gluons and instantons. The results are analytically continued
to Minkowski geometry, by interpreting the angle between the Wilson lines as
rapidity. We discuss the relevance of our results for the phenomenology of
near-forward hadronic processes at high energy, especially for processes with
multiple color exchanges
Chiral effective action with heavy quark symmetry
We derive an effective action combining chiral and heavy quark symmetry,
using approximate bosonization techniques of QCD. We explicitly show that the
heavy-quark limit is compatible with the large (number of color) limit in
the meson sector, and derive specific couplings between the light and heavy
mesons (, , ...) and their chiral partners. The relevance of this
effective action to solitons with heavy quarks describing heavy baryons is
discussed.Comment: 14 pages, SUNY-NTG-92/2