451 research outputs found
Quarkonium states in an anisotropic QCD plasma
We consider quarkonium in a hot QCD plasma which, due to expansion and
non-zero viscosity, exhibits a local anisotropy in momentum space. At short
distances the heavy-quark potential is known at tree level from the
hard-thermal loop resummed gluon propagator in anisotropic perturbative QCD.
The potential at long distances is modeled as a QCD string which is screened at
the same scale as the Coulomb field. At asymptotic separation the potential
energy is non-zero and inversely proportional to the temperature. We obtain
numerical solutions of the three-dimensional Schroedinger equation for this
potential. We find that quarkonium binding is stronger at non-vanishing
viscosity and expansion rate, and that the anisotropy leads to polarization of
the P-wave states.Comment: 18 pages, 6 figures, final version, to appear in PR
Explosive Decomposition in Ultrarelativistic Heavy Ion Collision
Recent results from Au+Au collisions at BNL-RHIC energy hint at explosive hadron production at the QCD transition rather than soft hydrodynamic evolution. We speculate that this is due to a rapid variation of the effective potential for QCD close to Tc. Performing real-time lattice simulations of an effective theory we show that the fast evolution of the potential leads to ``explosive'' spinodal decomposition rather than bubble nucleation or critical slowing down
Forward particle productions at RHIC and the LHC from CGC within local rcBK evolution
In order to describe forward hadron productions in high-energy nuclear
collisions, we propose a Monte-Carlo implementation of
Dumitru-Hayashigaki-Jalilian-Marian formula with the unintegrated gluon
distribution obtained numerically from the running-coupling BK equation. We
discuss influence of initial conditions for the BK equation by comparing a
model constrained by global fit of small-x HERA data and a newly proposed one
from the running coupling MV model.Comment: Talk given at conference Quark Matter 2011, 4 page
Two-point functions for SU(3) Polyakov Loops near T_c
We discuss the behavior of two point functions for Polyakov loops in a SU(3)
gauge theory about the critical temperature, T_c. From a Z(3) model, in mean
field theory we obtain a prediction for the ratio of masses at T_c, extracted
from correlation functions for the imaginary and real parts of the Polyakov
loop. This ratio is m_i/m_r = 3 if the potential only includes terms up to
quartic order in the Polyakov loop; its value changes as pentic and hexatic
interactions become important. The Polyakov Loop Model then predicts how
m_i/m_r changes above T_c.Comment: 5 pages, no figures; reference adde
Hydrodynamic Models for Heavy-Ion Collisions, and beyond
A generic property of a first-order phase transition in equilibrium, and in
the limit of large entropy per unit of conserved charge, is the smallness of
the isentropic speed of sound in the ``mixed phase''. A specific prediction is
that this should lead to a non-isotropic momentum distribution of nucleons in
the reaction plane (for energies around 40 AGeV in our model calculation). On
the other hand, we show that from present effective theories for low-energy QCD
one does not expect the thermal transition rate between various states of the
effective potential to be much larger than the expansion rate, questioning the
applicability of the idealized Maxwell/Gibbs construction. Experimental data
could soon provide essential information on the dynamics of the phase
transition.Comment: 10 Pages, 4 Figures. Presented at 241st WE-Heraeus Seminar: Symposium
on Fundamental Issues in Elementary Matter: In Honor and Memory of Michael
Danos, Bad Honnef, Germany, 25-29 Sep 200
Screening of heavy quark free energies at finite temperature and non-zero baryon chemical potential
We analyze the dependence of heavy quark free energies on the baryon chemical
potential (mu_b) in 2-flavour QCD using improved (p4) staggered fermions with a
bare quark mass of m/T = 0.4. By performing a 6th order Taylor expansion in the
chemical potential which circumvents the sign problem. The Taylor expansion
coefficients of colour singlet and colour averaged free energies are calculated
and from this the expansion coefficients for the corresponding screening masses
are determined. We find that for small mu_b the free energies of a static quark
anti-quark pair decrease in a medium with a net excess of quarks and that
screening is well described by a screening mass which increases with increasing
mu_b. The mu_b-dependent corrections to the screening masses are well described
by perturbation theory for T > 2 T_c. In particular, we find for all
temperatures above T_c that the expansion coefficients for singlet and colour
averaged screening masses differ by a factor 2.Comment: 14 page
The K/pi ratio from condensed Polyakov loops
We perform a field-theoretical computation of hadron production in large
systems at the QCD confinement phase transition associated with restoration of
the Z(3) global symmetry. This occurs from the decay of a condensate for the
Polyakov loop. From the effective potential for the Polyakov loop, its mass
just below the confinement temperature T_c is in between the vacuum masses of
the pion and that of the kaon. Therefore, due to phase-space restrictions the
number of produced kaons is roughly an order of magnitude smaller than that of
produced pions, in agreement with recent results from collisions of gold ions
at the BNL-RHIC. From its mass, we estimate that the Polyakov loop condensate
is characterized by a (spatial) correlation scale of 1/m_\ell ~ 1/2 fm. For
systems of deconfined matter of about that size, the free energy may not be
dominated by a condensate for the Polyakov loop, and so the process of
hadronization may be qualitatively different as compared to large systems. In
that vein, experimental data on hadron abundance ratios, for example K/pi, in
high-multiplicity pp events at high energies should be very interesting.Comment: 7 pages, 4 figures; discussion of the two-point function of Polyakov
Loops in small versus large systems adde
Dense Quarks, and the Fermion Sign Problem, in a SU(N) Matrix Model
We study the effect of dense quarks in a SU(N) matrix model of deconfinement.
For three or more colors, the quark contribution to the loop potential is
complex. After adding the charge conjugate loop, the measure of the matrix
integral is real, but not positive definite. In a matrix model, quarks act like
a background Z(N) field; at nonzero density, the background field also has an
imaginary part, proportional to the imaginary part of the loop. Consequently,
while the expectation values of the loop and its complex conjugate are both
real, they are not equal. These results suggest a possible approach to the
fermion sign problem in lattice QCD.Comment: 9 pages, 3 figure
Magnetic Characterization of Nanocrystalline Nickel Ferrite Films Processed by a Spin-Spraying Method
Highly crystalline nickel ferrite films with different chemical compositions were processed via the spin-spraying method and their morphological, structural and magnetic properties were subsequently investigated. Regardless of the chemical composition, films with variable thicknesses are constructed by 200â400 nm spherical grains grown in the direction normal to the substrate surface. Magnetization measurements show that the spinel ferrite films present a hysteretic behaviour at room temperature with a randomly oriented in-plane easy axis and an anisotropy constant K1 â â2.5 Ă 104 erg cmâ3 Furthermore, the absence of an angular dependence of the coercivity for the in-plane measurement of magnetization coupled with the âMâ-shaped angular dependence of the out-of-plane measurement, indicates that the anisotropy of this film is predominantly crystalline shape anisotropy
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