551 research outputs found
Width of the QCD transition in a Polyakov-loop DSE model
We consider the pseudocritical temperatures for the chiral and deconfinement
transitions within a Polyakov-loop Dyson-Schwinger equation approach which
employs a nonlocal rank-2 separable model for the effective gluon propagator.
These pseudocritical temperatures differ by a factor of two when the quark and
gluon sectors are considered separately, but get synchronized and become
coincident when their coupling is switched on. The coupling of the
Polyakov-loop to the chiral quark dynamics narrows the temperature region of
the QCD transition in which chiral symmetry and deconfinement is established.
We investigate the effect of rescaling the parameter T_0 in the Polyakov-loop
potential on the QCD transition for both the logarithmic and polynomial forms
of the potential. While the critical temperatures vary in a similar way, the
width of the transition is stronger affected for the logarithmic potential. For
this potential the character of the transition changes from crossover to a
first order one when T_0 < 210 MeV, but it remains crossover in the whole range
of relevant T_0 values for the polynomial form.Comment: 10 pages, 6 figures, results for polynomial form of Polyakov-loop
potential included, references added, final version to appear in Phys. Rev.
A Generalization of Slavnov-Extended Non-Commutative Gauge Theories
We consider a non-commutative U(1) gauge theory in 4 dimensions with a
modified Slavnov term which looks similar to the 3-dimensional BF model. In
choosing a space-like axial gauge fixing we find a new vector supersymmetry
which is used to show that the model is free of UV/IR mixing problems, just as
in the previously discussed model in arXiv:hep-th/0604154. Finally, we present
generalizations of our proposed model to higher dimensions.Comment: 25 pages, no figures; v2 minor correction
Heavy quark potential and quarkonia dissociation rates
Quenched lattice data for the quark-antiquark interaction (in terms of heavy
quark free energies) in the color singlet channel at finite temperatures are
fitted and used within the nonrelativistic Schroedinger equation formalism to
obtain binding energies and scattering phase shifts for the lowest eigenstates
in the charmonium and bottomonium systems in a hot gluon plasma. The partial
dissociation rate due to the Bhanot-Peskin process is calculated using
different assumptions for the gluon distribution function, including free
massless gluons, massive gluons, and massive damped gluons. It is demonstrated
that a temperature dependent gluon mass has an essential influence on the heavy
quarkonia dissociation, but that this process alone is insufficient to describe
the heavy quarkonia dissociation rates.Comment: 4 pages, 5 figures, contribution to the proceedings of the
International Conference on Hard and Electromagnetic Probes of High Energy
Nuclear Collisions, Ericeira, Portugal, Nov. 4-10, 200
On Rank Problems for Planar Webs and Projective Structures
We present old and recent results on rank problems and linearizability of
geodesic planar webs.Comment: 31 pages; LaTeX; corrected the abstract and Introduction; added
reference
Chiral surfaces self-assembling in one-component systems with isotropic interactions
We show that chiral symmetry can be broken spontaneously in one-component
systems with isotropic interactions, i.e. many-particle systems having maximal
a priori symmetry. This is achieved by designing isotropic potentials that lead
to self-assembly of chiral surfaces. We demonstrate the principle on a simple
chiral lattice and on a more complex lattice with chiral super-cells. In
addition we show that the complex lattice has interesting melting behavior with
multiple morphologically distinct phases that we argue can be qualitatively
predicted from the design of the interaction.Comment: 4 pages, 4 figure
On the Renormalizability of Noncommutative U(1) Gauge Theory - an Algebraic Approach
We investigate the quantum effects of the nonlocal gauge invariant operator
in the
noncommutative U(1) action and its consequences to the infrared sector of the
theory. Nonlocal operators of such kind were proposed to solve the infrared
problem of the noncommutative gauge theories evading the questions on the
explicit breaking of the Lorentz invariance. More recently, a first step in the
localization of this operator was accomplished by means of the introduction of
an extra tensorial matter field, and the first loop analysis was carried out
. We will complete this localization
avoiding the introduction of new degrees of freedom beyond those of the
original action by using only BRST doublets. This will allow us to make a
complete BRST algebraic study of the renormalizability of the theory, following
Zwanziger's method of localization of nonlocal operators in QFT.Comment: standard Latex no figures, version2 accepted in J. Phys A: Math Theo
Charmonium dynamics in heavy ion collisions
Applying the HSD transport approach to charmonium dynamics within the
'hadronic comover model' and the 'QGP melting scenario', we show that the
suppression pattern seen at RHIC cannot be explained by the interaction with
baryons, comoving mesons and/or by color screening mechanism. The interaction
with hadrons in the late stages of the collision (when the energy density falls
below the critical) gives a sizable contribution to the suppression. On the
other hand, it does not account for the observed additional charmonium
dissociation and its dependence on rapidity. Together with the failure of the
hadron-string models to reproduce high v2 of open charm mesons, this suggests
strong pre-hadronic interaction of c-cbar with the medium at high energy
densities.Comment: 6 pages, 2 figures, talk presented at the international conference on
"Strangeness in Quark Matter", 24-29 June 2007, Levoca, Slovaki
Charmonium dynamics in Au+Au collisions at sqrt(S)=200 GeV
The formation and suppression dynamics of J/Psi, Chi_c and Psi-Prime mesons
is studied within the HSD transport approach for Au+Au reactions at the top
RHIC energy of sqrt(S)=200 GeV. Two prominent models, which have been discussed
for more than a decade, are incorporated, i.e. the 'hadronic comover absorption
and reformation' model as well as the 'QGP threshold' scenario, and compared to
available experimental data. Our studies demonstrate that both scenarios -
compatible with experimental observation at SPS energies - fail severely at
RHIC energies. This combined analysis - together with the underestimation of
charm elliptic flow - proves that the dynamics of c, c-bar quarks are dominated
by partonic interactions in the strong QGP (sQGP) and can neither be modeled by
'hadronic' interactions nor described appropriately by color screening alone.Comment: 4 pages, 2 figure
Phase diagrams in nonlocal PNJL models constrained by Lattice QCD results
Based on lattice QCD-adjusted SU(2) nonlocal Polyakov--Nambu--Jona-Lasinio
(PNJL) models, we investigate how the location of the critical endpoint in the
QCD phase diagram depends on the strenght of the vector meson coupling, as well
as the Polyakov-loop (PL) potential and the form factors of the covariant
model. The latter are constrained by lattice QCD data for the quark propagator.
The strength of the vector coupling is adjusted such as to reproduce the slope
of the pseudocritical temperature for the chiral phase transition at low
chemical potential extracted recently from lattice QCD simulations. Our study
supports the existence of a critical endpoint in the QCD phase diagram albeit
the constraint for the vector coupling shifts its location to lower
temperatures and higher baryochemical potentials than in the case without it.Comment: 23 pages, 10 figures. Version accepted in Phys. Part. Nucl. Lett. (to
appear), references adde
Gauge Independence of IR singularities in Non-Commutative QFT - and Interpolating Gauges
IR divergences of a non-commutative U(1) Maxwell theory are discussed at the
one-loop level using an interpolating gauge to show that quadratic IR
divergences are independent not only from a covariant gauge fixing but also
independent from an axial gauge fixing.Comment: 11 pages, 2 figures, v1 minor correction
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