222 research outputs found
The quark-antiquark potential at finite temperature and the dimension two gluon condensate
A recently proposed phenomenological model, which includes non perturbative
effects from dimension two gluon condensates, is applied to analyze the
available lattice data for the heavy quark free energy in the deconfined phase
of quenched QCD. For large separations we recover previous results
for the Polyakov loop, exhibiting unequivocal condensate contributions. For the
potential at finite temperature and finite separation we find that a
good overall description of the lattice data can be achieved once the
condensate is properly accounted for. In addition, the model predicts a duality
between the zero temperature potential as a function of the
separation, on the one hand, and the quark selfenergy as a function of the
temperature, on the other, which turns out to be satisfied to a high degree by
the lattice data.Comment: 9 pages, 5 figure
Dimension 2 condensates and Polyakov Chiral Quark Models
We address a possible relation between the expectation value of the Polyakov
loop in pure gluodynamics and full QCD based on Polyakov Chiral Quark Models
where constituent quarks and the Polyakov loop are coupled in a minimal way. To
this end we use a center symmetry breaking Gaussian model for the Polyakov loop
distribution which accurately reproduces gluodynamics data above the phase
transition in terms of dimension 2 gluon condensate. The role played by the
quantum and local nature of the Polyakov loop is emphasized.Comment: 3 pages, 1 figure. Talk given at the IVth International Conference on
Quarks an Nuclear Physics, Madrid, June 5th-10th 200
Polyakov loop in chiral quark models at finite temperature
We describe how the inclusion of the gluonic Polyakov loop incorporates large
gauge invariance and drastically modifies finite temperature calculations in
chiral quark models after color neutral states are singled out. This generates
an effective theory of quarks and Polyakov loops as basic degrees of freedom.
We find a strong suppression of finite temperature effects in hadronic
observables triggered by approximate triality conservation (Polyakov cooling),
so that while the center symmetry breaking is exponentially small with the
constituent quark mass, chiral symmetry restoration is exponentially small with
the pion mass. To illustrate the point we compute some low energy observables
at finite temperature and show that the finite temperature corrections to the
low energy coefficients are suppressed due to color average of the
Polyakov loop. Our analysis also shows how the phenomenology of chiral quark
models at finite temperature can be made compatible with the expectations of
chiral perturbation theory. The implications for the simultaneous center
symmetry breaking-chiral symmetry restoration phase transition are also
discussed.Comment: 24 pages, 8 ps figures. Figure and appendix added. To appear in
Physical Review
Correlations between perturbation theory and power corrections in QCD at zero and finite temperature
The duality between QCD perturbative series and power corrections recently
conjectured by Narison and Zakharov is analyzed. We propose to study
correlations between both contributions as diagnostics tool. A very strong
correlation between perturbative and non perturbative contributions is observed
for several observables at zero and at finite temperature supporting the
validity of the dual description.Comment: 7 pages, 5 figures, 7 table
The Polyakov loop and the hadron resonance gas model
The Polyakov loop has been used repeatedly as an order parameter in the
deconfinement phase transition in QCD. We argue that, in the confined phase,
its expectation value can be represented in terms of hadronic states, similarly
to the hadron resonance gas model for the pressure. Specifically, L(T) \approx
1/2\sum_\alpha g_\alpha \,e^(-\Delta_\alpha/T), where g_\alpha are the
degeneracies and \Delta_\alpha are the masses of hadrons with exactly one heavy
quark (the mass of the heavy quark itself being subtracted). We show that this
approximate sum rule gives a fair description of available lattice data with
N_f=2+1 for temperatures in the range 150MeV<T<190MeV with conventional meson
and baryon states from two different models. For temperatures below 150MeV
different lattice results disagree. One set of data can be described if exotic
hadrons are present in the QCD spectrum while other sets do not require such
states.Comment: 5 pages, 4 figures. Error in normalization corrected. Excited states
included. Substantially revise
Chiral Lagrangian at finite temperature from the Polyakov-Chiral Quark Model
We analyze the consequences of the inclusion of the gluonic Polyakov loop in
chiral quark models at finite temperature. Specifically, the low-energy
effective chiral Lagrangian from two such quark models is computed. The tree
level vacuum energy density, quark condensate, pion decay constant and
Gasser-Leutwyler coefficients are found to acquire a temperature dependence.
This dependence is, however, exponentially small for temperatures below the
mass gap in the full unquenched calculation. The introduction of the Polyakov
loop and its quantum fluctuations is essential to achieve this result and also
the correct large counting for the thermal corrections. We find that new
coefficients are introduced at to account for the Lorentz
breaking at finite temperature. As a byproduct, we obtain the effective
Lagrangian which describes the coupling of the Polyakov loop to the Goldstone
bosons.Comment: 16 pages, no figure
QCD-Thermodynamics using 5-dim Gravity
We calculate the critical temperature and free energy of the gluon plasma
using the dilaton potential arXiv:0911.0627[hep-ph] in the gravity theory of
AdS/QCD. The finite temperature observables are calculated in two ways: first,
from the Page-Hawking computation of the free energy, and secondly using the
Bekenstein-Hawking proportionality of the entropy with the area of the horizon.
Renormalization is well defined, because the T=0 theory has asymptotic freedom.
We further investigate the change of the critical temperature with the number
of flavours induced by the change of the running coupling constant in the
quenched theory. The finite temperature behaviour of the speed of sound,
spatial string tension and vacuum expectation value of the Polyakov loop follow
from the corresponding string theory in AdS_5.Comment: 38 pages, 12 figure
Thermodynamics of AdS/QCD within the 5D dilaton-gravity model
We calculate the pressure, entropy density, trace anomaly and speed of sound
of the gluon plasma using the dilaton potential of Ref. arXiv:0911.0627[hep-ph]
in the dilaton-gravity theory of AdS/QCD. The finite temperature observables
are calculated from the Black Hole solutions of the Einstein equations, and
using the Bekenstein-Hawking equality of the entropy with the area of the
horizon. Renormalization is well defined, because the T=0 theory has asymptotic
freedom. Comparison with lattice simulations is made.Comment: 4 pages, 4 figures. To appear in the proceedings of 15th
International Conference in Quantum Chromodynamics (QCD 10), Montpellier,
France, 28 Jun - 3 Jul 201
Draft genome sequence of Pantoea ananatis strain AMG521, a rice plant growth-promoting bacterial endophyte isolated from the Guadalquivir Marshes in Southern Spain.
The rice endophyte Pantoea ananatis AMG521 shows several plant growth-promoting properties and promotes rice yield increases.Its draft genome was estimated at 4,891,568 bp with 4,704 coding sequences (CDS). The genome encodes genes for N-acylhomoserine lactone (AHL) synthases, AHL hydrolases, hyperadherence (yidQ, yidP, and yidR), fusaric acid resistance, andoxidation of lignin, highlighting its biotechnological potential
Numerical taxonomy of moderately halophilic Gram-negative bacteria from hypersaline soils
A total of 132 moderately halophilic bacteria were isolated from hypersaline soils with a C1- content between 2-36 and 12.72% (w/v) located near Alicante (S.E. Spain) and examined for 98 phenotypic characteristics including their response to cytological, physiological, biochemical and nutritional tests. They were submitted to a numerical analysis together with six reference strains using both simple matching (SsM)a nd Jaccard (S,) coefficients, and cluster analysis was carried out by the unweighted pair group method of association (UPGMA), single linkage and complete linkage. With the S, coefficient and UPGMA clustering, eight phenons were obtained at the 65% similarity level. From each phenon representative strains were chosen for the determination of DNA base composition and for electron microscopy. Bacteria belonging to phenons D, E, and F were assigned to the genus Alcaligenes. Phenon G included 27 strains assigned to Acinetobacter, but the high G + C composition (58.9 mol%) of a representative strain of this phenon suggests that it may represent a new taxon. Phenons A, B, and C were designated Flavobacterium and phenon H was Pseudomonas. The bacteria found in these environments are not related to those from hypersaline waters or normal soils
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