133 research outputs found
String Tension and Thermodynamics with Tree Level and Tadpole Improved Actions
We calculate the string tension, deconfinement transition temperature and
bulk thermodynamic quantities of the SU(3) gauge theory using tree level and
tadpole improved actions. Finite temperature calculations have been performed
on lattices with temporal extent N_tau = 3 and 4. Compared to calculations with
the standard Wilson action on this size lattices we observe a drastic reduction
of the cut-off dependence of bulk thermodynamic observables at high
temperatures. In order to test the influence of improvement on long-distance
observables at T_c we determine the ratio T_c/sqrt(sigma). For all actions,
including the standard Wilson action, we find results which differ only little
from each other. We do, however, observe an improved asymptotic scaling
behaviour for the tadpole improved action compared to the Wilson and tree level
improved actions.Comment: 20 pages, LaTeX2e File, 8 coloured Postscript figures, new analysis
added, recent Wilson action string tension results included, figures replace
QCD Thermodynamics with Improved Actions
The thermodynamics of the SU(3) gauge theory has been analyzed with tree
level and tadpole improved Symanzik actions. A comparison with the continuum
extrapolated results for the standard Wilson action shows that improved actions
lead to a drastic reduction of finite cut-off effects already on lattices with
temporal extent . Results for the pressure, the critical temperature,
surface tension and latent heat are presented. First results for the
thermodynamics of four-flavour QCD with an improved staggered action are also
presented. They indicate similarly large improvement factors for bulk
thermodynamics.Comment: Talk presented at LATTICE96(finite temperature) 4 pages, LaTeX2e
file, 6 eps-file
Renormalized Polyakov loops in many representations
We present a renormalization procedure for Polyakov loops which explicitly
implements the fact that the renormalization constant depends only on the
ultraviolet cutoff. Using this we study the renormalized Polyakov loops in all
representations upto the {\bf 27} of the gauge group SU(3). We find good
evidence for Casimir scaling of the Polyakov loops and for approximate large-N
factorization. By studying many loops together, we are able to show that there
is a matrix model with a single coupling which can describe the high
temperature phase of QCD, although it is hard to construct explicitly. We
present the first results for the non-vanishing renormalized octet loop in the
thermodynamic limit below the SU(3) phase transition, and estimate the
associated string breaking distance and the gluelump binding energy. By
studying the connection of the direct renormalization procedure with a
generalization of an earlier suggestion which goes by the name of the
renormalization procedure, we find that they are functionally equivalent.Comment: 17 pages, 24 figures, revtex
SU(3) Latent Heat and Surface Tension from Tree Level and Tadpole Improved Actions
We analyze the latent heat and surface tension at the SU(3) deconfinement
phase transition with tree level and tadpole improved Symanzik actions on
lattices with temporal extent and 4 and spatial extent , 6 and 8. In comparison to the standard Wilson action we do find a
drastic reduction of cut-off effects already with tree level improved actions.
On lattices with temporal extent results for the surface tension and
latent heat obtained with a tree level improved action agree well with those
obtained with a tadpole improved action. A comparison with
calculations, however, shows that results obtained with tadpole action remain
unaffected by cut-off effects even on this coarse lattice, while the tree level
action becomes sensitive to the cut-off. For the surface tension and latent
heat we find and , respectively.Comment: 11 pages, LaTeX2e File, 3 Postscript figure
Static quark anti-quark free energy and the running coupling at finite temperature
We analyze the free energy of a static quark anti-quark pair in quenched QCD
at short and large distances. From this we deduce running couplings, g^2(r,T),
and determine the length scale that separates at high temperature the short
distance perturbative regime from the large distance non-perturbative regime in
the QCD plasma phase. Ambiguities in the definition of a coupling beyond the
perturbative regime are discussed in their relation to phenomenological
considerations on heavy quark bound states in the quark gluon plasma. Our
analysis suggests that it is more appropriate to characterize the
non-perturbative properties of the QCD plasma phase close to T_c in terms
remnants of the confinement part of the QCD force rather than a strong
Coulombic force.Comment: 8 pages, 9 EPS-files, revtex
Staggered Fermion Actions with Improved Rotational Invariance
We introduce a class of improved actions for staggered fermions which to
O(p^4) and O(p^6), respectively, lead to rotationally invariant propagators. We
discuss the resulting reduction of flavour symmetry breaking in the meson
spectrum and comment on the improvement in the calculation of thermodynamic
observables.Comment: 3 pages and 4 figures, Contribution to Lattice 97 (Poster Session),
late
Heavy quark free energies for three quark systems at finite temperature
We study the free energy of static three quark systems in singlet, octet,
decuplet and average color channels in the quenched approximation and in
2-flavor QCD at finite temperature. We show that in the high temperature phase
singlet and decuplet free energies of three quark systems are well described by
the sum of the free energies of three diquark systems plus self energy
contributions of the three quarks. In the confining low temperature phase we
find evidence for a Y-shaped flux tube in SU(3) pure gauge theory, which is
less evident in 2-flavor QCD due to the onset of string breaking. We also
compare the short distance behavior of octet and decuplet free energies to the
free energies of single static quarks in the corresponding color
representations.Comment: 11 pages, 17 figure
The three flavour chiral phase transition with an improved quark and gluon action in lattice QCD
The finite-temperature chiral phase transition is investigated for three
flavours of staggered quarks on a lattice of temporal extent N_t=4. In the
simulation we use an improved fermion action which reduces rotational symmetry
breaking of the quark propagator (p4-action), include fat-links to improve the
flavour symmetry and use the tree level improved (1,2) gluon action. We study
the nature of the phase transition for quark masses of ma=0.025, ma=0.05 and
ma=0.1 on lattices with spatial sizes of 8^3 and 16^3.Comment: LATTICE98(hightemp), 3 pages, 7 figures, LaTeX2e-File, espcrc2.st
Thermodynamics of the PNJL model with nonzero baryon and isospin chemical potentials
We have extended the Polyakov-Nambu-Jona-Lasinio (PNJL) model for two
degenerate flavours to include the isospin chemical potential (). All
the diagonal and mixed derivatives of pressure with respect to the quark number
(proportional to baryon number) chemical potential () and isospin
chemical potential upto sixth order have been extracted at .
These derivatives give the generalized susceptibilities with respect to quark
and isospin numbers. Similar estimates for the flavour diagonal and
off-diagonal susceptibilities are also presented. Comparison to Lattice QCD
(LQCD) data of some of these susceptibilities for which LQCD data are
available, show similar temperature dependence, though there are some
quantitative deviations above the crossover temperature. We have also looked at
the effects of instanton induced flavour-mixing coming from the chiral
symmetry breaking 't Hooft determinant like term in the NJL part of the model.
The diagonal quark number and isospin susceptibilities are completely
unaffected. The off-diagonal susceptibilities show significant dependence near
the crossover. Finally we present the chemical potential dependence of specific
heat and speed of sound within the limits of chemical potentials where neither
diquarks nor pions can condense.Comment: 15 pages, 7 figures, Added discussions and references, version to
appear in Phys. Rev.
Susceptibilities and speed of sound from PNJL model
We present the Taylor expansion coefficients of the pressure in quark number
chemical potential , for the strongly interacting
matter as described by the PNJL model for two light degenerate flavours of
quarks u and d. The expansion has been done upto eighth order in , and
the results are consistent with recent estimates from Lattice. We have further
obtained the specific heat , squared speed of sound and the
conformal measure \cC.Comment: 13 pages, 8 figures, References added, some discussions on Fig. 4
modified, one table added, results unchanged, version to appear in Phys. Rev.
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