277 research outputs found
Present Status of Lattice QCD at nonzero T and \mu
I review a few selected topics in Lattice Quantum Chromo Dynamics, focusing
more on the recent results. These include i) the equation of state and speed of
sound, ii) J/\psi suppression, iii) flavour correlations and iv) the QCD phase
diagram in the \mu-T plane.Comment: 13 Pages including figures, Plenary Talk at the 9th Workshop on High
Energy Physics Phenomenology, ``WHEPP9'', Bhubaneswar, India, January 3-14,
2006, To appear in Praman
Screening correlators with chiral Fermions
We study screening correlators of quark-antiquark composites at T=2T_c, where
T_c is the QCD phase transition temperature, using overlap quarks in the
quenched approximation of lattice QCD. As the lattice spacing is changed from
1/4T to a=1/6T and 1/8T, we find that screening correlators change little, in
contrast with the situation for other types of lattice fermions. All
correlators are close to the ideal gas prediction at small separations. The
long distance falloff is clearly exponential, showing that a parametrization by
a single screening length is possible at distances z > 1/T. The correlator
corresponding to the thermal vector is close to the ideal gas value at all
distances, whereas that for the thermal scalar deviates at large distances.
This is examined through the screening lengths and momentum space correlators.
There is strong evidence that the screening transfer matrix does not have
reflection positivity.Comment: 10 pages, 9 fig
Pressure and non-linear susceptibilities in QCD at finite chemical potentials
When the free energy density of QCD is expanded in a series in the chemical
potential, mu, the Taylor coefficients are the non-linear quark number
susceptibilities. We show that these depend on the prescription for putting
chemical potential on the lattice, making all extrapolations in chemical
potential prescription dependent at finite lattice spacing. To put bounds on
the prescription dependence, we investigate the magnitude of the non-linear
susceptibilities over a range of temperature, T, in QCD with two degenerate
flavours of light dynamical quarks at lattice spacing 1/4T. The prescription
dependence is removed in quenched QCD through a continuum extrapolation, and
the dependence of the pressure, P, on mu is obtained.Comment: 15 pages, 2 figures. Data on chi_uuuu added, discussion enhance
Z2 Monopoles, Vortices, and the Deconfinement Transition in Mixed Action SU(2) Gauge Theory
Adding separate chemical potentials lambda and gamma for Z2 monopoles and
vortices respectively in the Villain form of the mixed fundamental-adjoint
action for the SU(2) lattice gauge theory, we investigate their role in the
interplay between the deconfinement and bulk phase transitions using Monte
Carlo techniques. Setting lambda to be nonzero, we find that the line of
deconfinement transitions is shifted in the coupling plane but it behaves
curiously also like the bulk transition line for large enough adjoint coupling,
as for lambda=0. In a narrow range of couplings, however, we find separate
deconfinement and bulk phase transitions on the same lattice for nonzero and
large lambda, suggesting the two to be indeed coincident in the region where a
first order deconfinement phase transition is seen. In the limit of large
lambda and gamma, we obtain only lines of second order deconfinement phase
transitions, as expected from universality.Comment: 18 pages, 10 figures include
Phase Transitions in SO(3) Lattice Gauge Theory
The phase diagram of SO(3) lattice gauge theory is investigated by Monte
Carlo techniques on both symmetric and asymmetric lattices with a view (i) to
understanding the relationship between the bulk transition and the
deconfinement transition, and (ii) to resolving the current ambiguity about the
nature of the high temperature phase. A number of tests, including an
introduction of a magnetic field and measurement of different correlation
functions in the phases with positive and negative values for the adjoint
Polyakov line, lead to the conclusion that the two phases correspond to the
same physical state. Studies on lattices of different sizes reveal only one
phase transition for this theory on all of them and it appears to have a
deconfining nature.Comment: Latex 19 pages, 9 figures. Minor changes in introduction and summary
sections. The version that appeared in journa
Anomalies at finite density and chiral fermions
Using perturbation theory in the Euclidean (imaginary time) formalism as well
as the non-perturbative Fujikawa method, we verify that the chiral anomaly
equation remains unaffected in the presence of nonzero chemical potential,
. We extend our considerations to fermions with exact chiral symmetry on
the lattice and discuss the consequences for the recent Bloch-Wettig proposal
for the Dirac operator at finite chemical potential. We propose a new simpler
method of incorporating and compare it with the Bloch-Wettig idea.Comment: 12 pages, 3 figures,some typos corrected, a better proof for the \mu
independence of anomaly is given in section IIB, v4: the published versio
Quark-Gluon Plasma: Status of Heavy Ion Physics
Lattice quantum chromodynamics (QCD), defined on a discrete space time
lattice, leads to a spectacular non-perturbative prediction of a new state of
matter, called quark-gluon plasma (QGP), at sufficiently high temperatures or
equivalently large energy densities. The experimental programs of CERN, Geneva
and BNL, New York of relativistic heavy ion collisions are expected to produce
such energy densities, thereby providing us a chance to test the above
prediction. After a brief introduction of the necessary theoretical concepts, I
will present a critical review of the experimental results already obtained by
the various experiments in order to examine whether QGP has already been
observed by them.Comment: 11 Pages, LaTeX, Plenary talk given at 6th Workshop in High Energy
Physics Phenomenology (WHEPP 6), Chennai (Madras), India, 3-15 Jan 2000 To
appear in Pramana, Journal of Physic
The continuum limit of quark number susceptibilities
We report the continuum limit of quark number susceptibilities in quenched
QCD. Deviations from ideal gas behaviour at temperature T increase as the
lattice spacing is decreased from T/4 to T/6, but a further decrease seems to
have very little effect. The measured susceptibilities are 20% lower than the
ideal gas values, and also 10% below the hard thermal loop (HTL) results. The
off-diagonal susceptibility is several orders of magnitude smaller than the HTL
results. We verify a strong correlation between the lowest screening mass and
the susceptibility. We also show that the quark number susceptibilities give a
reasonable account of the Wroblewski parameter, which measures the strangeness
yield in a heavy-ion collision.Comment: 8 pages, 5 figure
Potts Flux Tube Model at Nonzero Chemical Potential
We model the deconfinement phase transition in quantum chromodynamics at
nonzero baryon number density and large quark mass by extending the flux tube
model (three-state, three-dimensional Potts model) to nonzero chemical
potential. In a direct numerical simulation we confirm mean-field-theory
predictions that the deconfinement transition does not occur in a baryon-rich
environment.Comment: 14 pp RevTeX, 10 Postscript figures, submitted to Phys. Rev D.
(Corrected some typographical errors.
SU(3) Lattice Gauge Theory With Adjoint Action At Nonzero Temperature
We study the thermal phase diagram of pure SU(3) gauge theory with
fundamental and adjoint couplings. We improve previous estimates of the
position of the bulk transition line and determine the thermal deconfinement
transition lines for and 8. For the deconfinement
transition line splits cleanly away from the bulk transition line. With
increasing the thermal deconfinement transition lines shift to
increasingly weaker coupling, joining onto the bulk transition line at
increasingly larger in a pattern consistent with the usual
universality picture of lattice gauge theories.Comment: Talk presented by U. M. Heller at Lat94 conference, September 27 -
October 1, 1994, Bielefeld, Germany. self unwrapping postscript fil
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