1,265 research outputs found
Quark Mass and Flavour Dependence of the QCD Phase Transition
We analyze the quark mass and flavour dependence of the QCD phase transition
temperature. When the lightest pseudo-scalar meson mass (m_PS) is larger than 2
GeV the critical temperature is controlled by the gluonic sector of QCD alone.
For smaller values of the lightest meson mass the pseudo-critical temperature
decreases slowly with m_PS. For a large regime of meson masses the
pseudo-critical temperature of 2-flavour QCD is about 10% larger than in the
3-flavour case. On lattices with temporal extent N_t=4 an extrapolation to the
chiral limit yields T_c = 173(8) MeV and 154(8) MeV for 2 and 3-flavour QCD,
respectively. We also analyze dynamical quark mass effects on the screening of
the heavy quark potential. A detailed analysis of the heavy quark free energy
in 3-flavour QCD shows that close to T_c screening effects are approximately
quark mass independent already for pseudo-scalar meson masses m_PS = 800 MeV
and screening sets in at distances r = 0.3 fm.Comment: 25 pages, LaTeX2e File, 11 EPS-file
Group projection method in statistical systems
We discuss an application of group theoretical methods to the formulation of
the thermodynamics of systems constrained by the conservation laws described by
a semi--simple compact Lie group. A general projection method that allows to
construct a partition function for a given irreducible representation of the
Lie group is outlined. Applications of the method in Lattice Gauge Theory (LGT)
for non--zero baryon number and in the phenomenological description of particle
production in ultrarelativistic heavy ion collisions are also indicated.Comment: Invited talk presented at the XXIV International Colloquium on Group
Theoritical Methods in Physic
Magnetic Screening in Hot Non-Abelian Gauge Theory
We analyze the large distance and low-momentum behavior of the magnetic gluon
propagator of the SU(2) gauge theory at finite temperature. Lattice
calculations within the 4-dimensional as well as the effective, dimensionally
reduced 3-dimensional gauge theories in generalized Landau gauges and MAG show
that the magnetic propagator is strongly infrared suppressed in Landau gauges
but stays large and finite in MAG. Despite these differences in the
low-momentum behavior of the propagator calculated in different gauges the
magnetic fields are exponentially screened in all gauges considered. From the
propagator calculated in maximally Abelian gauge we find for the screening
mass, m_M = (1.48 +/- 0.17) T at T=2 T_c.Comment: 11 pages, LaTeX2e, new data added, conclusions unchanged. The final
version to appear in Phys. Lett.
Heavy ion collisions and lattice QCD at finite baryon density
We discuss a relation between the
QCD thermodynamics obtained from a statistical analysis of particle
production in heavy ion collisions at SPS and RHIC energies and recent LGT
results at finite chemical potential. We show that basic thermodynamic
properties obtained from the phenomenological statistical operator of a hadron
resonance gas that describes particle yields in heavy ion collisions are
consistent with recent LGT results. We argue that for the equation
of state derived from
Monte--Carlo simulations of two quark--flavor QCD at finite chemical
potential can be well described by a hadron resonance gas when using the same
set of approximations as used in LGT calculations. We examine the influence of
a finite quark mass on the position of the deconfinement transition in
temperature and chemical potential plane.Comment: To appear in the proceedings of 17in International Conference on
Ultra Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland,
California, 11-17 Jan 200
Flavor and Quark Mass Dependence of QCD Thermodynamics
We calculate the transition temperature in 2 and 3-flavor QCD using improved
gauge and staggered fermion actions on lattices with temporal extent Nt=4. We
find Tc=173(8)MeV and 154(8)MeV for nf=2 and 3, respectively. In the case of
3-flavor QCD we present evidence that the chiral critical point, i.e. the
second order endpoint of the line of first order chiral phase transitions,
belongs to the universality class of the 3d Ising model.Comment: Talk given at Lattice 2000 (Finite Temperature), 4 pages, 6
EPS-figure
The QCD phase diagram: A comparison of lattice and hadron resonance gas model calculations
We compare the lattice results on QCD phase diagram for two and three flavors
with the hadron resonance gas model (HRGM) calculations. Lines of constant
energy density have been determined at different baryo-chemical
potentials . For the strangeness chemical potentials , we use two
models. In one model, we explicitly set for all temperatures and
baryo-chemical potentials. This assignment is used in lattice calculations. In
the other model, is calculated in dependence on and
according to the condition of vanishing strangeness. We also derive an
analytical expression for the dependence of on by applying
Taylor expansion of . In both cases, we compare HRGM results on
diagram with the lattice calculations. The agreement is excellent,
especially when the trigonometric function of is truncated up to the
same order as done in lattice simulations. For studying the efficiency of the
truncated Taylor expansion, we calculate the radius of convergence. For zero-
and second-order radii, the agreement with lattice is convincing. Furthermore,
we make predictions for QCD phase diagram for non-truncated expressions and
physical masses. These predictions are to be confirmed by heavy-ion experiments
and future lattice calculations with very small lattice spacing and physical
quark masses.Comment: 25 pages, 8 eps figure
Hadron resonance gas and nonperturbative QCD vacuum at finite temperature
We study the nonperturbative QCD vacuum with two light quarks at finite
temperature in the framework of hadron resonance gas. Temperature dependence of
the quark and gluon condensates in the confined phase are obtained. We
demonstrate that the quark condensate and one half (chromo-electric component)
of gluon condensate evaporate at the same temperature, which corresponds to the
temperature of quark-hadron phase transition. Critical temperature is T_c~190
MeV when temperature shift of hadron masses is taken into account.Comment: 8 pages, 4 figures; to appear in JETP Lett.; v2: references adde
Charge fluctuations in chiral models and the QCD phase transition
We consider the Polyakov loop-extended two flavor chiral quark--meson model
and discuss critical phenomena related with the spontaneous breaking of the
chiral symmetry. The model is explored beyond the mean-field approximation in
the framework of the functional renormalisation group. We discuss properties of
the net-quark number density fluctuations as well as their higher cumulants. We
show that with the increasing net-quark number density, the higher order
cumulants exhibit a strong sensitivity to the chiral crossover transition. We
discuss their role as probes of the chiral phase transition in heavy-ion
collisions at RHIC and LHC.Comment: 4 pages, 3 figures, to appear in the proceedings of Quark Matter
2011, 23-28 May 2011, Annecy, Franc
Baryon-strangeness correlations: a diagnostic of strongly interacting matter
The correlation between baryon number and strangeness elucidates the nature
of strongly interacting matter, such as that formed transiently in high-energy
nuclear collisions. This diagnostic can be extracted theoretically from lattice
QCD calculations and experimentally from event-by-event fluctuations. The
analysis of present lattice results above the critical temperature severely
limits the presence of q-qbar bound states, thus supporting a picture of
independent (quasi)quarks.Comment: 4 pages, 2 eps figures, Revised: several sign typos have been fixed
(the PRL version is correct
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