1,291 research outputs found
Hadronic fluctuations in the QGP
We analyze fluctuations of quark number and electric charge, in 2-flavour QCD
at finite temperature and vanishing net baryon number density. In the hadronic
phase we find that an enhancement of charge fluctuations arises from
contributions of doubly charged hadrons to the thermodynamics. The rapid
suppression of fluctuations seen in the high temperature phase suggests that in
the QGP quark number and electric charge are predominantly carried by
quasi-particles with the quantum numbers of quarks.Comment: 4 pages, 6 EPS-files, talk presented at Quark Matter 2005, Budapes
Correlation functions of the energy-momentum tensor in SU(2) gauge theory at finite temperature
We calculate correlation functions of the energy-momentum tensor in the
vicinity of the deconfinement phase transition of (3+1)-dimensional SU(2) gauge
theory and discuss their critical behavior in the vicinity of the second order
deconfinement transition. We show that correlation functions of the trace of
the energy momentum tensor diverge uniformly at the critical point in
proportion to the specific heat singularity. Correlation functions of the
pressure, on the other hand, stay finite at the critical point. We discuss the
consequences of these findings for the analysis of transport coefficients, in
particular the bulk viscosity, in the vicinity of a second order phase
transition point.Comment: 24 pages, 6 figure
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
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
The Ising model universality of the electroweak theory
Lattice simulations have shown that the first order electroweak phase
transition turns into a regular cross-over at a critical Higgs mass m_{H,c}. We
have developed a method which enables us to make a detailed investigation of
the critical properties of the electroweak theory at m_{H,c}. We find that the
transition falls into the 3d Ising universality class. The continuum limit
extrapolation of the critical Higgs mass is m_{H,c} = 72(2) GeV, which implies
that there is no electroweak phase transition in the Standard Model.Comment: 3 pages, contribution to LATTICE98(electroweak
Fluctuations in the vicinity of the phase transition line for two flavor QCD
We study the susceptibilities of quark number, isospin number and electric
charge in numerical simulations of lattice QCD at high temperature and density.
We discuss the equation of state for 2 flavor QCD at non-zero temperature and
density. Derivatives of with respect to quark chemical potential
are calculated up to sixth order. From this Taylor series, the
susceptibilities are estimated as functions of temperature and .
Moreover, we comment on the hadron resonance gas model, which explains well our
simulation results below .Comment: 3 pages, 5 figures, Talk presented at Lattice2004(non-zero
Thermodynamics at Non-Zero Baryon Number Density: A Comparison of Lattice and Hadron Resonance Gas Model Calculations
We compare recent lattice studies of QCD thermodynamics at non-zero quark
chemical potential with the thermodynamics of a hadron resonance gas. We argue
that for T < Tc the equation of state derived from Monte--Carlo simulations of
two flavour QCD at non-zero chemical potential can be well described by a
hadron resonance gas when using the same set of approximations as used in
current lattice calculations. We estimate the importance of truncation errors
arising from the use of a Taylor expansion in terms of the quark chemical
potential and examine the influence of unphysically large quark masses on the
equation of state and the critical conditions for deconfinement.Comment: 15 pages, LaTex2e, 6 EPS-figures, minor corrections, reference 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
Free energies of static three quark systems
We study the behaviour of free energies of baryonic systems composed of three
heavy quarks on the lattice in SU(3) pure gauge theory at finite temperature.
For all temperatures above we find that the connected part of the singlet
(decuplet) free energy of the three quark system is given by the sum of the
connected parts of the free energies of -triplets (-sextets). Using
renormalized free energies we can compare free energies in different colour
channels as well as those of - and -systems on an unique energy scale.Comment: 5 pages, 6 figures, Contribution to Strong and Electroweak Matter
2004 (SEWM04), Helsinki, Finland 16-19 June 200
Comparing the drag force on heavy quarks in N=4 super-Yang-Mills theory and QCD
Computations of the drag force on a heavy quark moving through a thermal
state of strongly coupled N=4 super-Yang-Mills theory have appeared recently in
hep-th/0605158, hep-ph/0605199, and hep-th/0605182. I compare the strength of
this effect between N=4 gauge theory and QCD, using the static force between
external quarks to normalize the 't Hooft coupling. Comparing N=4 and QCD at
fixed energy density then leads to a relaxation time of roughly 2 fm/c for
charm quarks moving through a quark-gluon plasma at T=250 MeV. This estimate
should be regarded as preliminary because of the difficulties of comparing two
such different theories.Comment: 16 pages, 1 figure. v2: corrected estimate of eta/s, refs adde
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