29,848 research outputs found
RG flow of the Polyakov-loop potential: First status report
We study SU(2) Yang-Mills theory at finite temperature in the framework of
the functional renormalization group. We concentrate on the effective potential
for the Polyakov loop which serves as an order parameter for confinement. In
this first status report, we focus on the behaviour of the effective
Polyakov-loop potential at high temperatures. In addition to the standard
perturbative result, our findings provide information about the ``RG improved''
backreactions of Polyakov-loop fluctuations on the potential. We demonstrate
that these fluctuations establish the convexity of the effective potential.Comment: 10 pages, 2 figure
Volume Dependence of the Pion Mass from Renormalization Group Flows
We investigate finite volume effects on the pion mass and the pion decay
constant with renormalization group (RG) methods in the framework of a
phenomenological model for QCD. An understanding of such effects is important
in order to interpret results from lattice QCD and extrapolate reliably from
finite lattice volumes to infinite volume.
We consider the quark-meson-model in a finite Euclidean 3+1 dimensional
volume. In order to break chiral symmetry in the finite volume, we introduce a
small current quark mass. In the corresponding effective potential for the
meson fields, the chiral O(4)-symmetry is broken explicitly, and the sigma and
pion fields are treated individually. Using the proper-time renormalization
group, we derive renormalization group flow equations in the finite volume and
solve these equations in the approximation of a constant expectation value.
We calculate the volume dependence of pion mass and pion decay constant and
compare our results with recent results from chiral perturbation theory in
finite volume.Comment: 9 pages, 3 figures, talk given at "Hadronic Physics 2004 - Joint
meeting Heidelberg-Liege-Paris-Rostock", to appear in the proceedings, AIP
conference serie
Fusion of strings vs. percolation and the transition to the quark-gluon plasma
In most of the models of hadronic collisions the number of exchanged colour
strings grows with energy and atomic numbers of the projectile and target. At
high string densities interaction between them should melt them into the
quark-gluon plasma state. It is shown that under certain assumptions about the
the string interaction, a phase transition to the quark gluon plasma indeed
takes place in the system of many colour strings. It may be of the first or
second order (percolation), depending on the particular mechanism of the
interaction. The critical string density is about unity in both cases. The
critical density may have been already reached in central Pb-Pb collisions at
158 A GeV.Comment: 16 pages, 3 Postscript figure
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