187 research outputs found
On the renormalization of the Polyakov loop
We discuss a non-perturbative renormalization of n-point Polyakov loop
correlation functions by explicitly introducing a renormalization constant for
the Polyakov loop operator on a lattice deduced from the short distance
properties of 2-point correlators. We calculate this constant for the
SU(3)gauge theory.Comment: 5 pages, 1 figure, To appear in the proceedings of Workshop on Strong
and Electroweak Matter (SEWM 2002), Heidelberg, Germany, 2-5 Oct 200
Gribov Copies in the Minimal Landau Gauge: the Influence on Gluon and Ghost Propagators
We study the influence of Gribov copies on gluon and ghost propagators,
evaluated numerically in pure SU(2) lattice gauge theory in the minimal Landau
gauge. Simulations are done at four different values of (namely
= 0, 0.8, 1.6 and 2.7) and for volumes up to (up to at =
1.6). For the gluon propagator, Gribov noise seems to be of the order of
magnitude of the numerical accuracy, even at very small values of the coupling
. On the contrary, for the ghost propagator, Gribov noise is clearly
observable for the three values of in the strong-coupling regime. In
particular, data corresponding to the minimal Landau gauge are always smaller
than those obtained in a generic Landau gauge. This result can be qualitatively
explained.Comment: 19 pages, including three figures; minor modifications following
referee's suggestions. ZiF-MS-16/97 preprint. To appear in Nucl.Phys.
Critical behaviour and Scaling functions for the three-dimensional O(6) spin model with external field
We numerically investigate the three-dimensional O(6) model on 12^3 to 120^3
lattices. From Binder's cumulant at vanishing magnetic field we obtain the
critical coupling J_c=1.42865(5) and verify this value with the \chi^2-method.
The universal value of Binder's cumulant at this point is
g_r(J_c)=-1.94456(10). At the critical coupling we find the critical exponents
\nu=0.818(5), \beta=0.425(2) and \gamma=1.604(6) from a finite size scaling
analysis. We also determine the finite-size-scaling function on the critical
line and the equation of state. Our O(6)-result for the equation of state is
compared to the Ising, O(2) and O(4) results.Comment: 5 pages, 4 figures, To appear in the proceedings of Workshop on
Strong and Electroweak Matter (SEWM 2002), Heidelberg, Germany, 2-5 Oct 200
The Nonabelian Screening Potential Beyond the Leading Order
The nonabelian screening potential is calculated in the temporal axial gauge.
The Slavnov-Taylor identity is used to construct the three-gluon vertex
function from the inverse gluon propagator. After solving the Schwinger - Dyson
equation beyond leading order we find that the obtained momentum dependence of
the gluon self-energy at high temperature does not correspond to an attractive
QCD - Debye potential, but instead it is repulsive and power behaved () at large distance.Comment: 10 pages, LATEX, ( 1 figure not included), BI-TP 94/0
D-Branes in Topological String Theory
This thesis is concerned with D-branes in topological string theory, focusing
on the description of B-type D-branes in topological Landau-Ginzburg models.
Such D-branes are characterized by matrix factorizations of the Landau-Ginzburg
superpotential. After reviewing some aspects of topological string theory we
give a detailed discussion of matrix factorizations. We discuss methods to
calculate the effective superpotential in minimal models, putting emphasis on
an algorithm to calculate the effective superpotential via deformations of
matrix factorizations. We furthermore perform a non-trivial check of
homological mirror symmetry for the torus.Comment: PhD thesis, 147+9 pages, 10 figure
A Gravity Theory on Noncommutative Spaces
A deformation of the algebra of diffeomorphisms is constructed for
canonically deformed spaces with constant deformation parameter theta. The
algebraic relations remain the same, whereas the comultiplication rule (Leibniz
rule) is different from the undeformed one. Based on this deformed algebra a
covariant tensor calculus is constructed and all the concepts like metric,
covariant derivatives, curvature and torsion can be defined on the deformed
space as well. The construction of these geometric quantities is presented in
detail. This leads to an action invariant under the deformed diffeomorphism
algebra and can be interpreted as a theta-deformed Einstein-Hilbert action. The
metric or the vierbein field will be the dynamical variable as they are in the
undeformed theory. The action and all relevant quantities are expanded up to
second order in theta.Comment: 28 pages, v2: coefficient in equ. (10.15) corrected, references
added, v3: references added, published versio
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