title: Effective lattice theories for Polyakov loops

abstract:
  We derive effective actions for SU(2) Polyakov loops using inverse Monte
Carlo techniques. In a first approach, we determine the effective couplings by
requiring that the effective ensemble reproduces the single-site distribution
of the Polyakov loops. The latter is flat below the critical temperature
implying that the (untraced) Polyakov loop is distributed uniformly over its
target space, the SU(2) group manifold. This allows for an analytic
determination of the Binder cumulant and the distribution of the mean-field,
which turns out to be approximately Gaussian. In a second approach, we employ
novel lattice Schwinger-Dyson equations which reflect the SU(2) x SU(2)
invariance of the functional Haar measure. Expanding the effective action in
terms of SU(2) group characters makes the numerics sufficiently stable so that
we are able to extract a total number of 14 couplings. The resulting action is
short-ranged and reproduces the Yang-Mills correlators very well.


title: Fermions in 2D Lorentzian Quantum Gravity

abstract:
  We implement Wilson fermions on 2D Lorentzian triangulation and determine the
spectrum of the Dirac-Wilson operator. We compare it to the spectrum of the
corresponding operator in the Euclidean background. We use fermionic particle
to probe the fractal properties of Lorentzian gravity coupled to $c=1/2$ and
$c=4$ matter. We numerically determine the scaling exponent of the mass gap $M
\sim N^{-1/d_H}$ to be $d_H=2.11(5)$, and $d_H=1.77(3)$ for $c=1/2$ and $c=4$,
respectively


title: Kosterlitz Thouless Universality in Dimer Models

abstract:
  Using the monomer-dimer representation of strongly coupled U(N) lattice gauge
theories with staggered fermions, we study finite temperature chiral phase
transitions in (2+1) dimensions. A new cluster algorithm allows us to compute
monomer-monomer and dimer-dimer correlations at zero monomer density (chiral
limit) accurately on large lattices. This makes it possible to show
convincingly, for the first time, that these models undergo a finite
temperature phase transition which belongs to the Kosterlitz-Thouless
universality class. We find that this universality class is unaffected even in
the large N limit. This shows that the mean field analysis often used in this
limit breaks down in the critical region.


title:
Lattice extraction of $ K \to \pi \pi $ amplitudes to NLO in partially
  quenched and in full chiral perturbation theory

abstract:
  We show that it is possible to construct $\epsilon^\prime/\epsilon$ to NLO
using partially quenched chiral perturbation theory (PQChPT) from amplitudes
that are computable on the lattice. We demonstrate that none of the needed
amplitudes require three-momentum on the lattice for either the full theory or
the partially quenched theory; non-degenerate quark masses suffice.
Furthermore, we find that the electro-weak penguin ($\Delta I=3/2$ and 1/2)
contributions to $\epsilon^\prime/\epsilon$ in PQChPT can be determined to NLO
using only degenerate ($m_K=m_\pi$) $K\to\pi$ computations without momentum
insertion. Issues pertaining to power divergent contributions, originating from
mixing with lower dimensional operators, are addressed. Direct calculations of
$K\to\pi\pi$ at unphysical kinematics are plagued with enhanced finite volume
effects in the (partially) quenched theory, but in simulations when the sea
quark mass is equal to the up and down quark mass the enhanced finite volume
effects vanish to NLO in PQChPT. In embedding the QCD penguin left-right
operator onto PQChPT an ambiguity arises, as first emphasized by Golterman and
Pallante. With one version (the "PQS") of the QCD penguin, the inputs needed
from the lattice for constructing $K\to\pi\pi$ at NLO in PQChPT coincide with
those needed for the full theory. Explicit expressions for the finite
logarithms emerging from our NLO analysis to the above amplitudes are also
given.


title:
Nucleons Properties at Finite Lattice Spacing in Chiral Perturbation
  Theory

abstract:
  Properties of the proton and neutron are studied in partially-quenched chiral
perturbation theory at finite lattice spacing. Masses, magnetic moments, the
matrix elements of isovector twist-2 operators and axial-vector currents are
examined at the one-loop level in a double expansion in the light-quark masses
and the lattice spacing. This work will be useful in extrapolating the results
of simulations using Wilson valence and sea quarks, as well as simulations
using Wilson sea quarks and Ginsparg-Wilson valence quarks, to the continuum.


title: Scalar Mesons as qbar^2 q^2? Insight from the Lattice

abstract:
  I describe some insight obtained from a lattice calculation on the
possibility that the light scalar mesons are \qbar^2 q^2 states rather than
\qbar q. First I review some general features of \qbar^2 q^2 states in QCD
inspired quark models. Then I describe a lattice QCD calculation of
pseudoscalar meson scattering amplitudes, ignoring quark loops and quark
annihilation, which finds indications that for sufficiently heavy quarks there
is a stable four-quark bound state with JPC=0{++} and non-exotic flavor quantum
numbers.


title: A Review Of Two Novel Numerical Methods in QFT

abstract:
  We outline two alternative schemes to perform numerical calculations in
quantum field theory. In principle, both of these approaches are better suited
to study phase structure than conventional Monte Carlo. The first method,
Source Galerkin, is based on a numerical analysis of the Schwinger-Dyson
equations using modern computer techniques. The nature of this approach makes
dealing with fermions relatively straightforward, particularly since we can
work on the continuum. Its ultimate success in non-trivial dimensions will
depend on the power of a propagator expansion scheme which also greatly
simplifies numerical calculation of traditional perturbation graphs. The second
method extends Monte Carlo approaches by introducing a procedure to deal with
rapidly oscillating integrals.


title: The spectrum of D_s mesons from lattice QCD

abstract:
  The spectrum of orbitally excited $D_s$ mesons is computed in the continuum
limit of quenched lattice QCD. The results are consistent with the
interpretation that the narrow resonance in the $D_s \pi^0$ channel discovered
by the BABAR Collaboration is a $J^P=0^+$ $c\bar{s}$ meson. Furthermore, within
statistical errors, the $1^+-1^-$ and the $0^+-0^-$ mass splittings are equal,
in agreement with the chiral multiplet structure predicted by heavy hadron
chiral effective theory. On our coarsest lattice we present results from the
first study of orbitally excited $D_s$ mesons with two flavors of dynamical
quarks, with mass slightly larger than the strange quark mass. These results
are consistent with the quenched data.


title:
Quark mass dependence of masses and decay constants of the
  pseudo-Goldstone bosons in QCD

abstract:
  The dependence of the pseudoscalar meson masses and decay constants on sea
and valence quark masses is compared to next-to-leading order (NLO) Chiral
Perturbation Theory (ChPT). The numerical simulations with two light dynamical
quark flavors are performed with the Wilson-quark lattice action at gauge
coupling beta=5.1 and hopping parameters kappa=0.176, 0.1765, 0.177 on a 16^4
lattice. O(a) lattice artifacts are taken into account by applying chiral
perturbation theory for the Wilson lattice action. The values of the relevant
combinations of Gasser-Leutwyler constants L_4, L_5, L_6 and L_8 are estimated.


title:
Charge Radii of the Meson and Baryon Octets in Quenched and Partially
  Quenched Chiral Perturbation Theory

abstract:
  We calculate the electric charge radii of the SU(3) pseudoscalar mesons and
the SU(3) octet baryons in quenched and partially quenched chiral perturbation
theory. We work in the isospin limit, up to next-to-leading order in the chiral
expansion, and to leading order in the heavy baryon expansion. The results are
necessary for the extrapolation of future lattice calculations of meson and
baryon charge radii. We also derive expressions for the nucleon and pion charge
radii in SU(2) flavor away from the isospin limit.


title: Quenched charmonium spectrum

abstract:
  We study charmonium using the standard relativistic formalism in the quenched
approximation, on a set of lattices with isotropic lattice spacings ranging
from 0.1 to 0.04 fm. We concentrate on the calculation of the hyperfine
splitting between eta_c and J/psi, aiming for a controlled continuum
extrapolation of this quantity. The splitting extracted from the
non-perturbatively improved clover Dirac operator shows very little dependence
on the lattice spacing for $a \leq 0.1$ fm. The dependence is much stronger for
Wilson and tree-level improved clover operators, but they still yield
consistent extrapolations if sufficiently fine lattices, $a \leq 0.07$ fm ($a
M(\eta_c) \leq 1$), are used. Our result for the hyperfine splitting is
77(2)(6) MeV (where Sommer's parameter, r_0, is used to fix the scale). This
value remains about 30% below experiment. Dynamical fermions and OZI-forbidden
diagrams both contribute to the remainder. Results for the eta_c and J/psi wave
functions are also presented.


title:
Heavy--light decay constants in the continuum limit of quenched lattice
  QCD

abstract:
  We compute the decay constants for the heavy--light pseudoscalar mesons in
the quenched approximation and continuum limit of lattice QCD. Within the
Schrodinger Functional framework, we make use of the step scaling method, which
has been previously introduced in order to deal with the two scale problem
represented by the coexistence of a light and a heavy quark. The continuum
extrapolation gives us a value $f_{B_s} = 192(6)(4)$ MeV for the $B_s$ meson
decay constant and $f_{D_s} = 240(5)(5)$ MeV for the $D_s$ meson.


title: Lattice Results on the Connected Neutron Charge Radius

abstract:
  We describe a calculation using quenched lattice QCD of the connected part of
the neutron electric form factor for momentum transfers in the range $0.3 {\rm
GeV^2} \stackrel{<}{\sim} -q^2 \stackrel{<}{\sim} 1.0 {\rm GeV^2}$. We extract
the implied charge radius using a Galster parameterization and consider various
ways of extrapolating the neutron charge radius value to the chiral limit. We
find that the measured charge radii may be reconciled to experiment by standard
phenomenology and lowest or next to lowest order contributions from chiral
perturbation theory.


title: Analyticity and the phase diagram of QCD

abstract:
  Some consequences of the analyticity of the free energy (pressure) of QCD at
finite chemical potential are deduced. These include a method for numerical
exploration of the full phase diagram by a novel use of simulations at
imaginary chemical potential to extract Yang-Lee zeroes of the grand-canonical
partition function. We make use of, and comment on, CPT symmetries, positivity
of non-linear susceptibilities and the finiteness of screening lengths. We also
comment on the structure of zeroes expected for the usual picture of the phases
of QCD, following a discussion of the physics of imaginary chemical potential.


title: Simulating the Schroedinger functional with two pseudo-fermions

abstract:
  We report on simulations with two flavors of O(a) improved degenerate Wilson
fermions with Schroedinger functional boundary conditions. The algorithm which
is used is Hybrid Monte Carlo with two pseudo-fermion fields as proposed by M.
Hasenbusch. We investigate the numerical precision and sensitivity to
reversibility violations of this algorithm. A gain of a factor two in CPU cost
is reached compared with one pseudo-fermion field due to the larger possible
step-size.


title: The Matter and the Pseudoscalar Densities in Lattice QCD

abstract:
  The matter and the pseudoscalar densities inside a hadron are calculated via
gauge-invariant equal-time correlation functions. A comparison is made between
the charge charge and the matter density distributions for the pion, the rho,
the nucleon and the $\Delta^+$ within the quenched theory, and with two
flavours of dynamical quarks.


title:
The contribution of O(alpha) radiative corrections to the renormalised
  anisotropy and application to general tadpole improvement schemes: addendum
  to "One loop calculation of the renormalised anisotropy for improved
  anisotropic gluon actions on a lattice" [hep-lat/0208010]

abstract:
  General O(alpha) radiative corrections to lattice actions may be interpreted
as counterterms that give additive contributions to the one-loop
renormalisation of the anisotropy. The effect of changing the radiative
coefficients is thus easily calculable. In particular, the results obtained in
a previous paper for Landau mean link improved actions apply in any tadpole
improvement scheme. We explain how this method can be exploited when tuning
radiatively improved actions. Efficient methods for self-consistently tuning
tadpole improvement factors are also discussed.


title: General chiral gauge theories on the lattice

abstract:
  We still extend the large class of Dirac operators decribing massless
fermions on the lattice found recently, only requiring that such operators
decompose into Weyl operators. After deriving general relations and
constructions of operators, we study the basis representations of the chiral
projections. We then investigate correlation functions of Weyl fermions for any
value of the index, stressing the related conditions for basis transformations
and their consequences, and getting the precise behaviors under gauge
transformations and CP transformations. Various further developments include
considerations of the explicit form of the effective action and of a
representation of the general correlation functions in terms of alternating
multilinear forms. For comparison we also consider gauge-field variations and
their respective applications. Finally we compare with continuum perturbation
theory.


title:
Supersymmetry on a Euclidean Spacetime Lattice II: Theories with Eight
  Supercharges

abstract:
  We formulate Euclidean spacetime lattices whose continuum limits are
supersymmetric Yang-Mills theories with eight supercharges in two and three
dimensions. The lattice actions are themselves supersymmetric.


title: Quenched spectroscopy with fixed-point and chirally improved fermions

abstract:
  We present results from quenched spectroscopy calculations with the
parametrized fixed-point and the chirally improved Dirac operators. Both these
operators are approximate solutions of the Ginsparg-Wilson equation and have
good chiral properties. This allows us to work at small quark masses and we
explore pseudoscalar-mass to vector-mass ratios down to 0.28. We discuss meson
and baryon masses, their scaling properties, finite volume effects and compare
our results with recent large scale simulations. We find that the size of
quenching artifacts of the masses is strongly correlated with their
experimentally observed widths and that the gauge and hadronic scales are
consistent.


title:
Comment on: ``The Supersymmetric Ward-Takahashi Identity in 1-Loop
  Lattice Perturbation Theory. I. General Procedure'' by A. Feo;
  hep-lat/0305020

abstract:
  We comment on several issues concerning both the physics and authorship of
article hep-lat/0305020.


title:
On the scaling of computational particle physics codes on cluster
  computers

abstract:
  Many appplications in computational science are sufficiently
compute-intensive that they depend on the power of parallel computing for
viability. For all but the "embarrassingly parallel" problems, the performance
depends upon the level of granularity that can be achieved on the computer
platform.
  Our computational particle physics applications require machines that can
support a wide range of granularities, but in general, compute-intensive
state-of-the-art projects will require finely grained distributions. Of the
different types of machines available for the task, we consider cluster
computers.
  The use of clusters of commodity computers in high performance computing has
many advantages including the raw price/performance ratio and the flexibility
of machine configuration and upgrade. Here we focus on what is usually
considered the weak point of cluster technology; the scaling behaviour when
faced with a numerically intensive parallel computation. To this end we examine
the scaling of our own applications from numerical quantum field theory on a
cluster and infer conclusions about the more general case.


title:
Analysis of the Axial Anomaly on the Lattice with O(a)-improved Wilson
  Action

abstract:
  Flavor singlet and non-singlet axial Ward identities are investigated using
the Wilson formulation of lattice QCD with Clover O(a)-improvement, which
breaks explicitly chiral symmetry. The matching at one-loop order of all the
relevant renormalization constants with the continuum \bar{MS} scheme is
presented. Our calculations include: 1) the contributions arising from the
Clover term of the action; 2) the complete mixing of the gluon operator G
\tilde{G} with the divergence of the singlet axial current; 3) the use of both
local and extended definitions of the fermionic bilinear operators. A
definition of the gluon operator G \tilde{G} on the lattice outside the chiral
limit is proposed. Our definition takes into account the possible
power-divergent mixing with the pseudoscalar density, generated by the breaking
of chiral symmetry. A non-perturbative procedure for the evaluation of such
mixing constant is worked out. Finally, the renormalization properties of the
composite insertion of the topological charge operator relevant for the lattice
calculation of the neutron electric dipole moment, induced by the strong
CP-violating term of the QCD Lagrangian, are discussed.


title: The high temperature phase transition in SU(N) gauge theories

abstract:
  We calculate the continuum value of the deconfining temperature in units of
the string tension for SU(4), SU(6) and SU(8) gauge theories, and we
recalculate its value for SU(2) and SU(3). We find that the $N$-dependence for
$2 \leq N \leq 8$ is well fitted by $T_c/\sqrt{sigma} = 0.596(4) +
0.453(30)/N^2$, showing a rapid convergence to the large-N limit. We confirm
our earlier result that the phase transition is first order for $N \geq 3$ and
that it becomes stronger with increasing $N$. We also confirm that as $N$
increases the finite volume corrections become rapidly smaller and the phase
transition becomes visible on ever smaller volumes. We interpret the latter as
being due to the fact that the tension of the domain wall that separates the
confining and deconfining phases increases rapidly with $N$. We speculate on
the connection to Eguchi-Kawai reduction and to the idea of a Master Field.


title: N to Delta electromagnetic transition form factors from Lattice QCD

abstract:
  The magnetic dipole, the electric quadrupole and the Coulomb quadrupole
amplitudes for the transition $\gamma N\to \Delta$ are evaluated both in
quenched lattice QCD at $\beta=6.0$ and using two dynamical Wilson fermions
simulated at $\beta=5.6$. The dipole transition form factor is accurately
determined at several values of momentum transfer. On the lattices studied in
this work, the electric quadrupole amplitude is found to be non-zero yielding a
negative value for the ratio, $ R_{EM}$, of electric quadrupole to magnetic
dipole amplitudes at three values of momentum transfer.


title: Diquark condensation at strong coupling

abstract:
  The possibility of diquark condensation at sufficiently large baryon chemical
potential and zero temperature is analyzed in QCD at strong coupling. In
agreement with other strong coupling analysis, it is found that a first order
phase transition separates a low density phase with chiral symmetry
spontaneously broken from a high density phase where chiral symmetry is
restored. In none of the phases diquark condensation takes place as an
equilibrium state, but, for any value of the chemical potential, there is a
metastable state characterized by a non-vanishing diquark condensate. The
energy difference between this metastable state and the equilibrium state
decreases with the chemical potential and is minimum in the high density phase.
The results indicate that there is attraction in the quark-quark sector also at
strong coupling, and that the attraction is more effective at high baryon
density, but for infinite coupling it is not enough to produce diquark
condensation. It is argued that the absence of diquark condensation is not a
peculiarity of the strong coupling limit, but persists at sufficiently large
finite couplings.


title:
The QCD Phase Diagram for Three Degenerate Flavors and Small Baryon
  Density

abstract:
  We present results for the phase diagram of three flavor QCD for \mu_B ~ 500
MeV. Our simulations are performed with imaginary chemical potential \mu_I for
which the fermion determinant is positive. Physical observables are then fitted
by truncated Taylor series and continued to real chemical potential. We map out
the location of the critical line T_c(\mu_B) with an accuracy up to terms of
order (\mu_B/T)^6. We also give first results on a determination of the
critical endpoint of the transition and its quark mass dependence. Our results
for the endpoint differ significantly from those obtained by other methods, and
we discuss possible reasons for this.


title: Lattice HQET with exponentially improved statistical precision

abstract:
  We introduce an alternative discretization for static quarks on the lattice
retaining the O(a) improvement properties of the Eichten-Hill action. In this
formulation, statistical fluctuations are reduced by a factor which grows
exponentially with Euclidean time, x_0. For the first time, B-meson correlation
functions are computed with good statistical precision in the static
approximation for x_0>1 fm. At lattice spacings a \approx 0.1 fm, a \approx
0.08 fm and a \approx 0.07 fm the B_s-meson decay constant is determined in
static and quenched approximations. A correction due to the finite mass of the
b-quark is estimated by combining these static results with a recent
determination of F_Ds.


title: Axial Anomaly and Index of the Overlap Hypercube Operator

abstract:
  The overlap hypercube fermion is constructed by inserting a lattice fermion
with hypercubic couplings into the overlap formula. One obtains an exact
Ginsparg-Wilson fermion, which is more complicated than the standard overlap
fermion, but which has improved practical properties and is of current interest
for use in numerical simulations. Here we deal with conceptual aspects of the
overlap hypercube Dirac operator. Specifically, we evaluate the axial anomaly
and the index, demonstrating that the correct classical continuum limit is
recovered. Our derivation is non-perturbative and therefore valid in all
topological sectors. At the non-perturbative level this result had previously
only been shown for the standard overlap Dirac operator with Wilson kernel. The
new techniques which we develop to accomplish this are of a general nature and
have the potential to be extended to overlap Dirac operators with even more
general kernels.


title: Chiral Lagrangian Parameters for Scalar and Pseudoscalar Mesons

abstract:
  The results of a high-statistics study of scalar and pseudoscalar meson
propagators in quenched lattice QCD are presented. For two values of lattice
spacing, $\beta=5.7$ ($a \approx .18$ fm) and 5.9 ($a \approx .12$ fm), we
probe the light quark mass region using clover improved Wilson fermions with
the MQA pole-shifting ansatz to treat the exceptional configuration problem.
The quenched chiral loop parameters $m_0$ and $\alpha_{\Phi}$ are determined
from a study of the pseudoscalar hairpin correlator. From a global fit to the
meson correlators, estimates are obtained for the relevant chiral Lagrangian
parameters, including the Leutwyler parameters $L_5$ and $L_8$. Using the
parameters obtained from the singlet and nonsinglet pseudoscalar correlators,
the quenched chiral loop effect in the nonsinglet scalar meson correlator is
studied. By removing this QCL effect from the lattice correlator, we obtain the
mass and decay constant of the ground state scalar, isovector meson $a_0$.


title: The fermion determinant in (4,4) 2d lattice super-Yang-Mills

abstract:
  We find that the fermion determinant is not generally positive in a class of
lattice actions recently constructed by Cohen et al. [hep-lat/0307012]; these
are actions that contain an exact lattice supersymmetry and have as their
target (continuum) theory (4,4) 2-dimensional super-Yang-Mills. We discuss the
implications of this finding for lattice simulations and give some preliminary
results for the phase of the determinant in the phase-quenched ensemble.


title: Spectroscopy of Doubly-Charmed Baryons in Lattice QCD

abstract:
  We present results for masses of spin-1/2 and spin-3/2 double-charm baryons
in quenched lattice QCD, from an exploratory study using a non-perturbatively
improved clover action at beta=6.2. We have studied local operators and we
observe, after appropriate projections, a good signal for the ground states. We
also present results for single-charmed baryons and spin-splittings for both
double- and single-charmed states.


title:
Quark propagator and vertex: systematic corrections of hypercubic
  artifacts from lattice simulations

abstract:
  This is the first part of a study of the quark propagator and the vertex
function of the vector current on the lattice in the Landau gauge and using
both Wilson-clover and overlap actions. In order to be able to identify lattice
artifacts and to reach large momenta we use a range of lattice spacings. The
lattice artifacts turn out to be exceedingly large in this study. We present a
new and very efficient method to eliminate the hypercubic (anisotropy)
artifacts based on a systematic expansion on hypercubic invariants which are
not SO(4) invariant. A simpler version of this method has been used in previous
works. This method is shown to be significantly more efficient than the popular
``democratic'' methods. It can of course be applied to the lattice simulations
of many other physical quantities. The analysis indicates a hierarchy in the
size of hypercubic artifacts: overlap larger than clover and propagator larger
than vertex function. This pleads for the combined study of propagators and
vertex functions via Ward identities.


title: Meson and Baryon Spectroscopy on a Lattice

abstract:
  I review the results of hadron spectroscopy calculations from lattice QCD for
an intended audience of low energy hadronic physicists. I briefly introduce the
ideas of numerical lattice QCD. The various systematic errors, such as the
lattice spacing and volume dependence, in lattice QCD calculations are
discussed. In addition to the discussion of the properties of ground state
hadrons, I also review the small amount of work done on the spectroscopy of
excited hadrons and the effect of electromagnetic fields on hadron masses. I
also discuss the attempts to understand the physical mechanisms behind hadron
mass splittings.


title: Chaotic Quantization of Four-Dimensional U(1) Lattice Gauge Theory

abstract:
  We demonstrate that the quantized U(1) lattice gauge theory in four Euclidean
dimensions can be obtained as the long time limit of the corresponding
classical U(1) gauge theory in 4+1 dimensions. The Planck constant hbar is
related to the excitation energy and the lattice constant of this classical
template.


title:
Hamiltonian Study of Improved $U(1$ Lattice Gauge Theory in Three
  Dimensions

abstract:
  A comprehensive analysis of the Symanzik improved anisotropic
three-dimensional U(1) lattice gauge theory in the Hamiltonian limit is made.
Monte Carlo techniques are used to obtain numerical results for the static
potential, ratio of the renormalized and bare anisotropies, the string tension,
lowest glueball masses and the mass ratio. Evidence that rotational symmetry is
established more accurately for the Symanzik improved anisotropic action is
presented. The discretization errors in the static potential and the
renormalization of the bare anisotropy are found to be only a few percent
compared to errors of about 20-25% for the unimproved gauge action. Evidence of
scaling in the string tension, antisymmetric mass gap and the mass ratio is
observed in the weak coupling region and the behaviour is tested against
analytic and numerical results obtained in various other Hamiltonian studies of
the theory. We find that more accurate determination of the scaling
coefficients of the string tension and the antisymmetric mass gap has been
achieved, and the agreement with various other Hamiltonian studies of the
theory is excellent. The improved action is found to give faster convergence to
the continuum limit. Very clear evidence is obtained that in the continuum
limit the glueball ratio $M_{S}/M_{A}$ approaches exactly 2, as expected in a
theory of free, massive bosons.


title: Vortex structures in pure SU(3) lattice gauge theory

abstract:
  The structures of confining vortices which underlie pure SU(3) Yang-Mills
theory are studied by means of lattice gauge theory. Vortices and Z_3 monopoles
are defined as dynamical degrees of freedom of the Z_3 gauge theory which
emerges by center gauge fixing and by subsequent center projection. It is
observed for the first time for the case of SU(3) that these degrees of freedom
are sensible in the continuum limit: the planar vortex density and the monopole
density properly scales with the lattice spacing. By contrast to earlier
findings concerning the gauge group SU(2), the effective vortex theory only
reproduces 62% of the full string tension. On the other hand, however, the
removal of the vortices from the lattice configurations yields ensembles with
vanishing string tension. SU(3) vortex matter which originates from Laplacian
center gauge fixing is also discussed. Although these vortices recover the full
string tension, they lack a direct interpretation as physical degrees of
freedom in the continuum limit.


title: Wess-Zumino-Witten term on the lattice

abstract:
  We construct the Wess-Zumino-Witten (WZW) term in lattice gauge theory by
using a Dirac operator which obeys the Ginsparg-Wilson relation. Topological
properties of the WZW term known in the continuum are reproduced on the lattice
as a consequence of a non-trivial topological structure of the space of
admissible lattice gauge fields. In the course of this analysis, we observe
that the gauge anomaly generally implies that there is no basis of a Weyl
fermion which leads to a single-valued expectation value in the fermion sector.
The lattice Witten term, which carries information of a gauge path along which
the gauge anomaly is integrated, is separated from the WZW term and the
multivaluedness of the Witten term is shown to be related to the homotopy group
$\pi_{2n+1}(G)$. We also discuss the global $\SU(2)$ anomaly on the basis of
the WZW term.


title:
Correlation lengths and scaling functions in the three-dimensional O(4)
  model

abstract:
  We investigate numerically the transverse and longitudinal correlation
lengths of the three-dimensional O(4) model as a function of the external field
H. From our data we calculate the scaling function of the transverse
correlation length, and that of the longitudinal correlation length for T>T_c.
We show that the scaling functions do not only describe the critical behaviours
of the correlation lengths but encompass as well the predicted Goldstone
effects, in particular the H^{-1/2}-dependence of the transverse correlation
length for T<T_c. In addition, we determine the critical exponent
delta=4.824(9) and several critical amplitudes from which we derive the
universal amplitude ratios R_{chi}=1.084(18), Q_c=0.431(9), Q_2^T=4.91(8),
Q_2^L=1.265(24) and U_{xi}^c=1.99(1). The last result supports a relation
between the longitudinal and transverse correlation functions, which was
conjectured to hold below T_c but seems to be valid also at T_c.


title:
Electromagnetic Properties of the Baryon Decuplet in Quenched and
  Partially Quenched Chiral Perturbation Theory

abstract:
  We calculate electromagnetic properties of the decuplet baryons in quenched
and partially quenched chiral perturbation theory. We work at next-to-leading
order in the chiral expansion, leading order in the heavy baryon expansion, and
obtain expressions for the magnetic moments, charge radii, and electric
quadrupole moments. The quenched calculation is shown to be pathological since
only quenched chiral singularities are present at this order. We present the
partially quenched results for both the SU(2) and SU(3) flavor groups and use
the isospin limit in the latter. These results are necessary for proper
extrapolation of lattice calculations of decuplet electromagnetic properties.


title:
An Abelian effective action reproducing screening and confinement in
  quenched SU(2) QCD

abstract:
  In an Abelian projection SU(2) gluodynamics contains Abelian gauge fields
(diagonal degrees of freedom) and Abelian matter fields (off-diagonal degrees).
The matter fields are essential for the breaking of the adjoint string. We
obtain numerically the effective action of the Abelian fields in quenched SU(2)
QCD and show that the Abelian matter fields provide an essential contribution
to the total action even in the infrared region.


title:
QCD Dirac operator at nonzero chemical potential: lattice data and
  matrix model

abstract:
  Recently, a non-Hermitian chiral random matrix model was proposed to describe
the eigenvalues of the QCD Dirac operator at nonzero chemical potential. This
matrix model can be constructed from QCD by mapping it to an equivalent matrix
model which has the same symmetries as QCD with chemical potential. Its
microscopic spectral correlations are conjectured to be identical to those of
the QCD Dirac operator. We investigate this conjecture by comparing large
ensembles of Dirac eigenvalues in quenched SU(3) lattice QCD at nonzero
chemical potential to the analytical predictions of the matrix model. Excellent
agreement is found in the two regimes of weak and strong non-Hermiticity, for
several different lattice volumes.


title: Entropy of monopoles from percolating cluster in quenched SU(2) QCD

abstract:
  The length distribution and the monopole action of the infrared monopole
clusters are studied numerically in quenched SU(2) QCD. We determine the
effective entropy of the monopole currents which turns out to be a descending
function of the blocking scale, indicating that the effective degrees of
freedom of the extended monopoles are getting smaller as the blocking scale
increases.


title:
Parallel implementation of a lattice-gauge-theory code: studying quark
  confinement on PC clusters

abstract:
  We consider the implementation of a parallel Monte Carlo code for
high-performance simulations on PC clusters with MPI. We carry out tests of
speedup and efficiency. The code is used for numerical simulations of pure
SU(2) lattice gauge theory at very large lattice volumes, in order to study the
infrared behavior of gluon and ghost propagators. This problem is directly
related to the confinement of quarks and gluons in the physics of strong
interactions.


title: On the continuum limit of gauge-fixed compact U(1) lattice gauge theory

abstract:
  We investigate the continuum limit of a compact formulation of the lattice
U(1) gauge theory in 4 dimensions using a nonperturbative gauge-fixed
regularization. We find clear evidence of a continuous phase transition in the
pure gauge theory for all values of the gauge coupling (with gauge symmetry
restored). When probed with quenched staggered fermions with U(1) charge, the
theory clearly has a chiral transition for large gauge couplings. We identify
the only possible region in the parameter space where a continuum limit with
nonperturbative physics may appear.


title:
Blocked lattice monopoles in quenched SU(2) QCD and dual superconductor
  model

abstract:
  We study the action of the lattice monopoles in quenched SU(2) QCD in the
Maximal Abelian projection. We relate the lattice action of the monopole
currents to the monopole degrees of freedom of the continuum dual
superconductor model and obtain the value of the monopole condensate.


title:
A detailed study of the Abelian-projected SU(2) flux tube and its dual
  Ginzburg-Landau analysis

abstract:
  The color-electric flux tube of Abelian-projected (AP) SU(2) lattice gauge
theory in the maximally Abelian gauge (MAG) is revisited. It is shown that the
lattice Gribov copy effect in the MAG is crucial for the monopole-related parts
of the flux-tube profiles. Taking into account both the gauge fixing procedure
and the effect of finite quark-antiquark distance properly, the scaling
property of the flux-tube profile is confirmed. The quantitative relation
between the measured AP flux tube and the flux-tube solution of the U(1) dual
Abelian Higgs (DAH) model is also discussed. The fitting of the AP flux tube in
terms of the DAH flux tube indicates that the vacuum can be classified as
weakly type-I dual superconductor.


title: Mass dependence of the hairpin vertex in quenched QCD

abstract:
  The pseudoscalar ``hairpin'' vertex (i.e. quark-disconnected vertex) plays a
key role in quenched chiral perturbation theory. Direct calculations using
lattice simulations find that it has a significant dependence on quark mass. I
show that this mass dependence can be used to determine the quenched
Gasser-Leutwyler constant L5. This complements the calculation of L5 using the
mass dependence of the axial decay constant of the pion. In an appendix, I
discuss power counting for quenched chiral perturbation theory and describe the
particular scheme used in this paper.


title: Extending the Utility of Partially Quenched QCD

abstract:
  It has been proposed that partially quenched chiral perturbation theory can
be used together with partially quenched lattice QCD to determine the
low-energy constants of real QCD. We point out a complication of this approach
and show how it can be resolved. Partial quenching changes the chiral symmetry
group and introduces a new independent four-derivative operator. We explore the
effects of this new operator. We describe tree-level scattering processes to
which it contributes, and show how they can be used, in principle, to
deterimine its unknown coefficient. We also calculate its lowest-order
(one-loop) contribution to charged meson masses and decay constants. In
addition, we present the form of the analytic next-to-next-to-leading order
meson mass and decay constant corrections, which are needed for lattice fits.


title: Phase structure of (2+1)d strongly coupled lattice gauge theories

abstract:
  We study the chiral phase transition in (2+1)d strongly coupled U(N) lattice
gauge theories with staggered fermions. We show with high precision simulations
performed directly in the chiral limit that these models undergo a
Berezinski-Kosterlitz-Thouless (BKT) transition. We also show that this
universality class is unaffected even in the large N limit.


title: Confining strings in representations with common $n$-ality

abstract:
  We study the spectrum of confining strings in SU(3) pure gauge theory, by
means of lattice Monte Carlo simulations, using torelon operators in different
representations of the gauge group. Our results provide direct evidence that
the string spectrum is according to predictions based on $n$-ality. Torelon
correlations in the rank-2 symmetric channel appear to be well reproduced by a
two-exponential picture, in which the lowest state is given by the fundamental
string $\sigma_1=\sigma$, the heavier string state is such that the ratio
$\sigma_2/\sigma_1$ is approximately given by the Casimir ratio $C_{\rm
sym}/C_{\rm f} = 5/2$, and the torelon has a much smaller overlap with the
lighter fundamental string state.


title:
Gluodynamics in External Field: A Test of the Dual Superconductor
  Picture

abstract:
  We study gluodynamics in an external Abelian electromagnetic field within the
dual superconductor approach. We show that the SU(2) gluodynamics should
possess a deconfining phase transition at zero temperature at certain value of
the external field. A dual superconductor model for the SU(3) gauge theory in
external field predicts a rich phase structure containing confinement,
asymmetric confinement and deconfinement phases. These results can be used to
check the validity of the dual superconductor description of gluodynamics in
external fields. We also discuss the gauge-independence of the obtained
results.


title: Finite-Volume Partially-Quenched Two-Pion Amplitudes in the I=0 Channel

abstract:
  We present a study of the finite-volume two-pion matrix elements and
correlation functions of the I=0 scalar operator, in full and partially
quenched QCD, at one-loop order in chiral perturbation theory. In partially
quenched QCD, when the sea and valence light quark masses are not equal, the
lack of unitarity leads to the same inconsistencies as in quenched QCD and the
matrix elements cannot be determined. It is possible, however, to overcome this
problem by requiring the masses of the valence and sea quarks to be equal for
the u and d quarks while keeping the strange quark (s) quenched (or partially
quenched), but only in the kinematic region where the two-pion energy is below
the two-kaon threshold. Although our results are obtained at NLO in chiral
perturbation theory, they are more general and are also valid for non-leptonic
kaon decays (we also study the matrix elements of (8,1) operators, such as the
QCD penguin operator Q6). We point out that even in full QCD, where any
problems caused by the lack of unitarity are clearly absent, there are
practical difficulties in general, caused by the fact that finite-volume energy
eigenstates are linear combination of two-pion, two-kaon and two-eta states.
Our work implies that extracting Delta I=1/2, K-->pipi decay amplitudes from
simulations with m_s=m_{d,u} is not possible in partially quenched QCD (and is
very difficult in full QCD).


title: Lattice calculations of hadron properties

abstract:
  Recent lattice studies of hadron properties, in particular of exotic states
and charmonia are reviewed. Sea quark and quark mass effects are discussed as
well as decays and mixing.


title: A lattice theory for low energy fermions at finite chemical potential

abstract:
  We construct a lattice theory describing a system of interacting
nonrelativistic spin s=1/2 fermions at nonzero chemical potential. The theory
is applicable whenever the interparticle separation is large compared to the
range of the two-body potential, and does not suffer from a sign problem. In
particular, the theory could be useful in studying the thermodynamic limit of
fermion systems for which the scattering length is much larger than the
interparticle spacing, with applications to realistic atomic systems and dilute
neutron gases.

categories: hep-lat cond-mat.str-el nucl-th physics.atom-ph


title: Calorons and fermion zero-modes

abstract:
  Calorons in the confined phase for SU(n) gauge theory, having a non-trivial
Polyakov loop, "dissolve" in n monopole constituents for large enough instanton
scale parameters. We discuss recent results for these caloron solutions and
their fermion zero-modes, as well as the implications for lattice studies and
comment on the possible influence of the constituent monopoles on the instanton
size distribution.


title: Order from disorder in lattice QCD at high density

abstract:
  We investigate the properties of the ground state of strong coupling lattice
QCD at finite density. Our starting point is the effective Hamiltonian for
color singlet objects, which looks at lowest order as an antiferromagnet, and
describes meson physics with a fixed baryon number background. We concentrate
on uniform baryon number backgrounds (with the same baryon number on all
sites), for which the ground state was extracted in an earlier work, and
calculate the dispersion relations of the excitations. Two types of Goldstone
boson emerge. The first, antiferromagnetic spin waves, obey a linear dispersion
relation. The others, ferromagnetic magnons, have energies that are quadratic
in their momentum. These energies emerge only when fluctuations around the
large-N_c ground state are taken into account, along the lines of ``order from
disorder'' in frustrated magnetic systems. Unlike other spectrum calculations
in order from disorder, we employ the Euclidean path integral. For comparison,
we also present a Hamiltonian calculation using a generalized
Holstein-Primakoff transformation. The latter can only be constructed for a
subset of the cases we consider.


title: Topological susceptibility with the improved Asqtad action

abstract:
  Chiral perturbation theory predicts that in quantum chromodymamics light
dynamical quarks suppress the topological (instanton) susceptibility. We
investigate this suppression through direct numerical simulation using the
Asqtad improved lattice fermion action. This action holds promise for carrying
out nonperturbative simulations over a range of quark masses for which chiral
perturbation theory is expected to converge. To test the effectiveness of the
action in capturing instanton physics, we measure the topological
susceptibility as a function of quark masses with 2+1 dynamical flavors. Our
results, when extrapolated to zero lattice spacing, are consistent with
predictions of leading order chiral perturbation theory.
  Included in our study is a comparison of three methods for analyzing the
topological susceptibility: (1) the Boulder hypercubic blocking technique with
the Boulder topological charge operator, (2) the more traditional Wilson
cooling method with the twisted plaquette topological charge operator and (3)
the improved cooling method of de Forcrand, Perez, and Stamatescu and their
improved topological charge operator.


title: How light can the Higgs be?

abstract:
  It is widely believed that, for a given Top mass, the Higgs mass has a lower
bound: if m_Higgs is too small, the Higgs vacuum is unstable due to Top
dynamics. From vacuum instability, the state-of-the-art calculation of the
lower bound is close to the current experimental limit. Using non-perturbative
simulations and large N calculations, we show that the vacuum is in fact never
unstable. Instead, we investigate the existence of a new lower bound, based on
the intrinsic cut-off of this trivial theory.


title: Mesons at finite baryon density in (2+1)d

abstract:
  We discuss the critical properies of the three-dimensional Gross-Neveu model
at nonzero temperature and nonzero chemical potential. We also present
numerical and analytical results for the in-medium interaction due to scalar
meson exchange. Further, we discuss in-medium modifications of mesonic
dispersion relations and wavefunctions.


title: Naturally Light Fermions from Dimensional Reduction

abstract:
  We consider the 3-d Gross-Neveu model in the broken phase and construct a
stable brane world by means of a domain wall and an anti-wall. Fermions of
opposite chirality are localized on the walls and coupled through the 3-d bulk.
At large wall separation \beta the 2-d correlation length diverges
exponentially, hence a 2-d observer cannot distinguish this situation from a
2-d space-time. The 3-d 4-fermion coupling and \beta fix the effective 2-d
coupling such that the asymptotic freedom of the 2-d model arises. This
mechanism provides criticality without fine tuning.


title:
Determination of monopole condensate from monopole action in quenched
  SU(2) QCD

abstract:
  We study the effective monopole action obtained in the Maximal Abelian
projection of quenched SU(2) lattice QCD. We determine the quadratic part of
the lattice action using analytical blocking from continuum dual superconductor
model to the lattice model. The leading contribution to the quadratic action
depends explicitly on value of the monopole condensate. We show that the
analytical monopole action matches the numerically obtained action in quenched
SU(2) QCD with a good accuracy. The comparison of numerical and analytical
results gives us the value of the monopole condensate in quenched SU(2) QCD,
243(42) MeV.


title: Nucleon electromagnetic form factors from lattice QCD

abstract:
  It is imperative that lattice QCD serve to develop our understanding of
hadron structure and, where possible, to guide the interpretation of
experimental data. There is now a great deal of effort directed at the
calculation of the electroweak form factors of the nucleon, where for example,
measurements at Jefferson Laboratory have recently revealed surprising
behaviour in the ratio $G_E/G_M$. While, for the present, calculations within
the framework of lattice QCD are limited to relatively large quark mass, there
has been considerable progress in our understanding of how to extrapolate to
the chiral limit. Here we report the results of the application of these
techniques to the most recent form factor data from the QCDSF Collaboration.
The level of agreement with all of the form factors, for $Q^2$ below 1 GeV$^2$,
is already impressive.


title: 10 D Euclidean quantum gravity on the lattice

abstract:
  10 D Euclidean quantum gravity is investigated numerically using the
dynamical triangulation approach. It has been found that the behavior of the
model is similar to that of the lower dimensional models. However, it turns out
that there are a few features that are not present in the lower dimensional
models.


title: Dynamical fermions by global acceptance steps

abstract:
  A study of principle is conducted on the inclusion of the fermionic
determinant as a Metropolis acceptance correction. It is carried out in the 2-D
Schwinger model to prepare later applications to the Schr"odinger functional. A
mixed stochastic/determistic acceptance step is found that allows to include
some problematic modes in a way to avoid the collapse of the acceptance rate
due to fluctuations.


title: Chiral symmetry on a lattice with hopping interactions

abstract:
  The species doubling problem of the lattice fermion is resolved by
introducing hopping interactions that mix left- and right-handed fermions
around the momentum boundary. Approximate chiral symmetry is realized on the
lattice. The deviation of the fermion propagator from the continuum one is
small.


title: Numerical study of gluon propagators in Maximally Abelian gauge

abstract:
  Propagators of diagonal and off-diagonal gluons are studied numerically in
the Maximally Abelian gauge of the SU(2) lattice gauge theory. We have found
the strong enhancement of the diagonal gluon in the infrared region. The
enhancement factor is about 50 at the smallest available momentum, 325 MeV. We
discuss also various analytical fits to the propagators.


title: Low-dimensional long-range topological structure in the QCD vacuum

abstract:
  Lattice topological charge associated with Ginsparg-Wilson fermions exhibits
generic topological stability over quantum ensemble of configurations
contributing to the QCD path integral. Moreover, the underlying chiral symmetry
leads to the suppression of ultraviolet noise in the associated topological
charge densities ("chiral smoothing"). This provides a solid foundation for the
direct study of the role of topological charge fluctuations in the physics of
QCD vacuum. Using these tools it was recently demonstrated that: (a) there is a
well-defined space-time structure (order) in topological charge density
(defined through overlap fermions) for typical configurations contributing to
QCD path integral; (b) this fundamental structure is low-dimensional,
exhibiting sign-coherent behavior on subsets of dimension less than four and
not less than one; (c) the structure has a long-range global character
(spreading over maximal space-time distances) and is built around the locally
one-dimensional network of strong fields (skeleton). In this talk we elaborate
on certain aspects and implications of these results.


title: A BCS Gap on the Lattice

abstract:
  Monte Carlo simulations of the 3+1 dimensional NJL model are performed with
baryon chemical potential mu>0. For mu>Sigma_0, the constituent quark mass in
vacuum, chiral symmetry is restored and a diquark condensate <qq_+> forms. We
analyse the fermion propagator and find evidence for particle-hole mixing in
the vicinity of the Fermi surface and an energy gap Delta>0, both of which
provide evidence for superfluidity at high baryon density induced by a BCS
mechanism.
  At (mu a)=0.8 the ratio between the BCS gap and the vacuum quark mass is
Delta/Sigma_0=0.15(2).


title:
Monopoles in Abelian Polyakov gauge and projection (in)dependence of the
  dual superconductor mechanism of confinement

abstract:
  We discuss the effect of the choice of an Abelian projection on the dual
superconductor mechanism of confinement in SU(2) gluodynamics. Using
qualitative arguments we show that the dual superconductor Lagrangian
corresponding to the Abelian Polyakov gauge has a different structure compared
to the dual Lagrangian in the Maximal Abelian gauge. A difference between these
Lagrangians reflects the fact that in continuum limit the monopoles should be
static in the Abelian Polyakov gauge and therefore these monopoles can not give
rise to the confinement of static quarks. Using the Abelian Polyakov gauge as
an example, we show that (i) the dual superconductor scenario of confinement
may depend on the Abelian projection; (ii) the condensation of the Abelian
monopoles - which may be realized in any Abelian projection - is necessary but
not sufficient condition for confinement. These results do not exclude an
existence of a class of Abelian gauges in which the dual superconductor
scenario works well.


title: Spinodal Decomposition and the Deconfining Phase Transition

abstract:
  We study the Glauber dynamics of simple spin systems to identify dynamical
scenarios which may be of relevance for the deconfining phase transition in
heavy ion collisions.


title:
Does the crossover from perturbative to nonperturbative physics in QCD
  become a phase transition at infinite N ?

abstract:
  We present numerical evidence that, in the planar limit, four dimensional
Euclidean Yang-Mills theory undergoes a phase transition on a finite
symmetrical four-torus when the length of the sides $l$ decreases to a critical
value $l_c$. For $l>l_c$ continuum reduction holds so that at leading order in
$N$, there are no finite size effects in Wilson and Polyakov loops. This
produces the exciting possibility of solving numerically for the meson sector
of planar QCD at a cost substantially smaller than that of quenched SU(3).


title: $J/\psi$ and $\eta_c$ in the Deconfined Plasma from Lattice QCD

abstract:
  Analyzing correlation functions of charmonia at finite temperature ($T$) on
$32^3\times(32-96)$ anisotropic lattices by the maximum entropy method (MEM),
we find that $J/\psi$ and $\eta_c$ survive as distinct resonances in the plasma
even up to $T \simeq 1.6 T_c$ and that they eventually dissociate between $1.6
T_c$ and $1.9 T_c$ ($T_c$ is the critical temperature of deconfinement). This
suggests that the deconfined plasma is non-perturbative enough to hold
heavy-quark bound states. The importance of having sufficient number of
temporal data points in MEM analyses is also emphasized.


title: Glueballs and the Pomeron

abstract:
  We present our latest results on the glueball spectrum of SU(N) gauge
theories in 2+1 dimensions for spins ranging from 0 to 6 inclusive, as well as
preliminary results for SU(3) in 3+1 dimensions. Simple glueball models and the
relation of the even-spin spectrum to the 'Pomeron' are discussed.


title: Staggered Chiral Perturbation Theory

abstract:
  We discuss how to formulate a staggered chiral perturbation theory. This
amounts to a generalization of the Lee-Sharpe Lagrangian to include more than
one flavor (i.e. multiple staggered fields), which turns out to be nontrivial.
One loop corrections to pion and kaon masses and decay constants are computed
as examples in three cases: the quenched, partially quenched, and full
(unquenched) case. The results for the one loop mass and decay constant
corrections have already been presented in Ref. [1].


title: Analysis of finite temperature phase transition using level spacing

abstract:
  Let B be the largest spacing between adjacent eigenvalues of the Polyakov
loop. We propose to employ the distribution of B as an order parameter for the
finite temperature phase transition in SU(N) lattice gauge theories. Using
smeared links to reduce ultraviolet fluctuations, we carry out a test for the
gauge group SU(3).


title: Charmonia above the Deconfinement Phase Transition

abstract:
  Analyzing correlation functions of charmonia at finite temperature ($T$) on
$32^3\times(32-96)$ anisotropic lattices by the maximum entropy method (MEM),
we find that $J/\psi$ and $\eta_c$ survive as distinct resonances in the plasma
even up to $T \simeq 1.6 T_c$ and that they eventually dissociate between $1.6
T_c$ and $1.9 T_c$ ($T_c$ is the critical temperature of deconfinement). This
suggests that the deconfined plasma is non-perturbative enough to hold
heavy-quark bound states. The importance of having sufficient number of
temporal data points in the MEM analysis is also emphasized.


title:
Indications for Criticality at Zero Curvature in a 4d Regge Model of
  Euclidean Quantum Gravity

abstract:
  We re-examine the approach to four-dimensional Euclidean quantum gravity
based on the Regge calculus. A cut-off on the link lengths is introduced and
consequently the gravitational coupling and the cosmological constant become
independent parameters. We determine the zero curvature, $<R> =0$, line in the
coupling constant plane by numerical simulations. When crossing this line we
find a strong, probably first order, phase transition line with indications of
a second order endpoint. Beyond the endpoint the transition through the $<R>
=0$ line appears to be a crossover. Previous investigations, using the Regge or
the Dynamical Triangulation approach, dealt with a limit in which the first
order transition prevails.


title:
Glueball masses in 4d U(1) lattice gauge theory using the multi-level
  algorithm

abstract:
  We take a new look at plaquette-plaquette correlators in 4d compact U(1)
lattice gauge theory which are separated in time, both in the confined and the
deconfined phases. From the behaviour of these correlators we extract glueball
masses in the scalar as well as the axial-vector channels. Also in the
deconfined phase, the non-zero momentum axial-vector correlator gives us
information about the photon which appears as a massless particle in the
spectrum. Using the Luescher - Weisz multi-level algorithm, we are able to go
to large time separations which were not possible previously.


title:
Magnetic charge superselection in the deconfined phase of Yang-Mills
  theory

abstract:
  The vacuum expectation value of an operator carrying magnetic charge is
studied numerically for temperatures above the deconfinement temperature in
SU(2) and SU(3) gauge theory. By analyzing its finite size behaviour, this is
found to be exactly zero in the thermodynamical limit for any T > T_c whenever
the magnetic charge of the operator is different from zero. These results show
that magnetic charge is superselected in the hot phase of quenched QCD.


title:
External field dependence of the correlation lengths in the
  three-dimensional O(4) model

abstract:
  We investigate numerically the transverse and longitudinal correlation
lengths of the three-dimensional O(4) model as a function of the external field
H. In the low-temperature phase we verify explicitly the H^{-1/2}-dependence of
the transverse correlation length, which is expected due to the Goldstone modes
of the model. On the critical line we find the universal amplitude ratio xi^c_T
/ xi^c_L = 1.99(1). From our data we derive the universal scaling function for
the transverse correlation length. The H-dependencies of the correlation
lengths in the high temperature phase are discussed and shown to be in accord
with the scaling functions.


title: From short to long scales in the QCD vacuum

abstract:
  We study approximate decimations in SU(N) LGT that connect the short to long
distance regimes, and provide both upper and lower bounds on the exact
partition function. This leads to a representation of the exact partition
function in terms of successive decimations. The implications for a derivation
of confinement from first principles are discussed.


title: apeNEXT: A multi-TFlops Computer for Simulations in Lattice Gauge Theory

abstract:
  We present the APE (Array Processor Experiment) project for the development
of dedicated parallel computers for numerical simulations in lattice gauge
theories. While APEmille is a production machine in today's physics simulations
at various sites in Europe, a new machine, apeNEXT, is currently being
developed to provide multi-Tflops computing performance. Like previous APE
machines, the new supercomputer is largely custom designed and specifically
optimized for simulations of Lattice QCD.


title: When is the deconfinement phase transition universal?

abstract:
  Pure Yang-Mills theory has a finite-temperature phase transition, separating
the confined and deconfined bulk phases. Svetitsky and Yaffe conjectured that
if this phase transition is of second order, it belongs to the universality
class of transitions for particular scalar field theories in one lower
dimension. We examine Yang-Mills theory with the symplectic gauge groups Sp(N).
We find new evidence supporting the Svetitsky-Yaffe conjecture and make our own
conjecture as to which gauge theories have a universal second order
deconfinement phase transition.


title: SU(N) Gauge Theories Near $T_c$

abstract:
  We study the deconfinement phase transition in SU(N) gauge theories for
$N$=2,3,4,6,8. The transition is first order for $N \ge 3$, with the strength
increasing as $N$ increases. We extrapolate $T_c/\sqrt{\sigma}$ to the
continuum limit for each $N$, and observe a rapid approach to the large $N$
limit. As $N$ increases the phase transition becomes clear-cut on smaller
spatial volumes, indicating the absence of (non-singular) finite volume
corrections at $N=\infty$ -- reminiscent of large $N$ reduction. The observed
rapid increase of the inter-phase surface tension with $N$ may indicate that
for $N=\infty$ the deconfinement transition cannot, in practise, occur.


title:
Universality, vortices and confinement: modified SO(3) lattice gauge
  theory at non-zero temperature

abstract:
  We investigate the adjoint SU(2) lattice gauge theory in 3+1 dimensions with
the Wilson plaquette action modified by a Z(2) monopole suppression term. For
the zero-twist sector we report indications for the existence of a finite
temperature effect decoupled from the unphysical bulk transitions.


title: Chiral symmetry breaking and topology for all N

abstract:
  We investigate spontaneous chiral symmetry breaking in SU(N) gauge theories
at large N using overlap fermions. The exact zero modes and the low-lying modes
of the Dirac operator provide the tools to gain insight into the interplay
between chiral symmetry breaking and topology. We find that topology indeed
drives chiral symmetry breaking at N=3 as well as at large N. By comparing the
results on various volumes and at different lattice spacings we are able to
show that our conclusions are not affected by finite volume effects and also
hold in the continuum limit. We then address the question whether the topology
can be usefully described in terms of instantons.


title: Charmonium at finite temperature

abstract:
  We study charmoinum correlators and spectral functions at finite temperature
within the quenched approximation using isotropic lattices with lattice spacing
a^-1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of
the ground state charmonium spectral function above deconfinement, we find that
ground state charmonia (J/psi and eta_c) exist in the deconfined phase at least
up to temperatures as high as 1.5Tc. P-wave charmonia (chi_c) on the other hand
are dissociated already at 1.12Tc.


title:
Baryon Decuplet to Octet Electromagnetic Transitions in Quenched and
  Partially Quenched Chiral Perturbation Theory

abstract:
  We calculate baryon decuplet to octet electromagnetic transition form factors
in quenched and partially quenched chiral perturbation theory. We work in the
isospin limit of SU(3) flavor, up to next-to-leading order in the chiral
expansion, and to leading order in the heavy baryon expansion. Our results are
necessary for proper extrapolation of lattice calculations of these
transitions. We also derive expressions for the case of SU(2) flavor away from
the isospin limit.


title: Pressure and non-linear quark number susceptibilities in QCD

abstract:
  We report the first measurements of sixth order non-linear quark number
susceptibilities in continuum QCD. This extends our earlier computation of the
continuum limit of non-linear quark number susceptibilities and the pressure in
QCD for m/Tc=0.1. For T/Tc > 1.5, no phase transitions are observable for
mu<30T. Systematics of off-diagonal susceptibilities are reported. The equation
of state in the high temperature phase of the QCD plasma is constructed.


title: Vector and Axial-Vector Propagators in the \epsilon-Regime of QCD

abstract:
  Using quenched and unquenched chiral perturbation theory we compute vector
and axial current two-point functions at finite volume and fixed gauge field
topology, in the so-called \epsilon-regime of QCD. A comparison of these
results with finite volume lattice calculations allows to determine the
parameters of the corresponding chiral Lagrangians.


title: Perturbative Check of the Action and Energy Lattice Sum Rules

abstract:
  Lattice sum rules are checked using lattice perturbation theory. The action
sum rule gives a relation between the quark-antiquark potential, its
logarithmic derivative with respect to distance and the expectation value of
the action; the energy sum rule expresses the potential as the sum of the
energy in the gluon fields and of an anomalous term. Two different independent
calculations of the quark-antiquark potential are presented, and the
transversality of the gluonic vacuum polarization on the lattice is proven. The
crucial part of the action sum rule is an identity whose explicit check using
perturbation theory provides methods and results which are useful for checking
the energy sum rule. Additionally, the gauge invariance of the expectation
value of the Wilson loop up to next-to-leading order is proven. The possibility
of restricting the expectation value of the action to one fixed time slice is
discussed. The energy sum rule is checked perturbatively up to next-to-leading
order and shown to be satisfied with good numerical accuracy. The various
contributions to the quark-antiquark potential are analyzed, and the
restriction of the expectation value of the sum over all spatial plaquettes
(the energy in the magnetic fields) to one fixed time slice is examined.


title: Universality and scaling behavior of RG gauge actions

abstract:
  We study universality and scaling properties of RG gauge actions (Iwasaki and
DBW2). In the first part we consider the critical temperature T_{c} and compute
the reference energy scale r_{0} for critical couplings \beta_{c} corresponding
to N_{t}=3,4,6,8. The universality of T_{c}r_{0} between Iwasaki and Wilson
action is confirmed and the scaling behavior of the Iwasaki action is found to
be better than the one for the Wilson action. The results for the DBW2 action
show larger lattice artefacts. A continuum value T_{c}r_{0}=0.7498(50) is
extracted. We compute also the glueball masses for the states 0^{++} and
2^{++}, investigate the scaling of m_{0^{++}}r_{0} and m_{2^{++}}r_{0} and
point out practical problems which are due to the violation of positivity
present in the RG actions.


title:
Energy-entropy study of projected space-like monopoles in finite-T
  quenched SU(2) QCD

abstract:
  Properties of space-like monopoles projected on the 3D space in finite
temperature quenched SU(2) QCD are studied. The monopole energy is derived from
the effective action of the monopoles which is determined by an inverse
Monte-Carlo method. Then the entropy is fixed with the help of the
monopole-loop distribution.


title: The abelian projection revisited

abstract:
  Abelian projection is reanalysed in the frame of the SU(N) Higgs model. The
extension to QCD is discussed. It is shown that dual superconductivity of the
vacuum is an intrinsic property independent of the choice of the abelian
projection.


title: Nucleon mass, sigma term and lattice QCD

abstract:
  We investigate the quark mass dependence of the nucleon mass M_N. An
interpolation of this observable, between a selected set of fully dynamical
two-flavor lattice QCD data and its physical value, is studied using
relativistic baryon chiral perturbation theory up to order p^4. In order to
minimize uncertainties due to lattice discretization and finite volume effects
our numerical analysis takes into account only simulations performed with
lattice spacings a<0.15 fm and m_pi L>5. We have also restricted ourselves to
data with m_pi<600 MeV and m_sea=m_val. A good interpolation function is found
already at one-loop level and chiral order p^3. We show that the
next-to-leading one-loop corrections are small. From the p^4 numerical analysis
we deduce the nucleon mass in the chiral limit, M_0 approx 0.88 GeV, and the
pion-nucleon sigma term sigma_N= (49 +/- 3) MeV at the physical value of the
pion mass.


title: Geometry of the monopole clusters at different scales

abstract:
  We present results of measurements of various geometrical characteristics of
the monopole clusters in the maximally Abelian projection of SU(2) lattice
gauge theory. We observe scaling for the observables tested. Short clusters
correspond to random walks at small scale but have long-range correlations at
the hadronic scale. On the other hand, the percolating cluster at the hadronic
scale does not correspond to a random walk.


title:
Solving the local cohomology problem in U(1) chiral gauge theories
  within a finite lattice

abstract:
  In the gauge-invariant construction of abelian chiral gauge theories on the
lattice based on the Ginsparg-Wilson relation, the gauge anomaly is topological
and its cohomologically trivial part plays the role of the local counter term.
We give a prescription to solve the local cohomology problem within a finite
lattice by reformulating the Poincar\'e lemma so that it holds true on the
finite lattice up to exponentially small corrections. We then argue that the
path-integral measure of Weyl fermions can be constructed directly from the
quantities defined on the finite lattice.


title: On the non-Abelian Stokes theorem for SU(2) gauge fields

abstract:
  We derive a version of non-Abelian Stokes theorem for SU(2) gauge fields in
which neither additional integration nor surface ordering are required. The
path ordering is eliminated by introducing the instantaneous color orientation
of the flux. We also derive the non-Abelian Stokes theorem on the lattice and
discuss various terms contributing to the trace of the Wilson loop.


title: On the non-Abelian Stokes theorem in SU(2) gluodynamics

abstract:
  We discuss the non-Abelian Stokes theorem for SU(2) gauge fields which avoids
both additional integration variables and surface ordering. The idea is to
introduce the instant color orientation of the flux piercing the loop. The
non-Abelian Stokes theorem is also considered on the lattice and various terms
contributing to the trace of the Wilson loop are discussed.


title: Chiral Limit of Strongly Coupled Lattice QCD at Finite Temperatures

abstract:
  We use the recently proposed directed-path algorithm to study the chiral
limit of strongly coupled lattice QCD with staggered quarks at finite
temperatures. The new algorithm allows us to compute the chiral susceptibility
and the pion decay constant accurately on large lattices for massless quarks.
In the low temperature phase we find clear evidence for the singularities
predicted by chiral perturbation theory. We also show convincingly that the
chiral phase transition is of second order and belongs to the O(2) universality
class.


title: Kaon B Parameter in Quenched QCD

abstract:
  I calculate the kaon B-parameter with a lattice simulation in quenched
approximation. The lattice simulation uses an action possessing exact lattice
chiral symmetry, an overlap action. Computations are performed at two lattice
spacings, about 0.13 and 0.09 fm (parameterized by Wilson gauge action
couplings beta=5.9 and 6.1) with nearly the same physical volumes and quark
masses. I describe particular potential difficulties which arise due to the use
of such a lattice action in finite volume. My results are consistent with other
recent lattice determinations using domain-wall fermions.


title: Localization in lattice QCD (with emphasis on practical implications)

abstract:
  When Anderson localization takes place in a quenched disordered system, a
continuous symmetry can be broken spontaneously without accompanying Goldstone
bosons. Elaborating on this observation we propose a unified, microscopic
physical picture of the phase diagram of both quenched and unquenched QCD with
two flavors of Wilson fermions. The phase with Goldstone bosons -- by
definition the Aoki phase -- is always identified as the region where the
mobility edge of the (hermitian) Wilson operator is zero. We then discuss the
implications for domain-wall and overlap fermions. We conclude that both
formulations are valid only well outside the Aoki phase of the associated
Wilson-operator kernel, because this is where locality and chirality can be
both maintained.


title:
Numerical confirmation of analytic predictions for the finite volume
  mass gap of the XY-model

abstract:
  Recent exact predictions for the massive scaling limit of the two dimensional
XY-model are based on the equivalence with the sine-Gordon theory and include
detailed results on the finite size behavior. The so-called step-scaling
function of the mass gap is simulated with very high precision and found
consistent with analytic results in the continuum limit. To come to this
conclusion, an also predicted form of a logarithmic decay of lattice artifacts
was essential to use for the extrapolation.


title: Progress in building an International Lattice Data Grid

abstract:
  We report on progress in setting up the International Lattice Data Grid. We
describe the aims and objectives of the ILDG, what has been achieved during its
first year of activity and invite feedback from the community.


title: Random Matrix Theory and the Spectra of Overlap Fermions

abstract:
  The application of Random Matrix Theory to the Dirac operator of QCD yields
predictions for the probability distributions of the lowest eigenvalues. We
measured Dirac operator spectra using massless overlap fermions in quenched QCD
at topological charge \nu = 0, +- 1 and +- 2, and found agreement with those
predictions - at least for the first non-zero eigenvalue - if the volume
exceeds about (1.2 fm)^4.


title: Investigations on the deconfining phase transition in QCD

abstract:
  We investigate the deconfining phase transition in SU(3) pure gauge theory
and in full QCD with two flavors of staggered fermions by means of a gauge
invariant thermal partition functional. In the pure gauge case our finite size
scaling analysis is in agreement with the well known weak first order phase
transition. In the case of 2 flavors full QCD we find that the phase transition
is consistent with weak first order, contrary to the expectation of a crossover
for not too large quark masses.


title: Interplay of Monopoles and P-Vortices

abstract:
  We show that P-Vortices in the confinement phase of SU(2) lattice gauge
theory form one large percolating (infrared) cluster and a number of small
(ultraviolet) clusters. We discuss the interrelation of clusters of monopoles
in the maximal Abelian projection with clusters of P-vortices. To extract
P-vortices we use both direct and indirect central projections and find
qualitatively similar results.


title: Chiral perturbation theory for lattice QCD including O(a^2)

abstract:
  The O(a^2) contributions to the chiral effective Lagrangian for lattice QCD
with Wilson fermions are constructed. The results are generalized to partially
quenched QCD with Wilson fermions as well as to the "mixed'' lattice theory
with Wilson sea quarks and Ginsparg-Wilson valence quarks.


title: Self-tuning of the P-vortices

abstract:
  We observe that on the currently available lattices the non-Abelian action
associated with the P-vortices is ultraviolet divergent. On the other hand, the
total area of the vortices scales in physical units. Since both the ultraviolet
and infrared scales are manifested and there is no parameter to tune, the
observed phenomenon can be called self tuning.


title: Deconfining transition in two-flavor QCD

abstract:
  The order and the nature of the finite-temperature phase transition of QCD
with two flavors of dynamical quarks is investigated. An analysis of the
critical exponent of the specific heat is performed through finite-size and
finite-mass scaling of various susceptibilities. Dual superconductivity of QCD
vacuum is investigated using a disorder parameter, namely the v.e.v. of a
monopole creation operator. Hybrid R simulations were run at lattice spatial
sizes of $12^3$, $16^3$, $20^3$ and $32^3$ and temporal size $N_t=4$, with
quark masses in the range $am_q = 0.3 - 0.01$.


title: Low-Lying Nucleons from Chirally Improved Fermions

abstract:
  We report on our preliminary results on the low-lying excited nucleon spectra
which we obtain through a variational basis formed with three different
interpolators.


title: Comparing matrix models and QCD lattice data with chemical potential

abstract:
  We present a quantitative analysis of the microscopic Dirac spectrum which is
complex in the presence of a non-vanishing quark chemical potential. Data from
quenched SU(3) lattice simulations for different volumes V and small values of
the chemical potential are compared to analytical predictions from matrix
models. We confirm the existence of two distinct limits for weakly and strongly
nonhermitian Dirac operators. Good agreement is found in both limits,
confirming the different scaling of chemical potential and eigenvalues with the
volume.


title: Glueball masses in U(1) LGT using the multi-level algorithm

abstract:
  The multi-level algorithm allows, at least for pure gauge theories, reliable
measurement of exponentially small expectation values. The implementation of
the algorithm depends strongly on the observable one wants to measure. Here we
report measurement of glueball masses using the multi-level algorithm in 4
dimensional compact U(1) theory as a case study.


title: Heavy-Light Meson Semileptonic Decays with Staggered Light Quarks

abstract:
  We report on exploratory studies of heavy-light meson semileptonic decays
using Asqtad light quarks, NRQCD heavy quarks and Symanzik improved glue on
coarse quenched lattices. Oscillatory contributions to three-point correlators
coming from the staggered light quarks are found to be handled well by Bayesian
fitting methods. B meson decays to both the Goldstone pion and to one of the
point-split non-Goldstone pions are investigated. One-loop perturbative
matching of NRQCD/Asqtad heavy-light currents is incorporated.


title: Exact Lattice Supersymmetry from Topological Field Theory

abstract:
  We discuss the connection between supersymmetric field theories and
topological field theories and show how this connection may be used to
construct local lattice field theories which maintain an exact supersymmetry.
It is shown how metric independence of the continuum topological field theory
allows us to derive the lattice theory by blocking out of the continuum in a
deformed geometry. This, in turn, allows us to prove the cut-off independence
of certain supersymmetric Ward identities.


title:
$\gamma N \to \Delta$ transition form factors in Quenched and $N_F=2$
  QCD

abstract:
  Calculations of the magnetic dipole, electric quadrupole and Coulomb
quadrupole amplitudes for the transition $\gamma N\to \Delta$ are presented
both in quenched QCD and with two flavours of degenerate dynamical quarks.


title: Lattice QCD at finite isospin density and/or temperature

abstract:
  We simulate two-flavour lattice QCD with at a finite chemical potential
$\mu_I$ for isospin, and finite temperature. At small $\mu_I$, we determine the
position of the crossover from hadronic matter to a quark-gluon plasma as a
function of $\mu_I$. At larger $\mu_I$ we observe the phase transition from the
superfluid pion-condensed phase to a quark-gluon plasma, noting its change from
second order to first order as $\mu_I$ is increased. We also simulate
two-flavour lattice QCD at zero quark mass, using an action which includes an
additional 4-fermion interaction, at temperatures close to the chiral
transition on $N_t=8$ lattices.


title: Scaling Behavior of the Landau Gauge Overlap Quark Propagator

abstract:
  The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations are done on three lattices with different lattice spacings and
similar physical volumes to explore the approach of the quark propagator
towards the continuum limit. We have calculated the nonperturbative
momentum-dependent wavefunction renormalization function $Z(p^2)$ and the
nonperturbative mass function $M(p^2)$ for a variety of bare quark masses and
extrapolate to the chiral limit.
  We find the behavior of $Z(p^2)$ and $M(p^2)$ are in good agreement for the
two finer lattices in the chiral limit. The quark condensate is also
calculated.


title: Global Monte Carlo for fermions using ordered statistics

abstract:
  In this talk I discuss a new possibility for stochastic representation of the
fe rmion determinant. The method can be used for global Monte Carlo fermion
algorit hms and is tested in the case of the Schwinger model.


title: An Algorithm for Obtaining Reliable Priors for Constrained-Curve Fits

abstract:
  We introduce the ``Sequential Empirical Bayes Method'', an adaptive
constrained-curve fitting procedure for extracting reliable priors. These are
then used in standard augmented-chi-square fits on separate data. This better
stabilizes fits to lattice QCD overlap-fermion data at very low quark mass
where a priori values are not otherwise known. We illustrate the efficacy of
the method with data from overlap fermions, on a quenched $16^3\times 28$
lattice with spatial size La=3.2 fm and pion mass as low as $\sim$ 180 MeV.


title: Particle distributions in electroweak tachyonic preheating

abstract:
  We consider the out-of-equilibrium (quasi-) particle number distributions of
the Higgs and W-fields during electroweak tachyonic preheating. We model this
process by a fast quench, and perform classical real-time lattice simulations
in the SU(2)-Higgs model in three dimensions. We discuss how to define particle
numbers and effective energies using two-point functions in Coulomb and unitary
gauge, and consider some of the associated problems. After an initial
exponential growth in effective particle numbers, the system stabilises,
allowing us to extract effective masses, temperatures and chemical potentials
for the particles.


title: Fractal Structure of 4D Euclidean Simplicial Manifold

abstract:
  The fractal properties of four-dimensional Euclidean simplicial manifold
generated by the dynamical triangulation are analyzed on the geodesic distance
D between two vertices instead of the usual scale between two simplices. In
order to make more unambiguous measurement of the fractal dimension, we employ
a different approach from usual, by measuring the box-counting dimension which
is computed by counting the number of spheres with the radius D within the
manifold. The numerical result is consistent to the result of the random walk
model in the branched polymer region. We also measure the box-counting
dimension of the manifold with additional matter fields. Numerical results
suggest that the fractal dimension takes value of slightly more than 4 near the
critical point. Furthermore, we analyze the correlation functions as functions
of the geodesic distance. Numerically, it is suggested that the fractal
structure of four-dimensional simplicial manifold can be properly analyzed in
terms of the distance between two vertices. Moreover, we show that the behavior
of the correlation length regards the phase structure of 4D simplicial
manifold.


title: Lattice study on kaon nucleon scattering length in the I=1 channel

abstract:
  Using the tadpole improved clover Wilson quark action on small, coarse and
anisotropic lattices, $KN$ scattering length in the I=1 channel is calculated
within quenched approximation. The results are extrapolated towards the chiral
and physical kaon mass region. Finite volume and finite lattice spacing errors
are also analyzed and a result in the infinite volume and continuum limit is
obtained which is compatible with the experiment and the results from Chiral
Perturbation Theory.


title: $q\bar q$ and $2q2\bar q$ systems in terms of P-vortices

abstract:
  We study the action and the energy densities of the confining string in the
indirect Z(2) projection of SU(2) lattice gauge theory. We find that the width
of the confining string is proportional to the logarithm of the distance
between the quark and antiquark. In $2q2\bar{q}$ system we observe the effect
of the reconstruction of the flux tube when we change the distance between two
$q\bar{q}$ pairs.


title: Indications on the Higgs boson mass from lattice simulations

abstract:
  The `triviality' of $\Phi^4_4$ has been traditionally interpreted within
perturbation theory where the prediction for the Higgs boson mass depends on
the magnitude of the ultraviolet cutoff $\Lambda$. This approach crucially
assumes that the vacuum field and its quantum fluctuations rescale in the same
way. The results of the present lattice simulation, confirming previous
numerical indications, show that this assumption is not true. As a consequence,
large values of the Higgs mass $m_H$ can coexist with the limit $\Lambda\to
\infty $. As an example, by extrapolating to the Standard Model our results
obtained in the Ising limit of the one-component theory, one can obtain a value
as large as $m_H=760 \pm 21$ GeV, independently of $\Lambda$.


title: Simulations in the epsilon-Regime of Chiral Perturbation Theory

abstract:
  We discuss the potential of Ginsparg-Wilson fermion simulations in the
epsilon-regime of chiral perturbation theory, regarding the determination of
the leading low energy constants of the effective chiral Lagrangian. It turns
out to be very hard to measure observables in the topologically trivial sector.
There a huge statistics would be required, due to the frequent occurrence of
very small eigenvalues. Moreover, contact with chiral perturbation theory is
only established if the physical volume of the system is sufficiently large.


title: Comparison of analytic and numerical results in the XY-model

abstract:
  We study the two dimensional XY-model with high precision Monte Carlo
techniques and investigate the continuum approach of the step-scaling function
of its finite volume mass gap. The continuum extrapolated results are found
consistent with analytic predictions for the finite volume energy spectrum
based on the equivalence with sine-Gordon theory. To come to this conclusion it
was essential to use an also predicted form of logarithmic decay of lattice
artifacts for the extrapolation.


title: An analysis of the vector meson spectrum from lattice QCD

abstract:
  We re-analyse meson sector data from the CP-PACS collaboration's dynamical
simulations. Our analysis uses several different approaches, and compares the
standard naive linear fit with the Adelaide Anzatz. We find that setting the
scale using the J parameter gives remarkable agreement among data sets. Our
predictions for the rho and phi masses have very small statistical errors, ~ 3
MeV, but the discrepancy between the different fitting approaches is ~ 40 MeV.


title:
The two-dimensional Wess-Zumino model in the Hamiltonian lattice
  formulation

abstract:
  We investigate a Hamiltonian lattice version of the two-dimensional
Wess-Zumino model, with special emphasis to the pattern of supersymmetry
breaking. Results are obtained by Quantum Monte Carlo simulations and Density
Matrix Renormalization group techniques.


title: Quark Loop Effects in Semileptonic Form Factors for Heavy-Light Mesons

abstract:
  We present preliminary results of a determination of the semileptonic form
factor for the decay of pseudoscalar heavy-light mesons to pseudoscalar
light-light mesons in full QCD. In this preliminary study we focus on the
effects of dynamical quark loops. Accordingly, we compare results of
simulations with matched quenched and Asqtad dynamical gauge configurations.
The latter include three flavors of light quarks. Our simulation uses clover
Wilson valence quarks, treated in the Fermilab formalism. Preliminary results,
as yet uncorrected by continuum matching factors, suggest a measurable
enhancement in the form factor due to dynamical quark loops over the accessible
range of $q^2$.


title:
The long range properties of the compact U(1) lattice gauge theory with
  the multi-level algorithm

abstract:
  The 4D compact U(1) lattice gauge theory (LGT) in the confinement phase is
studied with the multi-level algorithm. The static potential, force and
flux-tube profile between two static charges are precisely measured from
correlation functions involving the Polyakov loop. Universality of the
coefficient of the 1/r correction to the static potential, known as the
Luescher term, and the transversal width of the flux-tube profile are
investigated.


title:
A numerical reinvestigation of the Aoki phase with N_f=2 Wilson fermions
  at zero temperature

abstract:
  We report on a numerical reinvestigation of the Aoki phase in lattice QCD
with two flavors of Wilson fermions where the parity-flavor symmetry is
spontaneously broken. For this purpose an explicitly symmetry-breaking source
term $h\bar{\psi} i \gamma_{5} \tau^{3}\psi$ was added to the fermion action.
The order parameter $<\bar{\psi} i \gamma_{5}\tau^{3}\psi>$ was computed with
the Hybrid Monte Carlo algorithm at several values of $(\beta,\kappa,h)$ on
lattices of sizes $4^4$ to $12^4$ and extrapolated to $h=0$. The existence of a
parity-flavor breaking phase can be confirmed at $\beta=4.0$ and 4.3, while we
do not find parity-flavor breaking at $\beta=4.6$ and 5.0.


title: The 2+2 anisotropic Wilson gluon action with applications

abstract:
  A generalization of anisotropic lattices to include a 2+2 discretization is
discussed. As a part of this program, we determine the one-loop correction to
the gluon self-energy and analyse the restoration of Lorentz invariance in
on-shell states for both the 2+2 and 3+1 cases. A 2+2 Wilson-like fermion
action is also considered.


title: The Aoki phase for N_f=2 Wilson fermions revisited

abstract:
  We report on a numerical reinvestigation of the Aoki phase in full lattice
QCD with two flavors of unimproved Wilson fermions. For zero temperature the
Aoki phase can be confirmed at inverse coupling $\beta=4.0$ and $\beta=4.3$,
but not at $\beta=4.6$ and $\beta=5.0$. At non-zero temperature the Aoki phase
was found to exist also at $\beta=4.6$.


title: Insight into nucleon structure from generalized parton distributions

abstract:
  The lowest three moments of generalized parton distributions are calculated
in full QCD and provide new insight into the behavior of nucleon
electromagnetic form factors, the origin of the nucleon spin, and the
transverse structure of the nucleon.


title:
Confinement-deconfinement and universal string effects from random
  percolation

abstract:
  The 't Hooft criterion leading to confinement out of a percolating cluster of
central vortices suggests defining a novel three-dimensional gauge theory
directly on a random percolation process. Wilson loop is viewed as a counter of
topological linking with the random clusters. Beyond the percolation threshold
large Wilson loops decay with an area law and show the universal shape effects
due to flux tube fluctuations. Wilson loop correlators define a non-trivial
glueball spectrum. The crumbling of the percolating cluster when one periodic
direction narrows accounts for the finite temperature deconfinement, which
belongs to 2D percolation universality class.


title:
The deconfinement phase transition in Yang-Mills theory with general Lie
  group G

abstract:
  We present numerical results for the deconfinement phase transition in Sp(2)
and Sp(3) Yang-Mills theories in (2+1)-D and (3+1)-D. We then make a conjecture
on the order of this phase transition in Yang-Mills theories with general Lie
groups G = SU(N), SO(N), Sp(N) and with exceptional groups G = G(2), F(4),
E(6), E(7), E(8).


title: A Transverse Lattice QCD Model for Mesons

abstract:
  QCD is analysed with two light-front continuum dimensions and two transverse
lattice dimensions. In the limit of large number of colours and strong
transverse gauge coupling, the contributions of light-front and transverse
directions factorise in the dynamics, and the theory can be analytically solved
in a closed form. An integral equation is obtained, describing the properties
of mesons, which generalises the 't Hooft equation by including spin degrees of
freedom. The meson spectrum, light-front wavefunctions and form factors can be
obtained by solving this equation numerically. These results would be a good
starting point to model QCD observables which only weakly depend on transverse
directions, e.g. deep inelastic scattering structure functions.


title: The Matter Density Distribution for Mesons and Baryons

abstract:
  The matter density distribution inside a hadron is evaluated using
gauge-invariant correlation functions within the quenched and the unquenched
theory. Comparison with the charge density distribution suggests that hadron
deformation is a consequence of the relativistic motion of the quarks.


title: Moments of nucleon spin-dependent generalized parton distributions

abstract:
  We present a lattice measurement of the first two moments of the
spin-dependent GPD H-tilde(x,xi,t). From these we obtain the axial coupling
constant and the second moment of the spin-dependent forward parton
distribution. The measurements are done in full QCD using Wilson fermions. In
addition, we also present results from a first exploratory study of full QCD
using Asqtad sea and domain-wall valence fermions.


title:
The continuum limit of perturbative coefficients calculated with a large
  field cutoff

abstract:
  We report MC calculations of perturbative coefficients for lattice scalar
field theory in dimensions 1, 2 and 3, where the large field contributions are
cutoff. This produces converging (instead of asymptotic) perturbative series.
We discuss the statistical errors and the lattice effects and show that
accurate calculations are possible even in a crossover region where no
approximation works. We show that the field cutoff is also a UV regulator. We
point out the relevance for QCD questions discussed by Tomboulis and Trottier
at this conference.


title: Axial anomaly in the reduced model: Higher representations

abstract:
  The topological charge in the $\U(N)$ vector-like reduced model can be
defined by using the overlap Dirac operator. We obtain its large $N$ limit for
a fermion in a general gauge-group representation under a certain restriction
of gauge field configurations which is termed $\U(1)$ embedding.


title: Deflation of Eigenvalues for Iterative Methods in Lattice QCD

abstract:
  Work on generalizing the deflated, restarted GMRES algorithm, useful in
lattice studies using stochastic noise methods, is reported. We first show how
the multi-mass extension of deflated GMRES can be implemented. We then give a
deflated GMRES method that can be used on multiple right-hand sides of $Ax=b$
in an efficient manner. We also discuss and give numerical results on the
possibilty of combining deflated GMRES for the first right hand side with a
deflated BiCGStab algorithm for the subsequent right hand sides.


title:
A precise determination of the decay constant of the D(s)-meson in
  quenched QCD

abstract:
  We present a precise determination of the leptonic decay constant F_D(s) of
the D(s)-meson in quenched lattice QCD. This work is particularly focused on
the analysis and discussion of all sources of systematic errors. We simulate
directly at the physical quark masses for five different lattice spacings
between 0.1fm and 0.03fm using O(a)-improvement. The finest lattice is still
work in progress. After taking the continuum limit and setting the scale with
the Kaon decay constant F_K=160MeV we arrive at a value of F_D(s)=252(9)MeV.
Setting the scale with the nucleon mass instead leads to a decrease of about
20MeV of F_D(s).


title: Penguin diagrams for the HYP staggered fermions

abstract:
  We present results of the one-loop corrections originating from the penguin
diagrams for the improved staggered fermion operators constructed using various
fat links such as Fat7, Fat7+Lepage, $\bar{\rm Fat7}$, HYP (I) and HYP (II).
The main results include the diagonal/off-diagonal mixing coefficients and the
matching formula between the continuum and lattice operators.


title:
Non-perturbative renormalization of the axial current with improved
  Wilson quarks

abstract:
  We present a new normalization condition for the axial current, which is
derived from the PCAC relation with non-vanishing mass.
  Using this condition reduces the O(r_0 m) corrections to the axial current
normalization constant Z_A for an easier chiral extrapolation in the cases,
where simulations at zero quark-mass are not possible. The method described
here also serves as a preparation for a determination of Z_A in the full
two-flavor theory.


title: Towards a precision computation of f_Bs in quenched QCD

abstract:
  We present a computation of the decay constant f_Bs in quenched QCD. Our
strategy is to combine new precise data from the static approximation with an
interpolation of the decay constant around the charm quark mass region. This
computation is the first step in demonstrating the feasability of a strategy
for f_B in full QCD. The continuum limits in the static theory and at finite
mass are taken separately and will be further improved.