title: O(a) errors in 3-D SU(N) Higgs theories

abstract:
  We compute the matching conditions between lattice and continuum 3-D SU(N)
Higgs theories, with both adjoint and fundamental scalars, at O(a), except for
additive corrections to masses and Higgs field operator insertions.


title:
Scaling of gauge balls and static potential in the confinement phase of
  the pure U(1) lattice gauge theory

abstract:
  We investigate the scaling behaviour of gauge-ball masses and static
potential in the pure U(1) lattice gauge theory on toroidal lattices. An
extended gauge field action $-\sum_P(\beta \cos\Theta_P + \gamma
\cos2\Theta_P)$ is used with $\gamma= -0.2$ and -0.5. Gauge-ball correlation
functions with all possible lattice quantum numbers are calculated. Most
gauge-ball masses scale with the non-Gaussian exponent $\nu_{ng}\approx 0.36$.
The $A_1^{++}$ gauge-ball mass scales with the Gaussian value $\nu_{g} \approx
0.5$ in the investigated range of correlation lengths. The static potential is
examined with Sommer's method. The long range part scales consistently with
$\nu_{ng}$ but the short range part tends to yield smaller values of $\nu$. The
$\beta$-function, having a UV stable zero, is obtained from the running
coupling. These results hold for both $\gamma$ values, supporting universality.
Consequences for the continuum limit of the theory are discussed.


title: The CP-PACS Project

abstract:
  The CP-PACS project is a five year plan, which formally started in April 1992
and has been completed in March 1997, to develop a massively parallel computer
for carrying out research in computational physics with primary emphasis on
lattice QCD. The initial version of the CP-PACS computer with a theoretical
peak speed of 307 GFLOPS with 1024 processors was completed in March 1996. The
final version with a peak speed of 614 GFLOPS with 2048 processors was
completed in September 1996, and has been in full operation since October 1996.
We describe the architecture, the final specification, the hardware
implementation, and the software of the CP-PACS computer. The CP-PACS has been
used for hadron spectroscopy production runs since July 1996. The performance
for lattice QCD applications and the LINPACK benchmark are given.


title: Balls in Boxes and Quantum Gravity

abstract:
  Four dimensional simplicial gravity has been studied by means of Monte Carlo
simulations for some time, the main outcome of the studies being that the model
undergoes a discontinuous phase transition between an elongated and a crumpled
phase when one changes the curvature (Newton) coupling. In the crumpled phase
there are singular vertices growing extensively with the volume of the system
whereas the elongated phase resembles a branched-polymer.
  We have postulated that this behaviour is a manifestation of the
constrained-mean-field scenario as realised in the Branched Polymer or
Balls-in-Boxes model. These models share all the features of 4D simplicial
gravity except that they exhibit a continuous phase transition. We note here
that this defect can be remedied by a suitable choice of ensemble.


title:
The $(\lambda \Phi^4)_4$ theory on the lattice: effective potential and
  triviality

abstract:
  We compute numerically the effective potential for the $(\lambda \Phi^4)_4$
theory on the lattice. Three different methods were used to determine the
critical bare mass for the chosen bare coupling value. Two different methods
for obtaining the effective potential were used as a control on the results. We
compare our numerical results with three theoretical descriptions. Our lattice
data are in quite good agreement with the ``Triviality and Spontaneous Symmetry
Breaking'' picture.


title: Lattice fermions with Majorana couplings

abstract:
  We analyse stability of almost massless Dirac mode in gauge models with
boundary (domain wall) fermions, and consider the possibility of decoupling one
of its chiral component by giving it a Majorana mass of the order of the
inverse lattice spacing. We argue that the chiral spectrum in such models is
always uncharged, so they can be implemented for defining the Weyl fermions
only in the real representation of the gauge group, for instance, in SUSY
models.


title:
Monte Carlo simulations of the CP^3 model and U(1) gauge theory in the
  presence of a theta-term

abstract:
  A theta-term, which couples to topological charge, is added to the
two-dimensional lattice CP^3 model and U(1) gauge theory. Monte Carlo
simulations are performed and compared to strong-coupling character expansions.
In certain instances, a flattening behavior occurs in the free-energy at
sufficiently large theta, but the effect is an artifact of the simulation
methods.


title: The Phase Diagram of the $U(2)\times U(2)$ Sigma Model

abstract:
  We study the phase diagram of the $U(2) \times U(2)$ scalar model in $d=4$
dimensions. We find that the phase transition is of first order in most of the
parameter space. The theory can still be relevant to continuum physics (as an
effective theory) provided the transition is sufficiently weakly first order.
This places restrictions on the allowed coupling constants.


title: Critical exponents in U(1) lattice gauge theory with a monopole term

abstract:
  We investigate critical properties of the phase transition in the
four-dimensional compact U(1) lattice gauge theory supplemented by a monopole
term for values of the monopole coupling $\lambda$ such that the transition is
of second order. It has been previously shown that at $\lambda= 0.9$ the
critical exponent is already characteristic of a second-order transition and
that it is different from the one of the Gaussian case. In the present study we
perform a finite size analysis at $\lambda=1.1$ to get information wether the
value of this exponent is universal.


title: A non-trivial spectrum for the trivial \phi^4 theory

abstract:
  It is pointed out that one-component \phi^4 lattice theory in four dimensions
has a non-perturbative sector which can be studied by means of an exact duality
transformation of its Ising limit. This duality maps it to a membrane model. As
a consequence, the \phi^4-theory turns out to have, in the broken symmetry
phase, a remarkably rich spectrum of physical states corresponding to membrane
excitations. A numerical study of the correlators between dual variables allows
to evaluate the masses of the first few states.


title: Intrinsic Geometric Structure of c=-2 Quantum Gravity

abstract:
  We couple c=-2 matter to 2-dimensional gravity within the framework of
dynamical triangulations. We use a very fast algorithm, special to the c=-2
case, in order to test scaling of correlation functions defined in terms of
geodesic distance and we determine the fractal dimension d_H with high
accuracy. We find d_H=3.58(4), consistent with a prediction coming from the
study of diffusion in the context of Liouville theory, and that the quantum
space-time possesses the same fractal properties at all distance scales
similarly to the case of pure gravity.


title: Gluon propagator and zero-momentum modes on the lattice

abstract:
  We investigate the propagators of 4D SU(2) gauge theory in Landau gauge by
Monte Carlo simulations. To be able to compare with perturbative calculations
we use large $\beta$ values. There the breaking of the Z(2) symmetry causes
large effects for all four lattice directions and doing the analysis in the
appropriate state gets important. We find that the gluon propagator in the
weak-coupling limit is strongly affected by zero-momentum modes.


title:
Screening Masses and Improvement in Pure SU(2) Lattice Gauge Theory at
  High Temperatures

abstract:
  From the long-distance behaviour of gluon and Polyakov loop correlation
functions we extract masses resp. energies in the electric and magnetic
sectors. We discuss their dependence on the temperature and on the momentum as
well as the relevance of an improvement of the lattice discretization of the
action.


title: The QCD vacuum

abstract:
  We review issues involved in understanding the vacuum, long-distance and
low-energy structure of non-Abelian gauge theories and QCD. The emphasis will
be on the role played by instantons.


title:
Topology, fermionic zero modes and flavor singlet correlators in finite
  temperature QCD

abstract:
  We extend our earlier results concerning the breaking of the U_A(1) symmetry
in finite temperature QCD. In particular, we use topological arguments to
investigate the chiral limit.


title:
Chaos in the Z(2) Gauge Model on a Generalized Bethe Lattice of
  Plaquettes

abstract:
  We investigate the Z(2) gauge model on a generalized Bethe lattice with three
plaquette representation of the action. We obtain the cascade of phase
transitions according to Feigenbaum scheme leading to chaotic states for some
values of parameters of the model. The duality between this gauge model and
three site Ising spin model on Husimi tree is shown. The Lyapunov exponent as a
new order parameter for the characterization of the model in the chaotic region
is considered. The line of the second order phase transition, which corresponds
to the points of the first period doubling bifurcation, is also obtained.


title:
Three-State Complex Valued Spins Coupled to Binary Branched Polymers in
  Two-Dimensional Quantum Gravity

abstract:
  A model of complex spins (corresponding to a non-minimal model in the
language of CFT) coupled to the binary branched polymer sector of quantum
gravity is considered. We show that this leads to new behaviour.


title:
Existence of Chiral-Asymmetric Zero Modes in the Background of
  QCD-Monopoles

abstract:
  We study topological aspects of the QCD vacuum structure in SU(2) lattice
gauge theory with the abelian gauge fixing. The index of the Dirac operator is
measured by using the Wilson fermion in the quenched approximation. We find
chiral-asymmetric zero modes in background fields dominated by QCD-monopoles
without any cooling.


title: Finite Temperature Phase Diagramm of QCD with improved Wilson fermions

abstract:
  We present first results of a study of two flavour QCD with Wilson fermions
at finite temperature. We have used tree level Symanzik improvement in both the
gauge and fermion part of the action. In a first step we explore the phase
diagramm on an $8^3 \times 4$ lattice, with particular emphasis on checking
Aoki's conjecture with an improved action.


title: Beyond the c=1 Barrier in Two-Dimensional Quantum Gravity

abstract:
  We introduce a simple model of touching random surfaces, by adding a chemical
potential rho for ``minimal necks'', and study this model numerically coupled
to a Gaussian model in d-dimensions (for central charge c = d = 0, 1 and 2).
For c <= 1, this model has a phase transition to branched polymers, for
sufficiently large rho. For c = 2, however, the extensive simulations indicate
that this transition is replaced by a cross-over behavior on finite lattices
--- the model is always in the branched polymer phase. This supports recent
speculations that, in 2d-gravity, the behavior observe in simulations for $c
\leq 1$, is dominated by finite size effects, which are exponentially enhanced
as c -> 1+.


title:
Singular Vertices in the Strong Coupling Phase of Four-Dimensional
  Simplicial Gravity

abstract:
  We study four-dimensional simplicial gravity through numerical simulation
with special attention to the existence of singular vertices, in the strong
coupling phase, that are shared by abnormally large numbers of four-simplices.
  We attempt to cure this disease by adding a term to the action which
suppresses such singular vertices. For a sufficiently large coefficient of the
additional term, however, the phase transition disappears and the system is
observed to be always in the branched polymer phase for any gravitational
constant.


title: Topology in SU(2) Yang-Mills theory

abstract:
  New results on the topology of the SU(2) Yang-Mills theory are presented. At
zero temperature we obtain the value of the topological susceptibility by using
the recently introduced smeared operators as well as a properly renormalized
geometric definition. Both determinations are in agreement. At non-zero
temperature we study the behaviour of the topological susceptibility across the
confinement transition pointing out some qualitative differences with respect
to the analogous result for the SU(3) gauge theory.


title: Massless Majorana fermion on the domain wall

abstract:
  We study the domain-wall formalism with additional Majorana mass term for the
unwanted zero mode, which has recently been proposed for lattice construction
of 4D N=1 super Yang-Mills theory without fine-tuning. Switching off the gauge
field, we study the dispersion relation of the energy eigenstates numerically,
and find that the method works for reasonable values of Majorana mass. We point
out, however, that a problem arises for too large Majorana mass, which can be
understood in terms of the seesaw mechanism.


title: Grand-canonical simulation of two-dimensional simplicial gravity

abstract:
  The string susceptibility exponents of dynamically triangulated 2-dimensional
surfaces with various topologies, such as a sphere, torus and double-torus,
were calculated by the grand-canonical Monte Carlo method. These simulations
were made for surfaces coupled to $d$-Ising spins ($d$=0,1,2,3,5). In each
simulation the area of surface was constrained to within 1000 to 3000 of
triangles, while maintaining the detailed-balance condition. The numerical
results show excellent agreement with theoretical predictions as long as $d
\leq 2$.


title: The spin content of the proton in full QCD

abstract:
  We present preliminary results on the proton spin structure function in full
QCD. The measurement has been done using 4 flavours of staggered fermions and
an improved definition of the lattice topological charge density.


title: Finite-size scaling study of the d=4 site-diluted Ising

abstract:
  We study the four dimensional site-diluted Ising model using finite-size
scaling techniques. We explore the whole parameter space (density-coupling) in
order to determine the Universality Class of the transition line. Our data are
compatible with Mean Field behavior plus logarithmic corrections.


title: A lattice determination of QCD field strength correlators

abstract:
  We study field strength correlators in presence of a static quark-antiquark
pair by use of lattice methods. The lattice data have been acquired recently in
the context of a determination of relativistic corrections to the static
interquark potential. We extract independent estimates of the form factors of
two point correlation functions and investigate the effect of higher order
correlators. Our results confirm the dominance of the two point correlators in
the regions of intermediate and large quark separations, and are compatible
with correlation length values obtained from different approaches.


title: SUSY on the lattice

abstract:
  The motivation and perspectives of numerical simulations of supersymmetric
Yang-Mills theories are reviewed.


title: Finite size effects at phase transition in compact U(1) gauge theory

abstract:
  We present and discuss the results of a Monte-Carlo simulation of the phase
transition in pure compact U(1) lattice gauge theory with Wilson action on a
hypercubic lattice with periodic boundary conditions. The statistics are large
enough to make a thorough analysis of the size dependence of the gap. In
particular we find a non-zero latent heat in the infinite volume limit. We also
find that the critical exponents $\nu$ and $\alpha$ are consistent with the
hyperscaling relation but confirm that the critical behavior is different from
a conventional first-order transition.


title: Block Algorithms for Quark Propagator Calculation

abstract:
  Computing quark propagators in lattice QCD is equivalent to solving large,
sparse linear systems with multiple right-hand sides. Block algorithms attempt
to accelerate the convergence of iterative Krylov-subspace methods by solving
the multiple systems simultaneously. This paper compares a block generalisation
of the quasi-minimal residual method (QMR), Block Conjugate Gradient on the
normal equation, Block Lanczos and ($\gamma_5$-symmetric) Block BiConjugate
Gradient.


title: An Extended Isgur-Paton Model: Agreement With the Lattice?

abstract:
  The spectrum for the pure gauge sector is calculated for an extended
Isgur-Paton model in 2+1 and 3+1 dimensions and compared to recent lattice
calculations of the glueball spectrum. The IP model is extended by inclusion of
a rigidity (curvature) term and, in D=2+1, mixing through a higer topological
contribution. For a choice of parameterizations, near quantitative agreement is
found for SU(3) in D=2+1, but in D=3+1 the extensions fail to remedy the
qualitative disagreement.


title:
Ehrenfest theorems for field strength and electric current in Abelian
  projected SU(2) lattice gauge theory

abstract:
  We derive an Ehrenfest theorem for SU(2) lattice gauge theory which, after
Abelian projection, relates the Abelian field strength and a dynamical electric
current and defines these operators for finite lattice spacing. Preliminary
results from the ongoing numerical test of the relation are presented,
including the contributions from gauge fixing and the Faddeev-Popov determinant
(the ghost fields) in the maximally Abelian gauge.


title: Matrix elements of four-fermion operators in the HQET

abstract:
  The B-$\bar B$ mixing, B-meson lifetimes, the $B_{s}$-$\bar{B}_{s}$ lifetime
difference and SUSY FCNC effects in $\Delta B=2$ processes are very important
measurable quantities in B-meson phenomenology whose theoretical predictions
depend on unknown matrix elements of several four-fermion operators. We present
preliminary results for the matrix elements of the relevant four-fermion
operators computed on a sample of 600 lattices of size $24^3\times 40$ at
$\beta=6.0$, using the SW--Clover action for light quarks with rotated light
quark propagators and the lattice version of the HQET for heavy quarks. As a
necessary ingredient of the calculation, we also present results for the
next-to-leading order matching of the full theory to the lattice HQET (one- and
two-loop anomalous dimensions, one-loop QCD-HQET matching coefficients and
one-loop continuum-lattice HQET matching coefficients).


title:
On the Parity-Flavor-Breaking Phase in QCD With Two Flavors of Wilson
  Fermions

abstract:
  We present further data in search of a parity-flavor-breaking phase in
simulations of dynamical QCD with two flavors of light Wilson fermions in the
strong coupling region. This is done on lattice sizes of 4^4 an up to 10^4 for
a variety of values of beta and kappa as well as the coefficient, h, of an
explicit breaking term included in the action. We confirm the existence of a
region in the beta-kappa plane where such a phase exists at beta=6/g^2 smaller
than 5.0 and above kappa_c.


title: Spectrum of the gauge Ising model in three dimensions

abstract:
  We present a high precision Monte Carlo study of the spectrum of the Ising
gauge theory in three dimensions in the confining phase. Using state of the art
Monte Carlo techniques we are able to accurately determine up to three masses
in a single channel. We compare our results with the SU(2) spectrum and with
the prediction of the Isgur-Paton model. Our data strongly support the
conjecture that the glueball spectrum is described by some type of flux tube
model. We also compare the spectrum with some recent results for the
correlation length in the 3d spin Ising model. This analysis sheds light on
some nontrivial features of the duality transformation.


title: Non-perturbative O(a) improvement of the vector current

abstract:
  We discuss non-perturbative improvement of the vector current, using the
Schroedinger Functional formalism. By considering a suitable Ward identity, we
compute the improvement coefficient which gives the O(a) mixing of the tensor
current with the vector one.


title: Universal Amplitude Ratios in the 3D Ising Model

abstract:
  We present a high precision Monte Carlo study of various universal amplitude
ratios of the three dimensional Ising spin model. Using state of the art
simulation techniques we studied the model close to criticality in both phases.
Great care was taken to control systematic errors due to finite size effects
and correction to scaling terms. We obtain $C_+/C_-=4.75(3)$,
$f_{+,2nd}/f_{-,2nd}=1.95(2)$ and $u^*=14.3(1)$. Our results are compatible
with those obtained by field theoretic methods applied to the $\phi^4$ theory
and high and low temperature series expansions of the Ising model.


title: Quenched Chiral Perturbation Theory to one loop

abstract:
  The divergences of the generating functional of quenched Chiral Perturbation
theory (qCHPT) to one loop are computed in closed form. We show how the
quenched chiral logarithms can be reabsorbed in the renormalization of the
$B_0$ parameter of the leading order Lagrangian. Finally, we do the chiral
power counting for the quenched case and show that also finite loop corrections
may diverge in the chiral limit.


title: Numerical study of SU(2) Yang-Mills theory with gluinos

abstract:
  We report on a numerical investigation of the SU(2) gauge theory with
gluinos.
  The low-lying spectrum in bosonic and fermionic channels is determined.
  Improvements of the multi-bosonic algorithm are discussed.


title: Various representations of infrared effective lattice QCD

abstract:
  We study various representations of the infrared effective theory of SU(2)
gluodynamics starting from the monopole action derived recently.
  We determine the coupling constants in the abelian-Higgs model directly from
lattice QCD and evaluate the type of the QCD vacuum. The string action is
derived using the BKT transformation on the lattice. At the classical level
this action reproduces the physical string tension with a good accuracy.


title: Frustration in Lattice Gauge Theory

abstract:
  We introduce a U(1) lattice gauge theory which incorporates explicit
frustration in $d>2$. We show, by identifying an appropiate order parameter and
through computer simulations, the existence of a frustrated region in the phase
diagram of the model. We study this phase diagram and the nature of the
transition lines.


title: Monte Carlo Renormalization Group calculation in $\lambda\phi^4_3$

abstract:
  We start by discussing some theoretical issues of renormalization group
transformations and Monte Carlo renormalization group technique. A method to
compute the anomalous dimension is proposed and investigated. As an
application, we find excellent values for critical exponents in $\lambda
\phi^4_3$. Some technical questions regarding the hybrid algorithm and strong
coupling expansions, used to compute the critical couplings of the canonical
surface, are also briefly discussed.


title: Topological structure in the SU(2) vacuum

abstract:
  We study the topological content of the vacuum of SU(2) pure gauge theory
using lattice simulations. We use a smoothing process based on the
renormalization group equation. This removes short distance fluctuations but
preserves long distance structure. The action of the smoothed configurations is
dominated by instantons, but they still show an area law for Wilson loops with
an unchanged string tension. The average radius of an instanton is about 0.2
fm, at a density of about 2 fm${}^{-4}$.


title: Further one-loop results in O(a) improved lattice QCD

abstract:
  Using the Schr\"odinger functional we have computed a variety of renormalized
on-shell correlation functions to one-loop order of perturbation theory. By
studying their approach to the continuum limit we have determined the O($a$)
counterterms needed to improve the quark mass and a number of isovector quark
bilinear operators.


title:
A Guide to Precision Calculations in Dyson's Hierarchical Scalar Field
  Theory

abstract:
  The goal of this article is to provide a practical method to calculate, in a
scalar theory, accurate numerical values of the renormalized quantities which
could be used to test any kind of approximate calculation. We use finite
truncations of the Fourier transform of the recursion formula for Dyson's
hierarchical model in the symmetric phase to perform high-precision
calculations of the unsubtracted Green's functions at zero momentum in
dimension 3, 4, and 5. We use the well-known correspondence between statistical
mechanics and field theory in which the large cut-off limit is obtained by
letting beta reach a critical value beta_c (with up to 16 significant digits in
our actual calculations). We show that the round-off errors on the magnetic
susceptibility grow like (beta_c -beta)^{-1} near criticality. We show that the
systematic errors (finite truncations and volume) can be controlled with an
exponential precision and reduced to a level lower than the numerical errors.
We justify the use of the truncation for calculations of the high-temperature
expansion. We calculate the dimensionless renormalized coupling constant
corresponding to the 4-point function and show that when beta -> beta_c, this
quantity tends to a fixed value which can be determined accurately when D=3
(hyperscaling holds), and goes to zero like (Ln(beta_c -beta))^{-1} when D=4.


title:
The electroweak phase transition at $m_H \simeq 80$ GeV from $L_t=2$
  lattices

abstract:
  We study the finite-temperature electroweak phase transition by numerical
simulations of the four-dimensional SU(2)-Higgs model on anisotropic lattices
with temporal extension $L_t=2$. The physically interesting parameter region of
Higgs masses near 80 GeV is reached, and recent results on some thermodynamic
quantities are presented.


title: Common Structures in 2,3 and 4D Simplicial Quantum Gravity

abstract:
  Two kinds of statistical properties of dynamical-triangulated manifolds (DT
mfds) have been investigated. First, the surfaces appearing on the boundaries
of 3D DT mfds were investigated. The string-susceptibility exponent of the
boundary surfaces ($\tilde{\gamma}_{st}$) of 3D DT mfds with $S^{3}$ topology
near to the critical point was obtained by means of a MINBU (minimum neck baby
universes) analysis; actually, we obtained $\tilde{\gamma}_{st} \approx -0.5$.
Second, 3 and 4D DT mfds were also investigated by determining the
string-susceptibility exponent near to the critical point from measuring the
MINBU distributions. As a result, we found a similar behavior of the MINBU
distributions in 3 and 4D DT mfds, and obtained $\gamma_{st}^{(3)} \approx
\gamma_{st}^{(4)} \approx 0$. The existence of common structures in simplicial
quantum gravity is also discussed.


title: The Perfect Quark-Gluon Vertex Function

abstract:
  We evaluate a perfect quark-gluon vertex function for QCD in coordinate space
and truncate it to a short range. We present preliminary results for the
charmonium spectrum using this quasi-perfect action.


title:
The role of diffeomorphisms in the integration over a finite dimensional
  space of geometries

abstract:
  Starting from the De Witt supermetric and limiting ourselves to a family of
geometries characterized by a finite number of geometric invariants we extract
the unique integration measure. Such a measure turns out to be a geometric
invariant, i.e. independent of the gauge fixed metric used for describing the
geometries. The measure is also invariant in form under an arbitrary change of
parameters describing the geometries. The additional functional integration on
the conformal factor makes the measure independent of the free parameter
intervening in the De Witt supermetric. The differences between the case D=2
and $D>2$ are evidenced.


title:
Random-matrix universality in the small-eigenvalue spectrum of the
  lattice Dirac operator

abstract:
  We analyze complete spectra of the lattice Dirac operator in SU(2) gauge
theory and demonstrate that the distribution of low-lying eigenvalues is
described by random matrix theory. We present possible practical applications
of this random-matrix universality. In particular, reliable extrapolations of
lattice gauge data to the thermodynamic limit are discussed.


title: Quantum chaos in QCD at finite temperature

abstract:
  We study complete eigenvalue spectra of the staggered Dirac matrix in
quenched QCD on a $6^3\times 4$ lattice. In particular, we investigate the
nearest-neighbor spacing distribution $P(s)$ for various values of $\beta$ both
in the confinement and deconfinement phase. In both phases except far into the
deconfinement region, the data agree with the Wigner surmise of random matrix
theory which is indicative of quantum chaos. No signs of a transition to
Poisson regularity are found, and the reasons for this result are discussed.


title: Three topics in the Schwinger model

abstract:
  1. We compare Monte Carlo results with analytic predictions for the fermion
condensate, in the massive one-flavour Schwinger model. 2. We illustrate on the
Schwinger model how to facilitate transitions between topological sectors by a
simple reweighting method. 3. We discuss exact, non-perturbative improvement of
the gauge sector.


title: Power corrections and perturbative coupling from lattice gauge thoeries

abstract:
  From the analysis of the perturbative expansion of the lattice regularized
gluon condensate, toghether with MC data, we present evidence of OPE-unexpected
dim-2 power corrections in the scaling behaviour of the Wilson loop. These can
be interpreted as an indication that in lattice gauge theories the running
coupling at large momentum contains contributions of order Q^2.


title:
Developments and new applications of numerical stochastic perturbation
  theory

abstract:
  A review of new developments in numerical stochastic perturbation theory
(NSPT) is presented. In particular, the status of the extension of the method
to gauge fixed lattice QCD is reviewed and a first application to compact
(scalar) QED is presented. Lacking still a general proof of the convergence of
the underlying stochastic processes, a self-consistent method for testing the
results is discussed.


title:
Yang-Mills classical solutions and fermionic zero modes from lattice
  calculations

abstract:
  We study a series of problems in classical Yang-Mills theories using lattice
methods. We first investigate SU(N) self-dual configurations on the torus with
twisted boundary conditions. We also study the zero modes of the Dirac equation
in topological non-trivial background Yang-Mills fields.


title: Implementing the Generalised Hybrid Monte-Carlo Algorithm

abstract:
  UKQCD's dynamical fermion project uses the Generalised Hybrid Monte-Carlo
(GHMC) algorithm to generate QCD gauge configurations for a non-perturbatively
O(a) improved Wilson action with two degenerate sea-quark flavours. We describe
our implementation of the algorithm on the Cray-T3E, concentrating on issues
arising from code verification and performance optimisation, such as parameter
tuning, reversibility, the effect of precision, the choice of matrix inverter
and the behaviour of different molecular dynamics integration schemes.


title: The Critical Scale of the Dual Superconductor Picture of QCD

abstract:
  The nonperturbative phenomena of QCD like color confinement is well described
through the dual superconductor picture in the Maximally Abelian (MA) gauge. In
this gauge, monopoles appear as important degrees of freedom composed by
nonabelian gauge fields. We investigate the peculiar size $R_c$ of the monopole
in the MA gauge, considering the theoretical similarity between spinglass and
the MA gauge fixing. As for the properties at larger scale than the monopole
size $R_c$, the system can be described by the dual superconductor theory with
local abelian fields. At shorter distances than $R_c$, such a dual Higgs theory
should be treated as a non-local field theory, and therefore one must take
another framework like the perturbative QCD. Thus, the monopole size gives a
critical scale on the change of the theoretical structure of QCD.


title: Prospects for perfect actions

abstract:
  The fixed-point (FP) action in QCD, although it is local and determined by
classical equations, is difficult to parametrize well and is expensive to
simulate. But the stake is high: the FP action has scale invariant instanton
solutions, has no topological artifacts, satisfies the index theorem on the
lattice, does not allow exceptional configurations, requires no tuning to get
the pion massless and is expected to reduce the cut-off effects significantly.
An overview is given including a discussion on tests in Yang-Mills theory, QCD
and $d=2$ spin and gauge models.


title: Monopole Current Dynamics and Color Confinement

abstract:
  Color confinement can be understood by the dual Higgs theory, where monopole
condensation leads to the exclusion of the electric flux from the QCD vacuum.
We study the role of the monopole for color confinement by investigating the
monopole current system. When the self-energy of the monopole current is small
enough, long and complicated monopole world-lines appear, which is a signal of
monopole condensation. In the dense monopole system, the Wilson loop obeys the
area-law, and the string tension and the monopole density have similar behavior
as the function of the self-energy, which seems that monopole condensation
leads to color confinement. On the long-distance physics, the monopole current
system almost reproduces essential features of confinement properties in
lattice QCD. In the short-distance physics, however, the monopole-current
theory would become nonlocal and complicated due to the monopole size effect.
This monopole size would provide a critical scale of QCD in terms of the dual
Higgs mechanism.


title: Applications of the overlap formalism to super Yang-Mills theories

abstract:
  We show that the idea to use the overlap formalism to formulate 4D N=1 super
Yang-Mills theory on the lattice without fine-tuning can be applied to 3D N=1
case as well. Another application we propose is a regularization of the IIB
matrix model, which is large N reduced model of 10D N=1 super Yang-Mills
theory.


title: Gauge-Fixing Approach to Lattice Chiral Gauge Theories

abstract:
  We report on recent progress with the definition of lattice chiral gauge
theories, using a lattice action that includes a discretized Lorentz
gauge-fixing term. This gauge-fixing term has a unique global minimum, and
allows us to use perturbation theory in order to study the influence of the
gauge degrees of freedom on the fermions. For the abelian case, we find, both
in perturbation theory and numerically, that the fermions remain chiral, and
that there are no doublers. More details on our approach, including a
discussion of how we evade the Nielsen-Ninomiya theorem, can be found in
hep-lat/9709115.


title: The Structure of Flux Tubes in Maximal Abelian Gauge

abstract:
  Various field strength correlators are investigated in the maximal abelian
projection of pure SU(2) lattice gauge theory. High precision measurements of
the colour fields, monopole currents, their curl and divergence allow for
detailed checks of the dual superconductor scenario. A further decomposition of
abelian observables into monopole and photon parts reveals that the flux tube
is built up from the monopole part alone.


title: Gauge-Fixing Approach to Lattice Chiral Gauge Theories, Part II

abstract:
  In this more technical part we give additional details on the gauge-fixing
approach presented in hep-lat/9709113. We also explain how the gauge-fixing
approach evades the Nielsen-Ninomiya no-go theorem.


title: Towards the Deconfinement Phase Transition in Hot Gauge Theories

abstract:
  The phase structure of hot gauge theories with dynamical matter fields is
reexamined in the canonical ensemble with respect to triality. We discuss
properties of chromoelectric and chromomagnetic sectors of the theory and show
whereas electric charges carrying a unit of Z(N) charge are screened at high
temperatures via dynamical matter loops, this is not the case for the Z(N)
magnetic flux. An order parameter is constructed to probe the realization of
local Z(N) symmetry in the magnetic sector. We argue this order parameter may
be used to detect the deconfinement phase transition which is defined in terms
of the screening mechanism.


title: Perfect Actions for Scalar Theories

abstract:
  We construct an optimally local perfect lattice action for free scalars of
arbitrary mass, and truncate its couplings to a unit hypercube. Spectral and
thermodynamic properties of this ``hypercube scalar'' are drastically improved
compared to the standard action. We also discuss new variants of perfect
actions, using anisotropic or triangular lattices, or applying new types of
RGTs. Finally we add a \lambda \phi^4 term and address perfect lattice
perturbation theory. We report on a lattice action for the anharmonic
oscillator, which is perfect to O(\lambda).


title: Finite Density QCD in the Chiral Limit

abstract:
  We present the first results of an exact simulation of full QCD at finite
density in the chiral limit. We have used a MFA (Microcanonical Fermionic
Average) inspired approach for the reconstruction of the Grand Canonical
Partition Function of the theory; using the fugacity expansion of the fermionic
determinant we are able to move continuously in the ($\beta -\mu$) plane with
$m=0$.


title: Domain Wall Fermions and Chiral Symmetry Restoration Rate

abstract:
  Domain Wall Fermions utilize an extra space time dimension to provide a
method for restoring the regularization induced chiral symmetry breaking in
lattice vector gauge theories even at finite lattice spacing. The breaking is
restored at an exponential rate as the size of the extra dimension increases.
As a precursor to lattice QCD studies the dependence of the restoration rate to
the other parameters of the theory and, in particular, the lattice spacing is
investigated in the context of the two flavor lattice Schwinger model.


title: D-Theory: Field Theory via Dimensional Reduction of Discrete Variables

abstract:
  A new non-perturbative approach to quantum field theory --- D-theory --- is
proposed, in which continuous classical fields are replaced by discrete
quantized variables which undergo dimensional reduction. The 2-d classical O(3)
model emerges from the (2+1)-d quantum Heisenberg model formulated in terms of
quantum spins. Dimensional reduction is demonstrated explicitly by simulating
correlation lengths up to 350,000 lattice spacings using a loop cluster
algorithm. In the framework of D-theory, gauge theories are formulated in terms
of quantum links --- the gauge analogs of quantum spins. Quantum links are
parallel transporter matrices whose elements are non-commuting operators. They
can be expressed as bilinears of anticommuting fermion constituents. In quantum
link models dimensional reduction to four dimensions occurs, due to the
presence of a 5-d Coulomb phase, whose existence is confirmed by detailed
simulations using standard lattice gauge theory. Using Shamir's variant of
Kaplan's fermion proposal, in quantum link QCD quarks appear as edge states of
a 5-d slab. This naturally protects their chiral symmetries without
fine-tuning. The first efficient cluster algorithm for a gauge theory with a
continuous gauge group is formulated for the U(1) quantum link model. Improved
estimators for Wilson loops are constructed, and dimensional reduction to
ordinary lattice QED is verified numerically.


title: Local bosonic versus HMC --- a CPU cost comparison

abstract:
  We compare the CPU cost of HMC to various implementations of the Hermitean
variant of L\"uscher's local bosonic algorithm (LBA) for 2D massive QED with
two flavours of Wilson fermions. We carefully scan a 3-dimensional parameter
subspace and find flat behaviour around the optimum. The gain factor of the
LBA, as compared to HMC, is slightly smaller for the Re-weighting method than
for the Metropolis variants and estimated to about 3.3 for the plaquette and
1.9 for the the meson correlator.


title: Improved actions of the staggered fermion

abstract:
  We have studied $O(a^2)$ improved lattice QCD with the staggered fermion by
using Symanzik's program. We find that there are 5 dimension-6 fermion
bilinears and gauge operators. In addition, there are 10 four-fermion operators
which are absent at the tree-level and tadpole-improved tree-level.


title: One loop calculation of QCD with domain-wall quarks

abstract:
  We calculate one loop corrections to the domain-wall quark propagator in QCD.
We show how the wave function is renormalized in this theory. Especially we are
interested in the behavior of the massless fermion mode, which exists near the
domain wall at the tree level. We show that this massless mode is stable
against the quantum correction.


title: A model for multi-quark systems

abstract:
  As a step towards understanding multi-quark systems abundant in nature we
construct a model that reproduces the binding energies of static four-quark
systems. These energies have been calculated using SU(2) lattice gauge theory
for a set of six different geometries representative of the general case. The
model is based on ground and excited state two-body potentials and multi-quark
interaction terms.


title: Non-perturbative quark mass renormalization

abstract:
  We show that the renormalization factor relating the renormalization group
invariant quark masses to the bare quark masses computed in lattice QCD can be
determined non-perturbatively. The calculation is based on an extension of a
finite-size technique previously employed to compute the running coupling in
quenched QCD. As a by-product we obtain the $\Lambda$--parameter in this theory
with completely controlled errors.


title: Mean-link tadpole improvement of SW and D234 actions

abstract:
  We investigate a tadpole-improved tree-level-O(a^3)-accurate action, D234c,
on coarse lattices, using the mean link in Landau gauge to measure the tadpole
contribution. We find that D234c shows much better rotational invariance than
Sheikholeslami-Wohlert, and that mean-link tadpole improvement gives much
better hadron mass scaling than plaquette tadpole improvement, with finite-a
errors at 0.25 fm of only a few percent. We explore the effects of possible
O(alpha_s) changes to the improvement coefficients, and find that the two
leading coefficients can be independently tuned: hadron masses are only
sensitive to the clover coefficient, while hadron dispersion relations are only
sensitive to the third derivative coefficient. Preliminary non-perturbative
tuning of these coefficients yields values that are consistent with the
expected size of perturbative corrections.


title: Finite Temperature Quark Confinement via Chromomagnetic Fields

abstract:
  A natural mechanism for finite temperature quark confinement arises via the
coupling of the adjoint Polyakov loop to the chromomagnetic field. Lattice
simulations and analytical results both support this hypothesis. Finite
temperature SU(3) lattice simulations show that a large external coupling to
the chromomagnetic field restores confinement at temperatures above the normal
deconfining temperature. A one-loop calculation of the effective potential for
SU(2) gluons in a background field shows that a constant chromomagnetic field
can drive the Polyakov loop to confining behavior, and the Polyakov loop can in
turn remove the well-known tachyonic mode associated with gluons in an external
chromomagnetic field. For abelian background fields, tachyonic modes are
necessary for confinement at one loop.


title:
Topological structure of the SU(3) vacuum and exceptional eigenmodes of
  the improved Wilson-Dirac operator

abstract:
  We present a study of the instanton size and spatial distributions in pure
SU(3) gauge theory using under-relaxed cooling. We also investigate the
low-lying eigenmodes of the (improved) Wilson-Dirac operator, in particular,
the appearance of zero-modes and their space-time localisation with respect to
instantons in the underlying gauge field.


title: Insight into Hadron Structure from Lattice QCD

abstract:
  A variety of evidence from lattice QCD is presented revealing the dominant
role of instantons in the propagation of light quarks in the QCD vacuum and in
light hadron structure. The instanton content of lattice gluon configurations
is extracted, and observables calculated from the instantons alone are shown to
agree well with those calculated using all gluons. The lowest 128
eigenfunctions of the Dirac operator are calculated and shown to exhibit zero
modes localized at the instantons. Finally, the zero mode contributions to the
quark propagator alone are shown to account for essentially the full strength
of the rho and pion resonances in the vector and pseudoscalar correlation
functions.


title:
Evidence of Instanton Effects in Hadrons from the Study of Low
  Eigenfunctions of the Dirac Operator

abstract:
  To elucidate the role in hadron structure of quark zero modes associated with
instantons, the lowest eigenfunctions of the Dirac operator have been
calculated in quenched QCD, full QCD, and full QCD with cooling. Eigenmodes
associated with a single instanton and an instanton-anti-instanton pair were
studied to understand the role of lattice artifacts for Wilson Fermions. By
truncating the spectral representation of the quark propagator, we show that
the rho and pion contributions to the vector and pseudoscalar correlation
functions are dominated by the zero-mode contributions.


title:
Gluon excitations of the static quark potential and the hybrid
  quarkonium spectrum

abstract:
  A comprehensive determination of the rich, low-lying spectrum of gluonic
excitations in the presence of a static quark-antiquark pair is presented. Our
results are obtained from several simulations on anisotropic lattices using an
improved action and a large set of gluonic operators. The hybrid quarkonium
states are studied in the quenched approximation using the Born-Oppenheimer
expansion and nonrelativistic lattice QCD.


title: Bag Picture of the Excited QCD Vacuum with Static Q-Qbar Source

abstract:
  The gluon excitations of the QCD vacuum are investigated in the presence of a
static quark-antiquark source. It is shown that the ground state potential and
the excitation spectrum of dynamical gluon degrees of freedom, as determined in
our lattice simulations, agree remarkably well with model predictions based on
the diaelectric properties of the confining vacuum described as a dual
superconductor. The strong chromoelectric field of the static Q-Qbar source
creates a bubble (bag) in the condensed phase where weakly interacting gluon
modes can be excited. Some features and predictions of the bag model are
presented and the chromoelectric vortex limit at large quark-antiquark
separation (string formation) is briefly discussed.


title: Confinement Properties in the Multi-Instanton System

abstract:
  We investigate the confinement properties in the multi-instanton system,
where the size distribution is assumed to be $ \rho^{-5} $ for the large
instanton size $ \rho $. We find that the instanton vacuum gives the area law
behavior of the Wilson loop, which indicates existence of the linear confining
potential. In the multi-instanton system, the string tension increases
monotonously with the instanton density, and takes the standard value $ \sigma
\simeq 1 GeV/fm $ for the density $ (N/V)^{{1/4}} = 200 MeV $. Thus, instantons
directly relate to color confinement properties.


title: B meson form factors from HQET simulations

abstract:
  We use simulations of heavy quark effective field theory to calculate the
Isgur-Wise function, and we demonstrate the feasibility of calculating the
matrix element for the $B \to \pi + \leptons$ decay in the lattice heavy quark
effective theory (HQET).


title: QCDSP - A status report

abstract:
  The QCDSP machine at Columbia University has grown to 2,048 nodes achieving a
peak speed of 100 Gigaflops. Software for quenched and Hybrid Monte Carlo (HMC)
evolution schemes has been developed for staggered fermions, with support for
Wilson and clover fermions under development. We provide an overview of the
runtime environment, the current status of the QCDSP construction program and
preliminary results not presented elsewhere in these proceedings.


title: Results for Quenched $B_K$ from JLQCD

abstract:
  A report is presented on our continued effort to elucidate the continuum
limit of $B_K$ using the quenched Kogut-Susskind quark action. By adding to our
previous simulations one more point at $\beta = 6.65$ employing a $56^3\times
96$ lattice, we now confirm the expected $O(a^2)$ behavior of $B_K$ with the
Kogut-Susskind action. A simple continuum extrapolation quadratic in $a$ leads
to $B_K$(NDR, 2 GeV) = 0.598(5). As our final value of $B_K$ in the continuum
we present $B_K$(NDR, 2 GeV)=0.628(42), as obtained by a fit including an
$\alpha_{\bar{MS}}(1/a)^2$ term arising from the lattice-continuum matching
with the one-loop renormalization.


title: Light Quark Physics with Dynamical Wilson Fermions

abstract:
  We present results for spectroscopy, quark masses and decay constants
obtained from SESAM's and TkL's large statistics simulations of QCD with two
dynamical Wilson fermions.


title: Bottomonium from NRQCD with Dynamical Wilson Fermions

abstract:
  We present results for the b \bar b spectrum obtained using an
O(M_bv^6)-correct non-relativistic lattice QCD action. Propagators are
evaluated on SESAM's three sets of dynamical gauge configurations generated
with two flavours of Wilson fermions at beta = 5.6. Compared to a quenched
simulation at equivalent lattice spacing we find better agreement of our
dynamical data with experimental results in the spin-independent sector but
observe no unquenching effects in hyperfine-splittings. To pin down the
systematic errors we have also compared quenched results in different
``tadpole'' schemes and used a lower order action.


title: CP-PACS Result for the Quenched Light Hadron Spectrum

abstract:
  The quenched hadron spectrum in the continuum obtained with the Wilson quark
action in recent simulations on the CP-PACS is presented. Results for the light
quark masses and the QCD scale parameter are reported.


title: Topology without cooling: instantons and monopoles near to deconfinement

abstract:
  In an attempt to describe the change of topological structure of pure SU(2)
gauge theory near deconfinement a renormalization group inspired method is
tested. Instead of cooling, blocking and subsequent inverse blocking is applied
to Monte Carlo configurations to capture topological features at a well-defined
scale. We check that this procedure largely conserves long range physics like
string tension. UV fluctuations and lattice artefacts are removed which
otherwise spoil topological charge density and Abelian monopole currents. We
report the behaviour of topological susceptibility and monopole current
densities across the deconfinement transition and relate the two faces of
topology to each other. First results of a cluster analysis are described.


title: Study of the chiral behavior of [the chiral condensate] in quenched QCD

abstract:
  The QCD phase transition is studied on 32^3x8 quenched lattices. One expects
from simple arguments that the quenched chiral condensate should diverge as the
chiral limit is approached. Previous studies have not been able to observe this
behavior, perhaps due to relatively large lattice spacings used. The topic is
revisited here on N_t=8 lattices, where the physical spacing is approximately
2(Gev^-1).


title: Heavy-Light Decay Constants from Wilson and Static Quarks

abstract:
  MILC collaboration results for \fB, \fBs, \fD, \fDs and their ratios are
presented. These results are still preliminary, but the analysis is close to
being completed. Sources of systematic error, both within the quenched
approximation and from quenching itself, are estimated. We find, for example,
$f_B=153\pm 10 {}^{+36}_{-13} {}^{+13}_{-0} MeV$, and $f_{B_s}/f_B = 1.10 \pm
0.02 {}^{+0.05}_{-0.03} {}^{+0.03}_{-0.02}$, where the errors are statistical,
systematic (within the quenched approximation), and systematic (of quenching),
respectively. The extrapolation to the continuum and the chiral extrapolation
are the largest sources of error. Present central values are based on linear
chiral extrapolations; a shift to quadratic extrapolations would raise $f_B$ by
$\approx20$ MeV and make the error within the quenched approximation more
symmetric.


title: SSOR Preconditioning of Improved Actions

abstract:
  We generalize local lexicographic SSOR preconditioning for the
Sheikholeslami-Wohlert improved Wilson fermion action and the truncated perfect
free fermion action. In our test implementation we achieve performance gains as
known from SSOR preconditioning of the standard Wilson fermion action.


title: Nonperturbative real time propagation at finite temperature

abstract:
  A new formalism will be presented in order to study real time evolution of
quantum systems at finite temperature. Probability distributions for
time-correlated observables will be studied non-perturbatively and fully
quantized. This works for various systems, including ones with tunneling
phenomena. We have obtained good results with some computational methods which
can be used on models with several degrees of freedom. Thus it looks feasible
to study vacuum tunneling in real time for relevant field theories at finite T.


title:
Scalar-gauge dynamics in (2+1) dimensions at small and large scalar
  couplings

abstract:
  We present the results of a detailed calculation of the excitation spectrum
of states with quantum numbers J^{PC}=0++, 1-- and 2++ in the three-dimensional
SU(2) Higgs model at two values of the scalar self-coupling and for fixed gauge
coupling. In the context of studies of the electroweak phase transition at
finite temperature these couplings correpond to tree-level, zero temperature
Higgs masses of 35 GeV and 120 GeV, respectively. We also study the properties
of Polyakov loop operators, which serve to test the confining properties of the
model in the symmetric phase. At both values of the scalar coupling we obtain
masses of bound states consisting entirely of gauge degrees of freedom
("W-balls"), which are very close to those obtained in the pure gauge theory.
We conclude that the previously observed, approximate decoupling of the scalar
and gauge sectors of the theory persists at large scalar couplings. We study
the crossover region at large scalar coupling and present a scenario how the
confining properties of the model in the symmetric phase are lost inside the
crossover by means of flux tube decay. We conclude that the underlying dynamics
responsible for the observed dense spectrum of states in the Higgs region at
large couplings must be different from that in the symmetric phase.


title:
Weak matrix elements: on the way to delta I = 1/2 rule and epsilon-prime
  with staggered fermions

abstract:
  We report progress in our lattice study of hadronic weak matrix elements
relevant for the Delta I = 1/2 rule and epsilon-prime. The presented results
are from our first runs on a quenched ensemble with beta=6.0 and a dynamical
Nf=2 ensemble with beta=5.7, using staggered gauge-invariant tadpole-improved
operators.


title:
The string tension in SU(N) gauge theory from a careful analysis of
  smearing parameters

abstract:
  We report a method to select optimal smearing parameters before production
runs and discuss the advantages of this selection for the determination of the
string tension.


title: The overlap passes a chiral dynamical test in two dimensions

abstract:
  A certain U(1) model in 2 dimensions, describing four right handed unit
charged Weyl fermions interacting with one doubly charged left handed Weyl
fermion, is exactly soluble and has massless Majorana-Weyl composites.
Instanton induced fermion number violation is essential for 't Hooft anomaly
consistency. The associated 't Hooft vertex can be analytically computed in the
continuum, including finite size corrections. This number is reproduced in a
dynamical simulation employing the overlap.


title: Gauge Freedom in Chiral Gauge Theory with Vacuum Overlap

abstract:
  Dynamical nature of the gauge degrees of freedom and its effect to fermion
spectrum are studied at $\beta=\infty$ for two- and four-dimensional nonabelian
chiral gauge theories in the vacuum overlap formalism. It is argued that the
disordered gauge degrees of freedom does not contradict to the chiral spectrum
of lattice fermion.


title:
Potentials between heavy-light mesons from lattice and inverse
  scattering theory

abstract:
  We extend our investigation of heavy-light meson-meson interactions to a
system consisting of a heavy-light meson and the corresponding antiparticle. An
effective potential is obtained from meson-antimeson Green-functions computed
in a quenched simulation with staggered fermions. Comparisons with a simulation
using an $O(a^2)$ tree-level and tadpole improved gauge action and a full QCD
simulation show that lattice discretization errors and dynamical quarks have no
drastic influence. Calculations from inverse scattering theory propose a
similar shape for $K\bar{K}$ potentials.


title: A First Taste of Dynamical Fermions with an O(a) Improved Action

abstract:
  We present the first results obtained by the UKQCD Collaboration using a
non-perturbatively $O(a)$ improved Wilson quark action with two degenerate
dynamical flavours.


title:
Two-body spectra of pseudoscalar mesons with an $O(a^2)$--improved
  lattice action using Wilson fermions

abstract:
  We extend our calculations with the second-order tree-level and tadpole
improved next-nearest-neighbor action to meson-meson systems. Correlation
matrices built from interpolating fields representing two pseudoscalar mesons
(pion-pion) with relative momenta p are diagonalized, and the mass spectrum is
extracted. Link variable fuzzing and operator smearing at both sinks and
sources is employed. Calculations are presented for two values of the hopping
parameter. The spectrum is used to discuss the residual interaction in the
meson-meson system.


title: Visualization of chiral condensate at finite temperature on the lattice

abstract:
  We perform an analysis of the topological and chiral vacuum structure of
four-dimensional QCD on the lattice at finite temperature. From correlation
functions we show the existence of local correlations between the topological
charge density and the quark condensate on gauge average. We comment on sizes
of clusters of nontrivial chiral condensate and of instantons in full QCD. By
analysis of individual gauge configurations, we demonstrate that at the places
in Euclidian space-time, where instantons are present, amplified production of
quark condensate occurs.


title: Lattice Chiral Fermions Through Gauge Fixing

abstract:
  We study a concrete lattice regularization of a U(1) chiral gauge theory. We
use Wilson fermions, and include a Lorentz gauge-fixing term and a gauge-boson
mass counterterm. For a reduced version of the model, in which the gauge fields
are constrained to the trivial orbit, we show that there are no species
doublers, and that the fermion spectrum contains only the desired states in the
continuum limit, namely charged left-handed (LH) fermions and neutral
right-handed (RH) fermions.


title: Visualization of topological structure and chiral condensate

abstract:
  We perform a mutual analysis of the topological and chiral vacuum structure
of four-dimensional QCD on the lattice at finite temperature. We demonstrate
that at the places where instantons are present, amplified production of quark
condensate takes place. It turns out for full QCD that the clusters of
nontrivial chiral condensate have a size of about 0.4 fm corresponding to the
instanton sizes in the same configurations.


title:
Visualization of topological objects in the deconfinement phase of pure
  QCD

abstract:
  In the last years it turned out that instantons and monopoles have a certain
local correlation in four-dimensional QCD. It was demonstrated by several
groups independently and by different methods that at the locations of
instantons also monopoles in the maximal abelian projection can be found with
enhanced probability. Further we observed such nontrivial correlation functions
in the deconfinement phase. We continue our visualization project to analyze
several specific gauge-field configurations.


title: Staggered Fermion Actions with Improved Rotational Invariance

abstract:
  We introduce a class of improved actions for staggered fermions which to
O(p^4) and O(p^6), respectively, lead to rotationally invariant propagators. We
discuss the resulting reduction of flavour symmetry breaking in the meson
spectrum and comment on the improvement in the calculation of thermodynamic
observables.


title:
Meson-meson scattering in the massive Schwinger model --- a status
  report

abstract:
  We discuss the possibility of extracting phase shifts from finite volume
energies for meson-meson scattering, where the mesons are fermion-antifermion
bound states of the massive Schwinger model with SU(2) flavour symmetry. The
existence of analytical strong coupling predictions for the mass spectrum and
for the scattering phases makes it possible to test the reliability of
numerical results.


title:
The Schr\"odinger functional running coupling with staggered fermions
  and its application to many flavor QCD

abstract:
  We discuss the Schr\"odinger functional in lattice QCD with staggered
fermions and relate it, in the classical continuum limit, to the Schr\"odinger
functional regularized with Wilson fermions. We compute the strong coupling
constant defined via the Schr\"odinger functional with staggered fermions at
one loop and show that it agrees with the continuum running coupling constant
in the Schr\"odinger functional formalism. We compute this running coupling in
the ``weak coupling phase'' of many flavor QCD numerically at several values of
the bare coupling and for several system sizes from $L/a=4$ to 12. The results
indicate that the $\beta$-function for 16 flavors has the opposite sign than
for few flavor QCD, in agreement with a recent claim, and with the perturbative
prediction.


title: Glueball matrix elements on anisotropic lattices

abstract:
  We describe a lattice calculation of the matrix elements relevant for
glueball production in $J / \psi$ radiative decays. The techniques for such a
calculation on anisotropic lattices with an improved action are outlined. We
present preliminary results showing the efficacy of the computational method.


title: Probing the CORE of the Haldane Conjecture

abstract:
  The COntractor REnormalization group method (CORE), originally developed for
application to lattice gauge theories, is very well adapted the study of spin
systems and systems with fermions. As an warmup exercise for studying Hubbard
models this method is applied to spin-1/2 and spin-1 anti-ferromagnets in one
space dimension in order to see if it is able to explain the physics of the
Haldane conjecture. The method not only provides support for Haldane's
conjecture but provides insight into the physics of a more general class of
spin-1 systems with Hamiltonians of the form $H= \sum_j
\vec{s}(j)\cdot\vec{s}(j+1) - \beta (\vec{s}(j)\cdot\vec{s}(j+1))^2$ about
which, until now, little was known.


title: Topology of full QCD

abstract:
  We study topological properties of SU(3) gauge theory using improved cooling.
In the absence of fermions, we measure a topological susceptibility of $(182(8)
MeV)^4$ and an instanton size $\sim 0.6$ fm. In the presence of light staggered
fermions and across the chiral transition, the susceptibility drops in a manner
consistent with the quenched case, and the instanton size changes little. No
significant formation of bound instanton-antiinstanton pairs is observed, in
particular not along the Euclidean time direction for $T > T_c$.


title: One-flavour QCD at finite temperature

abstract:
  We present results, for heavy to moderate quark masses, of a study of
thermodynamic properties of 1-flavour QCD, using the multiboson algorithm.
Finite-size scaling behaviour is studied on lattices of size $8^3\times 4$,
$12^3\times 4$ and $16^3\times 4$. It is shown that, for heavy quarks, the peak
of the Polyakov loop susceptibility grows linearly with the spatial volume,
indicating a first order phase transition. The deconfinement ratio and the
distribution of the norm of the Polyakov loop corroborate this result. For
moderately heavy quarks the first-order transition weakens and becomes a
crossover. We estimate the end point of the first-order phase transition to
occur at a quark mass of about 1.6 GeV.


title: Smeared Gauge Fixing

abstract:
  We present a new method of gauge fixing to standard lattice Landau gauge, Max
Re Tr $\sum_{\mu,x}U_{\mu,x}$, in which the link configuration is recursively
smeared; these smeared links are then gauge fixed by standard extremization.
The resulting gauge transformation is simultaneously applied to the original
links. Following this preconditioning, the links are gauge fixed again as
usual. This method is free of Gribov copies, and we find that for physical
parameters ($\beta \geq 2$ in SU(2)), it generally results in the gauge fixed
configuration with the globally maximal trace. This method is a general
technique for finding a unique minimum to global optimization problems.


title: The Role of Monopoles for Color Confinement

abstract:
  We study the role of the monopole for color confinement by using the monopole
current system. For the self-energy of the monopole current less than
ln$(2d-1)$, long and complicated monopole world-lines appear and the Wilson
loop obeys the area law, and therefore the monopole current system almost
reproduces essential features of confinement properties in the long-distance
physics. In the short-distance physics, however, the monopole-current theory
would become nonlocal due to the monopole size effect. This monopole size would
provide a critical scale of QCD in terms of the dual Higgs mechanism.


title: Random Surfaces and Lattice Gravity

abstract:
  In this talk I review some of the recent developments in the field of random
surfaces and the Dynamical Triangulation approach to simplicial quantum
gravity. In two dimensions I focus on the c=1 barrier and the fractal dimension
of two-dimensional quantum gravity coupled to matter with emphasis on the
comparison of analytic predictions and numerical simulations. Next is a survey
of the current understanding in 3 and 4 dimensions. This is followed by a
discussion of some problems in the statistical mechanics of membranes. Finally
I conclude with a list of problems for the future.


title: Progress and status of APEmille

abstract:
  We report on the progress and status of the APEmille project: a SIMD parallel
computer with a peak performance in the TeraFlops range which is now in an
advanced development phase. We discuss the hardware and software architecture,
and present some performance estimates for Lattice Gauge Theory (LGT)
applications.


title: The Charm Quarks's Mass

abstract:
  The charm quark's mass is determined from Monte Carlo calculations of the
$\bar{c}c$ spectrum. The main sources of uncertainty are perturbation theory
(for conversion to $\MSbar$), the continuum-limit extrapolation, Monte Carlo
statistics, and the effects of quenching. The (preliminary) result for the
$\MSbar$ mass is $\bar{m}_{ch}(m_{ch})=1.33\pm 0.08$ GeV.


title: Series Expansions for three-dimensional QED

abstract:
  Strong-coupling series expansions are calculated for the Hamiltonian version
of compact lattice electrodynamics in (2+1) dimensions, with 4-component
fermions. Series are calculated for the ground-state energy per site, the
chiral condensate, and the masses of `glueball' and positronium states.
Comparisons are made with results obtained by other techniques.


title:
SU(2) chiral Yang-Mills model on a lattice. Witten anomaly eaten by the
  lattice

abstract:
  Using a regularisation of the chiral SU(2) Yang-Mills model by an infinite
number of Pauli-Villars fields the doubler free gauge invariant lattice model
is constructed. Its continuum limit provides the recently proposed mechanism
for cancelation of Witten anomaly.


title:
Numerical Results for Transport Coefficients of Quark Gluon Plasma with
  Iwasaki's Improved Action

abstract:
  Numerical results for the transport coefficients of quark gluon plasma are
calculated by lattice simulation of SU(3) pure gauge model. The bulk viscosity
is consistent with zero. The shear viscosity is finite and increases with
temperature $T$ roughly as $T^{3}$, and around the finite temperature
transition points, it is slightly smaller than the typical hadron masses.


title: Topological Content of the Electroweak Sphaleron on the Lattice

abstract:
  3D electroweak sphalerons on the lattice are used as test configurations for
definitions of various topological defects. In the maximally Abelian gauge they
are shown to contain a symmetric array of Abelian monopoles and anti-monopoles
connected by two kinds of Abelian vortex strings. Gauge-invariant lattice
definitions of the Nambu monopole and the Z-vortex string are formulated which
correspond to Abelian projection from the unitary gauge. The sphalerons contain
in their core just one (non-Abelian) Nambu monopole-anti-monopole pair
(connected by a Z-string) in an unstable saddle point bound state. This
provides an example for the monopole-pair unbinding mechanism expected to work
at the electroweak phase transition. The definitions of defects developed here
will be used in future studies of topological aspects of this transition.


title: Glueballs and string breaking from full QCD

abstract:
  We present results on the static potential, and torelon and glueball masses
from simulations of QCD with two flavours of dynamical Wilson fermions on
$16^3\times 32$ and $24^3\times 40$ lattices at $\beta=5.6$.


title: Verification of O(a) improvement

abstract:
  The status of simulations using the non-perturbatively O(a) improved Wilson
action in the quenched approximation is reviewed. The impact of
non-perturbative improvement on the hadronic mass spectrum and the size of
residual lattice artefacts in spectral quantities and decay constants are
assessed.


title: A Note on the Action in d>4 Dynamical Triangulations

abstract:
  For dynamical triangulations in dimensions d<=4 the most general action has
two couplings. We note that the most general action for d=5 has three
couplings. We explore this larger coupling space using Monte Carlo simulations.
Initial results indicate evidence for non-trivial phase structure.


title:
Perturbative coefficients for improved actions by Monte Carlo at large
  $\beta$

abstract:
  Perturbative estimates of operator coefficients for improved lattice actions
are becoming increasingly important for precision simulations of many hadronic
observables. Following previous work by Dimm, Lepage, and Mackenzie, we
consider the feasibility of computing operator coefficients from numerical
simulations deep in the perturbative region of lattice theories. Here we
introduce a background field technique that may allow for the computation of
the coefficients of clover-field operators in a variety of theories. This
method is tested by calculations of the renormalized quark mass in lattice
NRQCD, and of the $O(\alpha_s)$ clover coefficient for Sheikholeslami-Wohlert
fermions. First results for the coefficient of the magnetic moment operator in
NRQCD are also presented.


title:
A Check of a D=4 Field-Theoretical Calculation Using the
  High-Temperature Expansion for Dyson's Hierarchical Model

abstract:
  We calculate the high-temperature expansion of the 2-point function up to
order 800 in beta. We show that estimations of the critical exponent gamma
based on asymptotic analysis are not very accurate in presence of confluent
logarithmic singularities. Using a direct comparison between the actual series
and the series obtained from a parametrization of the form (beta_c
-beta)^(-gamma) (Ln(beta_c -beta))^p +r), we show that the errors are minimized
for gamma =0.9997 and p=0.3351, in very good agreement with field-theoretical
calculations. We briefly discuss the related questions of triviality and
hyperscaling


title: A new phase structure in three-dimensional dynamical triangulation model

abstract:
  We investigate a new phase structure of the three-dimensional dynamical
triangulation model with an additional local term by Monte Carlo simulation. We
find that the first order phase transition observed for the naive
Einstein-Hilbert action terminates at a finite coefficient of the new term. The
phase transition turns into second order at the endpoint, beyond which it
becomes a crossover.


title: Three-Loop Results in QCD with Wilson Fermions

abstract:
  We calculate the third coefficient of the lattice beta function in QCD with
Wilson fermions, extending the pure gauge results of Luescher and Weisz; we
show how this coefficient modifies the scaling function on the lattice.
  We also calculate the three-loop average plaquette in the presence of Wilson
fermions. This allows us to compute the lattice scaling function both in the
standard and energy schemes.


title: Topological sectors and the pion mass

abstract:
  We study quenched and dynamical pion correlators in the two-flavour Schwinger
model (2D QED) both within topological charge sectors and averaged. The results
show that a clean-cut definition of a pion mass is no longer possible if
tunneling between sectors does not occur.
  PACS numbers: 11.15.Ha, 12.20.-m, 11.10.Kk


title: QED2 as a testbed for interpolations between quenched and full QCD

abstract:
  Lattice QED2 with the Wilson formulation of fermions is used as a convenient
model system to study artifacts of the quenched approximation on a finite
lattice. The quenched functional integral is shown to be ill-defined in this
system as a consequence of the appearance of exactly real modes for physical
values of the fermion mass.
  The location and frequency of such modes is studied as a function of lattice
spacing, lattice volume, topological charge and improved action parameters. The
efficacy of the recently proposed modified quenched approximation is examined,
as well as a new approach to the interpolation from the quenched to full
dynamical theory employing a truncated form of the fermion determinant.


title: SCRI Results With the Tadpole-Improved Clover Action

abstract:
  We compare light hadron spectroscopy using the Wilson and Clover fermionic
actions. We show that a Clover coefficient chosen using tadpole-improved
tree-level perturbation theory effectively eliminates the O(a) discretization
errors present in the Wilson action. We find that discretization errors in
light spectroscopy for both the Wilson and Clover actions are characterized by
an energy scale mu of about 200-300 MeV, indicating that these errors can be
reduced to the 5% level by using the Clover action at an inverse lattice
spacing of about 1.3 GeV.


title:
Chiral perturbation theory for K+ to pi+ pi0 decay in the continuum and
  on the lattice

abstract:
  We use one-loop chiral perturbation theory (ChPT) to compare lattice results
for the K+ to pi+ pi0 decay amplitude with the experimental value. Three
systematic effects: quenching, finite-volume effects, and the use of unphysical
values of quark masses and pion external momenta can be investigated. We find
that the corrections help in explaining the discrepancy between lattice and
experimental results. We also discuss the relation to B_K.


title:
Non-perturbative Renormalization of the Complete Basis of Four-fermion
  Operators and B-parameters

abstract:
  We present results on the B-parameters $B_K$, $B^{3/2}_7$ and $B^{3/2}_8$, at
$\beta=6.0$, with the tree-level Clover action. The renormalization of the
complete basis of dimension-six four-fermion operators has been performed
non-perturbatively. Our results for $B_K$ and $B^{3/2}_7$ are in reasonable
agreement with those obtained with the (unimproved) Wilson action. This is not
the case for $B^{3/2}_8$. We also discuss some subtleties arising from a
recently proposed modified definition of the B-parameters.


title:
The spectral dimension of the branched polymers phase of two-dimensional
  quantum gravity

abstract:
  The metric of two-dimensional quantum gravity interacting with conformal
matter is believed to collapse to a branched polymer metric when the central
charge c>1. We show analytically that the spectral dimension of such a branched
polymer phase is four thirds. This is in good agreement with numerical
simulations for large c.


title: Lattice HQET Calculation of the Isgur-Wise Function

abstract:
  We calculate the Isgur-Wise function on the lattice, simulating the light
quark with the Wilson action and the heavy quark with a direct lattice
implementation of the heavy-quark effective theory. Improved smearing functions
produced by a variational technique, MOST, are used to reduce the statistical
errors and to minimize excited-state contamination of the ground-state signal.
Calculating the required matching factors, we obtain $\xi'(1)=-0.64(13)$ for
the slope of the Isgur-Wise function in continuum-HQET in the $\barMS$ scheme
at a scale of $4.0 $GeV.


title: Real time simulations and the electroweak phase transition

abstract:
  We review recent developments in real-time simulations of SU(2)-Higgs theory
near the electroweak transition and related topics.


title: Non-perturbative improvement of operators with Wilson fermions

abstract:
  We outline two methods of constructing improved composite operators using
Wilson fermions.


title:
A new algorithm of Langevin simulation and its application to the SU(2)
  and SU(3) lattice gauge

abstract:
  The 2nd order Runge-Kutta scheme Langevin simulation of unquenched QCD in
pseudofermion method derived from our general theory shows a behaviour as a
function of the Langevin step t better than the Fukugita,Oyanagi,Ukawa's
scheme.


title: Coarse lattice results for glueballs and hybrids

abstract:
  A review of new results from lattice simulations of glueballs and heavy-quark
hybrid mesons is presented.


title: New results for non-perturbative order(a) improvement in light hadrons

abstract:
  We have results from light hadron simulations in quenched QCD at beta=6.0 and
6.2 using non-perturbatively improved Sheikholeslami-Wohlert fermions in an
effort to remove all order(a) effects. From looking at hadron masses and
splittings and the RG-invariant quark masses (where we have one point at
beta=5.7) we suggest this is plausible even with the limited data set. The
interpretation of the decay constants appears to be less clear.


title:
Finite-temperature chiral transitions in QCD with the Wilson quark
  action

abstract:
  We investigate the finite-temperature phase structure and the scaling of the
chiral condensate in lattice QCD with two degenerate light quarks, using a
renormalization group improved gauge action and the Wilson quark action. We
obtain a phase diagram which is consistent with that from the parity-flavor
breaking scenario. The scaling relation for the chiral condensate assuming the
critical exponents and the scaling function of the three dimensional O(4) model
is remarkably satisfied for a wide range of parameters. This indicates that the
chiral transition in two flavor QCD is of second order in the continuum limit.


title:
Critical parameters of N-vector spin models on 3d lattices from high
  temperature series extended to order beta^{21}

abstract:
  High temperature expansions for the free energy, the susceptibility and the
second correlation moment of the classical N-vector model [also denoted as the
O(N) symmetric classical spin Heisenberg model or as the lattice O(N) nonlinear
sigma model] have been extended to order beta^{21} on the simple cubic and the
body centered cubic lattices, for arbitrary N. The series for the second field
derivative of the susceptibility has been extended to order beta^{17}. An
analysis of the newly computed series yields updated estimates of the model's
critical parameters in good agreement with present renormalization group
estimates.


title:
The Gluon Propagator at High Temperature: Screening, Improvement and
  Non-Zero Momenta

abstract:
  We study the gluon propagator and the singlet potential in Landau gauge in
the deconfined phase of SU(2) lattice gauge theory, using both the standard
Wilson action and a tree-level Symanzik improved action. From the long-distance
behavior of correlation functions of temporal and spatial components of the
gauge fields we extract electric (m_e) and magnetic (m_m) screening masses. For
the magnetic mass we find m_m(T) = 0.456(6) g^2(T) T. The electric mass can be
described by a next-to leading order ansatz, obtained from one loop resummed
perturbation theory. However, the best description is given by m_e(T) =
\sqrt{1.70(2)} g(T) T. The electric screening mass thus is different from its
lowest order perturbative prediction even for temperatures as high as T \sim
10^4 T_c.


title: Non-perturbative improvement and renormalization of lattice operators

abstract:
  The Alpha Collaboration has proposed an optimal value for c_SW in the
Sheikholeslami-Wohlert action, chosen to remove O(a) effects. To measure
hadronic matrix elements to the same accuracy we need a method of finding O(a)
improved operators, and their renormalization constants. We determine the Z
factors by a non-perturbative method, measuring the matrix elements for single
quark states propagating through gauge fields in the Landau gauge. The data
show large effects coming from chiral symmetry breaking. This allows us to find
the improvement coefficients too, by requiring that the amount of chiral
symmetry breaking agrees with that predicted by the chiral Ward identities.


title: A lattice field theoretical model for high-$T_c$ superconductivity

abstract:
  We present a 2+1-dimensional lattice model for the copper oxide
superconductors and their parent compounds, in which both the charge and spin
degrees of freedom are treated dynamically. The spin-charge coupling parameter
is associated to the doping fraction in the cuprates. The model is able to
account for the various phases of the cuprates and their properties, not only
at low and intermediate doping but also for (highly) over-doped compounds. We
acquire a qualitative understanding of high-$T_c$ superconductivity as a
Bose-Einstein condensation of bound charge pairs.


title: Heavy Meson Spectroscopy at Beta=6.0

abstract:
  We present results of a quenched calculation of the heavy-light and
quarkonium spectrum using the tadpole improved clover action. We resolve
completely the triplet chi P-states in quarkonium systems, and obtain evidence
for fine structure of the heavy-light P-states. Approximate scaling of the
hyperfine splittings is observed, producing results that are significantly
below experiment.


title: The Deep-Inelastic Structure Functions of $\pi$ and $\rho$ Mesons

abstract:
  We compute the lower moments of the structure functions of $\pi$ and $\rho$.
Of particular interest are the spin-dependent structure functions of the $\rho$
as they give new information about quark binding effects.


title: Critical Behavior at the Chiral Phase Transition

abstract:
  Quantum chromodynamics with two zero mass flavors is expected to exhibit a
phase transition with O(4) critical behavior. Fixing the universality class is
important for phenomenology and for facilitating the extrapolation of
simulation data to physical quark mass values. At Lattice '96 the Tsukuba and
Bielefeld groups reported results from new simulations with dynamical staggered
quarks at $N_t = 4$, which suggested a departure from the expected critical
behavior. We report observations of similar deviations and discuss efforts in
progress to understand this phenomenon.


title:
Casimir Scaling from Center Vortices: Towards an Understanding of the
  Adjoint String Tension

abstract:
  We argue that the approximate ``Casimir scaling'' of the string tensions of
higher-representation Wilson loops is an effect due to the finite thickness of
center vortex configurations. It is shown, in the context of a simple model of
the Z(2) vortex core, how vortex condensation in Yang-Mills theory can account
for both Casimir scaling in intermediate size loops, and color-screening in
larger loops. An implication of our model is that the deviations from exact
Casimir scaling, which tend to grow with loop size, become much more pronounced
as the dimensionality of the group representation increases.


title:
1) The Influence of Gribov Copies on Gluon and Ghost Propagators in
  Landau Gauge and 2) A New Implementation of the Fourier Acceleration Method

abstract:
  We study the influence of Gribov copies on gluon and ghost propagators in
lattice Landau gauge. For the gluon propagator, Gribov noise seems to be of the
order of magnitude of the numerical accuracy. On the contrary, for the ghost
propagator, Gribov noise is clearly observable, at least in the strong-
coupling regime. We also observe, in the limit of large lattice volume, a gluon
propagator decreasing as the momentum goes to zero. Finally, we introduce an
implementation of the method of Fourier Acceleration which avoids the use of
the fast Fourier transform, being well suited for parallel and vector machines.
We apply it to the case of Landau gauge fixing, and study its performance on
APE computers.


title:
Scaling Contributions to the Free Energy in the 1/N Expansion of O(N)
  Nonlinear Sigma Models in d-Dimensions

abstract:
  Within the 1/N expansion of O(N) nonlinear $\sigma$ models for $d \leq 4$ it
is possible to separate consistently the spin-wave and the massive-mode
contributions to the scaling part of the free energy near criticality, and to
evaluate them to $O(1/N)$. For critical dimensions $d = 2+2/n$ the Abe-Hikami
anomaly is recovered, while for $d=2$ the removal of the spin-wave term is
justified.


title: Monopole Percolation in the Compact Abelian Higgs Model

abstract:
  We have studied the monopole-percolation phenomenon in the four dimensional
Abelian theory that contains compact U(1) gauge fields coupled to unitary norm
Higgs fields. We have determined the location of the percolation transition
line in the plane $(\beta_g, \beta_H)$. This line overlaps the confined-Coulomb
and the confined-Higgs phase transition lines, originated by a
monopole-condensation mechanism, but continues away from the end-point where
this phase transition line stops. In addition, we have determined the critical
exponents of the monopole percolation transition away from the phase transition
lines. We have performed the finite size scaling in terms of the monopole
density instead of the coupling, because the density seems to be the natural
parameter when dealing with percolation phenomena.


title:
Two loop expansion of the Schroedinger functional coupling alpha_SF in
  SU(3) lattice gauge theory

abstract:
  The two loop coefficient of the expansion of the Schroedinger functional
coupling in terms of the lattice coupling is calculated for the SU(3)
Yang-Mills theory. This coefficient is required to relate lattice data to the
MS-bar-coupling. As a byproduct of the calculation, the Schroedinger functional
is improved to two loop order and the three loop coefficient of the beta
function in the SF-scheme is derived.


title: The Running Coupling from the Quark-Gluon Vertex

abstract:
  We present results for the QCD running coupling obtained from measuring the
quark-gluon vertex in Landau gauge with suitable renormalisation conditions.
The issue of discretisation errors arising from the fermion action is
discussed.


title:
Two-Flavor Chiral Phase Transition in Lattice QCD with the
  Kogut-Susskind Quark Action

abstract:
  A summary is presented of a scaling study of the finite-temperature chiral
phase transition of two-flavor QCD with the Kogut-Susskind quark action based
on simulations on $L^3\times4$ ($L$=8, 12 and 16) lattices at the quark mass of
$m_q=0.075, 0.0375, 0.02$ and 0.01. We find a phase transition to be absent for
$m_q\geq 0.02$, and also quite likely at $m_q=0.01$. The quark mass dependence
of susceptibilities is consistent with a second-order transition at $m_q=0$.
The exponents, however, deviate from the O(2) and O(4) values theoretically
expected.


title: Hadron masses in qQCD with Wilson fermions near the chiral limit

abstract:
  In quenched lattice QCD with standard Wilson fermions the quark propagator is
computed very close to the chiral limit in the zero-temperature case. Starting
from our experience with lattice QED we employ a modified statistical method in
order to estimate reliably hadron masses.


title:
Effects of dynamical Wilson fermions and the phase structure of compact
  QED_4

abstract:
  By comparison of the quenched and full formulations of compact QED with
Wilson fermions we single out the effects of dynamical fermions on the `chiral
transition line' within the confinement phase. It is shown that this line
cannot correspond to the chiral limit of the theory for all values of the gauge
coupling. This seems to imply the existence of tri-critical points in this
theory, the phase structure of which has a close similarity to QCD at finite
temperature.


title:
Scaling Study of the Two-Flavor Chiral Phase Transition with the
  Kogut-Susskind Quark Action in Lattice QCD

abstract:
  We report on a study of two-flavor finite-temperature chiral phase transition
employing the Kogut-Susskind quark action and the plaquette gluon action in
lattice QCD for a lattice with $N_t=4$ temporal size. Hybrid R simulations of
$10^4$ trajectories are made at quark masses of $m_q=0.075, 0.0375, 0.02, 0.01$
in lattice units for the spatial sizes $8^3, 12^3$ and $16^3$. The spatial size
dependence of various susceptibilities confirm the previous conclusion of the
absence of a phase transition down to $m_q=0.02$. At $m_q=0.01$ an increase of
susceptibilities is observed up to the largest volume $16^3$ explored in the
present work. We argue, however, that this increase is likely to be due to an
artifact of too small a lattice size and it cannot be taken to be the evidence
for a first-order transition. Analysis of critical exponents estimated from the
quark mass dependence of susceptibilities shows that they satisfy hyperscaling
consistent with a second-order transition located at $m_q=0$. The exponents
obtained from larger lattice, however, deviate significantly from both those of
O(2), which is the exact symmetry group of the Kogut-Susskind action at finite
lattice spacing, and those of O(4) expected from an effective sigma model
analysis in the continuum limit.


title: Instanton, Monopole Condensation and Confinement

abstract:
  The confinement mechanism in the nonperturbative QCD is studied in terms of
topological excitation as QCD-monopoles and instantons. In the 't Hooft abelian
gauge, QCD is reduced into an abelian gauge theory with monopoles, and the QCD
vacuum can be regarded as the dual superconductor with monopole condensation,
which leads to the dual Higgs mechanism. The monopole-current theory extracted
from QCD is found to have essential features of confinement. We find also close
relation between monopoles and instantons using the lattice QCD. In this
framework, the lowest $0^{++}$ glueball (1.5 $\sim$ 1.7GeV) can be identified
as the QCD-monopole or the dual Higgs particle.


title: Improving Stochastic Estimator Techniques for Disconnected Diagrams

abstract:
  Disconnected diagrams are expected to be sensitive to the inclusion of
dynamical fermions. We present a feasibility study for the observation of such
effects on the nucleonic matrix elements of the axial vector current, using
SESAM full QCD vacuum configurations with Wilson fermions on $16^3\times 32$
lattices, at $\beta =5.6$. Starting from the standard methods developed by the
Kentucky and Tsukuba groups, we investigate the improvement from various
refinements thereof.


title:
Lattice QCD with domain wall quarks and applications to weak matrix
  elements

abstract:
  Using domain wall fermions, we estimate $B_K(\mu\approx 2 GeV)=0.628(47)$ in
quenched QCD which is consistent with previous calculations. At $\gbeta=6.0$
and 5.85 we find the ratio $f_K/m_\rho$ in agreement with the experimental
value, within errors. These results support expectations that $O(a)$ errors are
exponentially suppressed in low energy ($E\ll a^{-1}$) observables, and
indicate that domain wall fermions have good scaling behavior at relatively
strong couplings. We also demonstrate that the axial current numerically
satisfies the lattice analog of the usual continuum axial Ward identity.


title: Lattice Renormalization of Quark Operators

abstract:
  We have technically improved the non-perturbative renormalization method,
proposed by Martinelli et al., by using quark momentum sources and sinks.
Composite two-fermion operators up to three derivatives have been measured for
Wilson fermions and Sheikholeslami-Wohlert improved fermions in the quenched
approximation. The calculations are performed in the Landau gauge on 16^3x32
lattices at beta = 6.0 for 3 kappa values in each case. The improved sources
greatly decrease the statistical noise. We extract and discuss here
renormalization factors for local operators and moments of the structure
functions for Wilson fermions.


title:
Status of alpha_s determinations from the non-perturbatively
  renormalised three-gluon vertex

abstract:
  We demonstrate the feasibility of computing alpha_s from the lattice
three-gluon vertex in the Landau gauge. Data from 16^4 and 24^4 quenched
lattices at beta=6.0 are presented. Our main result is that 2-loop asymptotic
scaling is observed for momenta in the range 1.8-2.3 Gev, where lattice
artifacts appear to be under control.


title: The Schr\"odinger Functional and Non-Perturbative Improvement

abstract:
  After describing the Schr\"odinger functional for standard and improved gluon
and quark actions we present results for the non-perturbative clover
coefficients of the SW quark action coupled to the Wilson plaquette action for
$\beta \geq 5.7$, as well as the L\"uscher-Weisz one-loop tadpole improved
gauge action, both in the quenched approximation.


title: Polymeric Phase of Simplicial Quantum Gravity

abstract:
  We deduce the appearance of a polymeric phase in 4-dimensional simplicial
quantum gravity by varying the values of the coupling constants and discuss the
geometric structure of the phase in terms of ergodic moves. A similar result is
true in 3-dimensions.


title: CP-PACS results for quenched QCD spectrum with the Wilson action

abstract:
  We present progress report of a CP-PACS calculation of quenched QCD spectrum
with the Wilson quark action. Light hadron masses and meson decay constants are
obtained at $\beta=$5.9, 6.1, and 6.25 on lattices with a physical extent of 3
fm, and for the range of quark mass corresponding to $m_\pi/m_\rho \approx
0.75$ $-$ 0.4. Nucleon mass at each $\beta$ appears to be a convex function of
quark mass, and consequently the value at the physical quark mass is much
smaller than previously thought. Hadron masses extrapolated to the continuum
limit exhibits a significant deviation from experimental values: with $K$ meson
mass to fix strange quark mass, strange meson and baryon masses are
systematically lower. Light quark masses determined from the axial Ward
identity are shown to agree with those from perturbation theory in the
continuum limit. Decay constants of mesons are also discussed.


title: Heavy Quark Physics From Lattice QCD

abstract:
  We review the application of lattice QCD to the phenomenology of b- and
c-quarks. After a short discussion of the lattice techniques used to evaluate
hadronic matrix elements and the corresponding systematic uncertainties, we
summarise results for leptonic decay constants, B--Bbar mixing, semileptonic
and rare radiative decays. A discussion of the determination of heavy quark
effective theory parameters is followed by an explanation of the difficulty in
applying lattice methods to exclusive nonleptonic decays.


title: Heavy Hybrids from NRQCD

abstract:
  We present results for the exotic $0^{+-}$ and $1^{-+}$ $b\bar{b}g$ hybrids
at $\beta=6.0$. A leading order NRQCD action is used to generate the heavy
quark propagators. The optimisation of operators is discussed and we compare
our results to the predictions of recent potential calculations.


title:
Hadron spectroscopy and static quark potential in full QCD: A comparison
  of improved actions on the CP-PACS

abstract:
  We present first results from a full QCD calculation on the CP-PACS,
comparing various actions at $a^{-1} \sim 1 GeV$ and $m_\pi/m_\rho \approx
0.7$--0.9. We use the plaquette and a renormalization group improved action for
the gluons, and the Wilson and the SW-Clover action for quarks. We find that
significant improvements in the hadron spectrum results from improving the
quarks, while the gluon improvement is required for a rotationally invariant
static potential. An ongoing effort towards exploring the chiral limit in full
QCD is described.


title: FFT for the APE Parallel Computer

abstract:
  We present a parallel FFT algorithm for SIMD systems following the `Transpose
Algorithm' approach. The method is based on the assignment of the data field
onto a 1-dimensional ring of systolic cells. The systolic array can be
universally mapped onto any parallel system. In particular for systems with
next-neighbour connectivity our method has the potential to improve the
efficiency of matrix transposition by use of hyper-systolic communication. We
have realized a scalable parallel FFT on the APE100/Quadrics massively parallel
computer, where our implementation is part of a 2-dimensional hydrodynamics
code for turbulence studies. A possible generalization to 4-dimensional FFT is
presented, having in mind QCD applications.


title: Moving NRQCD

abstract:
  I discuss the derivation and applications of Moving NRQCD (MNRQCD), a
generalization of NRQCD which allows the treatment of heavy quarks moving with
a finite velocity. This formalism is vital in reducing discretization errors in
calculations of large recoil decays, such as B --> K^* + gamma or the
Isgur-Wise function at large w.