title: Preliminary heavy-light decay constants from the MILC collaboration

abstract:
  Preliminary results from the MILC collaboration for $f_B$, $f_{B_s}$, $f_D$,
$f_{D_s}$ and their ratios are presented. We compute in the quenched
approximation at $\beta=6.3$, 6.0 and 5.7 with Wilson light quarks and static
and Wilson heavy quarks. We attempt to quantify systematic errors due to finite
volume, finite lattice spacing, large $am$, and fitting and extrapolation
uncertainties. The hopping parameter approach of Henty and Kenway is used to
treat the heavy quarks; the sources are Coulomb gauge gaussians.


title: On the reliable measurement of the gluon condensate in lattice QCD

abstract:
  We propose to calculate the gluon condensate in lattice QCD in an indirect
way by extracting it from the correlator of hadronic currents of heavy quarks.
Moments (derivatives with respect to momentum at vanishing momentum) of the
vector and pseudoscalar correlators are evaluated. The contribution of the
continuum spectrum in addition to the low-lying resonance is observed in
accordance with qualitative expectations. Finite size effects are observed and
shown to be insignificant for heavy quarks and moderate lattices. A practical
definition of the nonperturbatively renormalized heavy quark mass is given.


title: Heavy Baryon Spectroscopy

abstract:
  We present the preliminary results of an exploratory study of heavy baryon
spectroscopy, using the $O(a)$-improved fermionic action. Estimates of masses
and splittings at the charm and beauty physical limit are reported.


title: APE Results of Hadron Masses in Full QCD Simulations

abstract:
  We present numerical results obtained in full QCD with 2 flavors of Wilson
fermions. We discuss the relation between the phase of Polyakov loops and the
{\bf sea} quarks boundary conditions. We report preliminary results about the
HMC autocorrelation of the hadronic masses, on a $16^3 \times 32$ lattice
volume, at $\beta=5.55$ with $k_{sea}=0.1570$.


title:
Dynamical fermion mass generation by strong gauge interaction shielded
  by a scalar field

abstract:
  The strongly coupled lattice gauge models with confined fermion and scalar
matter fields, which in a certain phase break dynamically a global chiral
symmetry, are reconsidered from the point of view of the existence of heavy
fermions. If these models are interpreted as describing a new strong force
beyond the standard model, such heavy fermions can arise as neutral bound
states of the fundamental fermion and scalar. The discussed mechanism could be
considered as an alternative to the Higgs mechanism.


title: The SU(3) running coupling from lattice gluons

abstract:
  We provide numerical results for the running coupling in $SU(3)$ Yang-Mills
theory as determined from an analysis of lattice two and three-point gluon
correlation functions. The coupling is evaluated directly, from first
principles, by defining suitable renormalisation constants from the lattice
triple gluon vertex and gluon propagator. For momenta larger than 2 GeV, the
coupling is found to run according to the 2-loop asymptotic formula. The
influence of lattice artifacts on the results appears negligible within the
precision of our measurements, although further work on this point is in
progress.


title: Update on the lattice calculation of $B \to K^* \gamma$

abstract:
  We summarise our current results for calculations of the form factors for $B
\to K^* \gamma$, and their extrapolation to the physical b-quark mass.


title: NRQCD and Static Systems -- A General Variational Approach

abstract:
  We present initial results from Monte Carlo simulations of NRQCD-light,
static-light, and NRQCD-NRQCD mesons, using a variational technique (MOST), as
part of our ongoing calculation of the $f_{B}$ decay constant. The basis states
for the variational calculation are quark-antiquark operators separated by all
possible relative distances not equivalent under the cubic group (for example,
for a $20^{3}$ lattice there are 286 operators). The efficacy of the method is
demonstrated by the good plateaus obtained for the ground state and the clean
extraction of the wave functions of the ground and first radially excited
state.


title: Phase Transitions in lattice QED

abstract:
  The main objective of the work presented here is to understand the appearance
of phase transitions in pure gauge and scalar lattice QED. Main results are as
follows: Pure gauge compact QED with PBC shows a monopole percolation phenomena
coupled to the monopole condensation. Pure gauge compact QED with Fixed
Boundary Conditions (spherical topology) shows a behaviour compatible with a
second order phase transition The $\gamma\to\infty$ limit of Non Compact Scalar
QED with PBC is related to the Villain form of compact QED and also to the Loop
Model for QED, showing a first order phase transition. Numerical a analysis of
a third rank abelian Z(2) theory shows an intriguing behaviour over the phase
transition that may be originated by point-like topological excitations.


title: Spin dependent potentials from SU(2) gauge theory

abstract:
  We present results on spin dependent potentials from lattice simulations of
SU(2) gauge theory. The Coulomb like short range part of the central potential
is identified as a mixed vector-scalar exchange while the linear long range
part is pure scalar.


title:
Polyakov loop and spin correlators on finite lattices A study beyond the
  mass gap

abstract:
  We derive an analytic expression for point-to-point correlation functions of
the Polyakov loop based on the transfer matrix formalism. For the $2d$ Ising
model we show that the results deduced from point-point spin correlators are
coinciding with those from zero momentum correlators. We investigate the
contributions from eigenvalues of the transfer matrix beyond the mass gap and
discuss the limitations and possibilities of such an analysis. The finite size
behaviour of the obtained $2d$ Ising model matrix elements is examined. The
point-to-point correlator formula is then applied to Polyakov loop data in
finite temperature $SU(2)$ gauge theory. The leading matrix element shows all
expected scaling properties. Just above the critical point we find a Debye
screening mass $~\mu_D/T\approx4~$, independent of the volume.


title: Extrapolation Methods for the Dirac Inverter in Hybrid Monte Carlo

abstract:
  In Hybrid Monte Carlo(HMC) simulations for full QCD, the gauge fields evolve
smoothly as a function of Molecular Dynamics (MD) time. Thus we investigate
improved methods of estimating the trial solutions to the Dirac propagator as
superpositions of the solutions in the recent past. So far our best
extrapolation method reduces the number of Conjugate Gradient iterations per
unit MD time by about a factor of 4. Further improvements should be forthcoming
as we further exploit the information of past trajectories.


title:
Pseudoscalar correlators and the problem of the chiral limit in the
  compact lattice QED with Wilson fermions

abstract:
  The phase diagram for the compact lattice QED with Wilson fermions is shown.
We discuss different methods for the calculation of the 'pion' mass $m_{\pi}$
near the chiral transition point $\kappa_c(\beta )$.


title:
Recent progress in the theory of random surfaces and simplicial quantum
  gravity

abstract:
  Some of the recent developments in the theory of random surfaces and
simplicial quantum gravity is reviewed. For 2d quantum gravity this includes
the failure of Regge calculus, our improved understanding of the $c>1$ regime,
some surprises for q-state Potts models with $q > 4$, attempts to use
renormalization group techniques, new critical behavior of random surface
models with extrinsic curvature and improved algorithms. For simplicial quantum
gravity in higher dimensions it includes a discussion of the exponential
entropy bound needed for the models to be well defined, the question of
``computational ergodicity'' and the question of how to extract continuum
behavior from the lattice simulations.


title: Nucleon masses in strong magnetic fields

abstract:
  We compute the variation of the masses of the proton and the neutron induced
by the presence of a strong external magnetic field. We discuss the choice of
the wave function and different techniques how to apply the magnetic field. The
results obtained from a 24 16^2 8 and a 16^2 8^2 lattice are compared with a
phenomenological approach.


title:
Dynamical fermion simulations using Luescher's local bosonic action
  algorithm

abstract:
  The two-flavour Schwinger model is used to test the local boson action
algorithm of M Luescher. The autocorrelation time is found to rise linearly
with the number of auxiliary boson fields. An extension to the algorithm is
proposed which exactly reproduces the full dynamical partition function for any
number of boson fields.


title: Structural Properties of the Lattice Heavy Quark Effective Theory

abstract:
  We discuss two related aspects of the lattice version of the heavy quark
effective theory (HQET). They are the effects of heavy quark modes with large
momenta, near the boundary of the Brillouin zone, and the renormalization of
the lattice HQET. We argue that even though large momentum modes are present,
their contributions to heavy-light bound states and perturbative loop integrals
are dynamically suppressed and vanish in the continuum limit. We also discuss a
new feature of the renormalization of the lattice HQET not present in the
continuum theory, namely that the classical velocity is finitely renormalized.


title: Finite temperature QCD: progress and outstanding problems

abstract:
  I review recent progress in numerical simulations of finite temperature
quantum chromodynamics and discuss the status of some outstanding problems.
Included is (1) a discussion of recent results determining the temperature of
the ``phase transition'' in full QCD, (2) a scaling analysis of the Polyakov
loop variable, leading to the determination of a constituent quark free energy,
(3) studies of critical behavior near the phase transition in two-flavor QCD,
(4) a discussion of problems and new results in thermodynamic simulations with
Wilson fermions, (5) recent results in pure gauge theory with a mixed
fundamental/adjoint action, and (6) the nonperturbative determination of the
equation of state with dynamical fermions included. Finally I mention briefly
new developments in efforts to construct a phenomenology of deconfinement and
chiral symmetry restoration, namely (7) the dual superconducting model and (8)
the instanton model.


title: Decays rates for S- and P-wave bottomonium

abstract:
  We use the Bodwin-Braaten-Lepage factorization scheme to separate the long-
and short-distance factors that contribute to the decay rates of $\Upsilon$,
$\eta_b$ (S-wave) and $\chi_b$,$h_b$ (P-wave). The long distance matrix
elements are calculated on the lattice in the quenched approximation using a
non-relativistic formulation of the $b$ quark dynamics.


title: Nature of the finite temperature transition in QCD with strange quark

abstract:
  The finite temperature transition in QCD is studied using Wilson quarks for
the cases of $N_F=2$, 3 and 2+1. For $N_F=2$ the transition is smooth in the
chiral limit on both $\nt=4$ and 6 lattices. For $N_F=3$, clear two state
signals are observed for $\beta\leq4.7$ on $8^2\times10 \times4$ and
$12^3\times4$ lattices, which implies the transition is first order for $m_q
\simm{<} 140$ MeV. For $N_F=2+1$ we study two cases of $m_s \simeq 150$ and 400
MeV with $m_u=m_d \simeq 0$. In contrast to a previous result with staggered
quarks, two state signals are clearly observed for both cases, suggesting a
first order QCD phase transition in the real world.


title: A Lattice Study of Semi-leptonic Decays of $D$-Mesons

abstract:
  We present results of a lattice computation of the matrix elements of the
vector and axial-vector currents which are relevant for the semi-leptonic
decays $D \rightarrow K$ and $D \rightarrow K^*$. The computations are
performed in the quenched approximation to lattice QCD on a $24^3 \times 48$
lattice at $\beta=6.2$ using an $O(a)$-improved fermionic action.


title: A lattice study of the quark propagator and vertex function

abstract:
  We report on the status of a study of the quark propagator and quark-gluon
vertex in momentum space. Quark propagators have been generated at beta=6.0
using the O(a)-improved Sheikholeslami-Wohlert action and fixed to the Landau
gauge. The first results for the quark pole mass and field renormalisation
constant are reported, and plans for future work are presented.


title: The Coulomb-Higgs transition of the three-parameter U(1)-Higgs model

abstract:
  We find a first order Coulomb--Higgs phase transition at moderately large
values of the coupling $\lambda$, and no evidence for a change of order at any
finite value of it.


title:
Sphaleron transition rate at high temperature in the 1+1 D abelian Higgs
  model

abstract:
  New results for the rate are presented using the canonical ensemble in the
classical approximation on a spatial lattice. We find that the rate at high
temperatures is proportional to $T^2$, and strongly dependent on the lattice
spacing $a$. We conclude that a better effective action is needed for the
classical approximation.


title:
On $T$ dependence of the static potential $V(T;{\vec R})$ in a finite
  volume

abstract:
  We study the dependence on $T$ of the static potential $V(T;{\vec R})$
defined from Wilson loops and from Polyakov loop correlators on a finite
lattice. For this study we employ a simple model with confinement, and compare
with MC results.


title: Color Flux Profiles in SU(2) Lattice Gauge Theory

abstract:
  Results of a high statistics study of chromo field distributions around
static sources in pure SU(2) gauge theory on lattices of volumes $16^4$,
$32^4$, and $48^3\times 64$ at $\beta=2.5$, $2.635$, and $2.74$ are presented.
We establish string formation up to physical distances as large as 2 fm.


title: Spin Chains and Chiral Lattice Fermions

abstract:
  The generalization of Lorentz invariance to solvable two-dimensional lattice
fermion models has been formulated in terms of Baxter's corner transfer matrix.
In these models, the lattice Hamiltonian and boost operator are given by
fermionized nearest-neighbor Heisenberg spin chain operators. The
transformation properties of the local lattice fermion operators under a boost
provide a natural and precise way of generalizing the chiral structure of a
continuum Dirac field to the lattice. The resulting formulation differs from
both the Wilson and staggered (Kogut-Susskind) prescriptions. In particular, an
axial $Q_5$ rotation is sitewise local, while the vector charge rotation mixes
nearest neighbors on even and odd sublattices.


title: Structure of flux tube in SU(2) lattice gauge theory

abstract:
  The structure of the flux tube is studied in $SU(2)$ QCD from the standpoint
of the abelian projection theory. It is shown that the flux distributions of
the orthogonal electric field and the magnetic field are produced by the effect
that the abelian monopoles in the maximally abelian (MA) gauge are expelled
from the string region.


title: Towards the continuum limit with quenched staggered quarks

abstract:
  We extend previous work on finite-size effects with dynamical staggered
quarks to the quenched approximation. We again emphasize the large volume limit
that is of interest for spectrum calculations which may hope to approach the
experimental values. Relying on new calculations at $6/g^2=5.7$ and recent work
with weaker couplings, we extrapolate to the continuum limit and find a nucleon
to rho mass ratio in close agreement with the experimental value and the value
obtained by extrapolations from calculations with Wilson quarks. Additional
calculations that should be done to improve the reliability of the
extrapolation are discussed.


title:
How to Accurately Extract the Running Coupling of QCD from Lattice
  Potential Data

abstract:
  By (a) using an expression for the LATTICE potential of QCD in terms of a
CONTINUUM running coupling and (b) globally parameterizing this coupling to
interpolate between 2- (or higher-) loop QCD in the UV and the flux tube
prediction in the IR, we can perfectly fit lattice data for the potential down
to ONE lattice spacing and at the same time extract the running coupling to
high precision. This allows us to quantitatively check the accuracy of 2-loop
evolution, compare with the Lepage-Mackenzie estimate of the coupling extracted
from the plaquette, and determine the scale $r_0$ ten times more accurately
than previously possible. For pure SU(3) we find that the coupling scales on
the percent level for $\beta \geq 6$.


title: Finite ma corrections for sea quark matrix elements

abstract:
  We discuss the finite $ma$ corrections associated with the computation of sea
quark matrix elements. We find them to differ from the standard normalization
used for valence quarks and to depend strongly on the Lorentz structure of the
current under consideration. Phenomenological implications of these results are
briefly discussed in two examples. We also mention how the magnitude of the
correction factors can be reduced by using a 2-link improved action.


title: Quenched QED on a momentum space lattice

abstract:
  We discuss the advantages of using the momentum space lattice method for
studying the phase diagram of quenched QED_4. Preliminary results of a
numerical simulation are presented. They indicate that the method avoids the
contamination by 4-fermi interactions which plagues the conventional position
space non-compact formulation.


title:
Scalar and axial vector matrix elements of proton in quenched QCD:
  Calculation of both connected and disconnected contributions

abstract:
  $\pi$-$N$ $\sigma$ term and proton axial vector matrix elements are
calculated including disconnected contributions with a variant wall source
method using the Wilson quark action at $\beta=5.7$ in quenched QCD. For the
$\sigma$ term, we find $\sigma_{disc}/\sigma_{conn}=2.35(46)$ and
$\sigma=44(6)$MeV--60(9)MeV. The fraction of proton spin carried by quarks is
$\Delta\Sigma=\Delta{u}+\Delta{d}+\Delta{s}=+0.638(54)-0.347(46)-0.109(30)=
+0.18(10)$.


title: String tension and monopoles in $T \neq 0$ SU(2) QCD

abstract:
  Monopole and photon contributions to abelian Wilson loops are calculated
using Monte-Carlo simulations of finite-temperature $SU(2)$ QCD in the
maximally abelian gauge. The string tension is reproduced by monopole
contribution alone also in finite temperature SU(2) QCD. The spatial string
tension scales as $\sqrt{\sigma} \propto g^{2}(T)T$ and is reproduced almost by
monopole contribution alone. Each configuration has one long monopole loop, and
the long monopole loops alone are responsible for the string tension in the
confinement phase. On the other hand, the spatial string tension in the
deconfinement phase is reproduced by wrapped monopole loops alone.


title: New algorithm for gauge fixing in SU(2) lattice gauge theory

abstract:
  An overrelaxed variant of simulated annealing is applied to the problem of
maximally abelian gauge fixing. The superiority of this algorithm over the
commonly used relaxation procedure is demonstrated. Biases on non gauge
invariant quantities due to gauge fixing ambiguities are discussed.


title: Fermion-Fermion Scattering in the Gross-Neveu Model - a Status Report

abstract:
  Encouraged by the successful applications of L\"uscher's method to
boson--boson scattering we discuss the possibility of extracting scattering
phase shifts from finite--volume energies for fermion--fermion scattering in
the Gross--Neveu model.


title:
Four-quark energies in SU(2) lattice Monte Carlo using a tetrahedral
  geometry

abstract:
  This contribution -- a continuation of earlier work -- reports on recent
developments in the calculation and understanding of 4-quark energies generated
using lattice Monte Carlo techniques.


title: Topological Updating Schemes: A Case Study In 3-d U(1)

abstract:
  We study a topological updating scheme in three dimensional U(1) gauge
theory. Some expectations for four dimensional SU(N) gauge theories are
discussed.


title: Anisotropic Gauge Theories: A Numerical Study of the Fu-Nielsen Model

abstract: We study numerically 4+1 dimensional pure gauge theory.


title: The QCD Spectrum

abstract:
  Recent results in light hadron spectroscopy are reviewed. Attention is given
to the requirements of precision determinations in lattice gauge theory.
Different methods for extracting the running coupling constant $\alpha_S$ are
compared. Some recent results in determining the nature of the interaction
between static quarks are also discussed.


title: Massless Fermions on the Lattice

abstract:
  We consider a nonlocal lattice action for fermions fermion doubling in
lattice theories. It is shown, that it is possible to avoid the fermionic
doubling in the case of free fermions, but this approach does not reproduce
results for the effective action for gauge fields in the continuum theory,
because the high frequency fermion modes have a strong dependence on the gauge
field.


title: Strongly Interacting Higgs Sector without Technicolor

abstract:
  Simulation results are presented on Higgs mass calculations in the
spontaneously broken phase of the Higgs sector in the minimal Standard Model
with a higher derivative regulator. A heavy Higgs particle is found in the TeV
mass range in the presence of a complex conjugate ghost pair at higher
energies. The ghost pair evades easy experimental detection. As a finite and
unitary theory in the continuum, this model serves as an explicit and simple
example of a strongly interacting Higgs sector without technicolor.


title: QCD on Coarse Lattices

abstract:
  We show that the perturbatively-improved gluon action for QCD, once it is
tadpole-improved, gives accurate results even with lattice spacings as large as
0.4~fm. {\em No\/} tuning of the couplings is required. Using this action and
lattice spacing, we obtain a static potential that is rotationally invariant to
within a few percent, the spin-averaged charmonium spectrum accurate to within
30--40~MeV, and scaling to within 5--10\%. We demonstrate that simulations on
coarse lattices are several orders of magnitude less costly than simulations
using current methods.


title: Form Factors for Semileptonic Decays of Heavy-Light Hadrons

abstract:
  The strong coupling lattice QCD solution \cite{APtifr} for the Isgur-Wise
functions, parametrising the semileptonic decay form factors of hadrons
containing a single heavy quark, is reviewed. Several useful features connected
with the result are pointed out.


title: SU(2) potentials in quantum gravity

abstract:
  We present investigations of the potential between static charges from a
simulation of quantum gravity coupled to an SU(2) gauge field on $6^{3}\times
4$ and $8^{3}\times 4$ simplicial lattices. In the well-defined phase of the
gravity sector where geometrical expectation values are stable, we study the
correlations of Polyakov loops and extract the corresponding potentials between
a source and sink separated by a distance $R$. In the confined phase, the
potential has a linear form while in the deconfined phase, a screened Coulombic
behavior is found. Our results indicate that quantum gravitational effects do
not destroy confinement due to non-abelian gauge fields.


title:
Thermal Phase Transition in Mixed Action SU(3) Lattice Gauge Theory and
  Wilson Fermion Thermodynamics

abstract:
  We study the thermal phase diagram of pure SU(3) lattice gauge theory with
fundamental and adjoint couplings. We improve previous estimates of the
position of the bulk transition line and determine the thermal deconfinement
transition lines for $N_t=2,4,6,$ and 8. The endpoint of the bulk transition
line $(\beta_f, \beta_a)=(4.00(7), 2.06(8))$ improves upon earlier estimates
obtained using smaller lattice sizes. For $N_t > 4$ the deconfinement
transition line splits cleanly away from the bulk transition line. With
increasing $N_t$ the thermal deconfinement transition lines shift to
increasingly weaker coupling, joining onto the bulk transition line at
increasingly larger $\beta_a$ in a pattern consistent with the usual
universality picture of lattice gauge theories. We also discuss the possible
consequences of an induced adjoint term from the fermionic determinant and
determine this induced term numerically with a microcanonical demon method for
two flavors of dynamical Wilson fermions.


title: One Spin Trace Formalism for $ B_K $

abstract:
  It has been known for some time that there are two methods to calculate $ B_K
$ with staggered fermions: one is the two spin trace formalism and the other is
the one spin trace formalism. Until now, the two spin trace formalism has been
exclusively used for weak matrix element calculations with staggered fermions.
Here, the one spin trace formalism to calculate $ B_K $ with staggered fermions
is explained. It is shown that the one spin trace operators require additional
chiral partner operators in order to keep the continuum chiral behavior. The
renormalization of the one spin trace operators is described and compared with
the two spin trace formalism.


title: On the screening of the potential between adjoint sources in $QCD_3$

abstract:
  We calculate the potential between adjoint sources in $SU(2)$ pure gauge
theory in three dimensions. We investigate whether the potential saturates at
large separations due to the creation of a pair of gluelumps, colour-singlet
states formed when glue binds to an adjoint source.


title:
Accurate hadron spectroscopy on blocked configurations by
  tadpole-renormalized, clover-improved Wilson quark action

abstract:
  We compare the quenched hadron spectrum on blocked and unblocked lattices for
the Wilson quark action, the clover action and the tadpole-improved clover
action. The latter gives a spectrum markedly closer to the original one, even
though the cutoff is 1/a ~ 500 Mev.


title: Scalar Glueball Decay

abstract:
  We evaluate the coupling constant for the lightest scalar glueball to decay
to pseudoscalar meson pairs. The calculation is done in the valence
approximation on a $16^3 \times 24$ lattice at $\beta = 5.70$ for two different
values of pseudoscalar meson mass.


title: Cooling in QCD Spectroscopy

abstract:
  We test the cooling algorithm with gluonic and staggered hadronic
spectroscopy on $SU(3)$ gauge field configurations generated with two flavors
of staggered dynamical fermions. We find cooling is not reliable as the basis
for improved hadronic operators. We also find that performing cooling sweeps to
reveal more clearly the topological properties of the gauge fields eliminates
the spin structure of the hadron spectrum.


title:
The continuum limit of the lattice Gribov problem, and a solution based
  on Hodge decomposition

abstract:
  We study gauge fixing via the standard local extremization algorithm for
2-dimensional $U(1)$. On a lattice with spherical topology $S^2$ where all
copies are lattice artifacts, we find that the number of these 'Gribov' copies
diverges in the continuum limit. On a torus, we show that lattice artifacts can
lead to the wrong evaluation of the gauge-invariant correlation length, when
measured via a gauge-fixed procedure; this bias does not disappear in the
continuum limit. We then present a new global approach, based on Hodge
decomposition of the gauge field, which produces a unique smooth field in
Landau gauge, and is economically powered by the FFT. We also discuss the use
of this method for examining topological objects, and its extensions to
non-abelian gauge fields.


title: Partition Function Zeros in Non-compact QED

abstract:
  The lowest zeros of the lattice partition function for non-compact QED are
found in the complex fermion mass plane on $6^4$, $8^4$ and $10^4$ lattices at
intermediate values of the coupling. The scaling of the low lying zeros with
lattice size is analysed.


title: Quenched results on $B$ Mesons with NRQCD

abstract:
  Preliminary results on spectrum and decay constant of $B$ mesons from a
quenched simulation at $\beta = 6.0$ on an $16^3\times48$ lattice are
discussed. The heavy quark has been implemented using both an NRQCD and the
static formulation, the light one with a clover improved Wilson formulation.
Both the NRQCD Hamiltonian and the heavy-light current consistently include
terms of $O(1/M_{Q})$, the inverse heavy quark mass.


title: A numerical attempt on the Chiral Schwinger Model

abstract:
  The chiral Schwinger model is formulated in the wilson-fermion formulation on
the lattice and then simulated by the complex langevin algorithm. The
simulation is done both without and with gauge fixing to the Lorentz gauge for
the compact gauge links. Some preliminary results are presented which indicate
that the complex langevin is well behaving with the complex chiral fermion
determinant.


title: More on random-lattice fermions

abstract:
  The lattice fermion determinants, in a given background gauge field, are
evaluated for two different kinds of random lattices and compared to those of
naive and wilson fermions in the continuum limit. While the fermion doubling is
confirmed on one kind of lattices, there is positive evidence that it may be
absent for the other, at least for vector interactions in two dimensions.
Combined with previous studies, arbitrary randomness by itself is shown to be
not a sufficient condition to remove the fermion doublers.


title: Renormalons on the Lattice

abstract:
  We present the first lattice calculation of the B-meson binding energy
$\labar$ and of the kinetic energy $\lambda_1/2 m_Q$ of the heavy-quark inside
the pseudoscalar B-meson. In order to cancel the ambiguities due to the
ultraviolet renormalons present in the operator matrix elements, this
calculation has required the non-perturbative subtraction of the power
divergences present in the Lagrangian operator $\energy$ and in the kinetic
energy operator $\kkinetic$. The non-perturbative renormalization of the
relevant operators has been implemented by imposing suitable renormalization
conditions on quark matrix elements in the Landau gauge.


title: Precision $\Upsilon$ and $J/\Psi$ spectroscopy with lattice NRQCD

abstract:
  We present new results on $\Upsilon$ and $J/\Psi$ spectroscopy using Lattice
NRQCD. Charmonium results at quenched $\beta$ = 5.7 show agreement with
experiment within understood systematic errors. We compare bottomonium results
at quenched $\beta$s 6.0 and 5.7 and show that the $1P-1S$ splitting scales
with $\Lambda_V$, provided a correction is applied for the $\cal{O}$$(a^{2})$
errors inherent in the gluon field configurations. There is a clear scale
difference between charmonium and bottomonium results in the quenched
approximation. We compare quenched results at $\beta$=6.0 for bottomonium with
those obtained on HEMCGC configurations at $\beta$=5.6 using 2 light flavours
of dynamical quarks. We show that extrapolations to $n_f$ = 3 are consistent
with experiment for the ratio of the $2S-1S$ splitting to that of the $1P-1S$.
We extract a value for the $\Upsilon$-$\eta_b$ splitting extrapolated to $n_f$
= 3.


title: Evidence for a Critical Behavior in $4D$ Pure Compact QED

abstract:
  We present evidence about a critical behavior of $4D$ compact QED (CQED) pure
gauge theory. Regularizing the theory on lattices homotopic to a sphere, we
present evidence for a critical, i.e. second order like behavior at the
deconfinement phase transition for certain values of the coupling parameter
$\gamma$.


title: Effective Scalar Theory of the Electroweak Phase Transition

abstract:
  This talk summarizes results obtained from simulating a three dimensional
pure Order Parameter (OP) model of the Electroweak Phase Transition (EWPT). Its
detailed presentation appears in \cite{karsch}.


title: The Forgotten Potts Models

abstract:
  The q=10 and q=200 state Potts models coupled to 2d gravity are investigated
numerically and shown to have continuous phase transitions, contrary to their
behavior on a regular lattice. Critical exponents are extracted and possible
critical behavior for general q-state Potts models coupled to gravity is
discussed.


title:
Finite Temperature Transition in Two Flavor QCD with Renormalization
  Group Improved Action

abstract:
  The finite temperature transition or crossover in QCD with two degenerate
Wilson quarks is investigated using a renormalization group improved action. At
$\beta=2.0$ and 2.1 where $a^{-1} \sim 1.0-1.2$ GeV, the expectation value of
the Polyakov loop and the pion screening mass on an $8^3 \times 4$ lattice vary
smoothly with the hopping parameter through the transition/crossover. The quark
screening mass in the high temperature phase agrees well with that in the low
temperature phase calculated on an $8^4$ lattice. The smooth transition of the
observables is totally different from the sharp transition found for the
standard action at $\beta=5.0$ and 5.1 where $a^{-1}$ is also $1.0-1.2$ GeV.


title: Towards a Lattice Calculation of the Nucleon Structure Functions

abstract:
  We have initiated a programme to compute the lower moments of the unpolarised
and polarised deep inelastic structure functions of the nucleon in the quenched
approximation. We review our progress to date.


title:
On strongly coupled quenched QED4, again: chiral symmetry breaking,
  Goldstone mechanism and the nature of the continuum limit

abstract:
  We explore the possibility of a trivial continuum limit of strongly coupled
quenched QED4 by contrasting our results with a Nambu--Jona Lasinio equation of
state. The data does not compare favorably with such scenario. We study in
detail the interplay of chiral symmetry breaking with the Goldstone mechanism,
and clarify some puzzling features of past results.


title: Quenched QCD at finite density: $g=1$ and $g=\infty$

abstract:
  We report on our ongoing effort to understand quenched lattice QCD at finite
baryon number density. The quenched theory is sensitive to the baryon mass both
at strong coupling and in the scaling region. However, we find that the
quenched model is pathological for $\mu > m_\pi/2$ at $\beta= 6.0$, in
agreement with past Lanczos analyses of the Dirac operator.


title: Towards a perfect fixed point action for SU(3) gauge theory

abstract:
  We present an overview of the construction and testing of actions for SU(3)
gauge theory which are approximate fixed points of renormalization group
equations (at $\beta\rightarrow \infty$). Such actions are candidates for use
in numerical simulations on coarse lattices.


title: $\pi N \sigma$ Term and Quark Spin Content of the Nucleon

abstract:
  We report results of our calculation on the $\pi N\sigma$ term and quark spin
content of the nucleon on the quenched $16^3 \times 24$ lattice at $\beta =
6.0$. The disconnected insertions which involve contributions from the sea
quarks are calculated with the stochastic $Z_2$ noise algorithm. As a physical
test of the algorithm, we show that the forward matrix elements of the vector
and pseudoscalar currents for the disconnected insertions are indeed consistent
with the known results of zero. We tried the Wuppertal smeared source and found
it to be more noisy than the point source. With unrenormalized
$m_q=4.42(17)$MeV, we find the $\pi N\sigma$ term to be $39.2\pm 5.2$ MeV. The
strange quark condensate in the nucleon is large, i.e. $\langle
N|\bar{s}s|N\rangle = 1.16 \pm 0.54$. For the quark spin content, we find
$\Delta u =0.78\pm 0.07$, $\Delta d =-0.42\pm 0.07$, and $\Delta s = -0.13\pm
0.06$. The flavor-singlet axial charge $g_A^1 = \Delta \Sigma =0.22\pm 0.09 $.


title: Gauge Theory in d=2+1 at High Temperature: Z_N interface

abstract:
  We calculate on the lattice the interface tension in the SU(2) pure gauge
theory in d=2+1 at high temperature. The result is compared to the perturbative
prediction. The agreement confirms applicability of the perturbation theory in
this case.


title: Finite Temperature QCD Interfaces Out of Equilibrium

abstract:
  The properties of interfaces in non-equilibrium situations are studied by
constructing a density matrix with a space-dependent temperature. The
temperature gradient gives rise to new terms in the equation for the order
parameter. Surface terms induced in effective actions by abrupt temperature
changes provide a natural theoretical framework for understanding the occurence
of both continuous and discontinuous behavior in the order parameter. Monte
Carlo simulation of pure QCD shows both kinds of interfacial behavior.
Perturbation theory predicts a universal profile in the high temperature phase,
which can be tested by Monte Carlo simulation.


title: Low-Temperature Series for Ising Model by Finite-Lattice Method

abstract:
  We have calculated the low-temperature series for the second moment of the
correlation function in $d=3$ Ising model to order $u^{26}$ and for the free
energy of Absolute Value Solid-on-Solid (ASOS) model to order $u^{23}$, using
the finite-lattice method.


title: Semi-Leptonic Decays of $B$-Mesons

abstract:
  Form factors relevant for semi-leptonic $B\to D,\ D^*$ decays are obtained in
quenched lattice QCD. Tests of heavy-quark symmetry as well as determinations
of the Isgur-Wise function and $|V_{cb}|$ are presented.


title:
Probing the Continuum Limit in Non-Compact QED: New Results on Large
  Lattices

abstract:
  We present new Monte Carlo results in non-compact lattice QED with staggered
fermions down to m_0 = 0.005. This extends our previous investigations on the
nature of the continuum limit of QED.


title:
Point-to-point Hadron Correlation Functions using the
  Sheikholeslami--Wohlert Action

abstract:
  We calculate correlations between hadronic current operators as a function of
their spatial separation, in a quenched lattice QCD simulation at $\beta=6.2$
on a $24^3\times48$ lattice. The lattice fermion formulation used is that due
to Sheikholeslami and Wohlert. The correlation functions are then compared with
the corresponding quantities calculated in the infinite volume chiral limit of
the non-interacting theory. The ratio of the two quantities contains
information on the vacuum structure of QCD. Results obtained are consistent
with previous studies, and with known hadron phenomenology, although certain
features of the fermion action used make it impossible to probe the $r\to0$
limit directly, thus limiting the accuracy possible.


title: Topological structures and phases in U(1) gauge theory

abstract:
  We show that topological properties of minimal Dirac sheets as well as of
currents lines characterize the phases unambiguously. We obtain the minimal
sheets reliably by a suitable simulated-annealing procedure.


title: Dynamical-parameter algorithm for U(1) gauge theory

abstract:
  We present an algorithm for Monte Carlo simulations which is able to overcome
the suppression of transitions between the phases in compact U(1) lattice gauge
theory in 4 dimensions.


title: The status of US Teraflops-scale projects

abstract:
  The current status of United States projects pursuing Teraflops-scale
computing resources for lattice field theory is discussed. Two projects are in
existence at this time: the Multidisciplinary Teraflops Project, incorporating
the physicists of the QCD Teraflops Collaboration, and a smaller project,
centered at Columbia, involving the design and construction of a 0.8 Teraflops
computer primarily for QCD.


title: Hadron masses on a 16^3 x 40 lattice at \beta = 5.7

abstract:
  We report on the hadron mass spectrum obtained on a 16^3 x 40 lattice in full
QCD at \beta = 5.7 using two flavors of staggered fermions with m a = 0.01. We
study the effective mass plateaus for different sized sources. Our mass results
are slightly lighter than our earlier 16^3 x 32 calculation. The Landau gauge
\Delta is quite different from the Coulomb gauge \Delta.


title: Critical Behavior of the chiral condensate at the QCD phase transition

abstract:
  We study the critical behavior of the chiral condensate near the QCD phase
transition in the background of two fixed light dynamical (sea) quarks. We
study the condensate for $5.245 \leq \beta \leq 5.3$ and $10^{-10} \leq m_{val}
\leq 10$


title: An Effective Action for Finite Temperature QCD with Fermions

abstract:
  Using lattice perturbation theory at finite temperature, we compute for
staggered fermions the one-loop fermionic corrections to the spatial and
temporal plaquette couplings as well as the leading $Z_N$ symmetry breaking
coupling. Numerical and analytical considerations indicate that the finite
temperature corrections to the zero-temperature calculation of A. Hasenfratz
and T. DeGrand are small for small values of $\kappa = {1\over 2m_F}$, but
become significant for intermediate values of $\kappa$. The effect of these
finite temperature corrections is to ruin the agreement of the
Hasenfratz-DeGrand calculation with Monte Carlo data. We conjecture that the
finite temperature corrections are suppressed nonperturbatively at low
temperatures, resolving this apparent disagreement. The $Z_N$ symmetry breaking
coupling is small; we argue that it may change the order of the transition
while having little effect on the critical value of $\beta$.


title: Hot electroweak matter

abstract:
  This talk summarises recent results on lattice Monte Carlo studies of finite
T electroweak phase transition. Particular attention is given to the 3d
effective theory approach, replacing the full 4d theory by a three dimensional
effective theory of the modes constant in imaginary time.


title: Quantum gravity and spin systems

abstract:
  A new method for nonperturbative investigations of quantum gravity is
presented in which the simplicial path integral is approximated by the
partition function of a spin system. This facilitates analytical and numerical
computations considerably. In two dimensions equivalence to an Ising model with
ternary couplings is recovered. First simulations in four dimensions indicate
strong similarities to the phase structure of original Regge theory.


title: Monopole density around static color sources

abstract:
  We analyze the vacuum structure with respect to magnetic monopoles of
quenched QCD in the presence of static color sources. Distributions of the
monopole density around static quarks and mesons are computed in both phases of
QCD. We observe a suppression of the monopole density in the vicinity of
external sources. In the confinement phase the density of color magnetic
monopoles is reduced along the flux tube between a static quark-antiquark pair.


title: K^0--\bar{K}^0 mixing in full lattice QCD

abstract:
  There are at least two methods to calculate $ B_K $ with staggered fermions:
one is the two spin trace formalism and the other is the one spin trace
formalism. We have performed numerical simulations on a $ 16^3 \times 40 $
lattice in full QCD with $ \beta = 5.7 $ and a dynamical quark mass 0.01 in
lattice units. We try various sources to select only the pseudo-Goldstone
bosons and compare the various results.


title:
Complex-Temperature Singularities in the $d=2$ Ising Model. III.
  Honeycomb Lattice

abstract:
  We study complex-temperature properties of the uniform and staggered
susceptibilities $\chi$ and $\chi^{(a)}$ of the Ising model on the honeycomb
lattice. From an analysis of low-temperature series expansions, we find
evidence that $\chi$ and $\chi^{(a)}$ both have divergent singularities at the
point $z=-1 \equiv z_{\ell}$ (where $z=e^{-2K}$), with exponents
$\gamma_{\ell}'= \gamma_{\ell,a}'=5/2$. The critical amplitudes at this
singularity are calculated. Using exact results, we extract the behaviour of
the magnetisation $M$ and specific heat $C$ at complex-temperature
singularities. We find that, in addition to its zero at the physical critical
point, $M$ diverges at $z=-1$ with exponent $\beta_{\ell}=-1/4$, vanishes
continuously at $z=\pm i$ with exponent $\beta_s=3/8$, and vanishes
discontinuously elsewhere along the boundary of the complex-temperature
ferromagnetic phase. $C$ diverges at $z=-1$ with exponent $\alpha_{\ell}'=2$
and at $v=\pm i/\sqrt{3}$ (where $v = \tanh K$) with exponent $\alpha_e=1$, and
diverges logarithmically at $z=\pm i$. We find that the exponent relation
$\alpha'+2\beta+\gamma'=2$ is violated at $z=-1$; the right-hand side is 4
rather than 2. The connections of these results with complex-temperature
properties of the Ising model on the triangular lattice are discussed.


title: The Perturbative Method Fails in Non-Abelian Models

abstract:
  It is shown that perturbation theory in $2D$ nonlinear $\sigma$-models as
well gauge theories in dimension $D\geq 2$ produces answers that depend on
boundary conditions even after the infinite volume limit has been taken. This
unphysical phenomenon occurs only in the non-Abelian versions of those models,
starting at $O(1/\beta^2)$. It is not present in the true (nonperturbatively
defined) models and represents a failure of the perturbative method. It is
related to a hitherto unnoticed type of low-lying excitation, dubbed
super-instanton, that dominates the low-temperature (= weak coupling) regime of
these models.


title: Chiral limit of QCD

abstract:
  This talk contains an analysis of quenched chiral perturbation theory and its
consequences. The chiral behavior of a number of quantities such as the pion
mass $m_\pi^2$, the Bernard-Golterman ratios $R$ and $\chi$, the masses of
nucleons, and the kaon B-parameter are examined to see if the singular terms
induced by the additional Goldstone boson,$\eta'$, are visible in present data.
The overall conclusion (different from what I presented at the lattice meeting)
of this analysis is that, with some caveats on the extra terms induced by
$\eta'$ loops, the standard expressions break down when extrapolating the
quenched data with $m_q < m_s/2$ to physical light quarks. I then show that due
to the single and double poles in the quenched $\eta'$, the axial charge of the
proton cannot be calculated using the Adler-Bell-Jackiw anomaly condition. I
conclude with a review of the status of the calculation of light quark masses
from lattice QCD.


title: Efficient Hadronic Operators in Lattice Gauge Theory

abstract:
  We study operators to create hadronic states made of light quarks in quenched
lattice gauge theory. We construct non-local gauge-invariant operators which
provide information about the spatial extent of the ground state and excited
states. The efficiency of the operators is shown by looking at the wave
function of the first excited state, which has a node as a function of the
spatial extent of the operator. This allows one to obtain an uncontaminated
ground state for hadrons.


title:
Strong coupling expansion for scattering phases in hamiltonian lattice
  field theories - II. SU(2) gauge theory in (2+1) dimensions

abstract:
  A recently proposed method for a strong coupling analysis of scattering
phenomena in hamiltonian lattice field theories is applied to the $\SU2$
Yang-Mills model in $(2+1)$ dimensions. The calculation is performed up to
second order in the hopping parameter. All relevant quantities that
characterize the collision between the lightest glueballs in the elastic region
-- cross section, phase shifts, resonance parameters -- are determined.


title:
The Numerical Estimation of the Error Induced by the Valence
  Approximation

abstract:
  We describe a systematic expansion for full QCD. The leading term in the
expansion gives the valence approximation. The expansion reproduces full QCD if
an infinite number of higher terms are included.


title:
Numerical Simulations of an SU(2)_L x SU(2)_R-symmetric Higgs-Yukawa
  Model on the QUADRICS Q16

abstract:
  We report on our work on the SU(2)_L x SU(2)_R symmetric Higgs Yukawa Model
with mirror fermion action. Our model describes a fermion Higgs system in the
limit of vanishing gauge coupling. Setting the bare Yukawa coupling of the
mirror fermions G_\chi to zero, we want to determine the triviality bounds on
the renormalized Yukawa coupling of the fermions G_{R\psi} and the scalar
self-coupling g_R on 8^3x16 and 16^3x32 lattices.


title: Theta Vacua, Confinement and the Continuum Limit

abstract:
  We investigate the dependence of the CP^3 model and of the SU(2) Yang-Mills
theory on the vacuum angle theta. The CP^3 model exhibits a first order
deconfining phase transition in theta. The critical value of theta runs from pi
in the strong coupling limit towards zero as beta is taken to infinity.
Qualitatively the same behavior is found in the SU(2) Yang-Mills theory in four
dimensions. We discuss the renormalization group trajectories. Only the line
with theta = 0 allows the cut-off to go to infinity, while the lines with theta
> 0 end on the line of first order phase transitions. Thus theta is forced to
zero in the continuum limit.


title: Can baryogenesis occur on the lattice?

abstract:
  We examine the question of how baryogenesis can occur in lattice models of
the Standard Model where there is a global $U(1)$ symmetry which is accompanied
by an exactly conserved fermion number. We demonstrate that fermion creation
and annihilation can occur in these models {\em despite} this exact fermion
number conservation, by explicitly computing the spectral flow of the
hamiltonian in the two dimensional U(1) axial model with Wilson fermions. For
comparison we also study the closely related Schwinger model where a similar
mechanism gives rise to anomalous particle creation and annihilation.


title:
Application of Multicanonical Multigrid Monte Carlo Method to the
  Two-Dimensional $\phi^4$-Model: Autocorrelations and Interface Tension

abstract:
  We discuss the recently proposed multicanonical multigrid Monte Carlo method
and apply it to the scalar $\phi^4$-model on a square lattice. To investigate
the performance of the new algorithm at the field-driven first-order phase
transitions between the two ordered phases we carefully analyze the
autocorrelations of the Monte Carlo process. Compared with standard
multicanonical simulations a real-time improvement of about one order of
magnitude is established. The interface tension between the two ordered phases
is extracted from high-statistics histograms of the magnetization applying
histogram reweighting techniques.


title:
Monte Carlo simulation of $1+1$-dimensional $\phi^4$ quantum field
  theory

abstract:
  We report results of a Monte Carlo simulation of the $\phi^4$ quantum field
theory using multigrid simulation techniques and a refined discretization
scheme. The resulting accuracy of our data allows for a significant test of an
analytical approximation based on a variational ansatz. While the variational
approximation is well reproduced for a large range of parameters we find
significant deviations for low temperatures and large couplings.


title: Fitting Correlated Hadron Mass Spectrum Data

abstract:
  We discuss fitting hadronic Green functions versus time $t$ to extract mass
values in quenched lattice QCD. These data are themselves strongly correlated
in $t$. With only a limited number of data samples, the method of minimising
correlated $\chi^2$ is unreliable. We explore several methods of modelling the
correlations among the data set by a few parameters which then give a stable
and sensible fit even if the data sample is small. In particular these models
give a reliable estimate of the goodness of fit.


title: Current Renormalisation Constants with an O(a)-improved Fermion Action

abstract:
  Using chiral Ward identities, we determine the renormalisation constants of
bilinear quark operators for the Sheikholeslami-Wohlert action lattice at
beta=6.2. The results are obtained with a high degree of accuracy. For the
vector current renormalisation constant we obtain Z_V=0.817(2)(8), where the
first error is statistical and the second is due to mass dependence of Z_V.
This is close to the perturbative value of 0.83. For the axial current
renormalisation constant we obtain Z_A = 1.045(+10 -14), significantly higher
than the value obtained in perturbation theory. This is shown to reduce the
difference between lattice estimates and the experimental values for the
pseudoscalar meson decay constants, but a significant discrepancy remains. The
ratio of pseudoscalar to scalar renormalisation constants, Z_P/Z_S, is less
well determined, but seems to be slightly lower than the perturbative value.


title: Heavy-light baryonic mass splittings from the lattice

abstract:
  We present lattice estimates of the mass of the heavy-light baryons
$\Lambda_b$ and $\Xi_b$ obtained using propagating heavy quarks. For
$\Lambda_b$ our result is $M_{\Lambda_b}=5.728 \pm 0.144 \pm 0.018$ GeV, after
extrapolation to the continuum limit and in the quenched approximation.


title: Master Wilson loop operators in large-N lattice QCD$_2$

abstract:
  An explicit solution is found for the most general independent correlation
functions in lattice QCD$_2$ with Wilson action. The large-$N$ limit of these
correlations may be used to reconstruct the eigenvalue distributions of Wilson
loop operators for arbitrary loops. Properties of these spectral densities are
discussed in the region $\beta<\beta_c={1\over 2}$.


title:
3d physics and the electroweak phase transition: a framework for lattice
  Monte Carlo analysis

abstract:
  We discuss a framework relying on both perturbative and non-perturbative
lattice computations which will be able to reliably determine the parameters of
the EW phase transition. A motivation for the use of 3d effective theory in the
lattice simulations, rather than the complete 4d one, is provided. We introduce
and compute on the 2-loop level a number of gauge-invariant order parameters --
condensates, which can be measured with high accuracy in MC simulations. The
relation between MSbar and lattice condensates is found, together with the
relation between lattice couplings and continuum parameters (the constant
physics curves). These relations are exact in the continuum limit.


title: Results from a Non-Perturbative Renormalization of Lattice Operators

abstract:
  We propose a general renormalization method, which avoids completely the use
of lattice perturbation theory. We present the results from its numerical
applications to two-fermion operators on a $16^3 \times 32$ lattice, at
$\beta=6.0$.


title: Architectural choices for the Columbia 0.8 Teraflops machine

abstract:
  We discuss the hardware design choices made in our 16K-node 0.8 Teraflops
supercomputer project, a machine architecture optimized for full QCD
calculations. The efficiency of the conjugate gradient algorithm in terms of
balance of floating-point operations, memory handling and utilization, and
communication overhead is addressed. We also discuss the technological
innovations and software tools that facilitate hardware design and what
opportunities these give to the academic community.


title: Universality, Scaling and Topology with a Modified Lattice Action

abstract:
  We examined the effect of a complete suppression of a lattice artifact, the
negative plaquettes, on physical quantities, such as the critical temperature,
the string tension, the topological charge, glueball masses, and their ratios.


title: Latest Results from Heavy Quark Simulations

abstract:
  The status of b-bbar and c-cbar calculations, numerical and analytic, are
reviewed. The extraction of alpha_s and quark masses from spectrum calculations
is discussed. The NRQCD and Improved Heavy Wilson formulations of heavy quarks
are compared, and recent calculations using a Heavy Staggered formulation are
discussed.


title: Strong coupling expansion of chiral models

abstract:
  A general precedure is outlined for an algorithmic implementation of the
strong coupling expansion of lattice chiral models on arbitrary lattices. A
symbolic character expansion in terms of connected values of group integrals on
skeleton diagrams may be obtained by a fully computerized approach.


title: Asymptotic scaling from strong coupling in 2-d lattice chiral models

abstract:
  Two dimensional $N=\infty$ lattice chiral models are investigate by a strong
coupling analysis. Strong coupling expansion turns out to be predictive for the
evaluation of continuum physical quantities, to the point of showing asymptotic
scaling (within 5\%).


title: Strong-coupling expansion of chiral models

abstract:
  The strong-coupling character expansion of lattice models is reanalyzed in
the perspective of its complete algorithmization. The geometric problem of
identifying, counting, and grouping together all possible contributions is
disentangled from the group-theoretical problem of weighting them properly. The
first problem is completely solved for all spin models admitting a
character-like expansion and for arbitrary lattice connectivity. The second
problem is reduced to the evaluation of a class of invariant group integrals
defined on simple graphs. Since these integrals only depend on the global
symmetry of the model, results obtained for principal chiral models can be used
without modifications in lattice gauge theories. By applying the techniques and
results obtained we study the two-dimensional principal chiral models on the
square and honeycomb lattice. These models are a prototype field theory sharing
with QCD many properties. Strong-coupling expansions for Green's functions are
derived up to 15th and 20th order respectively. Large-$N$ and $N=\infty$
results are presented explicitly. Related papers are devoted to a discussion of
the results.


title: Running coupling constant and correlation length from Wilson loops

abstract:
  We consider a definition of the QCD running coupling constant $\alpha(\mu)$
related to Wilson loops of size $r{\times}t$ with arbitrary fixed $t/r$. The
schemes defined by these couplings are very close to the $\overline{\rm MS}$
scheme (i.e.\ the one-loop perturbative correction to the coupling is small)
for all values of $t/r$; in the $t/r\to\infty$ limit, the ``$q\bar q$ force''
scheme is recovered, where the coupling constant is related to the
quark-antiquark force. We discuss the possibility of applying finite-size
scaling techniques to the Monte Carlo evaluation of $\alpha(\mu)$ up to very
large momentum scales. We propose a definition of correlation length, also
related to Wilson loops, which should make such a computation feasible.


title: Nonperturbative ``Lattice Perturbation Theory''

abstract:
  We discuss a program for replacing standard perturbative methods with Monte
Carlo simulations in short distance lattice gauge theory calculations.


title: Strong coupling analysis of the large-N 2-d lattice chiral models

abstract:
  Two dimensional large-N chiral models on the square and honeycomb lattices
are investigated by a strong coupling analysis. Strong coupling expansion turns
out to be predictive for the evaluation of continuum physical quantities, to
the point of showing asymptotic scaling. Indeed in the strong coupling region a
quite large range of beta values exists where the fundamental mass agrees,
within about 5% on the square lattice and about 10% on the honeycomb lattice,
with the continuum predictions in the %%energy scheme.


title: Large-N phase transition in lattice 2-d principal chiral models

abstract:
  We investigate the large-N critical behavior of 2-d lattice chiral models by
Monte Carlo simulations of U(N) and SU(N) groups at large N. Numerical results
confirm strong coupling analyses, i.e. the existence of a large-N second order
phase transition at a finite $\beta_c$.


title: Phase Diagram of QCD at Finite Temperatures with Wilson Fermions

abstract:
  Phase diagram of QCD with Wilson fermions for various numbers of flavors
$N_F$ is discussed. Our simulations mainly performed on a lattice with the
temporal size $N_t =4$ indicate the following: The chiral phase transition is
of first order when $3 \le N_F \le 6$, while it is continuous when $N_F=2$. For
the realistic case of massless u and d quarks and the strange quark with $m_q =
150$ MeV, the phase transition is first order. The sharp transition in the
intermediate mass region for $N_F=2$ at $N_t=4$ observed by the MILC group
disappears when an RG improvement is made for the pure gauge action.


title: Two dimensional twisted chiral fermions on the lattice

abstract:
  It is shown that the lattice overlap correctly reproduces the chiral
determinant on a two dimensional torus in the presence of nontrivial background
Polyakov loop variables.


title:
Complex-Temperature Properties of the 2D Ising Model with $\beta H = \pm
  i \pi/2$

abstract:
  We study the complex-temperature properties of a rare example of a
statistical mechanical model which is exactly solvable in an external
symmetry-breaking field, namely, the Ising model on the square lattice with
$\beta H = \pm i \pi/2$. This model was solved by Lee and Yang \cite{ly}. We
first determine the complex-temperature phases and their boundaries. From a
low-temperature, high-field series expansion of the partition function, we
extract the low-temperature series for the susceptibility $\chi$ to
$O(u^{23})$, where $u=e^{-4K}$. Analysing this series, we conclude that $\chi$
has divergent singularities (i) at $u=u_e=-(3-2^{3/2})$ with exponent
$\gamma_e'=5/4$, (ii) at $u=1$, with exponent $\gamma_1'=5/2$, and (iii) at
$u=u_s=-1$, with exponent $\gamma_s'=1$. We also extract a shorter series for
the staggered susceptibility and investigate its singularities. Using the exact
result of Lee and Yang for the free energy, we calculate the specific heat and
determine its complex-temperature singularities. We also carry this out for the
uniform and staggered magnetisation.


title: Status of the CP-PACS Project

abstract:
  The CP-PACS Project, which started in April 1992, is a five-year plan to
develop a massively parallel computer for carrying out research in
computational physics with primary emphasis on lattice QCD. This article
describes the architectural design of the CP-PACS computer, the entire
computing system including the front end and mass storage, and results of
benchmarks for the expected performance for lattice QCD applications.


title: Monopole effects on Polyakov loop and its gauge independence in QCD

abstract:
  Monte-Carlo simulations of abelian projection in $T \neq 0$ pure lattice QCD
show that
  1)\ Polyakov loops written in terms of abelian link fields alone play a role
of an order parameter of deconfinement transition
  2)\ the abelian Polyakov loops are decomposed into contributions from Dirac
strings of monopoles and from photons
  3)\ vanishing of the abelian Polyakov loops in the confinement phase is due
to the Dirac strings alone and the photons give a finite contribution in both
phases.
  Moreover, these results appear to hold good in unitary gauges. This suggests
that monopole condensation as the color confinement mechanism is gauge
independent.


title: Monopoles and deconfinement transition in finite temperature $SU(2)$ QCD

abstract:
  We investigate the role of monopoles in the deconfinement transition of
finite temperature $SU(2)$ QCD in the maximally abelian gauge. In the
confinement phase a long monopole loop exists in each configuration, whereas no
long loop exists in the deep deconfinement region. Balancing of the energy and
the entropy of loops of the maximally extended monopoles can explain the
occurrence of the deconfinement transition.


title: Low-Temperature Expansion of the Free Energy in ASOS Model

abstract:
  We calculate the low-temperature series of the free energy in absolute-value
solid-on-solid (ASOS) model to order $u^{23}$ using finite-lattice method. The
property of the obtained series and the behavior of their Pad\'e approximants
confirms us that the roughening transition in ASOS model is of
Kosterlitz-Thouless type.


title: Duals of nonabelian gauge theories in $D$ dimensions

abstract:
  The dual of an arbitrary $D$-dimensional nonabelian lattice gauge theory,
obtained after character expansion and integration over the gauge group, is
shown to be a {\em local} lattice theory in the eigenspace of the Casimir
operators. For $D\leq4$ we also provide the explicit form of the action as a
product of character expansion coefficients and Racah coefficients. The
representation can be used to facilitate strong coupling expansions.
Furthermore, the possibility of simulations, at weak coupling, in the dual
representation, is also discussed.


title:
Monte Carlo and Renormalization Group Effective Potentials in Scalar
  Field Theories

abstract:
  We study constraint effective potentials for various strongly interacting
$\phi^4$ theories. Renormalization group (RG) equations for these quantities
are discussed and a heuristic development of a commonly used RG approximation
is presented which stresses the relationships among the loop expansion, the
Schwinger-Dyson method and the renormalization group approach. We extend the
standard RG treatment to account explicitly for finite lattice effects.
Constraint effective potentials are then evaluated using Monte Carlo (MC)
techniques and careful comparisons are made with RG calculations. Explicit
treatment of finite lattice effects is found to be essential in achieving
quantitative agreement with the MC effective potentials. Excellent agreement is
demonstrated for $d=3$ and $d=4$, O(1) and O(2) cases in both symmetric and
broken phases.


title: QCD Thermodynamics at $N_t=8$ and 12

abstract:
  We present results from studies of high temperature QCD with two flavors of
Kogut-Susskind quarks on $16^3\times 8$ lattices at a quark mass of
$am_q=0.00625$ and on $24^3\times 12$ lattices at quark masses $am_q=0.008$ and
0.016. The value of the crossover temperature is consistent with that obtained
on coarser lattices and/or at larger quark masses. Results are presented for
the chiral order parameter and for the baryon number susceptibility.


title: Noncompact Gauge-Invariant Simulations of U(1), SU(2), and SU(3)

abstract:
  We have applied a new gauge-invariant, noncompact, Monte Carlo method to
simulate the $U(1)$, $SU(2)$, and $SU(3)$ gauge theories on $8^4$ and $12^4$
lattices. The Creutz ratios of the Wilson loops agree with the exact results
for $U(1)$ for $\beta \ge 0.5$ apart from a renormalization of the charge. The
$SU(2)$ and $SU(3)$ Creutz ratios robustly display quark confinement at $\beta
= 0.5$ and $\beta = 2$, respectively. At much weaker coupling, the $SU(2)$ and
$SU(3)$ Creutz ratios agree with perturbation theory after a renormalization of
the coupling constant. For $SU(3)$ the scaling window is near $ \beta = 2 $,
and the relation between the string tension $\sigma $ and our lattice QCD
parameter $ \Lambda_L $ is $\sqrt{\sigma} \approx 5 \Lambda_L$.


title: Hubbard Model with Luscher fermions

abstract:
  First applications of the new algorithm simulating dynamical fermions are
reported. The method reproduces previous results obtained with different
techniques.


title: Dependence of Lattice Hadron Masses on External Magnetic Fields

abstract:
  We study the variation of the hadron masses in the presence of external
magnetic fields of strength of the order of the masses themselves. We identify
the main factors affecting the lattice simulation results: - the boundary
discontinuities for $eB << 2\pi / L^2 a^2$. - the SU(6) choice of the hadron
wave-function. We confirm qualitatively the earlier theoretical ansatz on the
linear behaviour of the masses with the magnetic field and, as a by-product, we
improve the lattice measurements of the nucleon magnetic moments. However our
systematic and statistical errors preclude us from measuring the theoretically
predicted field strength at which the proton becomes heavier than the neutron.


title: Improved Currents for Heavy Quarks

abstract:
  We discuss lattice artifacts for matrix elements of hadrons containing one or
more heavy quark. In particular, we analyze interrelations between lattice
artifacts and the $1/m_Q$ expansion. The implications for calculations of
heavy-light decay constants and of semi-leptonic form factors are discussed.


title: First order phase transitions of spin systems

abstract:
  I review some numerical ways to determine the parameters of systems close to
a first order phase transition point: energy and specific heat of the
coexisting phases and interface tension. Numerical examples are given for the
2-d $q$ states Potts model.


title:
The Ising transition in 2D simplicial quantum gravity - can Regge
  calculus be right?

abstract:
  We report a high statistics simulation of Ising spins coupled to 2D quantum
gravity in the Regge calculus approach using triangulated tori with up to
$512^2$ vertices. For the constant area ensemble and the $dl/l$ functional
measure we definitively can exclude the critical exponents of the Ising phase
transition as predicted for dynamically triangulated surfaces. We rather find
clear evidence that the critical exponents agree with the Onsager values for
static regular lattices, independent of the coupling strength of an $R^2$
interaction term. For exploratory simulations using the lattice version of the
Misner measure the situation is less clear.


title: Measure dependence of 2D simplicial quantum gravity

abstract:
  We study pure 2D Euclidean quantum gravity with $R^2$ interaction on
spherical lattices, employing Regge's formulation. We attempt to measure the
string susceptibility exponent $\gamma_{\rm str}$ by using a finite-size
scaling Ansatz in the expectation value of $R^2$. To check on effects of the
path integral measure we investigate two scale invariant measures, the
"computer" measure $dl/l$ and the Misner measure $dl/\sqrt A$.


title: Fractal Behaviour in the O(3) Model

abstract:
  We study domain formation in the two-dimensional O(3) model near criticality.
The fractal dimension of these domains is determined with good statistical
accuracy.


title: Finite $ma$ corrections for sea quark matrix elements on the lattice

abstract:
  We compute the $ma$ dependence of lattice renormalization factors for sea
quark matrix elements. The results differ from the $(1+ma)$ correction factor
commonly used for valence quarks and connected current insertions. We find that
for sea quarks, the correction factors are in general larger and depend
strongly on the Lorentz structure of the current under consideration. Results
are presented both for the Wilson action and for the 2-link improved action of
Hamber and Wu. Phenomenological implications are also briefly discussed in two
examples.


title: Logarithmic Corrections to Scaling in the Two Dimensional $XY$--Model

abstract:
  By expressing thermodynamic functions in terms of the edge and density of
Lee--Yang zeroes, we relate the scaling behaviour of the specific heat to that
of the zero field magnetic susceptibility in the thermodynamic limit of the
$XY$--model in two dimensions. Assuming that finite--size scaling holds, we
show that the conventional Kosterlitz--Thouless scaling predictions for these
thermodynamic functions are not mutually compatable unless they are modified by
multiplicative logarithmic corrections. We identify these logarithmic
corrections analytically in the case of the specific heat and numerically in
the case of the susceptibility. The techniques presented here are general and
can be used to check the compatibility of scaling behaviour of odd and even
thermodynamic functions in other models too.


title: Topological Density and Instantons on a Lattice

abstract:
  We present an update on the study of topological structure of QCD. Issues
addressed include a comparison between the plaquette and the geometric methods
of calculating the topological density. We show that the improved gauge action
based on sqrt(3) blocking transformation suppresses the formation of
topologically charged dislocations with low action. Using a cooling method we
identify the instantons' location, estimate their size and density, and
calculate the renormalization constant Z_Q for the plaquette method.


title: Proton Spin Structure from Lattice QCD

abstract:
  A lattice QCD calculation of the proton matrix element of the flavor singlet
axial-vector current is reported. Both the connected and disconnected
contributions are calculated, for the latter employing the variant method of
wall source without gauge fixing. From simulations in quenched QCD with the
Wilson quark action on a $16^3\times 20$ lattice at $\beta=5.7$ (the lattice
spacing $a\approx 0.14$fm), we find $\Delta\Sigma=\Delta u+\Delta d+\Delta
s=+0.638(54)-0.347(46)-0.109(30) = +0.18(10)$ with the disconnected
contribution to $\Delta u$ and $\Delta d$ equal to $-0.119(44)$, which is
reasonably consistent with the experiment.


title: Finite Density Results for Wilson Fermions Using the Volume Method

abstract:
  Nonzero chemical potential studies with Wilson fermions should avoid the
proliferation of flavor-equivalent nucleon states encountered with staggered
formulation of fermions. However, conventional wisdom has been that finite
baryon density calculations with Wilson fermions will be prohibitively
expensive. We demonstrate that the volume method applied to Wilson fermions
gives surprisingly stable results on a small number of configurations. It is
pointed out that this method may be applied to any local or nonlocal gauge
invariant quantity. Some illustrative results for $<\overline{\psi}\psi>$ and
$< J >$ at various values of $\mu$ in a quenched lattice simulation are given.


title: QCD AT FINITE BARYON DENSITY WITH t-ASYMMETRIC FERMIONS

abstract:
  Susskind's continuous-time fermions, with two flavours, can be latticized
using a one-sided time derivative. We are presently investigating the
interacting case, where we hope to find the onset at finite $\mu$ at the right
place due to the reduced number of flavours. As for these fermions there is
only a discrete chiral symmetry left over, the lightness of pions in the broken
phase has to be investigated.


title: Semileptonic Decays of Heavy Mesons: A Status Report

abstract:
  We present intermediate results on our ongoing investigation concerning
semileptonic decays of heavy pseudoscalar mesons into pseudoscalar and vector
mesons. The corresponding formfactors are evaluated at several momenta and
appropriate combinations of four light and four heavy quarks, which are chosen
to allow for an extrapolation into the B Meson region. In order to obtain clear
groundstate signals we apply gauge invariant ``Wuppertal'' smearing to the
quarks. The analysis is based on 32 quenched gauge configurations of size $24^3
\times 64$ at $\beta=6.3$, with Wilson fermions.


title: First-Order Signals in Compact QED with Monopole Suppressed Boundaries

abstract:
  Pure gauge compact QED on hypercubic lattices is considered with periodically
closed monopole currents suppressed. We compute observables on sublattices
which are nested around the centre of the lattice in order to locate regions
where translation symmetry is approximately recovered. Our Monte Carlo
simulations on $24^4$-lattices give indications for a first-order nature of the
U(1) phase transition.


title: $B\to K^* \gamma$ decay on APE

abstract:
  We present results for the radiative decay $B\to K^* \gamma$, obtained by
using the Clover action at $\beta = 6.0$ on APE. The compatibility between the
scaling laws predicted by the Heavy Quark Effective Theory (HQET) and pole
dominance is discussed. The final result depends crucially on the assumed
$q^2$-dependence of the form factors.


title: Phenomenology from 100 large lattices

abstract:
  We present a status report on simulations being done on $32^3 \times 64$
lattices at $\beta = 6.0$ using quenched Wilson fermions. Phenomenologically
relevant results for the spectrum, decay constants, the kaon B-parameter $B_K$,
$B_7$, $B_8$, semi-leptonic and $B\to K^* \gamma$ form factors are given based
on a statistical sample of 100 configurations.


title: Prospects of Solving Grand Challenge Problems

abstract:
  The recent woes of the supercomputer industry and changes in federal funding
have caused some scientists to re-evaluate the means by which they hope to
solve Grand Challenge problems. I evaluate the potential of Massively Parallel
Processors (MPP) within this context and the state of today's MPP. I stress
that for solving large-scale problems MPP are crucial and that it is essential
to seek a balance between CPU performance, memory access time, inter-node
communications, and I/O. To achieve this it is important to preserve certain
characteristics of the hardware while selecting the hottest processor to design
the machine around. I emphasize that for long term stability and growth of
parallel computing priority should be given to standardizing software so that
the same code can run on different platforms and on machines ranging from
clusters of workstations to MPP.


title: Measuring the Hausdorff Dimension of Quantum Mechanical Paths

abstract:
  We measure the propagator length in imaginary time quantum mechanics by Monte
Carlo simulation on a lattice and extract the Hausdorff dimension $d_{H}$. We
find that all local potentials fall into the same universality class giving
$d_{H}=2$ like the free motion. A velocity dependent action ($S \propto \int dt
\mid \vec{v} \mid^{\alpha}$) in the path integral (e.g. electrons moving in
solids, or Brueckner's theory of nuclear matter) yields $d_{H}=\frac{\alpha
}{\alpha - 1}$ if $\alpha > 2$ and $d_{H}=2$ if $\alpha \leq 2$. We discuss the
relevance of fractal pathes in solid state physics and in $QFT$, in particular
for the Wilson loop in $QCD$.


title: Entropy per Baryon in Strong Coupling QCD

abstract:
  The entropy per baryon is studied in the strong coupling large dimension $d$
limit of lattice QCD with staggered fermions. The partition function is
calculated for non-zero chemical potential and temperature using the $1/d$
expansion. It is found that the entropy per baryon ratio is almost continuous
across the transition from the the quark-gluon to the hadronic phase. The
relevance of these results for heavy ion collisions is discussed.


title: Study of the Decoupling of Heavy Fermions in a Z_2 Scalar-Fermion Model

abstract:
  According to one-loop perturbation theory, fermions whose masses are totally
generated from Yukawa couplings do not decouple in the heavy mass limit. We
investigate this issue nonperturbatively in a 4-dimensional $Z_2$
scalar-fermion model with staggered fermions. Our data at intermediate and
stronger Yukawa couplings on $8^4$ and $12^4$ lattices suggest the
nondecoupling of heavy fermions as predicted from one-loop calculation.
However, at the strongest Yukawa coupling where a possible multi-critical point
may come into play, we cannot be conclusive.


title:
On the Interplay of Monopoles and Chiral Symmetry Breaking in
  Non-Compact Lattice QED

abstract:
  Non-compact lattice QED is simulated for various numbers of fermion species
$N_f$ ranging from 8 through 40 by the exact Hybrid Monte Carlo algorithm. Over
this range of $N_f$, chiral symmetry breaking is found to be strongly
correlated with the effective monopoles in the theory. For $N_f$ between 8 and
16 the chiral symmetry breaking and monopole percolation transitions are second
order and coincident. Assuming powerlaw critical behavior, the correlation
length exponent for the chiral transition is identical to that of monopole
percolation. This result supports the conjecture that monopole percolation
``drives" the nontrivial chiral transition. For $N_f$ between 20 and 32, the
monopoles experience a first order condensation transition coincident with a
first order chiral transition. For $N_f$ as large as 40 both transitions are
strongly suppressed. The data at large $N_f (N_f \mathrel {\mathpalette \vereq
>} 20)$ is interpreted in terms of a strongly interacting monopole gas-liquid
transition.


title: The Heavy Quark Masses from Quarkonia

abstract:
  We report on the status of the determination of the heavy quark masses from
our calculation of the quarkonia spectra. All sources of systematic errors that
enter the quark mass determination are accounted for. We explicitly keep $ma
\neq 0$ in the perturbative calculation relating the bare lattice mass to a
renormalized mass. Our results are still preliminary.


title: Monopole currents and Dirac sheets in U(1) lattice gauge theory

abstract:
  We show that the phases of the 4-dimensional compact U(1) lattice gauge
theory are unambiguously characterized by the topological properties of minimal
Dirac sheets as well as of monopole currents lines. We obtain the minimal
sheets by a simulated-annealing procedure. Our results indicate that the
equivalence classes of sheet structures are the physical relevant quantities
and that intersections are not important. In conclusion we get a
percolation-type view of the phases which holds beyond the particular boundary
conditions used.


title: Hadron Scattering Lengths in Lattice QCD

abstract:
  Lattice QCD calculation of s-wave hadron scattering lengths in the channels
\pi-\pi, \pi-N, K-N, {\bar K}-N and N-N is carried out in the quenched QCD at
$\beta=6/g^2=5.7$. A variant of the method of wall sourceis developed for this
purpose, which reduces the computer time by a factor L^3 on an L^3xT lattice
compared to the conventional point source method and avoids the Fierz mixing
problem. A version of the method in which gauge configurations are not fixed to
any gauge can be extended to calculate disconnected quark loop con- tributions
in hadron two- and three-point functions. An analytical estimate of statistical
errors for this method is worked out, and the magnitude of errors without and
with gauge fixing is compared for the case of \pi-\pi four-point functions
calculated with the KS quark action. For \pi-\pi scattering both I=0 and 2
scattering lengths are evaluated using the KS and Wilson quark actions on a
12^3x20 lattice. For the same size of lattice, \pi-N, K-N and {\bar K}-N
scattering lenghts are calculated with the Wilson quark action. For the \pi-\pi
and \pi-N cases simulation results are consistent with the predictions of
current algebra and PCAC within one to two standard deviations up to quite
heavy quark masses corresponding to $m_\pi/m_\rho\approx 0.74$, while for the
K-N and {\bar K}-N cases the agreement is within a factor of two. For N-N scat-
tering simulations with the Wilson action on a 20^4 lattice with heavy quarks
with $m_\pi/m_\rho\approx 0.74-0.95$, where the deuteron is expected to become
unbound from a phenomenological study with one-boson exchange potentials, show
that the nucleon-nucleon force is attractive for both spin triplet and singlet
channels, and that the scattering lengths are substantially larger compared to
those for the \pi-\pi and \pi-N cases even for such heavy quarks.


title: Universal fluctuations in spectra of the lattice Dirac operator

abstract:
  Recently, Kalkreuter obtained the complete Dirac spectrum for an $SU(2)$
lattice gauge theory with dynamical staggered fermions on a $12^4$ lattice for
$\beta =1.8$ and $\beta=2.8$. We performed a statistical analysis of his data
and found that the eigenvalue correlations can be described by the Gaussian
Symplectic Ensemble. In particular, long range fluctuations are strongly
suppressed: the variance of a sequence of levels containing $n$ eigenvalues on
average is given by $\Sigma_2(n) \sim\frac 1{2\pi^2}(\log n + {\rm const.})$
instead of $\Sigma_2(n) = n$ for a random sequence of levels. Our findings are
in agreement with the anti-unitary symmetry of the lattice Dirac operator for
$N_c=2$ with staggered fermions which differs from the continuuum theory. For
$N_c = 3$ we predict that the eigenvalue correlations are given by the Gaussian
Unitary Ensemble.


title: The Chiral Extension of Lattice QCD

abstract:
  The chiral extension of Quantum Chromodynamics (XQCD) adds to the standard
lattice action explicit pseudoscalar meson fields for the chiral condensates.
With this action, it is feasible to do simulations at the chiral limit with
zero mass Goldstone modes. We review the arguments for why this is expected to
be in the same universality class as the traditional action. We present
preliminary results on convergence of XQCD for naive fermions and on the
methodology for introducing counter terms to restore chiral symmetry for Wilson
fermions.


title: Chiral Fermions on the Lattice

abstract:
  The overlap approach to chiral gauge theories on arbitrary $D$--dimensional
lattices is studied. The doubling problem and its relation to chiral anomalies
for $D=2$ and 4 is examined. In each case it is shown that the doublers can be
eliminated and the well known perturbative results for chiral anomalies can be
recovered. We also consider the multi--flavour case and give the general
criteria for the construction of anomaly free chiral gauge theories on
arbitrary lattices. We calculate the second order terms in a continuum
approximation to the overlap formula in $D$ dimensions and show that they
coincide with the bilinear part of the effective action of $D$--dimensional
Weyl fermions coupled to a background gauge field. Finally, using the same
formalism we reproduce the correct Lorentz, diffeomorphism and gauge anomalies
in the coupling of a Weyl fermion to 2--dimensional gravitational and Maxwell
fields.


title: Screening in (2+1)D pure gauge theory at high temperatures

abstract:
  We compute heavy quark potentials in pure gauge $SU(3)$ at high temperatures
in $2+1$ dimensions and confront them with expectations emerging from
perturbative calculations.


title: Hadron Properties just before Deconfinement

abstract:
  We have investigated hadron screening masses, the chiral condensate, and the
pion decay constant close to the deconfinement phase transition in the confined
phase of QCD. The simulations were done in the quenched approximation, on a
lattice of size \mbox{$32^{3}\times 8$}. We examined temperatures ranging from
$0.75\tc$ up to $0.92\tc$. We see no sign of a temperature dependence in the
chiral condensate or the meson properties, but some temperature dependence for
the nucleon screening mass is not excluded.


title:
Topological charge density renormalization in the presence of dynamical
  fermions

abstract:
  We study the renormalization group behaviour of the topological charge
density in full QCD on the lattice. We propose a way of extracting the
necessary renormalization functions from Monte Carlo simulations.


title:
Perturbation Theory at Finite Extent of Fifth Dimension for Vacuum
  Overlap Formula of Chiral Determinant -- Continuum Limit Case --

abstract:
  Taking into account of the boundary condition in the fifth direction which is
derived from the lattice Wilson fermion, we develop a theory of
five-dimensional fermion with kink-like and homogeneous masses in finite extent
of the fifth dimension. The boundary state wave functions are constructed
explicitly and the would-be vacuum overlap is expanded by using the propagator
of the theory. The subtraction is performed unambiguously at the finite extent
with the help of the dimensional regularization. Then the limit of the infinite
extent is evaluated. The consistent anomaly in four dimensional theory is
finitely obtained. Each contribution to the vacuum polarization is vector-like.
It is the lack of the massless mode in the fermion with negative homogeneous
mass that leads to the correct chiral normalization. Gauge noninvariant piece
remains due to the breaking of the boundary condition by the dimensional
regularization.


title:
A Self Consistent Study of the Phase Transition in the Scalar
  Electroweak Theory at Finite Temperature

abstract:
  We propose the study of the phase transition in the scalar electroweak theory
at finite temperature by a two - step method. It combines i) dimensional
reduction to a 3-dimensional {\it lattice\/} theory via perturbative blockspin
transformation, and ii) either further real space renormalization group
transformations, or solution of gap equations, for the 3d lattice theory. A gap
equation can be obtained by using the Peierls inequality to find the best
quadratic approximation to the 3d action. % This method avoids the lack of self
consistency of the usual treatments which do not separate infrared and
UV-problems by introduction of a lattice cutoff. The effective 3d lattice
action could also be used in computer simulations.


title:
From Spectroscopy to the Strong Coupling Constant with Heavy Wilson
  Quarks

abstract:
  In this work we present lattice calculations of the masses of P-wave mesons
using Monte Carlo simulations. Our valence fermions are defined by the Wilson
action. Our gauge fields are generated with both dynamical staggered fermions
at a lattice coupling $\beta\equiv 6/g^2=5.6$ for sea quark masses of
$am_q=0.010$ and 0.025, and in the quenched approximation at $\beta=6.0$. We
present results for charm and charmonium spectroscopy and use them to compute
the strong coupling constant $\alpha_s$. We compare our results to those of
other recent lattice calculations and experiments.


title:
The relation between the waveguide and overlap implementations of
  Kaplan's domain wall fermions

abstract:
  Recently, Narayanan and Neuberger proposed that the fermion determinant for a
lattice chiral gauge theory be defined by an overlap formula. The motivation
for that formula comes from Kaplan's five dimensional lattice domain wall
fermions. In the case that the target continuum theory contains $4n$ chiral
families, we show that the effective action defined by overlap formula is
identical to the effective action of a modified waveguide model that has extra
bosonic ghost fields. This raises serious questions about the viability of the
overlap formula for defining chiral gauge theories on the lattice.


title:
Landau Ginzberg model and deconfinement transition for extended SU(2)
  action

abstract:
  We compute the effective action in terms of the Polyakov loop for the
3-dimensional pure fundamental-adjoint SU(2) lattice gauge theory at non-zero
temperatures using the strong coupling expansion. In the extended coupling
plane we show the existence of a tricritical point where the nature of the
deconfinement transition undergoes a change from second to first order. The
resulting phase structure is in excellent agreement with the Monte Carlo
results both in the fundamental and adjoint directions. The possible
consequences of our results on universality are discussed.


title: The U(1) Gross-Neveu Model at Non-Zero Chemical Potential

abstract:
  The four-fermi model with continuous chiral symmetry is studied in three
dimensions at non-zero chemical potential $\mu$ using both the $1/N_f$
expansion and computer simulations. For strong coupling this model
spontaneously breaks its U(1) chiral symmetry at zero chemical potential and
the Goldstone mechanism is realized through massless pions. The computer
simulation predicts a critical chemical potential $\mu_c$ close to the lightest
fermion mass in the model. As $\mu$ is increased beyond $\mu_c$, the pion
screening mass increases rapidly from zero to a nonvanishing value indicating
symmetry restoration. Some lessons are drawn relevant to lattice QCD
simulations at non-zero $\mu$.


title:
Two-loop relation between the bare lattice coupling and the MSbar
  coupling in pure SU(N) gauge theories

abstract:
  We report the result of a computation of the relation between the
renormalized coupling in the MSbar scheme of dimensional regularization and the
bare coupling in the standard lattice formulation of the SU(N) Yang-Mills
theory to two-loop order of perturbation theory and discuss some of its
implications.


title: Phase Transition in the Two Dimensional Classical XY Model

abstract:
  For the two dimensional classical XY model we present extensive high
-temperature -phase bulk data extracted based on a novel finite size scaling
(FSS) Monte Carlo technique, along with FSS data near criticality. Our data
verify that $\eta=1/4$ sets in near criticality, and clarify the nature of
correction to the leading scaling behavior. However, the result of standard FSS
analysis near criticality is inconsistent with other predictions of
Kosterlitz's renormalization group approach.


title:
An Effective Action for Finite Temperature Lattice Gauge Theories with
  Dynamical Fermions

abstract:
  Dynamical fermions induce via the fermion determinant a gauge-invariant
effective action. In principle, this effective action can be added to the usual
gauge action in simulations, reproducing the effects of closed fermion loops.
Using lattice perturbation theory at finite temperature, we compute for
staggered fermions the one-loop fermionic corrections to the spatial and
temporal plaquette couplings as well as the leading $Z_N$ symmetry breaking
coupling. A. Hasenfratz and T. DeGrand have shown that $\beta_c$ for dynamical
staggered fermions can be accurately estimated by the formula $\beta_c =
\beta^{\rm pure}_c - \Delta\beta_F$ where $\Delta\beta_F$ is the shift induced
by the fermions at zero temperature. Numerical and analytical results indicate
that the finite temperature corrections to the zero-temperature calculation of
A. Hasenfratz and T. DeGrand are small for small values of $\kappa = {1\over
2m_F}$, but become significant for intermediate values of $\kappa$. The effect
of these finite temperature corrections is to ruin the agreement of the
Hasenfratz-DeGrand calculation with Monte Carlo data. We argue, however, that
the finite temperature corrections are suppressed nonperturbatively at low
temperatures, resolving this apparent disagreement. The $Z_N$ symmetry breaking
coupling is small; we argue that it changes the order of the transition while
having little effect on the critical value of $\beta$.


title: Evidence for hard chiral logarithms in quenched lattice QCD

abstract:
  We present the first direct evidence that quenched QCD differs from full QCD
in the chiral ($m_q \rightarrow 0$) limit, as predicted by chiral perturbation
theory, from our quenched lattice QCD simulations at $\beta = 6/g^2 = 6.0$. We
measured the spectrum of light hadrons on $16^3 \times 64$, $24^3 \times 64$
and $32^3 \times 64$, using staggered quarks of masses $m_q=0.01$, $m_q=0.005$
and $m_q=0.0025$. The pion masses showed clear evidence for logarithmic
violations of the PCAC relation $m_{\pi}^2 \propto m_q$, as predicted by
quenched chiral perturbation theory. The dependence on spatial lattice volume
precludes this being a finite size effect. No evidence was seen for such chiral
logarithms in the behaviour of the chiral condensate
$\langle\bar{\psi}\psi\rangle$.


title:
Scaling behavior of the four-point renormalized coupling constant in the
  two dimensional O(2) and O(3) non-linear sigma models

abstract:
  We report thermodynamic values of four-point renormalized coupling constant
calculated by Monte Carlo simulations in the continuum limits of the lattice
versions of the two-dimensional O(2) and O(3) non-linear sigma models. In each
case the critical index of the coupling constant vanishes, which leads to
hyperscaling (non-triviality).


title: Static Quark Potentials in Quantum Gravity

abstract:
  We present potentials between static charges from simulations of quantum
gravity coupled to an SU(2) gauge field on $6^{3}\times 4$ and $8^{3}\times 4$
simplicial lattices. The action consists of the gravitational term given by
Regge's discrete version of the Euclidean Einstein action and a gauge term
given by the Wilson action, with coupling constants $m_{p}^{2}$ and $\beta$
respectively. In the well-defined phase of the gravity sector where geometrical
expectation values are stable, we study the correlations of Polyakov loops and
extract the corresponding potentials between a source and sink separated by a
distance $R$. We compare potentials on a flat simplicial lattice with those on
a fluctuating Regge skeleton. In the confined phase, the potential has a linear
form while in the deconfined phase, a screened Coulombic behavior is found. Our
results indicate that quantum gravitational effects do not destroy confinement
due to non-abelian gauge fields.


title: Parallel Cluster Labeling for Large-Scale Monte Carlo Simulations

abstract:
  We present an optimized version of a cluster labeling algorithm previously
introduced by the authors. This algorithm is well suited for large-scale Monte
Carlo simulations of spin models using cluster dynamics on parallel computers
with large numbers of processors. The algorithm divides physical space into
rectangular cells which are assigned to processors and combines a serial local
labeling procedure with a relaxation process across nearest-neighbor
processors. By controlling overhead and reducing inter-processor communication
this method attains good computational speed-up and efficiency. Large systems
of up to 65536 X 65536 spins have been simulated at updating speeds of 11
nanosecs/site (90.7 million spin updates/sec) using state-of-the-art
supercomputers. In the second part of the article we use the cluster algorithm
to study the relaxation of magnetization and energy on large Ising models using
Swendsen-Wang dynamics. We found evidence that exponential and power law
factors are present in the relaxation process as has been proposed by Hackl et
al.


title: Failure of Universality in Noncompact Lattice Field Theories

abstract:
  The nonuniversal behavior of two noncompact nonlinear sigma models is
described. When these theories are defined on a lattice, the behavior of the
order parameter (magnetization) near the critical point is sensitive to the
details of the lattice definition. This is counter to experience and to
expectations based on the ideas of universality.


title:
SU(2) Lattice Gauge Theory with Logarithmic Action: Scaling and
  Universality

abstract:
  We investigate a version of SU(2) lattice gauge theory with a logarithmic
action. The model is found to exhibit confinement, contrary to previous claims
in the literature. Comparing ratios of physical quantities, like
$\sqrt{\sigma}/T_c$, we find that the model belongs to the same universality
class as the standard SU(2) lattice gauge theory with Wilson action. Like the
positive plaquette model, the model with logarithmic action has a monotonic
$\beta$-function, without the famous dip exhibited by the Wilson action. Short
distance dislocations affecting the definition of topology are slightly more
suppressed than for the positive plaquette model.


title: Statistical Models on Spherical Geometries

abstract:
  We use a one-dimensional random walk on $D$-dimensional hyper-spheres to
determine the critical behavior of statistical systems in hyper-spherical
geometries. First, we demonstrate the properties of such a walk by studying the
phase diagram of a percolation problem. We find a line of second and first
order phase transitions separated by a tricritical point. Then, we analyze the
adsorption-desorption transition for a polymer growing near the attractive
boundary of a cylindrical cell membrane. We find that the fraction of adsorbed
monomers on the boundary vanishes exponentially when the adsorption energy
decreases towards its critical value.