title: Exploring confinement by cooling: A study of compact QED$_3$

abstract:
  The role of monopoles in the confining behavior of compact lattice $QED_3$ is
studied using an adiabatic cooling method. Monopole-antimonopole pairs with
large separation suvive cooling and the presence or absence of such plasma
monopoles provides a useful classification of the lattice gauge field
configurations at large $\beta$. By calculating observables in subsets of gauge
field configurations which contain or do not contain plasma monopoles it is
seen that, in compact $QED_3$, monopoles dominate the long distance physics,
e.g., the string tension, linear confining potential and dynamical mass
generation. On the other hand, the spin-spin interaction is essentially
unaffected by monopoles.


title: Compact QED in Landau Gauge: a lattice gauge fixing case study

abstract:
  We derive different representations of compact QED fixed to Landau gauge by
the lattice Faddeev-Popov procedure. Our analysis finds that (A)Nielsen-Olesen
vortices arising from the compactness of the gauge-fixing action are {\it
quenched\/}, that is, the Faddeev-Popov determinant cancels them out and they
do not influence correlation functions such as the photon propagator; (B)Dirac
strings are responsible for the nonzero mass pole of the photon propagator.
Since in $D=3+1$ the photon mass undergoes a rapid drop to zero at $\beta_c$,
the deconfinement point, this result predicts that Dirac strings must be
sufficiently dilute at $\beta > \beta_c$. Indeed, numerical simulations reveal
that the string density undergoes a rapid drop to near zero at $\beta\sim
\beta_c$.


title: Canonical Quantization of Two Dimensional Gauge Fields

abstract:
  $SU(N)$ gauge fields on a cylindrical spacetime are canonically quantized via
two routes revealing almost equivalent but different quantizations. After
removing all continuous gauge degrees of freedom, the canonical coordinate
$A_\mu$ (in the Cartan subalgebra $\h$) is quantized. The compact route, as in
lattice gauge theory, quantizes the Wilson loop $W$, projecting out gauge
invariant wavefunctions on the group manifold $G$. After a Casimir energy
related to the curvature of $SU(N)$ is added to the compact spectrum, it is
seen to be a subset of the non-compact spectrum. States of the two
quantizations with corresponding energy are shifted relative each other, such
that the ground state on $G$, $\chi_0(W)$, is the first excited state
$\Psi_1(A_\mu)$ on $\h$. The ground state $\Psi_0(A_\mu)$ does not appear in
the character spectrum as its lift is not globally defined on $G$. Implications
for lattice gauge theory and the sum over maps representation of two
dimensional QCD are discussed.


title:
Exact renormalization-group analysis of first order phase transitions in
  clock models

abstract:
  We analyze the exact behavior of the renormalization group flow in
one-dimensional clock-models which undergo first order phase transitions by the
presence of complex interactions. The flow, defined by decimation, is shown to
be single-valued and continuous throughout its domain of definition, which
contains the transition points. This fact is in disagreement with a recently
proposed scenario for first order phase transitions claiming the existence of
discontinuities of the renormalization group. The results are in partial
agreement with the standard scenario. However in the vicinity of some fixed
points of the critical surface the renormalized measure does not correspond to
a renormalized Hamiltonian for some choices of renormalization blocks. These
pathologies although similar to Griffiths-Pearce pathologies have a different
physical origin: the complex character of the interactions. We elucidate the
dynamical reason for such a pathological behavior: entire regions of coupling
constants blow up under the renormalization group transformation. The flows
provide non-perturbative patterns for the renormalization group behavior of
electric conductivities in the quantum Hall effect.


title: Finite Size Analysis of the One-dimensional $q = \infty$ Clock Model

abstract:
  We analyze the finite size scaling of the $q$-state clock model in the $q
\rightarrow \infty$ limit. The behaviors of the specific heat, Binder-Landau
and U4 cumulants agree with the Borgs-Koteck\'y ans\"atz for first order phase
transitions. However, we find that the leading correction to the position of
the extremal points of these quantities is not universal. On the other hand,
the finite size corrections to the mass gap behave like for second order phase
transitions. In particular, the curves corresponding to different size
approximations do not cross in the vicinity of the transition points. The
feature is associated to the existence of a divergent correlation length and
holds for a wider class of models.


title: Finite-size and quark mass effects on the QCD spectrum with two flavors

abstract:
  We have carried out spectrum calculations with two flavors of dynamical
Kogut-Susskind quarks on four lattice sizes from $8^3\times 24$ to
$16^3\times24$ at couplings that correspond to chiral symmetry restoration for
a lattice with 6 time slices. We estimate that the linear spatial sizes of the
lattices range from 1.8 to 3.6 fm. We find significant finite size effects for
all particles between the smallest and largest volume with the larger quark
mass that we study, $am_q=0.025$, where $a$ is the lattice spacing. The nucleon
experiences the largest effect of about 6 percent. We also study a lighter
quark mass, $am_q=0.0125$, on the two largest lattices. Effects of the
dynamical and valence quark masses on the hadron spectrum are studied both
directly, by comparing the two simulations, and by extracting mass derivatives
from the correlation functions. We do not find much improvement in the nucleon
to rho mass ratio as we decrease the quark mass at this lattice spacing.
Finally, we report on an unsuccessful attempt to see effects of the $\rho
\rightarrow 2\pi$ decay on the $\rho$ mass, and on studies of Wilson and
Kogut-Susskind hadron masses with large valence quark masses. (The paper is
also available via anonymous ftp in a compressed PostScript file:
fuji.physics.indiana.edu:/pub/milc/paper.ps.Z .)


title:
Variational Approach to Real-Time Evolution of Yang-Mills Gauge Fields
  on a Lattice

abstract:
  Applying a variational method to a Gaussian wave ansatz, we have derived a
set of semi-classical evolution equations for SU(2) lattice gauge fields, which
take the classical form in the limit of a vanishing width of the Gaussian wave
packet. These equations are used to study the quantum effects on the classical
evolutions of the lattice gauge fields.


title: Nucleon Axial Form Factor from Lattice QCD

abstract:
  Results for the isovector axial form factors of the proton from a lattice QCD
calculation are presented for both point-split and local currents. They are
obtained on a quenched $16^{3} \times 24$ lattice at $\beta= 6.0$ with Wilson
fermions for a range of quark masses from strange to charm. We determine the
finite lattice renormalization for both the local and point-split currents of
heavy quarks. Results extrapolated to the chiral limit show that the $q^2$
dependence of the axial form factor agrees reasonably well with experiment. The
axial coupling constant $g_A$ calculated for the local and the point-split
currents is about 6\% and 12\% smaller than the experimental value
respectively.


title: 3 Into 2 Doesn't Go: (almost) chiral gauge theory on the lattice

abstract:
  Kaplan recently proposed a novel lattice chiral gauge theory in which the
bare theory is defined on $(2n+1)$-dimensions, but the continuum theory emerges
in $2n$-dimensions. We explore whether the resulting theory reproduces all the
features of continuum chiral gauge theory in the case of two-dimensional axial
Schwinger model. We find that one can arrange for the two-dimensional
perturbation expansion to be reproduced successfully. However, the theory fails
to reproduce the 2-dimensional fermion nonconservation.


title: The Three-Loop Lattice Free Energy

abstract:
  We calculate the free energy of SU(N) gauge theories on the lattice, to three
loops. Our result, combined with Monte Carlo data for the average plaquette,
gives a more precise estimate of the gluonic condensate.


title:
Correlation Functions of Hadron Currents in the QCD Vacuum Calculated in
  Lattice QCD

abstract:
  Point-to-point vacuum correlation functions for spatially separated hadron
currents are calculated in quenched lattice QCD on a $16^3\times 24$ lattice
with $6/g^2=5.7$. The lattice data are analyzed in terms of dispersion
relations, which enable us to extract physical information from small distances
where asymptotic freedom is apparent to large distances where the hadronic
resonances dominate. In the pseudoscalar, vector, and axial vector channels
where experimental data or phenomenological information are available,
semi-quantitative agreement is obtained. In the nucleon and delta channels,
where no experimental data exist, our lattice data complement experiments.
Comparison with approximations based on sum rules and interacting instantons
are made, and technical details of the lattice calculation are described.


title: Fixed Point Actions for Wilson Fermions

abstract:
  Iterating renormalization group transformations for lattice fermions the
Wilson action is driven to fixed points of the renormalization group. A line of
fixed points is found and the fixed point actions are computed analytically.
They are local and may be used to improve scaling in lattice QCD. The action at
the line's endpoint is chirally invariant and still has no fermion doubling.
The Nielsen-Ninomiya theorem is evaded because in this case the fixed point
action is nonlocal. The use of this action for a construction of lattice chiral
fermions is discussed.


title: Elastic anomaly of heavy fermion systems in a crystalline field

abstract:
  An elastic anomaly, observed in the heavy fermi liquid state of Ce alloys
(for example, CeCu$_6$ and CeTe), is analyzed by using the infinite-$U$
Anderson lattice model. The four atomic energy levels are assumed for
f-electrons. Two of them are mutually degenerate. A small crystalline splitting
$2\Delta$ is assumed between two energy levels. The fourfold degenerate
conduction bands are also considered in the model. We solve the model using the
mean field approximation to slave bosons, changing the Fermi energy in order to
keep the total electron number constant. The nonzero value of the mean field of
the slave bosons persists over the temperatures much higher than the Kondo
temperature. This is the effect of the constant electron number. Next, the
linear susceptibility with respect to $\Delta$ is calculated in order to obtain
the renomalized elastic constant. The resulting temperature dependence of the
constant shows the downward dip. We point out the relation of our finding with
the experimental data.


title:
Partially Quenched Gauge Theories and a Application to Staggered
  Fermions

abstract:
  We extend our lagrangian technique for chiral perturbation theory for
quenched QCD to include theories in which only some of the quarks are quenched.
We discuss the relationship between the partially quenched theory and a theory
in which only the unquenched quarks are present. We also investigate the
peculiar infrared divergences associated with the $\eta'$ in the quenched
approximation, and find the conditions under which such divergences can appear
in a partially quenched theory. We then apply our results to staggered fermion
QCD in which the square root of the fermion determinant is taken, using the
observation that this should correspond to a theory with four quarks, two of
which are quenched. [Uses harvmac macro package. No postscipt for the figures
is available (sorry), but the figures are simple and we include do-it-yourself
instructions for drawing them.]


title: Phase Structure of SU(2) Lattice Gauge Theory with Quantum Gravity

abstract:
  We investigate 4$d$ SU(2) lattice gauge theory with Regge--Einstein quantum
gravity on a dynamically coupled Regge skeleton. To overview the phase diagram
we perform simulations on a small $2\cdot 4^3$ system. Evidence for an
entropy--dominated disordered, an entropy--dominated ordered and an
ill--defined region is presented.


title:
Comment on ``Savvidy Ferromagnetic Vacuum in Three-Dimensional Latice
  Gauge Theory''

abstract:
  We analyze SU(2) gauge theory in a constant chromomagnetic field in three
dimensions. Our analysis instead of supporting the existence of a non-trivial
minimum in the effective potential, corroborates the evidence of the unstable
modes on the lattice.


title:
Influence of Implementation on the Properties of Pseudorandom Number
  Generators with a Carry Bit

abstract:
  We present results of extensive statistical and bit level tests on three
implementations of a pseudorandom number generator algorithm using the lagged
Fibonacci method with an occasional addition of an extra bit. First
implementation is the RCARRY generator of James, which uses subtraction. The
second is a modified version of it, where a suggested error present in the
original implementation has been corrected. The third is our modification of
RCARRY such that it utilizes addition of the carry bit. Our results show that
there are no significant differences between the performance of these three
generators.


title: A Lattice Computation of the Decay Constants of $B$ and $D$ Mesons

abstract:
  A lattice calculation of the pseudoscalar decay constant of heavy-light
mesons is reported. Results are obtained (in the quenched approximation) from
lattices at $\beta=6.3$ through a procedure that interpolates between the
static approximation of Eichten and the conventional ("heavy" Wilson fermion)
method. The previously observed discrepancy between these two approaches has
been resolved: we find the scaling quantity $f\sqrt{M}$ to be significantly
smaller than previous calculations had indicated ({\it e.g.} at $\beta=6.0$);
in addition, we discuss a modification which is required in normalizing the
conventional amplitude to correct for large-$am$ lattice errors. This change
guarantees that $f\sqrt{M}$ will smoothly approach its value in the static
limit. From the numerical interpolation of the static and intermediate-mass
results, we find, in units of MeV, $f_B=187(10)\pm34\pm15$,
$f_{B_s}=207(9)\pm34\pm22$, $f_D=208(9)\pm35\pm12$ and
$f_{D_s}=230(7)\pm30\pm18$, where the first error is statistical and the second
two are estimates of systematics due to 1) fitting and large-$am$ effects and
2) scaling. In addition, using lattices at $\beta=6.3$, $\beta=6.0$ and
$\beta=5.7$ and extrapolating to the limit of zero lattice spacing, we have
computed $f_K/f_\pi = 1.08\pm.03\pm.08$ in the quenched approximation.


title: Gribov Copies in Lattice QCD

abstract:
  We have performed an exhaustive search for Gribov copies on the lattice and
their possible dependence from finite temperature effects. We show that, for
each value of lattice size, Gribov copies are dense in configuration space at
low temperature but their density tend to lower when the temperature increases.
We have investigated lattice sizes running from $16^3\times 8$ to $16^4$.


title:
Scaling, asymptotic scaling and Symanzik improvement. Deconfinement
  temperature in SU(2) pure gauge theory

abstract:
  We report on a high statistics simulation of SU(2) pure gauge field theory at
finite temperature, using Symanzik action. We determine the critical coupling
for the deconfinement phase transition on lattices up to 8 x 24, using Finite
Size Scaling techniques. We find that the pattern of asymptotic scaling
violation is essentially the same as the one observed with conventional, not
improved action. On the other hand, the use of effective couplings defined in
terms of plaquette expectation values shows a precocious scaling, with respect
to an analogous analysis of data obtained by the use of Wilson action, which we
interpret as an effect of improvement.


title:
Staggered fermions for chiral gauge theories: Test on a two-dimensional
  axial-vector model

abstract:
  As a first step towards constructing chiral models on the lattice with
staggered fermions, we study a U(1) model with axial-vector coupling to an
external gauge field in two dimensions. In our approach gauge invariance is
broken, but it is restored in the classical continuum limit. We find that the
continuum divergence relations for the vector and axial-vector currents are
reproduced, up to contact terms, which we determine analytically. The current
divergence relations are also studied numerically for smooth external gauge
fields with topological charge zero. We furthermore investigate the effect of
fluctuating gauge transformations and of gauge configurations with non-trivial
topological charge.


title:
Measure of Autocorrelation Times of Local Hybrid Monte Carlo Algorithm
  for Lattice QCD

abstract:
  We report on a study of the autocorrelation times of the local version of the
Hybrid Monte Carlo (LHMC) algorithm for pure gauge $SU(3)$. We compare LHMC to
standard multi-hit Metropolis and to the global version of the same HMC. For
every algorithm we measure the autocorrelation time for a variety of
observables and the string tension as a function of beta. The measurements
performed on 8^4 and 16^4 lattices indicate that the autocorrelation time of
LHMC is significantly shorter than for the other two algorithms.


title:
Properties of the Abelian Projection Fields in $SU(N)$ Lattice
  Gluodynamics

abstract:
  't~Hooft's abelian projection of $SU(N)$ gauge theory yields $N$ mutually
constrained, compact abelian fields which are permutationally equivalent. We
formulate the notion of ``species permutation'' symmetry of the $N$ abelian
projection fields and discuss its consequences for cross-species correlators.
We show that at large $N$ cross-species interactions are ${1\over N}$
suppressed relative to same-species interactions. Numerical simulations at
$N=3$ support our symmetry arguments and reveal the existence of inter-species
interactions of size ${\cal O\/}\bigl({1\over N-1}\bigr)$ as analytically
predicted.


title: Spacelike Wilson Loops at Finite Temperature

abstract:
  In the high temperature phase of Yang-Mills theories, large spatial Wilson
loops show area law behaviour with a string tension that grows with increasing
temperature. Within the framework of the commonly used string picture we use a
large scale expansion, which allows us to determine the string tension from
measurements of intermediate and symmetric Wilson loops.


title: Can a Logarithmically Running Coupling Mimic a String Tension?

abstract:
  It is shown that a Coulomb potential using a running coupling slightly
modified from the perturbative form can produce an interquark potential that
appears nearly linear over a large distance range. Recent high-statistics SU(2)
lattice gauge theory data fit well to this potential without the need for a
linear string-tension term. This calls into question the accuracy of string
tension measurements which are based on the assumption of a constant
coefficient for the Coulomb term. It also opens up the possibility of obtaining
an effectively confining potential from gluon exchange alone.


title: Chiral Defect Fermions and the Layered Phase

abstract:
  Chiral defect fermions on the lattice in 4+1 dimensions are analyzed using
mean field theory. The fermion propagator has a localized chiral mode in weak
coupling but loses it when the coupling in the unphysical fifth direction
becomes too large. A layered phase \`a la Fu-Nielsen appears where the theory
is vector-like in every layer.


title:
A Comperative Study of Gauge Fixing Procedures on the Connection
  Machines CM2 and CM5

abstract:
  Gauge fixing is a frequent task encountered in practical lattice gauge theory
calculations. We review the performance characteristics of some standard
gauging procedures for non-abelian gauge theories, implemented on the parallel
machines CM2 and CM5.


title:
Thermal Fluctuations of Chern-Simons Numbers in the Lattice SU(2) Higgs
  Model

abstract:
  We study the temperature dependence of the Chern-Simons number fluctuations
in the SU(2) Higgs Model on Euclidean lattices with spatial sizes up to 20^3.
Temperatures well above the Higgs phase transition $T_H$ are achieved on
anisotropic lattices. Numerical results are compared to perturbative results on
finite lattices as well as in continuum perturbation theory. We find
qualitative agreement with perturbative estimates and see at high temperatures
a tendency towards static configurations. Up to temperatures $T \simeq 2T_H$ we
find indication that tunneling between vacuums with different Chern-Simons
numbers are still exponentially suppressed. (Full PostScript file available via
Email from plache@physw.uni-bielefeld.de )


title: Monte Carlo Study of Topological Defects in the 3D Heisenberg Model

abstract:
  We use single-cluster Monte Carlo simulations to study the role of
topological defects in the three-dimensional classical Heisenberg model on
simple cubic lattices of size up to $80^3$. By applying reweighting techniques
to time series generated in the vicinity of the approximate infinite volume
transition point $K_c$, we obtain clear evidence that the temperature
derivative of the average defect density $d\langle n \rangle/dT$ behaves
qualitatively like the specific heat, i.e., both observables are finite in the
infinite volume limit. This is in contrast to results by Lau and Dasgupta [{\em
Phys. Rev.\/} {\bf B39} (1989) 7212] who extrapolated a divergent behavior of
$d\langle n \rangle/dT$ at $K_c$ from simulations on lattices of size up to
$16^3$. We obtain weak evidence that $d\langle n \rangle/dT$ scales with the
same critical exponent as the specific heat.As a byproduct of our simulations,
we obtain a very accurate estimate for the ratio $\alpha/\nu$ of the
specific-heat exponent with the correlation-length exponent from a finite-size
scaling analysis of the energy.


title: Spectral properties and lattice-size dependences in cluster algorithms

abstract:
  Simulation results of Ising systems for several update rules, observables,
and dimensions are analyzed. The lattice-size dependence is discussed for the
autocorrelation times and for the weights of eigenvalues, giving fit results in
the case of power laws. Implications of spectral properties are pointed out and
the behavior of a particular observable not governed by detailed balance is
explained.


title: Cluster dynamics for first-order phase transitions in the Potts model

abstract:
  An algorithm for Monte Carlo simulations is proposed in which the parameter
controlling the strength of the transition becomes a dynamical variable and in
which efficient transitions are achieved by cluster steps. It allows to avoid
the strongly suppressed tunneling between the phases by travelling easily via
the second order region. Numerical results for the Potts model are presented
which demonstrate the advantages of the method.


title:
Constraints on the Existence of Chiral Fermions in Interacting Lattice
  Theories

abstract:
  It is shown that an interacting theory, defined on a regular lattice, must
have a vector-like spectrum if the following conditions are satisfied:
(a)~locality, (b)~relativistic continuum limit without massless bosons, and
(c)~pole-free effective vertex functions for conserved currents.
  The proof exploits the zero frequency inverse retarded propagator of an
appropriate set of interpolating fields as an effective quadratic hamiltonian,
to which the Nielsen-Ninomiya theorem is applied.


title:
The Spatial String Tension in the Deconfined Phase of the
  (3+1)-Dimensional SU(2) Gauge Theory

abstract:
  We present results of a detailed investigation of the temperature dependence
of the spatial string tension in SU(2) gauge theory. We show, for the first
time, that the spatial string tension is scaling on the lattice and thus is
non-vanishing in the continuum limit. It is temperature independent below Tc
and rises rapidly above. For temperatures larger than 2Tc we find a scaling
behaviour consistent with sigma_s(T) = 0.136(11) g^4(T) T^2, where g(T) is the
2-loop running coupling constant with a scale parameter determined as Lambda_T
= 0.076(13) Tc.


title: A Lattice Study of the Gluon Propagator in Momentum Space

abstract:
  We consider pure glue QCD at beta=5.7, beta=6.0 and beta=6.3. We evaluate the
gluon propagator both in time at zero 3-momentum and in momentum space. From
the former quantity we obtain evidence for a dynamically generated effective
mass, which at beta=6.0 and beta=6.3 increases with the time separation of the
sources, in agreement with earlier results. The momentum space propagator G(k)
provides further evidence for mass generation. In particular, at beta=6.0, for
k less than 1 GeV, the propagator G(k) can be fit to a continuum formula
proposed by Gribov and others, which contains a mass scale b, presumably
related to the hadronization mass scale. For higher momenta Gribov's model no
longer provides a good fit, as G(k) tends rather to follow an inverse power
law. The results at beta=6.3 are consistent with those at beta=6.0, but only
the high momentum region is accessible on this lattice. We find b in the range
of three to four hundred MeV and the exponent of the inverse power law about
2.7. On the other hand, at beta=5.7 (where we can only study momenta up to 1
GeV) G(k) is best fit to a simple massive boson propagator with mass m. We
argue that such a discrepancy may be related to a lack of scaling for low
momenta at beta=5.7. {}From our results, the study of correlation functions in
momentum space looks promising, especially because the data points in Fourier
space turn out to be much less correlated than in real space.


title: On the absence of chiral fermions in interacting lattice theories

abstract:
  We consider interacting theories with a compact internal symmetry group on a
regular lattice. We show that the spectrum is necessarily vector-like provided
the following conditions are satisfied: (a)~weak form of locality,
(b)~relativistic continuum limit without massless bosons, and (c)~pole-free
effective vertex functions for conserved currents.
  The proof exploits the zero frequency inverse retarded propagator of an
appropriate set of interpolating fields as an effective quadratic hamiltonian,
to which the Nielsen-Ninomiya theorem is applied.
  The main results of this paper have been reported in WIS-93/56-JUNE-PH,
hep-lat/9306023.


title: Finite-Size Scaling in the $O(N)$ $\phi^4_4$ Model

abstract:
  Perturbation theory and renormalization group methods are used to derive a
finite-size scaling theory for the partition function zeroes and thermodynamic
functions in the $O(n)$ $\phi^4$ model in four dimensions. The leading
power--law scaling behaviour is the same as that of the mean field theory.
There exist, however, multiplicative logarithmic corrections which are linked
to the triviality of the theory.


title:
Scaling Study of Pure Gauge Lattice QCD by Monte Carlo Renormalization
  Group Method

abstract:
  The scaling behavior of pure gauge SU(3) in the region $\beta=5.85 - 7.60$ is
examined by a Monte Carlo Renormalization Group analysis. The coupling shifts
induced by factor 2 blocking are measured both on 32$^4$ and 16$^4$ lattices
with high statistics. A systematic deviation from naive 2-loop scaling is
clearly seen. The mean field and effective coupling constant schemes explain
part, but not all of the deviation. It can be accounted for by a suitable
change of coupling constant, including a correction term ${\cal O}(g^7)$ in the
2-loop lattice $\beta$-function. Based on this improvement,
$\sqrt{\sigma}/\Lambda_{\overline {MS}}^{n_f=0}$ is estimated to be $2.2(\pm
0.1)$ from the analysis of the string tension $\sigma$.


title: A Lattice Calculation of the Isgur-Wise Function

abstract:
  We calculate the Isgur-Wise function ($\xi_0$) by measuring the heavy-heavy
meson transition matrix element on the lattice in the quenched approximation.
The standard Wilson action is used for both the heavy and the light quarks. Our
numerical results are compared with various model calculations and experimental
data. In particular, using a linear fit, we find $\rho^2 = 1.24\pm .26 \pm .26
$. (The slope of $\xi_0$ at the zero-recoil point is $-\rho^2$.) Using instead
the parametrization of $\xi_0$ suggested by Neubert and Rieckert and fitting
the lattice data up to $v\cdot v' \sim 1.2$, we find
$\rho^2_{NR}=1.41\pm.19\pm.19$


title: Chiral Determinant as an Overlap of Two Vacua

abstract:
  The effective action induced by chiral fermions can be written, formally, as
an overlap of two states. These states are the Fock ground states of
Hamiltonians for fermions in even dimensional space with opposite sign mass
terms coupled to identical static vector potentials. A perturbative analysis of
the overlap in the continuum framework produces the correct anomaly for Abelian
gauge fields in two dimensions. When a lattice transfer matrix formalism is
applied in the direction perpendicular to a domain wall on which chiral
fermions live a lattice version of the overlap is obtained. The real part of
the overlap is nonperturbatively defined and previous work indicates that the
real part of the vacuum polarization tensor in four dimensions has the correct
continuum limit for a chiral theory. The phase of the overlap represents the
imaginary part of the chiral action and suffers from ambiguities.


title: The Kramers equation simulation algorithm I. Operator analysis

abstract:
  Using an operatorial formalism, we study the Kramers equation and its
applications to numerical simulations. We obtain classes of algorithms which
may be made precise at every desired order in the time step $\epsilon$ and with
a set of free parameters which can be used to reduce autocorrelations. We show
that it is possible to use a global Metropolis test to restore Detailed
Balance.


title:
The Kramers equation simulation algorithm II. An application to the
  Gross-Neveu model

abstract:
  We continue the investigation on the applications of the Kramers equation to
the numerical simulation of field theoretic models. In a previous paper we have
described the theory and proposed various algorithms. Here, we compare the
simplest of them with the Hybrid Monte Carlo algorithm studying the
two-dimensional lattice Gross-Neveu model. We used a Symanzik improved action
with dynamical Wilson fermions. Both the algorithms allow for the determination
of the critical mass. Their performances in the definite phase simulations are
comparable with the Hybrid Monte Carlo. For the two methods, the numerical
values of the measured quantities agree within the errors and are compatible
with the theoretical predictions; moreover, the Kramers algorithm is safer from
the point of view of the numerical precision.


title:
Quenched Light Hadron Mass Spectrum and Decay Constants: the effects of
  $O(a)$-Improvement at $\beta=6.2$

abstract:
  We compare the light hadron spectrum and decay constants for quenched QCD at
$\beta=6.2$ using an $O(a)$-improved nearest-neighbour Wilson fermion action
with those obtained using the standard Wilson fermion action on the same set of
18 gauge configurations. For pseudoscalar meson masses in the range
330--800~MeV, we find no significant difference between the results for the two
actions. The scales obtained from the string tension and mesonic sector are
consistent, but differ from that derived from baryon masses. The ratio of the
pseudoscalar decay constant to the vector meson mass increases slowly with
quark mass as observed experimentally.


title: Dirac sheets and gauge fixing in $U(1)$ lattice gauge theory

abstract:
  Photon correlators in $~U(1)~$ pure gauge theory for different lattice
actions are considered under the Lorentz gauge condition. They are shown to
depend strongly on the gauge fixing ambiguity and on the corresponding
existence of Dirac sheets. For the Coulomb phase a gauge fixing algorithm is
proposed which avoids Dirac sheets and allows to find the global extremum of
the non-local gauge condition. Sorry, figures are not included and can be sent
by ordinary mail.


title: Fermionic Field Theory and Gauge Interactions on Random Lattices

abstract:
  Random-lattice fermions have been shown to be free of the doubling problem if
there are no interactions or interactions of a non-gauge nature. However, gauge
interactions impose stringent constraints as expressed by the Ward-Takahashi
identities which could revive the free-field suppressed doubler modes in loop
diagrams. After introducing a formulation for fermions on a new kind of random
lattice, we compare random, naive and Wilson fermions in two dimensional
Abelian background gauge theory. We show that the doublers are revived for
random lattices in the continuum limit, while demonstrating that gauge
invariance plays the critical role in this revival. Some implications of the
persistent doubling phenomenon on random lattices are also discussed.


title: Adjoint Wilson Line in SU(2) Lattice Gauge Theory

abstract:
  The behavior of the adjoint Wilson line in finite-temperature, $SU(2)$,
lattice gauge theory is discussed. The expectation value of the line and the
associated excess free energy reveal the response of the finite-temperature
gauge field to the presence of an adjoint source. The value of the adjoint line
at the critical point of the deconfining phase transition is highlighted. This
is not calculable in weak or strong coupling. It receives contributions from
all scales and is nonanalytic at the critical point. We determine the general
form of the free energy. It includes a linearly divergent term that is
perturbative in the bare coupling and a finite, nonperturbative piece. We use a
simple flux tube model to estimate the value of the nonperturbative piece. This
provides the normalization needed to estimate the behavior of the line as one
moves along the critical curve into the weak coupling region.


title: Semi-Analytical Solution of the $\phi^4$ Theory on an $F_4$ Lattice

abstract:
  Investigating the cutoff dependence of the Higgs mass triviality bound, the
$\phi^4$ theory is formulated on an $F_4$ lattice which preserves Lorentz
invariance to a higher degree than the commonly used hypercubic lattice. I
solve this model non-perturbatively by evaluating the high temperature
expansion through 13th order following the approach of L\"uscher and Weisz. The
results are continued across the transition line into the broken phase by
integrating the perturbative RG equations. In the broken phase, the
renormalized coupling never exceeds 2/3 of the tree level unitarity bound when
$\Lambda/m_R \geq 2$. The results confirm recent Monte Carlo data and I obtain
as an upper bound for the Higgs mass $m_R/f_\pi \leq 2.46 \pm 0.02_{\rm HTE}
\pm 0.08_{\rm PT}$ at $\Lambda/m_R=2$.


title: Two dimensional SU(N) x SU(N) chiral models on the lattice

abstract:
  Lattice $SU(N)\times SU(N)$ chiral models are analyzed by strong and weak
coupling expansions and by numerical simulations. $12^{th}$ order strong
coupling series for the free and internal energy are obtained for all $N\geq
6$. Three loop contributions to the internal energy and to the lattice
$\beta$-function are evaluated for all $N$ and non-universal corrections to the
asymptotic $\Lambda$ parameter are computed in the ``temperature'' and the
``energy'' scheme. Numerical simulations confirm a faster approach to
asymptopia of the energy scheme. A phenomenological correlation between the
peak in the specific heat and the dip of the $\beta$-function is observed.
Tests of scaling are performed for various physical quantities, finding
substantial scaling at $\xi \gtrsim 2$. In particular, at $N=6$ three different
mass ratios are determined numerically and found in agreement, within
statistical errors of about 1\%, with the theoretical predictions from the
exact S-matrix theory.


title:
Finite size scaling analysis of intermittency moments in the two
  dimensional Ising model

abstract:
  Finite size scaling is shown to work very well for the block variables used
in intermittency studies on a 2-d Ising lattice. The intermittency exponents so
derived exhibit the expected relations to the magnetic critical exponent of the
model. Email contact: pesch@amoco.saclay.cea.fr


title: On Spin and Matrix Models in the Complex Plane

abstract:
  We describe various aspects of statistical mechanics defined in the complex
temperature or coupling-constant plane. Using exactly solvable models, we
analyse such aspects as renormalization group flows in the complex plane, the
distribution of partition function zeros, and the question of new
coupling-constant symmetries of complex-plane spin models. The double-scaling
form of matrix models is shown to be exactly equivalent to finite-size scaling
of 2-dimensional spin systems. This is used to show that the string
susceptibility exponents derived from matrix models can be obtained numerically
with very high accuracy from the scaling of finite-$N$ partition function zeros
in the complex plane.


title: A Determination of Interface Free Energies

abstract:
  We determine the interface free energy $F_{o.d.}$ between disordered and
ordered phases in the q=10 and q=20 2-d Potts models using the results of
multicanonical Monte Carlo simulations on $L^2$ lattices, and suitable finite
volume estimators. Our results, when extrapolated to the infinite volume limit,
agree to high precision with recent analytical calculations. At the transition
point $\beta_t$ the probability distribution function of the energy exhibits
two maxima. Their locations have $1/L^2$ corrections, in contradiction with
claims of $1/L$ behavior made in the literature. Our data show a flat region
inbetween the two maxima which characterizes two domain configurations.


title:
"The Ising model on spherical lattices: dimer versus Monte Carlo
  approach"

abstract:
  We study, using dimer and Monte Carlo approaches, the critical properties and
finite size effects of the Ising model on honeycomb lattices folded on the
tetrahedron. We show that the main critical exponents are not affected by the
presence of conical singularities. The finite size scaling of the position of
the maxima of the specific heat does not match, however, with the scaling of
the correlation length, and the thermodynamic limit is attained faster on the
spherical surface than in corresponding lattices on the torus.


title: Towards an Abelian Formulation of Lattice QCD Confinement

abstract:
  We probe for operators occurring in the APQCD(``abelian-projected QCD'')
action by evaluating abelian-projected $1$-plaquette spectral densities in pure
gauge $SU(3)$ fixed to maximal abelian gauge. Couplings $B_{APQCD}(q,L)$ are
extracted from the spectral densities for each representation $q$, $L\times L$
plaquette. While APQCD is dominated by a $q=L=1$ resonance, we also find
evidence for weakly coupled $L=2$ plaquettes. Moreover, since $B_{APQCD}(1,1) >
B_{QED}(1,1)$ even if $\beta_{QED} > \beta_c$, $L>1$ plaquettes must be
significant since APQCD is confining.


title: Some Comments on Multigrid Methods for Computing Propagators

abstract:
  I make three conceptual points regarding multigrid methods for computing
propagators in lattice gauge theory: 1) The class of operators handled by the
algorithm must be stable under coarsening. 2) Problems related by symmetry
should have solution methods related by symmetry. 3) It is crucial to
distinguish the vector space $V$ from its dual space $V^*$. All the existing
algorithms violate one or more of these principles.


title: A General Limitation on Monte Carlo Algorithms of Metropolis Type

abstract:
  We prove that for any Monte Carlo algorithm of Metropolis type, the
autocorrelation time of a suitable ``energy''-like observable is bounded below
by a multiple of the corresponding ``specific heat''. This bound does not
depend on whether the proposed moves are local or non-local; it depends only on
the distance between the desired probability distribution $\pi$ and the
probability distribution $\pi^{(0)}$ for which the proposal matrix satisfies
detailed balance. We show, with several examples, that this result is
particularly powerful when applied to non-local algorithms.


title: New Universality Classes for Two-Dimensional $\sigma$-Models

abstract:
  We argue that the two-dimensional $O(N)$-invariant lattice $\sigma$-model
with mixed isovector/isotensor action has a one-parameter family of nontrivial
continuum limits, only one of which is the continuum $\sigma$-model constructed
by conventional perturbation theory. We test the proposed scenario with a
high-precision Monte Carlo simulation for $N=3,4$ on lattices up to $512 \times
512$, using a Wolff-type embedding algorithm. [CPU time $\approx$ 7 years IBM
RS-6000/320H] The finite-size-scaling data confirm the existence of the
predicted new family of continuum limits. In particular, the $RP^{N-1}$ and
$N$-vector models do not lie in the same universality class.


title: Lyapunov Spectra in SU(2) Lattice Gauge Theory

abstract:
  We develop a method for calculating the Lyapunov characteristic exponents of
lattice gauge theories. The complete Lyapunov spectrum of SU(2) gauge theory is
obtained and Kolmogorov-Sinai entropy is calculated. Rapid convergence with
lattice size is found.


title: Calculations of hadronic matrix elements using lattice qcd

abstract:
  I give a brief introduction to the scope of lattice QCD calculations in our
effort to extract the fundamental parameters of the standard model. This goal
is illustrated by two examples. First I discuss the extraction of CKM matrix
elements from measurements of form factors for semi-leptonic decays of
heavy-light pseudoscalar mesons such as $D \to Ke\nu$. Second, I present the
status of results for the kaon $B$ parameter relevant to CP violation. I
conclude the talk with a short outline of our experiences with optimizing QCD
codes on the CM5.


title:
Computation of the Spatial String Tension in High Temperature SU(2)
  Gauge Theory

abstract:
  A detailed investigation of the temperature dependence of the spatial string
tension $\sigma_s$ in $SU(2)$ gauge theory is presented. A sustained
performance of 3~GFLOPS on a 64K Connection Machine CM-2 equivalent has been
achieved. Scaling of $\sigma_s$ between $\beta=2.5115$ and $\beta=2.74$, on
large lattices, is demonstrated. Below the critical temperature, $T_c$,
$\sigma_s$ remains constant. For temperatures larger than $2T_c$ the
temperature dependence can be parametrized by $\sigma_s(T) = (0.369\pm 0.014)^2
g^4(T)T^2$, where $g(T)$ is a 2-loop running coupling constant with the scale
parameter determined as $\Lambda_T = (0.076\pm 0.013)T_c$.


title: Perfect lattice action for asymptotically free theories

abstract:
  There exist lattice actions which give cut--off independent physical
predictions even on coarse grained lattices. Rotation symmetry is restored, the
spectrum becomes exact and, in addition, the classical equations have scale
invariant instanton solutions. This perfect action can be made short ranged. It
can be determined by combining analytical calculations with numerical
simulations on small lattices. We illustrate the method and the benefits on the
$d=2$ non--linear $\sigma$--model.


title: On the Transition from Crystalline to Dynamically Triangulated Surfaces

abstract:
  We consider methods of interpolating between the crystalline and dynamically
triangulated random surface models. We argue that actions based on the
deviation from six of the coordination number at a site are inadequate and
propose an alternative based on Alexander moves. Two simplified models, one of
which has a phase transition and the other of which does not, are discussed.


title: Lattice Perturbation Theory by Langevin Dynamics

abstract:
  We present an application of the standard Langevin dynamics to the problem of
weak coupling perturbative expansions for Lattice QCD. This method can be
applied to the computation of the most general observables. In this preliminary
work we will concentrate in particular on the computation of the perturbative
terms of the $1\times 1$ Wilson loop, up to fourth order. It is shown that a
stochastic gauge fixing is a possible solution to the problem of divergent
fluctuations which affect higher order coefficients.


title: Semi-leptonic Decays of Heavy Flavours on a Fine Grained Lattice

abstract:
  We present the results of a numerical calculation of semi-leptonic form
factors relevant for heavy flavour meson decays into light mesons, at
$\beta=6.4$ on a $24^3 \times 60$ lattice, using the Wilson action in the
quenched approximation. We obtain $f^+_K(0)=0.65\pm 0.18$, $V(0)=0.95\pm 0.34$,
$A_1(0)=0.63\pm 0.14 $ and $A_2(0)=0.45\pm 0.33 $. We also obtain
$A_1(q^2_{max})=0.62\pm 0.09$, $V(0)/A_1(0)=1.5\pm 0.28 $ and
$A_2(0)/A_1(0)=0.7\pm 0.4$. The results for $f^+_K(0)$, $V(0)$ and $A_1(0)$ are
consistent with the experimental data and with previous lattice determinations
with larger lattice spacings. In the case of $A_2(0)$ the errors are too large
to draw any firm conclusion. We have also extrapolated the form factors to the
B meson, showing a behaviour compatible with the predictions by the heavy quark
effective theory (HQET). Within large uncertainties, our results suggest that
$A_2/A_1$ increases with the heavy quark mass. We also get very rough estimates
for the partial decay widths $B \rightarrow \pi l \nu_l)=\vert V_{ub} \vert^2
(12 \pm 8) 10^{12} s^{-1}$ and $\Gamma(B \rightarrow \rho l \nu_l)=\vert V_{ub}
\vert^2 (13 \pm12) 10^{12} s^{-1}$, which can be used to give upper bounds on
the rates


title:
Perturbative renormalization factors for bilinear and four-quark
  operators for Kogut-Susskind fermions on the lattice

abstract:
  Renormalization factors for bilinear and four-quark operators with the
Kogut-Susskind fermion action are perturbatively calculated to one-loop order
in the general covariant gauge. Results are presented both for gauge invariant
and non-invariant operators. For four-quark operators the full renormalization
matrix for a complete set of operators with two types of color contraction
structures are worked out and detailed numerical tables are given.


title:
Non-gauge fixing approach to chiral gauge theories using staggered
  fermions

abstract:
  We investigate a proposal for the construction of models with chiral fermions
on the lattice using staggered fermions. In this approach the gauge invariance
is broken by the coupling of the staggered fermions to the gauge fields.
Motivated by previous results in the non-gauge invariant massive Yang-Mills
theory and certain gauge-fermion models we aim at a dynamical restoration of
the gauge invariance in the full quantum model. If the gauge symmetry breaking
is not too severe, this procedure could lead in the continuum limit to the
desired gauge invariant chiral gauge theory. This scenario is very attractive
since it does not rely on gauge fixing. We investigate a simple realization of
this approach in a U(1) axial-vector model with dynamical fermions in four
dimensions.


title: Glueball Mass Predictions of the Valence Approximation to Lattice QCD

abstract:
  We evaluate the infinite volume, continuum limit of glueball masses in the
valence (quenched) approximation to lattice QCD. For the lightest states with
$J^{PC}$ of $0^{++}$ and $2^{++}$, we obtain $m_0 = 1340 \pm 160$ MeV and $m_2
= 1900 \pm 320$ MeV.


title: Chiral Fermions on the Lattice

abstract:
  An expression for the lattice effective action induced by chiral fermions in
any even dimensions in terms of an overlap of two states is shown to have
promising properties in two dimensions: The correct abelian anomaly is
reproduced and instantons are suppressed.


title: Test of the Skyrme Effective Field Theory Using Quenched Lattice QCD

abstract:
  The Skyrme effective field theory is tested by evaluating nucleon ground
state matrix elements of the correlation functions for two flavor density
operators and two pseudoscalar density operators in the Skyrme model and
comparing them with results in quenched lattice QCD. The possiblility of using
quenched lattice QCD to study higher-order terms in effective field theory is
also discussed.


title: Fresh look on triality

abstract:
  Investigating the $Z_3$ symmetry in Quantum Chromodynamics (QCD) we show that
full QCD with a vacuum of vanishing baryonic number does not lead to metastable
phases. Rather in QCD with dynamical fermions, the degeneracy of $Z_3$ phases
manifests itself in observables without open triality.


title:
The Static Quark-Antiquark Potential: A ``Classical'' Experiment On The
  Connection Machine CM-2

abstract:
  We describe the Wuppertal university pilot project in applied parallel
computing. We report on a comprehensive high statistics determination of the
static quark-antiquark potential and related quantities from quenched quantum
chromodynamics. New data for the string tension and the plaquette action for
the region 5.5 < beta < 6.8 is presented.


title: Stochastic Estimation with $Z_2$ Noise

abstract:
  We introduce a $Z_2$ noise for the stochastic estimation of matrix inversion
and discuss its superiority over other noises including the Gaussian noise.
This algorithm is applied to the calculation of quark loops in lattice quantum
chromodynamics that involves diagonal and off-diagonal traces of the inverse
matrix. We will point out its usefulness in its applications to estimating
determinants, eigenvalues, and eigenvectors, as well as its limitations based
on the structure of the inverse matrix.


title: Manifestly Gauge Invariant Models of Chiral Lattice Fermions

abstract:
  A manifestly gauge invariant lattice action for nonanomalous chiral models is
proposed which leads in the continuum limit to the theory free of doublers.


title: Dgsos on DTRS

abstract:
  We perform simulations of a discrete gaussian solid on solid (DGSOS) model on
dynamical $\phi^3$ graphs, which is equivalent to coupling the model to 2d
quantum gravity, using the cluster algorithms recently developed by Evertz
et.al.for use on fixed lattices. We find evidence from the growth of the
width-squared in the rough phase of KT-like behaviour, which is consistent with
theoretical expectations. We also investigate the cluster statistics, dynamical
critical exponent and lattice properties, and compare these with the dual XY
model.


title: Bit Level Correlations in Some Pseudorandom Number Generators

abstract:
  We present results of extensive bit level tests on some pseudorandom number
generators which are commonly used in physics applications. The generators have
first been tested with an extended version of the $d$-tuple test. Second, we
have developed a novel {\it cluster test} where a physical analogy of the
binary numbers with the two dimensional Ising model has been utilized. We
demonstrate that the new test is rather powerful in finding periodic
correlations on bit level. Results of both test methods are presented for each
bit of the output of the generators. Some generators exhibit clear bit level
correlations but we find no evidence of discernible correlations for
generators, which have recently produced systematic errors in Monte Carlo
simulations.


title: The Isgur-Wise Function from the Lattice

abstract:
  We calculate the Isgur-Wise function by measuring the elastic scattering
amplitude of a $D$ meson in the quenched approximation on a $24^3\times48$
lattice at $\beta=6.2$, using an $O(a)$-improved fermion action. Fitting the
resulting chirally-extrapolated Isgur-Wise function to Stech's
relativistic-oscillator parametrization, we obtain a slope parameter
$\rho^2=1.2+7-3. We then use this result, in conjunction with heavy-quark
symmetry, to extract $V_{cb}$\ from the experimentally measured $\bar B\to
D^*l\bar\nu\,$\ differential decay width. We find
$|V_{cb}|\sqrt{\tau_B/1.48{\mathrm ps}}= 0.038 +2-2 +8-3, where the first set
of errors is due to experimental uncertainties, while the second is due to the
uncertainty in our lattice determination of $\rho^2$.


title: Quenched Heavy-Light Decay Constants

abstract:
  We present results for heavy-light decay constants, using both propagating
quarks and the static approximation, in O(a)-improved, quenched lattice QCD. At
beta=6.2 on a 24^3x48 lattice we find f_D=185 +4-3(stat)+42-7(syst) MeV,
f_B=160 +6-6 +53-19 MeV, f_{D_s}/f_D=1.18 +2-2 and f_{B_s}/f_B=1.22 +4-3, in
good agreement with earlier studies. From the static theory we obtain
f_B^stat=253 +16-15 +105-14 MeV. We also present results from a simulation at
beta=6.0 on a 16^3x48 lattice, which are consistent with those at beta=6.2. In
order to study the effects of improvement, we present a direct comparison of
the results using both the Wilson and the improved action at beta=6.0.


title:
Large Loops of Magnetic Current and Confinement in Four Dimensional
  $U(1)$ Lattice Gauge Theory

abstract:
  We calculate the heavy quark potential from the magnetic current due to
monopoles in four dimensional $U(1)$ lattice gauge theory. The magnetic current
is found from link angle configurations using the DeGrand-Toussaint
identification method. The link angle configurations are generated in a cosine
action simulation on a $24^4$ lattice. The magnetic current is resolved into
large loops which wrap around the lattice and simple loops which do not.
Wrapping loops are found only in the confined phase. It is shown that the long
range part of the heavy quark potential, in particular the string tension, can
be calculated solely from the large, wrapping loops of magnetic current.


title: A New visita to the SU(N) gauge field confinement

abstract:
  Based on our exact effective spin model, the zero temperature $SU(N)$ gauge
field confinement has been studied by the deconfinement-confinement phase
transition order parameter, i.e. the Wilson line, rather than the quark
antiquark potential. The procedure would allow one to study the confinement in
the true continuum limit. For the $(1+1)$ $SU(2)$ gauge field, the confinement
and a linear zero temperature Polyakov quark antiquark potential were shown. It
is also shown, for the first time, that the Polyakov and Wilson potentials are
identical.


title: Determining the order of SU(3) deconfining phase transition

abstract:
  An effective spin model for the finite temperature non-abelian lattice gauge
theory is derived. The outcome is the surprising result that only nearest
neighbor coupling survives, thus confirming the well known numerical results
that the deconfining phase transition of the (3+1)-dimensional $SU(3)$ pure
gauge theory is first order.


title: On a mean field approximation for Higgs-Yukawa systems

abstract:
  We discuss the phase structure of a lattice Higgs-Yukawa system in the
variational mean field approximation with contributions of fermionic
determinant being calculated in a ladder approximation. In particular, we
demonstrate that in this approximation the ferrimagnetic phase in the $Z_2$
model with naive fermions can appear as an artifact of a finite lattice and
that the phase diagram for this model on infinite lattice changes qualitatively
at space-time dimension $D = 4$ compared with those at $D > 4$.


title: The Light Hadron Spectrum and Decay Constants in Quenched Lattice QCD

abstract:
  We present results for light hadrons composed of both degenerate and
non-degenerate quarks in quenched lattice QCD. We calculate masses and decay
constants using 60 gauge configurations with an $O(a)$--improved fermion action
at $\beta = 6.2$. Using the $\rho$ mass to set the scale, we find hadron masses
within two to three standard deviations of the experimental values (given in
parentheses): $m_{K^*}=868\er{9}{8}$~MeV (892~MeV),
$m_{\phi}=970\err{20}{10}$~MeV (1020~MeV), $m_N=820\err{90}{60}$~MeV (938~MeV),
$m_\Delta=1300\errr{100}{100}$~MeV (1232~MeV) and
$m_\Omega=1650\err{70}{50}$~MeV (1672~MeV). Direct comparison with experiment
for decay constants is obscured by uncertainty in current renormalisations.
However, for ratios of decay constants we obtain $f_K/f_\pi=1.20\er{3}{2}$
(1.22) and $f_\phi/f_\rho=1.13\er{2}{3}$ (1.22).


title: Interface Tension in Quenched QCD

abstract:
  We calculate the tension $\sigma$ of the interface between the confined and
deconfined phases by the histogram method in SU(3) lattice gauge theory for
temporal extents of 4 and 6 using the recent high-statistics data by QCDPAX
collaboration. The results are $\sigma/T_c^3 = 0.0292(22)$ and 0.0218(33) for
$N_t=4$ and 6, respectively. The ratio $\sigma/T_c^3$ shows a scaling violation
similar to that already observed for the latent heat $\latent$. However, we
find that the physically interesting dimensionless combinations
$(\sigma^{3}/\latent^2 T)^{1/2}$ and $\sigma T/ \latent$ scale within the
statistical errors.


title: Critical Exponent for the Density of Percolating Flux

abstract:
  This paper is a study of some of the critical properties of a simple model
for flux. The model is motivated by gauge theory and is equivalent to the Ising
model in three dimensions. The phase with condensed flux is studied. This is
the ordered phase of the Ising model and the high temperature, deconfined phase
of the gauge theory. The flux picture will be used in this phase. Near the
transition, the density is low enough so that flux variables remain useful.
There is a finite density of finite flux clusters on both sides of the phase
transition. In the deconfined phase, there is also an infinite, percolating
network of flux with a density that vanishes as $T \rightarrow T_{c}^{+}$. On
both sides of the critical point, the nonanalyticity in the total flux density
is characterized by the exponent $(1-\alpha)$. The main result of this paper is
a calculation of the critical exponent for the percolating network. The
exponent for the density of the percolating cluster is $ \zeta = (1-\alpha) -
(\varphi-1)$. The specific heat exponent $\alpha$ and the crossover exponent
$\varphi$ can be computed in the $\epsilon$-expansion. Since $\zeta <
(1-\alpha)$, the variation in the separate densities is much more rapid than
that of the total. Flux is moving from the infinite cluster to the finite
clusters much more rapidly than the total density is decreasing.


title:
A Precise Determination of the Running Coupling in the SU(3) Yang-Mills
  Theory

abstract:
  A non-perturbative finite-size scaling technique is used to study the
evolution of the running coupling (in a certain adapted scheme) in the SU(3)
Yang-Mills theory. At low energies contact is made with the fundamental
dynamical scales, such as the string tension K, while at larger energies the
coupling is shown to evolve according to perturbation theory. In that regime
the coupling in the MS-bar scheme of dimensional regularization is obtained
with an estimated total error of a few percent.


title:
Static Friction Phenomena in Granular Materials: Coulomb Law vs.
  Particle Geometry

abstract:
  The static as well as the dynamic behaviour of granular material are
determined by dynamic {\it and} static friction. There are well known methods
to include static friction in molecular dynamics simulations using scarcely
understood forces. We propose an Ansatz based on the geometrical shape of
nonspherical particles which does not involve an explicit expression for static
friction. It is shown that the simulations based on this model are close to
experimental results.


title: Glueball-Like Screening Masses in Pure SU(3) at Finite Temperatures

abstract:
  We investigate the finite-temperature excitation spectrum in the gluon sector
of $SU(3)$ pure gauge theory through measurements of screening masses in
correlations of loop operators. We develop the classification of such operators
under the symmetry group of the `$z$-slice'. In the confined phase of the
theory, we find that the spectrum dynamically realises the zero temperature
symmetries. We observe a large thermal shift of the $0^{++}$ glueball mass. In
the deconfined phase, the spectrum distinguishes between operators coupling to
electrically and magnetically polarised gluon fields. The former yields a
screening mass equal to the Wilson-line screening mass; the latter, a method
for the measurement of the magnetic mass in the high-temperature limit.


title: On the Measure of Simplicial Quantum Gravity in Four Dimensions

abstract:
  We study quantum gravity in the path-integral formulation using the Regge
calculus. In spite of the unbounded gravitational action the existence of an
entropy-dominated phase is confirmed. The influence of various types of
measures on this phase structure is investigated and our results are compared
with those obtained by dynamical triangulation.


title: Instantons from over-improved cooling

abstract:
  Lattice artefacts are used, through modified lattice actions, as a tool to
find the largest instantons in a toroidal geometry [0,L]^3X[0,T] for T to
infinity. It is conjectured that the largest instanton is associated with
tunnelling through a sphaleron. Existence of instantons with at least 8
parameters can be proven with the help of twisted boundary conditions in the
time direction. Numerical results for SU(2) gauge theory obtained by cooling
are presented to demonstrate the viability of the method.


title:
Phase diagrams of a Higgs-Yukawa system with chirally invariant lattice
  fermion actions

abstract:
  We study the phase structure of a $Z_2$ lattice Higgs-Yukawa system with
different forms of chirally invariant lattice fermion actions: naive, two types
of non-local actions, and a mirror fermion action. The calculations are
performed in the variational mean field approximation with contribution of
fermionic determinant being calculated in a ladder approximation. We
demonstrate that the phase structure of the system crucially depends on the
form of the lattice fermion action, despite the fact that the Higgs field
couples to fermions in the same local way. A possibility of defining chiral
gauge theories based on mirror fermion action is briefly discussed.


title:
Hadron Spectrum and Matrix Elements in QCD with Dynamical Wilson
  Fermions at 6/g^2=5.3

abstract:
  We present results of a lattice simulation of quantum chromodynamics with two
degenerate flavors of dynamic Wilson fermions at $6/g^2=5.3$ at each of two
dynamical fermion hopping parameters, $\kappa=0.1670$ and 0.1675, corresponding
to pion masses in lattice units of about 0.45 and 0.31. The simulations include
three other values of valence quark mass, in addition to the dynamical quarks.
We present calculations of masses and of the decay constants of vector mesons
and of pseudoscalars, including the D-meson decay constant. The effects of sea
quarks on matrix elements and spectroscopy are small.


title: The Nielsen-Ninomiya ``No-Go'' Theorem is False

abstract:
  The Nielsen-Ninomiya no-go theorem asserts that chiral Weyl~(``neutrino'')
fields cannot exist on lattices. However, the actual mathematical arguments
advanced in the theorem fail to make that case. The theorem leaves the problem
of lattice neutrinos completely open; it identifies no obstacle which would
prevent us from discretizing chiral theories.
  (INFORMAL ABSTRACT: Have you too, like every second person in the field, been
citing the Nielsen-Ninomiya theorem but have not read or analyzed it? Then,
this paper will wake you up. Reading it is a prerequisite to doing any good
work in chiral lattice physics.)


title: Weyl Neutrinos on a Lattice: An Explicit Construction

abstract:
  Introducing a new and universally applicable discretizing technique, I
construct a class of local and unitary lattice theories of Weyl neutrinos; this
solves a longstanding and allegedly unsolvable problem in quantum field theory.
En route, I also prove a general ``go'' theorem that all Lagrangian-density
based continuum quantum field theories can be lattice-regularized.
  (INFORMAL ABSTRACT: You didn't study the Nielsen-Ninomiya theorem, only
trusted the authors to have proven ``the absence of neutrinos on a lattice''.
Well, they didn't. Nor can anyone else: every continuum theory can be
lattice-regularized. A proof of that, plus an explicit construction of lattice
neutrinos: if you read only one paper this year, here it is! From now on, this
is how chiral fermions should be latticized. All else is gaslight.)


title: Perturbative analysis for Kaplan's lattice chiral fermions

abstract:
  Perturbation theory for lattice fermions with domain wall mass terms is
developed and is applied to investigate the chiral Schwinger model formulated
on the lattice by Kaplan's method. We calculate the effective action for gauge
fields to one loop, and find that it contains a longitudinal component even for
anomaly-free cases. From the effective action we obtain gauge anomalies and
Chern-Simons current without ambiguity. We also show that the current
corresponding to the fermion number has a non-zero divergence and it flows off
the wall into the extra dimension. Similar results are obtained for a proposal
by Shamir, who used a constant mass term with free boundaries instead of domain
walls.


title:
Investigation of the Domain Wall Fermion Approach to Chiral Gauge
  Theories on the Lattice

abstract:
  We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.


title: Lattice Gauge Theory -- Present Status

abstract:
  Lattice gauge theory is our primary tool for the study of non-perturbative
phenomena in hadronic physics. In addition to giving quantitative information
on confinement, the approach is yielding first principles calculations of
hadronic spectra and matrix elements. After years of confusion, there has been
significant recent progress in understanding issues of chiral symmetry on the
lattice. (Talk presented at HADRON 93, Como, Italy, June 1993.)


title: Baryon Density Correlations in High Temperature Hadronic Matter

abstract:
  As part of an ongoing effort to characterize the high temperature phase of
QCD, in a numerical simulation using the staggered fermion scheme, we measure
the quark baryon density in the vicinity of a fixed test quark at high
temperature and compare it with similar measurements at low temperature and at
the crossover temperature. We find an extremely weak correlation at high
temperature, suggesting that small color singlet clusters are unimportant in
the thermal ensemble. We also find that at $T = 0.75\ T_c$ the total induced
quark number shows a surprisingly large component attributable to baryonic
screening. A companion simulation of a simple flux tube model produces similar
results and also suggests a plausible phenomenological scenario: As the
crossover temperature is approached from below, baryonic states proliferate.
Above the crossover temperature the mean size of color singlet clusters grows
explosively, resulting in an effective electrostatic deconfinement.


title: Anomalous fermion number violation and numerical simulations

abstract:
  After discussing the problem of lattice regularization of chiral gauge
theories, a simple model for anomalous fermion number violation is formulated
which can be numerically studied with present day technique. Exploratory
results of numerical simulations of a two-dimensional U(1) Higgs model are
presented.


title:
Renormalization Group Study of the soliton mass on the (lambda
  Phi^4)_{1+1} lattice model

abstract:
  We compute, on the $(\lambda \Phi^4)_{1+1}$ model on the lattice, the soliton
mass by means of two very different numerical methods. First, we make use of a
``creation operator'' formalism, measuring the decay of a certain correlation
function. On the other hand we measure the shift of the vacuum energy between
the symmetric and the antiperiodic systems. The obtained results are fully
compatible.
  We compute the continuum limit of the mass from the perturbative
Renormalization Group equations. Special attention is paid to ensure that we
are working on the scaling region, where physical quantities remain unchanged
along any Renormalization Group Trajectory. We compare the continuum value of
the soliton mass with its perturbative value up to one loop calculation. Both
quantities show a quite satisfactory agreement. The first is slightly bigger
than the perturbative one; this may be due to the contributions of higher order
corrections.


title:
A Portable High-Quality Random Number Generator for Lattice Field Theory
  Simulations

abstract:
  The theory underlying a proposed random number generator for numerical
simulations in elementary particle physics and statistical mechanics is
discussed. The generator is based on an algorithm introduced by Marsaglia and
Zaman, with an important added feature leading to demonstrably good statistical
properties. It can be implemented exactly on any computer complying with the
IEEE--754 standard for single precision floating point arithmetic.


title: A Consumer's Guide to Lattice QCD Results

abstract:
  I present an overview of recent lattice QCD results on hadron spectroscopy
and matrix elements. Case studies include light quark spectroscopy, the
determination of $\alpha_s$ from heavy quark spectroscopy, the D-meson decay
constant, a calculation of the Isgur-Wise function, and some examples of the
(lack of) effect of sea quarks on matrix elements. The review is intended for
the non-expert. Talk presented at the 1993 Slac Summer Institute


title: Scaling of Pseudo-Critical Couplings in Two-Flavour QCD

abstract:
  We study the scaling behaviour of the pseudo-critical couplings for the
chiral phase transition in two-flavour QCD. We show that all existing results
from lattice simulations on lattices with temporal extent $N_\tau = 4$, 6 and 8
can be mapped onto a universal scaling curve. The relevant combination of
critical exponents, $\beta\delta$, is consistent with the scaling behaviour
expected for a second order phase transition with $O(4)$ exponents. At present,
scaling according to the $O(2)$ symmetry group can, however, not be ruled out.


title: Instantons and Surface Tension at a First-Order Transition

abstract:
  We study the dynamics of the first order phase transition in the two
dimensional 15-state Potts model, both at and off equilibrium. We find that
phase changes take place through nucleation in both cases, and finite volume
effects are described well through an instanton computation. Thus a dynamical
measurement of the surface tension is possible. We find that the order-disorder
surface tension is compatible with perfect wetting. An accurate treatment of
fluctuations about the instanton solution is seen to be of great importance.


title:
Almost Gauge Invariant Lattice Actions for Chiral Gauge Theories, using
  Laplacian Gauge Fixing

abstract:
  It is described how to obtain an almost gauge invariant lattice action $S$
for chiral gauge theories, or other models in which a straightforward
discretization leads to a lattice action $S^\pr$ in which gauge invariance is
broken. The lattice action is `almost' gauge invariant, because a local gauge
transformation leaves the action the same, up to a global gauge transformation.
In this approach the action $S$ for all gauge fields on a gauge orbit is the
same as that of the action $S^\pr$ evaluated for the gauge field fixed to a
smooth gauge. To define $S$ unambiguously, it must be possible to compute the
gauge fixed field unambiguously. This rules out gauge conditions which suffer
from Gribov ambiguities but it can be achieved by using the recently proposed
Laplacian gauge. When using the almost gauge invariant action $S$ in a
numerical simulation, it is not necessary to fix the gauge, and hence gauge
fixing terms and Fadeev-Popov ghosts are not required. A hybrid Monte Carlo
algorithm for simulations with this new action is described and tested on a
simple toy model.


title: 2D O(3) + 2D QG

abstract:
  It has been suggested that the peak in the specific heat observed numerically
for random surface actions with extrinsic curvature on dynamical lattices might
be the result of a low mass bound state in an asymptotically free theory,
rather than the signal for a real phase transition. The $O(3)$ model on a fixed
lattice displays just such behaviour, but in general transitions appear to be
weakened when the models concerned are put on dynamical lattices (ie coupled to
2d quantum gravity). We have therefore performed simulations of the $O(3)$
model on dynamical $\phi^3$ graphs to see if there is still a peak in the
specific heat and compared the results with those on fixed lattices.


title: Perturbative Corrections for Staggered Four-Fermion Operators

abstract:
  We present results for one-loop matching coefficients between continuum
four-fermion operators, defined in the Naive Dimensional Regularization scheme,
and staggered fermion operators of various types. We calculate diagrams
involving gluon exchange between quark lines, and ``penguin'' diagrams
containing quark loops. For the former we use Landau gauge operators, with and
without $O(a)$ improvement, and including the tadpole improvement suggested by
Lepage and Mackenzie.For the latter we use gauge-invariant operators. Combined
with existing results for two-loop anomalous dimension matrices and one-loop
matching coefficients, our results allow a lattice calculation of the
amplitudes for $K\bar K$ mixing and $K\to\pi\pi$ decays with all corrections of
$O(g^2)$ included. We also discuss the mixing of $\Delta S=1$ operators with
lower dimension operators, and show that, with staggered fermions, only a
single lower dimension operator need be removed by non-perturbative
subtraction.


title: Zooming-in on the SU(2) fundamental domain

abstract:
  For SU(2) gauge theories on the three-sphere we analyse the Gribov horizon
and the boundary of the fundamental domain in the 18 dimensional subspace that
contains the tunnelling path and the sphaleron and on which the energy
functional is degenerate to second order in the fields. We prove that parts of
this boundary coincide with the Gribov horizon with the help of bounds on the
fundamental modular domain.


title: Anomalies and chiral defect fermions

abstract:
  Chiral defect fermions in the background of an external, $2n$ dimensional
gauge field are considered. Assuming first a finite extra dimension, we
calculate the axial anomaly in a vector-like, gauge invariant model for
arbitrary $n$, and the consistent anomaly in a gauge {\it variant} model with a
chiral spectrum. For technical reasons, the latter calculation is limited to
the $2+1$ dimensional case. We also show that the infinite lattice chiral
model, when properly defined, is in fact a limiting case of the above
gauge-variant model. The behaviour of this model with a dynamical gauge field
is discussed.


title: Semileptonic form factors of heavy-light mesons from lattice QCD

abstract:
  The form factors for the semileptonic decays of heavy-light pseudoscalar
mesons of the type $D \to Ke\nu$ are studied in quenched lattice QCD at
$\beta=6.0$ using Wilson fermions. We explore new numerical techniques for
improving the signal and study $O(a)$ corrections using three different lattice
transcriptions of the vector current. We present a detailed discussion of the
relation of these lattice currents to the continuum vector current and show
that the disagreement between the previous results is to a large extent due to
the value of $Z_V$ used in the calculations. We also present results for the
decay constants of light-light, heavy-light and heavy-heavy mesons.


title: The Nambu--Jona-Lasinio Model of QCD on the Lattice

abstract:
  In an effort to investigate some of the low energy properties of QCD, in
particular those related to chiral symmetry breaking, as well as to obtain
insights on the behavior of an interacting theory of fermions on the lattice,
the two flavor Nambu--Jona-Lasinio model with $SU(2) \times SU(2)$ chiral
symmetry is studied on the four--dimensional hypercubic lattice using large $N$
techniques and numerical simulations. Naive and Wilson fermions are considered
and transparent results are obtained regarding the following: the scalar and
pseudoscalar spectrum, the approach to the continuum and chiral limits, the
size of the $1/N$ corrections, and the effects of the zero momentum fermionic
modes on finite lattices. Also, some interesting observations are made by
viewing the model as an embedding theory of the Higgs sector. Note: The full ps
file of this preprint is also available via anonymous ftp to ftp.scri.fsu.edu.
To get the ps file, ftp to this address and use for username "anonymous" and
for password your name. The file is in the directory pub/vranas (to go to that
directory type: cd pub/vranas) and is called NJL.ps (to get it type: get
NJL.ps)


title: Meson Decay Constants from the Valence Approximation to Lattice QCD

abstract:
  We evaluate $f_{\pi}/ m_{\rho}$, $f_K/ m_{\rho}$, $1/f_{\rho}$, and $
m_{\phi}/(f_{\phi} m_{\rho})$, extrapolated to physical quark mass, zero
lattice spacing and infinite volume, for lattice QCD with Wilson quarks in the
valence (quenched) approximation. The predicted ratios differ from experiment
by amounts ranging from 12\% to 17\% equivalent to between 0.9 and 2.8 times
the corresponding statistical uncertainties.


title: Monopole Condensation and Confinement in SU(2) QCD (1)

abstract:
  An effective monopole action is derived from vacuum configurations after
abelian projection in the maximally abelian gauge in $SU(2)$ QCD. Entropy
dominance over energy of monopole loops is seen on the renormalized lattice
with the spacing $b>b_c\simeq 5.2\times10^{-3} \Lambda_L^{-1}$ when the
physical volume of the system is large enough. QCD confinement may be
interpreted as the (dual) Meissner effect due to the monopole condensation.


title: Monopole Condensation and Confinement in SU(2) QCD (2)

abstract:
  Monopole and photon contributions to Wilson loops are calculated using
Monte-Carlo simulations of SU(2) QCD in the maximally abelian gauge. The string
tensions of SU(2) QCD are well reproduced by extended monopole contributions
alone.


title:
Momentum Lattice Simulation on a Small Lattice Using Stochastic
  Quantization

abstract:
  We have studied the scalar $\phi^4$-model in the symmetric phase and the
non--compact $U(1)$ gauge theory on a momentum lattice using the Langevin
equation for generating configurations. In the $\phi^4$-model we have analyzed
the renormalized mass and in the $U(1)$-model we have analyzed the Wilson loop
operator. We used a second order algorithm for solving the Langevin equation,
and we looked for the convergence rate of the method. We studied the stochastic
time needed to generate equilibrium configurations and compared first and
second order schemes for both models.


title:
Comparison of Monte Carlo Results for the 3D Ising Interface Tension and
  Interface Energy with (Extrapolated) Series Expansions

abstract:
  We compare Monte Carlo results for the interface tension and interface energy
of the 3-dimensional Ising model with Pad\'e and inhomogeneous differential
approximants of the low temperature series that was recently extended by Arisue
to $17^{\rm th}$ order in $u=\exp(-4\beta)$. The series is expected to suffer
from the roughening singularity at $u\approx 0.196$. The comparison with the
Monte Carlo data shows that the Pad\'e and inhomogeneous differential
approximants fail to improve the truncated series result of the interface
tension and the interface energy in the region around the roughening
transition. The Monte Carlo data show that the specific heat displays a peak in
the smooth phase. Neither the truncated series nor the Pad\'e approximants find
this peak. We also compare Monte Carlo data for the energy of the ASOS model
with the corresponding low temperature series that we extended to order
$u^{12}$.


title: The Physical Phase of Dimensionally Reduced Gauge Theories

abstract:
  We investigate the relationship between the high temperature deconfined phase
of the SU(2) gauge theory to the phases of the corresponding three dimensional
adjoint Higgs model. For various temperatures we simulate the effective theory
in a neighbourhood of the physical states, that is of those values of the
coupling constants that describe the infrared behaviour of the four dimensional
theory and which have been calculated by applying dimensional reduction
techniques. We show that the physical points belong to the confined phase of
the SU(2) adjoint Higgs model.


title: A Cluster Method for the Ashkin--Teller Model

abstract:
  A cluster Monte Carlo algorithm for the Ashkin-Teller (AT) model is
constructed according to the guidelines of a general scheme for such
algorithms. Its dynamical behaviour is tested for the square lattice AT model.
We perform simulations on the line of critical points along which the exponents
vary continuously, and find that critical slowing down is significantly
reduced. We find continuous variation of the dynamical exponent $z$ along the
line, following the variation of the ratio $\alpha/\nu$, in a manner which
satisfies the Li-Sokal bound $z_{cluster}\geq\alpha/\nu$, that was so far
proved only for Potts models.


title:
Monte Carlo Simulation of 2-D Quantum Gravity as Open Dynamically
  Triangulate Random Surfaces

abstract:
  We describe a Monte Carlo procedure for the simulation of dynamically
triangulate random surfaces with a boundary (topology of a disk). The algorithm
keeps the total number of triangles fixed, while the length of the boundary is
allowed to fluctuate. The algorithm works in the presence of matter fields. We
here present results for the pure gravity case. The algorithm reproduces the
theoretical expectations.


title: Discretized Laplacians on an Interval and their Renormalization Group

abstract:
  The Laplace operator admits infinite self-adjoint extensions when considered
on a segment of the real line. They have different domains of essential
self-adjointness characterized by a suitable set of boundary conditions on the
wave functions. In this paper we show how to recover these extensions by
studying the continuum limit of certain discretized versions of the Laplace
operator on a lattice. Associated to this limiting procedure, there is a
renormalization flow in the finite dimensional parameter space describing the
dicretized operators. This flow is shown to have infinite fixed points,
corresponding to the self-adjoint extensions characterized by scale invariant
boundary conditions. The other extensions are recovered by looking at the other
trajectories of the flow.


title: Quark Mass Renormalization on the Lattice with Staggered Fermions

abstract:
  The QCD light quark mass renormalized at a 1 GeV scale in the $ \overline{MS}
$ scheme is obtained from the numerical results of the lattice QCD simulation
with staggered fermions. The primary emphasis is given to the connection
between the lattice and continuum parameters. The results are compared with
those from the QCD sum rule.


title: The running coupling from lattice gauge theory:

abstract:
  I discuss some calculations of the running coupling in SU($N$) gauge theories
from lattice simulations, centering on the work of the UKQCD collaboration.
This talk is introductory in nature; full details have been published
elsewhere.


title: Critical Behaviour of the 3d Gross-Neveu and Higgs-Yukawa Models

abstract:
  We measure the critical exponents of the three dimensional Gross-Neveu model
with two four-component fermions. The exponents are inferred from the scaling
behaviour of observables on different lattice sizes. We also calculate the
exponents, through a second order epsilon-expansion around 4d, for the three
dimensional Higgs-Yukawa model, which is expected to be in the same
universality class and we find that the exponents agree. We conclude that the
equivalence of the two models remains valid in 3d at fixed small N_f values.


title:
An Algorithm for Dynamic Load Balancing of Synchronous Monte Carlo
  Simulations on Multiprocessor Systems

abstract:
  We describe an algorithm for dynamic load balancing of geometrically
parallelized synchronous Monte Carlo simulations of physical models. This
algorithm is designed for a (heterogeneous) multiprocessor system of the MIMD
type with distributed memory. The algorithm is based on a dynamic partitioning
of the domain of the algorithm, taking into account the actual processor
resources of the various processors of the multiprocessor system.


title:
A New Way to Set the Energy Scale in Lattice Gauge Theories and its
  Application to the Static Force and $\alpha_s$ in SU(2) Yang--Mills Theory

abstract:
  We introduce a hadronic scale $R_0$ through the force $F(r)$ between static
quarks at intermediate distances $r$. The definition $F(R_0)R_0^2=1.65$ amounts
to $R_0 \simeq 0.5$~fm in phenomenological potential models. Since $R_0$ is
well defined and can be calculated accurately in a Monte Carlo simulation, it
is an ideal quantity to set the scale. In SU(2) pure gauge theory, we use new
data (and $R_0$ to set the scale) to extrapolate $F(r)$ to the continuum limit
for distances $r=0.18$~fm to $r=1.1$~fm. Through $R_0$ we determine the energy
scale in the recently calculated running coupling, which used the recursive
finite size technique to reach large energy scales. Also in this case, the
lattice data can be extrapolated to the continuum limit. The use of one loop
Symanzik improvement is seen to reduce the lattice spacing dependence
significantly.
  Warning: The preprint is not completely fresh, but maybe you haven't seen
it...


title: The nature of the thermal phase transition with Wilson quarks

abstract:
  We describe a series of simulations of high temperature QCD with two flavors
of Wilson quarks aimed at clarifying the nature of the high temperature phase
found in current simulations. Most of our work is with four time slices,
although we include some runs with six and eight time slices for comparison. In
addition to the usual thermodynamic observables we study the quark mass defined
by the divergence of the axial current and the quark propagator in the Landau
gauge. We find that the sharpness of the $N_t=4$ thermal transition has a
maximum around $\kappa=0.19$ and $6/g^2=4.8$.


title:
Interface Tensions and Perfect Wetting in the Two-Dimensional
  Seven-State Potts Model

abstract:
  We present a numerical determination of the order-disorder interface tension,
\sod, for the two-dimensional seven-state Potts model. We find
$\sod=0.0114\pm0.0012$, in good agreement with expectations based on the
conjecture of perfect wetting. We take into account systematic effects on the
technique of our choice: the histogram method. Our measurements are performed
on rectangular lattices, so that the histograms contain identifiable plateaus.
The lattice sizes are chosen to be large compared to the physical correlation
length. Capillary wave corrections are applied to our measurements on finite
systems.


title: Ising Model Universality for Two-Dimensional Lattices

abstract:
  We use the single-cluster Monte Carlo update algorithm to simulate the Ising
model on two-dimensional Poissonian random lattices of Delaunay type with up to
80\,000 sites. By applying reweighting techniques and finite-size scaling
analyses to time-series data near criticality, we obtain unambiguous support
that the critical exponents for the random lattice agree with the exactly known
exponents for regular lattices, i.e., that (lattice) universality holds for the
two-dimensional Ising model.


title: Fitting Correlated Data

abstract:
  We discuss fitting correlated data - with the example of hadron mass
spectroscopy in mind. The main conclusion is that the method of minimising
correlated $\chi^2$ is unreliable if the data sample is too small.


title: A Study of the Nambu--Jona-Lasinio Model on the Lattice

abstract:
  We present our full analysis of the two flavor Nambu--Jona-Lasinio model with
$SU(2) \times SU(2)$ chiral symmetry on the four--dimensional hypercubic
lattice with naive and Wilson fermions. We find that this model is an excellent
toy field theory to investigate issues related to lattice QCD. We use the large
$N$ approximation to leading order in $1/N$ to obtain non perturbative
analytical results over almost the whole parameter range. By using numerical
simulations we estimate that the size of the $1/N$ corrections for most of the
quantities we consider are small and in this way we strengthen the validity of
the leading order large $N$ calculations. We obtain results regarding the
approach to the continuum chiral limit, the effects of the zero momentum
fermionic modes on finite lattices and the scalar and pseudoscalar spectrum.
Note: The full ps file of this preprint is also available via anonymous ftp to
ftp.scri.fsu.edu. To get the ps file, ftp to this address and use for username
"anonymous" and for password your complete E-mail address. The file is in the
directory pub/vranas (to go to that directory type: cd pub/vranas) and is
called NJL_long.ps (to get it type: get NJL_long.ps)


title:
Capillary Wave Approach to Order-Order Fluid Interfaces in the 3D
  Three-State Potts Model

abstract:
  The physics of fluid interfaces between domains of different magnetization in
the ordered phase of the 3D three-state Potts model is studied by means of a
Monte Carlo simulation. It is shown that finite--size effects in the interface
free energy are well described by the capillary wave model at two loop order,
supporting the idea of the universality of this description of fluid interfaces
in 3D statistical models.


title:
Towards Multigrid Methods for Propagators of Staggered Fermions with
  Improved Averaging and Interpolation Operators

abstract:
  A Dirac choice for the averaging kernel $C$ is implemented numerically. This
improved kernel will be needed in gauge covariant multigrid computations for
propagators of staggered fermions. Results for $C$ and the variational coarse
grid operator will be given in 2-$d$ $SU(2)$ gauge fields. C++ is advocated for
future algorithm development.


title: C-Periodicity and the Physical Mass in the 3-State Potts Model

abstract:
  The standard infinite-volume definition of connected correlation function and
particle mass in the 3-state Potts model can be implemented in Monte Carlo
simulations by using C-periodic spatial boundary conditions. This avoids both
the breaking of translation invariance (cold wall b.c.) and the phase-dependent
and thus possibly biased evaluation of data (periodic boundary cconditions).
The numerical feasibility of the standard definitions is demonstrated by sample
computations on a 24*24*48 lattice.


title:
The crossover from first to second-order finite size scaling: A
  numerical study Christian Borgs

abstract:
  We consider a particular case of the two dimensional
  Blume-Emery-Griffiths model to study the finite-size scaling for a field
driven first-order phase transition with two coexisting phases not related by a
symmetry. For low temperatures we verify the asymptotic (large volume)
predictions of the rigorous theory of Borgs and Kotecky, including the
predictions concerning the so-called equal-weight versus equal-height
controversy. Near the critical temperature we show that all data fit onto a
unique curve, even when the correlation length xi becomes comparable to or
larger then the size of the system, provided the linear dimension L of the
system is rescaled by xi.


title: Full QCD on APE100 Machines

abstract:
  We present the first tests and results from a study of QCD with two flavours
of dynamical Wilson fermions using the Hybrid Monte Carlo Algorithm (HMCA) on
APE100 machines.


title: Compact U(1)xU(1) Model with Minimal Interspecies Interaction

abstract:
  We introduce a minimally interacting pure gauge compact U(1)xU(1) model
consistent with abelian projection symmetries. This paradigm, whose
interactions are entirely due to compactness, illustrates how compactness can
contribute to interspecies interactions. Furthermore, it has a much richer
phase structure(including a magnetically confining phase) than obtained by
naively tensoring together two compact U(1) copies.


title: $B \to K^* \gamma$: Penguins on the Lattice

abstract:
  We calculate the leading-order matrix element for the decay $B \to K^*
\gamma$ in the quenched approximation of lattice QCD on a $24^3 \times 48$
lattice at $\beta=6.2$, using an O(a)-improved fermion action. Extrapolating
the quark masses to their physical values we obtain an on-shell form factor of
$T_1(q^2=0)=0.15+12-14$, where the errors quoted are purely statistical. We
find $T_1$ is approximately independent of the spectator quark mass and extract
$T_1(q^2=0)=0.15+5-4$ if this independence is assumed. We compare this with the
same form factor derived (in the Standard Model) from the CLEO experimental
branching ratio of $BR(B \to K^* \gamma) = (4.5 \pm 1.5 \pm 0.9) \times
10^{-5}$ and find the results to be consistent within statistical errors.


title:
The SU(2) $\times$ SU(2) chiral spin model in terms of SO(3) and Z$_2$
  variables: vortices and disorder

abstract:
  We rewrite the two-dimensional SU(2)$\times$ SU(2) chiral spin model in terms
of SO(3) and {\bf Z}$_2$ degrees of freedom. The transformation, which is
motivated by a similar representation of the corresponding lattice gauge theory
in higher dimensions, exhibits the presence of dynamical SO(3) vortices and
associated strings. We present arguments that (pairs of) SO(3) vortices with
long strings play a crucial role in disordering the spin system at arbitrarily
low temperatures.


title: Radial Excited States for Heavy Quark Systems in NRQCD

abstract:
  Following the Non-Relativistic QCD approach we use a gauge invariant smearing
method with factorization to measure the excitation energies for a heavy
$Q\bar{Q}$ system on a $24^3\times 48$ lattice at $\beta=6.2$. The results come
from averaging over an ensemble of 60 QCD configurations. In order to enhance
the signal from each configuration we use wall sources for quark propagators.
The quark Hamiltonian contains only the simplest non-relativistic kinetic
energy term. The results are listed for a range of bare quark masses. The mass
splittings are insensitive to this variable though there are a slight trends
with increasing quark mass. For an appropriate choice of UV cut-off
($a^{-1}=3.2$Gev) the mass spectrum compares reasonably well with the
experimental values for the spin-averaged energy gaps of the $\Upsilon$ system.
We also present results for the $DE$ and $DT$ waves for the lowest bare quark
mass. The results are consistent with degeneracy between the two types of $D$
wave. This encourages the idea that even with our simple quark Hamiltonian the
departure from rotational invariance is not great.


title:
A New Approach to the Problem of Dynamical Quarks in Numerical
  Simulations of Lattice QCD

abstract:
  Lattice QCD with an even number of degenerate quark flavours is shown to be a
limit of a local bosonic field theory. The action of the bosonic theory is real
and bounded from below so that standard simulation algorithms can be expected
to apply. The feasibility of such calculations is discussed, but no practical
tests have yet been made.


title: Geometric Measurement of Topological Susceptibility on Large Lattices

abstract:
  The topological susceptibility of the quenched QCD vacuum is measured on
large lattices for three $\beta$ values from $6.0$ to $6.4$. Charges possibly
induced by $O(a)$ dislocations are identified and shown to have little effect
on the measured susceptibility. As $\beta$ increases, fewer such questionable
charges are found. Scaling is checked by examining the ratios of the
susceptibility to previously existing values of the rho mass, string tension,
F-pi, and lambda-lattice.


title: The Running Coupling From Lattice QCD

abstract:
  A recent lattice calculation of the QCD running coupling is presented. The
coupling is extracted from the force between two static quarks in the framework
of the valence quark approximation. A value of the Lambda-parameter for zero
quark flavours is determined: Lambda_msbar=0.630(38)\sqrt{\sigma}
=293(18)^{+25}_{-63} MeV. The first error is statistical, the second stems from
the overall scale uncertainty in the string tension sigma. Combining this value
with results from full QCD lattice simulations, we end up with the estimate
$\Lambda^{(4)}_{\overline{MS}}=129(8)^{+43}_{-60}$~MeV or
$\alpha_{\overline{MS}}(m_Z)=0.102^{+06}_{-11}$.


title: $B \to K^* + \gamma$ and $B_s \to \phi + \gamma$ on the Lattice

abstract:
  A lattice calculation of the form factors that determine the ``hadronization
ratios'', such as $R_{K^*}$ and $R_{\phi}$, where $R_{K^*} \equiv [\Gamma ($B
\to K^* \gamma$)/\Gamma(b \to s \gamma)]$, is presented in the quenched
approximation. Lattice data shows strong evidence for the scaling law suggested
by heavy quark symmetry for one of the form factors ({\it i.e.}\ $T_2$). The
data also gives strong support for the simple pole ansatz for the $q^2$
dependence of $T_2$ in the range of available $q^2$. We thus find $T_2(0) = .10
\pm.01\pm.03$ yielding $R_{K^*} =(6.0\pm1.2\pm3.4)\%$; we also find
$R_{\phi}=(6.6\pm1.3\pm3.7)\%$.


title: Random Walks in Noninteger Dimension

abstract:
  One can define a random walk on a hypercubic lattice in a space of integer
dimension $D$. For such a process formulas can be derived that express the
probability of certain events, such as the chance of returning to the origin
after a given number of time steps. These formulas are physically meaningful
for integer values of $D$. However, these formulas are unacceptable as
probabilities when continued to noninteger $D$ because they give values that
can be greater than $1$ or less than $0$. In this paper we propose a random
walk which gives acceptable probabilities for all real values of $D$. This
$D$-dimensional random walk is defined on a rotationally-symmetric geometry
consisting of concentric spheres. We give the exact result for the probability
of returning to the origin for all values of $D$ in terms of the Riemann zeta
function. This result has a number-theoretic interpretation.


title: The pi-N Sigma term - a lattice investigation

abstract:
  A lattice calculation of the pi-N sigma term is described using dynamical
staggered fermions. Preliminary results give a sea term comparable in magnitude
to the valence term.