title: Analyzing the spectrum of general, non-hermitian Dirac operators

abstract:
  We discuss the computational problems when analyzing general, non-hermitian
matrices and in particular the un-modified Wilson lattice Dirac operator. We
report on our experiences with the Implicitly Restarted Arnoldi Method. The
eigenstates of the Wilson-Dirac operator which have real eigenvalues and
correspond to zero modes in the continuum are analyzed by correlating the size
of the eigenvalues with the chirality of the eigenstates.


title: Static potential in the SU(2) Higgs model

abstract:
  We present results for the static potential in the confinement phase of the
SU(2) Higgs model on the lattice. Introducing a suitable matrix correlation
function we observe string breaking at a distance r_b ~ 1.8 r_0, where the
length scale r_0 has a value r_0 ~ 0.5 fm in QCD. The method presented here may
lead the way towards a treatment of string breaking in QCD.


title: Hybrid and Orbitally Excited Mesons in Full QCD

abstract:
  We present results for the hybrid meson spectrum produced by gluonic
excitations in full QCD using Wilson fermions. For the spin-exotic mesons with
J^{PC}=1^{-+}, 0^{+-}, and 2^{+-} we find the lightest state to be 1^{-+} with
a mass of 1.9(2) GeV. Results obtained for orbitally excited mesons are also
presented.


title:
New universality class of chiral symmetry breaking in the strongly
  coupled U(1) $\chi U \phi$ model

abstract:
  We describe a 4D U(1) lattice gauge theory with charged scalar $\phi$ and
fermion $\chi$ matter fields ($\chi U \phi$ model). At sufficiently strong
gauge coupling, the chiral symmetry is broken and the mass of the unconfined
composite fermion $F = \bar{\chi} \phi $ is generated dynamically by gauge
interaction. The scalar supresses this symmetry breaking and induces a line of
second order transitions with scaling properties similar to the
Nambu--Jona-Lasinio model. However, in the vicinity of a particular,
tricritical point the scaling properties are different. Here we study the
effective Yukawa coupling between the massive fermion and the Goldstone boson.
The perturbative triviality bound of Yukawa models is nearly saturated. The
theory is similar to strongly coupled Yukawa models except the occurrence of an
additional state -- a gauge ball of mass $m_S \simeq 1/2 m_F$. This, and
non-classical values of tricritical exponents suggest that at the tricritical
point the $\chi U \phi$ model constitutes a new universality class.
Nevertheless, it might be a microscopic model for the Higgs-Yukawa mechanism of
symmetry breaking.


title: Grassmann integrals by machine

abstract:
  I present a numerical algorithm for direct evaluation of multiple Grassmann
integrals. The approach is exact and suffers no Fermion sign problems. Memory
requirements grow exponentially with the interaction range and the transverse
size of the system. Low dimensional systems of order a thousand Grassmann
variables can be evaluated on a workstation.


title:
Embedded Topological Defects in Electroweak Theory: From Percolating
  Networks to Sphalerons

abstract:
  New defects (Z-vortices and Nambu monopoles) are found to become
thermodynamically relevant for the broken phase near to the (weakly first
order) electroweak phase transition, and below the crossover for higher Higgs
mass. The symmetric phase is characterized by vortex condensation
(percolation). The percolation transition persists in the crossover region. The
quasiclassical nature of the vortices is supported by correlations with Higgs
field and gauge field energy. Sphalerons are shown to be related to monopolium
bound states.


title: Partial Restoration of Flavor Symmetry for Chiral Staggered Fermions

abstract:
  At non-zero lattice spacing the flavor symmetry of staggered fermions is
broken to a discrete subgroup. We show that in the chiral limit the flavor
symmetry of the pion effective Lagrangian enlarges to an SO(4) subgroup of the
continuum SU(4) symmetry. This provides an explanation for observed
degeneracies in the pion spectrum.


title: S-wave charmed mesons in lattice NRQCD

abstract:
  Heavy-light mesons can be studied using the 1/M expansion of NRQCD, provided
the heavy quark mass is sufficiently large. Calculations of the S-wave charmed
meson masses from a classically and tadpole-improved action are presented. A
comparison of O(1/M), O(1/M^2) and O(1/M^3) results allows convergence of the
expansion to be discussed. It is shown that the form of discretized heavy quark
propagation must be chosen carefully.


title: Further Evidence of a Smooth Phase in 4D Simplicial Quantum Gravity

abstract:
  Four-dimensional (4D) simplicial quantum gravity coupled to U(1) gauge fields
has been studied using Monte-Carlo simulations. A negative string
susceptibility exponent is observed beyond the phase-transition point, even if
the number of vector fields (NV) is 1. We find a scaling relation of the
boundary volume distributions in this new phase. This scaling relation suggests
a fractal structure similar to that of 2D quantum gravity. Furthermore,
evidence of a branched polymer-like structure is suggested far into the
weak-coupling region, even for NV > 1. As a result, we propose new phase
structures and discuss the possibility of taking the continuum limit in a
certain region between the crumpled and branched polymer phases.


title:
Lattice calculation of the strangeness and electromagnetic nucleon form
  factors

abstract:
  We report on recent lattice QCD calculations of the strangeness magnetic
moment of the nucleon and the nucleon electromagnetic form factors, when we
allow the electromagnetic current to connect to quark loops as well as to the
valence quarks. Our result for the strangeness magnetic moment is
G_M^s(0)=-0.36+/-0.20. The sea contributions from the u and d quarks are about
80% larger. However, they cancel to a large extent due to their electric
charges, resulting in a smaller net sea contribution of -0.097+/-0.037 mu_N to
the nucleon magnetic moment. As far as the neutron to proton magnetic moment
ratio is concerned, this sea contribution tends to cancel out the cloud-quark
effect from the Z-graphs and results in a ratio of -0.68+/-0.04 which is close
to the SU(6) relation and the experiment. The strangeness Sachs electric
mean-square radius <r_s^2>_E is found to be small and negative and the total
sea contributes substantially to the neutron electric form factor.


title: The structure of the gluon propagator

abstract:
  The gluon propagator has been calculated for quenched QCD in the Landau gauge
at beta=6.0 for volumes 16^3x48 and 32^3x64, and at beta=6.2 for volume
24^3x48$. The large volume and different lattice spacings allow us to identify
and minimise finite volume and finite lattice spacing artefacts. We also study
the tensor structure of the gluon propagator, confirming that it obeys the
lattice Landau gauge condition.


title: Modelling the gluon propagator

abstract:
  Scaling of the Landau gauge gluon propagator calculated at beta=6.0 and at
beta=6.2 is demonstrated. A variety of functional forms for the gluon
propagator calculated on a large (32^3x64) lattice at beta=6.0 are
investigated.


title: Finite Temperature Phase Diagram of QCD with improved Wilson Fermions

abstract:
  We present results of an ongoing study of two flavour QCD with Wilson
fermions at finite temperature. We have used tree level Symanzik improvement in
both the gauge and fermion part of the action. The phase diagram was previously
determined on an $8^3 \times 4$ lattice and the existence of Aoki's phase
demonstrated. On our current lattice of $12^2 \times 24 \times 4$ we have
extended the set of observables and studied chiral and thermal properties at
light quark masses.


title: Ginsparg-Wilson relation and lattice Weyl fermions

abstract:
  We demonstrate that in the topologically trivial gauge sector the
Ginsparg-Wilson relation for lattice Dirac operators admits an exactly gauge
invariant path integral formulation of the Weyl fermions on a lattice.


title: Decorrelating Topology with HMC

abstract:
  The investigation of the decorrelation efficiency of the HMC algorithm with
respect to vacuum topology is a prerequisite for trustworthy full QCD
simulations, in particular for the computation of topology sensitive
quantities. We demonstrate that for mpi/mrho ratios <= 0.69 sufficient
tunneling between the topological sectors can be achieved, for two flavours of
dynamical Wilson fermions close to the scaling region beta=5.6. Our results are
based on time series of length 5000 trajectories.


title: Four-quark systems

abstract:
  In order to understand the binding of four static quarks, flux distributions
corresponding to these binding energies are studied in quenched SU(2) and also
related to a model for the energies. The potential relevant to string breaking
between two heavy-light mesons is measured in quenched SU(3) using stochastic
estimates of light quark propagators with the Sheikholeslami-Wohlert action.


title: Monopole Condensation and Color Confinement

abstract:
  New evidence is discussed of monopole condensation in the vacuum of SU(2) and
SU(3) gauge theories. Monopoles defined by different abelian projections do
condense in the transition to the confined phase and show the same behavior.
For SU(2) critical indices are determined by finite size scaling analysis and
the results agree with the 3d Ising Model, as expected.


title:
Quark masses and the chiral condensate with a non-perturbative
  renormalization procedure

abstract:
  We determine the quark masses and the chiral condensate in the MSbar scheme
at NNLO from Lattice QCD in the quenched approximation at beta=6.0, beta=6.2
and beta=6.4 using both the Wilson and the tree-level improved SW-Clover
fermion action. We extract these quantities using the Vector and the Axial Ward
Identities and non-perturbative values of the renormalization constants. We
compare the results obtained with the two methods and we study the O(a)
dependence of the quark masses for both actions.


title: A Preconditioner for Improved Fermion Actions

abstract:
  SSOR preconditioning of fermion matrix inversions which is parallelized using
a locally-lexicographic lattice sub-division, has been shown to be very
efficient for standard Wilson fermions. We demonstrate here the power of this
method for the Sheikholeslami-Wohlert improved fermion action and for a
renormalization group improved action incorporating couplings of the lattice
fermion fields up to the diagonal in the unit hypercube.


title: A Ginzburg-Landau Analysis of the Colour Electric Flux Tube

abstract:
  In a simulation of SU(2) gauge theory we investigate, after maximal Abelian
projection, the dual Maxwell equations for colour field and monopole current
distributions around a static quark-antiquark pair Q_ Q in vacuo. Within the
dual superconductor picture we carry out a Ginzburg-Landau type analysis of the
flux tube profile. As a result we can determine the coherence length of the GL
wave function related to the monopole condensate, xi = .25(3) fm, to be
compared to the penetration length, lambda = >.15(2) fm (scaled with the string
tension).


title: Lattice Approach to Diquark Condensation in Dense Matter

abstract:
  Results are presented of a Monte Carlo simulation of a 2+1 dimensional
Gross-Neveu model with SU(2)xSU(2) chiral symmetry at non-zero baryon chemical
potential, corresponding to non-zero baryon density. The phenomenon of quark
pair condensation is sought via measurement of a two point function. For
sufficiently large chemical potential there is a sharp transition between a
phase where the chiral symmetry is broken by a standard chiral condensate and
one where a scalar diquark condensate, qq, is non-zero. Global U(1) baryon
number symmetry may remain unbroken, however, due to the absence of long range
order in the phase of qq.


title: Non-analyticity of the Callan-Symanzik beta-function of O(N) models

abstract:
  In the framework of the 1/N-expansion we show that the Callan-Symanzik beta-
function associated with the four-point coupling g is non-analytic at its zero,
i.e. at the fixed-point value g^* of g. This behavior can be interpreted by
renormalization group arguments, and written in terms of scaling correction
exponents. We obtain accurate determinations of g^* in 3-d and 2-d by
exploiting two alternative approaches: the (4-d)-expansion and the
high-temperature expansion. These results are compared with the available
estimates by other approaches, such as the fixed-dimension perturbative
expansion, Monte Carlo simulations, etc... We also present results for the
n-point renormalized coupling constants that parameterize the behavior of the
effective potential in the high- and low- temperature phases.


title: SU(2) vacuum dynamics in applied external magnetic field

abstract:
  The vacuum dynamics of SU(2) lattice gauge theory is studied by means of a
gauge-invariant effective action, both at zero and finite temperature. Working
with lattices up to 32^4 we check the scaling of the energy density with the
magnetic length. We find that the screening at zero temperature of the applied
external magnetic field weakens by increasing the temperature.


title:
(lambda Phi^4)_4 theory on the lattice: evidence for a non-trivial
  rescaling of the scalar condensate

abstract:
  A lattice simulation in the broken phase of four-dimensional (lambda Phi^4)
theory in the Ising limit suggests that, in the continuum limit, the scalar
condensate rescales by a factor different from the conventional wavefunction
renormalization. Possible effects on the present bounds of the Higgs mass are
discussed.


title: Current Renormalisation in NRQCD for Semi-leptonic $B\to D$ Decays

abstract:
  We present a calculation of the renormalisation constants for the temporal
vector current, $Z_{V_0}$ and spatial axial current, $Z_{A_k}$, to
$O(\alpha_s/M)$ for $B\to D$ transitions using the $O(1/M)$ NRQCD action for
both $b$ and $c$ quarks evaluated for a large range of mass parameters.
Considerations for the renormalisation of the spatial vector current and the
temporal axial current are discussed and initial results for a mixed lattice
current are presented for the spatial vector current.


title: What's new with the electroweak phase transition?

abstract:
  We review the status of non-perturbative lattice studies of the electroweak
phase transition. In the Standard Model, the complete phase diagram has been
reliably determined, and the conclusion is that there is no phase transition at
all for the experimentally allowed Higgs masses. In the Minimal Supersymmetric
Standard Model (MSSM), in contrast, there can be a strong first order
transition allowing for baryogenesis. Finally, we point out possibilities for
future simulations, such as the problem of CP-violation at the MSSM electroweak
phase boundary.


title: Measuring an entropy in heavy ion collisions

abstract:
  We propose to use the coincidence method of Ma to measure an entropy of the
system created in heavy ion collisions. Moreover we estimate, in a simple
model, the values of parameters for which the thermodynamical behaviour sets
in.


title: Gauge-invariant strings in the 3d U(1)+Higgs theory

abstract:
  We describe how the strings, which are classical solutions of the continuum
three-dimensional U(1)+Higgs theory, can be studied on the lattice. The effect
of an external magnetic field is also discussed and the first results on the
string free energy are presented. It is shown that the string free energy can
be used as an order parameter when the scalar self-coupling is large and the
transition is continuous.


title:
On the Definition of Gauge Field Operators in Lattice Gauge-Fixed
  Theories

abstract:
  We address the problem of defining the gluon field on the lattice in terms of
the natural link variables. Different regularized definitions are shown,
through non perturbative numerical computation, to converge towards the same
continuum renormalized limit.


title: Spectrum of the fixed point Dirac operator in the Schwinger model

abstract:
  Recently, properties of the fixed point action for fermion theories have been
pointed out indicating realization of chiral symmetry on the lattice. We check
these properties by numerical analysis of the spectrum of a parametrized fixed
point Dirac operator investigating also microscopic fluctuations and fermion
condensation.


title:
Rigorous control of the non-perturbative corrections to the double
  expansion in $g$ and $g^2\ln(g)$ for the $\phi^4_3$-trajectory in the
  hierarchical approximation

abstract:
  We study the renormalization invariant trajectory of the
$\phi^4$-perturbation of the free field fixed point in the hierarchical
approximation. We parametrize it by a running $\phi^4$-coupling $g$ with linear
step $\beta$-function. We rigorously control the non-perturbative corrections
to finite order approximants from double perturbation theory in $g$ and
$g^2\ln(g)$. The construction uses a contraction mapping for the extended
renormalization group composed of a hierarchical block spin transformation with
a flow of $g$.


title: Pseudoscalar decay constant in the heavy light systems

abstract:
  We discuss the size of the higher order terms in the NRQCD expansion of the
pseudoscalar decay constant. Power law divergences in the matrix elements
contributing to the pseudoscalar decay constant are also investigated.


title:
Thermodynamics of Lattice QCD with massless quarks and chiral 4-fermion
  interactions

abstract:
  We have simulated lattice QCD with an irrelevant 4-fermion interaction and 2
zero mass quarks. The chiral phase transition is observed to be second order
and we discuss extraction of critical exponents.


title: Asymptotic Scaling, Casimir Scaling, and Center Vortices

abstract:
  We report on two recent developments in the center vortex theory of
confinement: (i) the asymptotic scaling of the vortex density, as measured in
Monte Carlo simulations; and (ii) an explanation of Casimir scaling and the
adjoint string tension, in terms of the center vortex mechanism.


title: On the Universality of Matrix Models for Random Surfaces

abstract:
  We present an alternative procedure to eliminate irregular contributions in
the perturbation expansion of c=0-matrix models representing the sum over
triangulations of random surfaces, thereby reproducing the results of Tutte [1]
and Brezin et al. [2] for the planar model. The advantage of this method is
that the universality of the critical exponents can be proven from general
features of the model alone without explicit determination of the free energy
and therefore allows for several straightforward generalizations including
cases with non-vanishing central charge c< 1.


title: Gauge-invariant quark-antiquark nonlocal condensates in lattice QCD

abstract:
  We study, by numerical simulations on a lattice, the behaviour of the
gauge-invariant quark-antiquark nonlocal condensates in the QCD vacuum with
dynamical fermions. A determination is also done in the quenched approximation
and the results are compared with the full-QCD case. The fermionic correlation
length is extracted and compared with the analogous gluonic quantity.


title: SU(3) Gauge Theory with Adjoint Fermions

abstract:
  We analyze the finite temperature phase diagram of QCD with fermions in the
adjoint representation. The simulations performed with four dynamical Majorana
fermions, which is equivalent to two Dirac fermions, show that the
deconfinement and chiral phase transitions occur at two distinct temperatures,
$T_{\rm chiral} \simeq 6.65 T_{\rm deconf}$. While the deconfinement transition
is first order we find evidence for a continuous chiral transition. We also
present potentials for $T<T_{\rm deconf}$ and $T_{\rm deconf}<T< T_{\rm
chiral}$ both for fundamental and adjoint fermion-antifermion pairs.


title: Quantum chaos and QCD at finite chemical potential

abstract:
  We investigate the distribution of the spacings of adjacent eigenvalues of
the lattice Dirac operator. At zero chemical potential $\mu$, the
nearest-neighbor spacing distribution $P(s)$ follows the Wigner surmise of
random matrix theory both in the confinement and in the deconfinement phase.
This is indicative of quantum chaos. At nonzero chemical potential, the
eigenvalues of the Dirac operator become complex. We discuss how $P(s)$ can be
defined in the complex plane. Numerical results from an SU(3) simulation with
staggered fermions are compared with predictions from non-hermitian random
matrix theory, and agreement with the Ginibre ensemble is found for $\mu\approx
0.7$.


title: Universal and non-universal behavior in Dirac spectra

abstract:
  We have computed ensembles of complete spectra of the staggered Dirac
operator using four-dimensional SU(2) gauge fields, both in the quenched
approximation and with dynamical fermions. To identify universal features in
the Dirac spectrum, we compare the lattice data with predictions from chiral
random matrix theory for the distribution of the low-lying eigenvalues. Good
agreement is found up to some limiting energy, the so-called Thouless energy,
above which random matrix theory no longer applies. We determine the dependence
of the Thouless energy on the simulation parameters using the scalar
susceptibility and the number variance.


title: Thermodynamics of two-colour QCD

abstract:
  We discuss the thermodynamics of two-colour QCD with four flavours of
staggered quarks on 8^3x4 and 16^3x4 lattices. In our simulations we use the
Naik action for the fermions and a (1,2) tree-level improved gauge action. We
analyze the deconfinement and chiral phase transitions for four different quark
masses (m=0.1,0.05,0.025,0.015). Contrary to three-colour QCD the peak in the
Polyakov loop susceptibility decreases with decreasing quark mass. This
reflects an early breaking of the string in the heavy quark potential, which we
verify explicitly by calculating the heavy quark potential at finite
temperature using Polyakov loop correlations.


title: Universality, Scaling and Triviality in a Hierarchical Field Theory

abstract:
  Using polynomial truncations of the Fourier transform of the RG
transformation of Dyson's hierarchical model, we show that it is possible to
calculate very accurately the renormalized quantities in the symmetric phase.
Numerical results regarding the corrections to the scaling laws, (i.e finite
cut-off dependence) triviality, hyperscaling, universality and high-accuracy
determinations of the critical exponents are discussed.


title: Ground State Entropy in Potts Antiferromagnets and Chromatic Polynomials

abstract:
  We discuss recent results on ground state entropy in Potts antiferromagnets
and connections with chromatic polynomials. These include rigorous lower and
upper bounds, Monte Carlo measurements, large--$q$ series, exact solutions, and
studies of analytic properties. Some related results on Fisher zeros of Potts
models are also mentioned.


title:
QCD strings ending on domain walls --- a complete wetting phenomenon in
  SUSY QCD

abstract:
  In the context of M-theory, Witten has argued that an intriguing phenomenon
occurs, namely that QCD strings can end on domain walls. We present a simpler
explanation of this effect using effective field theory to describe the
behavior of the Polyakov loop and the gluino condensate in N = 1 supersymmetric
QCD. We describe how domain walls separating distinct confined phases appear in
this effective theory and how these interfaces are completely wet by a film of
deconfined phase at the high-temperature phase transition. This gives the
Polyakov loop a non-zero expectation value on the domain wall. Consequently, a
static test quark which is close to the interface has a finite free energy and
the string emanating from it can end on the wall.


title: String Breaking in Quenched QCD

abstract:
  We present preliminary quenched results on a new operator for the
investigation of string-breaking within SU(2)-colour QCD. The ground-state of a
spatially-separated static-light meson-antimeson pair is a combination of a
state with two distinct mesons, expected to dominate for large separations, and
a state where the light-quarks have annihilated, which contributes for short
distances. The crossover between these two regimes provides a measure of the
string-breaking scale length.


title: Semi-leptonic decays of heavy mesons

abstract:
  We present results of a lattice computation of the matrix elements of the
vector currents which are relevant for the semileptonic decays of D to K, D to
pi and B to pi. The computations are performed in the quenched approximation on
a 24^3x48 lattice at beta=6.2, using an O(a) non-perturbatively improved
fermionic action.


title: Light quark masses using domain wall fermions

abstract:
  We compute the one-loop self-energy correction to the massive domain wall
quark propagator. Combining this calculation with simulations at several gauge
couplings, we estimate the strange quark mass in the continuum limit. The
perturbative one-loop mass renormalization is comparable to that for Wilson
quarks and considerably smaller than that for Kogut-Susskind quarks. Also,
scaling violations appear mild in comparison to other errors at present. Given
their good chiral behavior and these features, domain wall quarks are
attractive for evaluating the light quark masses. Our preliminary quenched
result is m_s(2 GeV) = 82(15) MeV in the ${\bar{MS}}$ scheme.


title: The Pion-Nucleon sigma-Term with Dynamical Wilson Fermions

abstract:
  We calculate connected and disconnected contributions to the flavour singlet
scalar density amplitude of the nucleon in a full QCD lattice simulation with
$n_f=2$ dynamical Wilson fermions at $\beta=5.6$ on a $16^3 \times 32$ lattice.
We find that both contributions are of similar size at the light quark mass. We
arrive at the estimate $\sigma_{\pi N} = 18(5)$MeV. Its smallness is directly
related to the apparent decrease of $u$, $d$ quark masses when unquenching QCD
lattice simulations. The $y$ parameter can be estimated from a semi-quenched
analysis, in which there are no strange quarks in the sea, the result being
$y=0.59(13)$.}


title: Vector decay constants in quarkonia

abstract:
  Lattice NRQCD with leading finite lattice spacing errors removed is used to
simulate heavy-heavy vector decay constants. Quenched simulations are performed
at three values of the coupling and fifteen values of the quark mass. The
improved gauge action with plaquettes and rectangles is used. Landau link
improvement is used throughout. "Perturbative" and nonperturbative meson masses
are compared. One-loop perturbative matching between lattice and continuum
heavy-heavy vector currents is performed. The data is consistent with the
vector meson decay constant being proportional to the square root of its mass.


title: Genetic Algorithm for SU(2) Gauge Theory on a 2-dimensional Lattice

abstract:
  An algorithm is proposed for the simulation of pure SU(N) lattice gauge
theories based on Genetic Algorithms(GAs). We apply GAs to SU(2) pure gauge
theory on a 2 dimensional lattice and show the results, the action per
plaquette and Wilson loops, are consistent with those by Metropolis method(MP)s
and Heatbath method(HB)s. Thermalization speed of GAs is especially faster than
the simple MPs.


title: Dynamical Properties of Large N Reduced Model of Yang-Mills Theory

abstract:
  We study the large N reduced model of D-dimensional Yang-Mills theory with
special attention to the dynamical aspects related to the eigenvalues of the
NxN matrices, which correspond to the space-time coordinates in the IIB matrix
model. We define a quantity which represents the uncertainty of the space-time
coordinates and show that it is of the same order as the extent of the space
time, which means that the classical space-time picture is maximally broken.
The absence of the SSB of the Lorentz invariance is also shown.


title:
One-loop renormalization factors and mixing coeffecients of bilinear
  quark operators for improved gluon and quark actions

abstract:
  We calculate one-loop renormalization factors and mixing coefficients of
bilinear quark operators for a class of gluon actions with six-link loops and
O(a)-improved quark action. The calculation is carried out by evaluating
on-shell Green's functions of quarks and gluons in the standard perturbation
theory. We find a general trend that finite parts of one-loop coefficients are
reduced approximately by a factor two for the renormalization-group improved
gluon actions compared with the case of the standard plaquette gluon action.


title:
Two-dimensional Gross-Neveu Model with Wilson Fermion Action at Finite
  Temperature and Density

abstract:
  We analytically investigate the 2-dimensional Gross-Neveu model at finite
temperature and density using Wilson fermion action. The relation between the
phase structure on the lattice and that in the continuum is clarified.


title: The large-N phase transition of lattice SU(N) gauge theories

abstract:
  We investigate the large-N phase transition of lattice SU(N) gauge theories
in the Wilson formulation, by performing a Monte Carlo simulation of the
twisted Eguchi-Kawai model. A variant of the multicanonical algorithm allows a
detailed exploration of the phase transition and a precise determination of the
transition temperature.


title: News on Disconnected Diagrams

abstract:
  We present evidence for disconnected contributions to the $\sigma_{\pi N}$
term and the flavor singlet axial coupling $g_A^0$ of the proton on full QCD
configurations, which are obtained by means of improved stochastic estimator
techniques. Furthermore we discuss results from the fermionic determination of
the topological charge of the QCD vacuum (in the spirit of the Athiya-Singer
theorem) again achieved with stochastic estimator methods. It turns out that
this approach provides an monitor for the tunneling efficiency of the HMC on
QCD with dynamical Wilson fermions which is independent on the pure gluonic
method that implies cooling.


title:
Calculation of f_B and the ``Isgur-Wise Function'' using a
  non-perturbatively improved fermion action

abstract:
  We present a calculation of f_B and of the form factors for the semi-leptonic
decay B -> D l nu in the quenched approximation to QCD. Results are generated
on lattices at beta = 6.2, using an O(a)-improved fermion action, with the
clover coefficient determined non-perturbatively.


title: SW action for the lattice Schwinger model

abstract:
  We study some aspects of the ${\cal O}(a)$ improved Sheikholeslami-Wohlert
(SW) action for the lattice Schwinger model. We find some improvement
concerning the distribution of eigenvalues of the Dirac operator and of the
masses but little or no improvement for rotational invariance of correlators or
dispersion relations.


title: The Massive Schwinger Model in a Fast Moving Frame

abstract:
  We present a non-perturbative study of the massive Schwinger model. We use a
Hamiltonian approach, based on a momentum lattice corresponding to a fast
moving reference frame, and equal time quantization.


title: Lattice Study of the $H$ Dibaryon

abstract:
  The mass of the lowest spin-zero, strangeness-$(-2)$ flavor singlet state in
the dibaryon sector has been calculated in quenched QCD on $16^3\times32$ and
$24^3\times32$ lattices at $\beta=5.85$ to study whether the energy of the
proposed $H$ dibaryon is near or below the $\Lambda\Lambda$ threshold.
Preliminary results indicate that finite lattice volume artifacts overestimate
the binding, and that on the largest lattice $m_H$ is of the order of $100\MeV$
above the $\Lambda\Lambda$ threshold.


title: Gluon Propagator in the Landau Gauge fixed Lattice QCD Simulation

abstract:
  We measured the gluon propagator in the Landau gauge fixed QCD Langevin
simulation and studied the infra-red behaviour of the gluon propagator. The 4^3
x 8 lattice simulation was done for quenched $\beta=3,4,5$ and unquenched
$\beta=4, \kappa=0.1,0.15,0.2$ using each 100 independent samples. The Landau
gauge fixing was done by an extension of the Fourier acceleration method with
the condition Max|div A|<10^{-4}, and the field A is related to the link
variable by U=exp A instead of the usual U-linear definition. We confirmed
gauge fixing with smearing preconditioning works perfectly for the purpose of
finding the global minimum of the squared norm of the gauge field when $\beta$
is large(e.g. $\beta=5$). Our simulation results suggests the possibility of a
realization of the infrared behaviour of the Gribov-Zwanziger theory.


title: An analysis of 4-quark energies in SU(2) lattice Monte Carlo

abstract:
  Energies of four-quark systems with the tetrahedral geometry measured by the
static quenched SU(2) lattice Monte Carlo method are analyzed by parametrizing
the gluon overlap factor in the form exp(-[bs EA+{\sqrt bs}FP]) where A and P
are the area and the perimeter defined mainly by the positions of the four
quarks, bs is the string constant in the 2-quark potentials and E, F are
constants.


title: The new definition of lattice gauge fields and the Landau gauge

abstract:
  The Landau gauge fixing algorithm in the new definition of gauge fields is
presented. In this algorithm a new solver of the Poisson equations based on the
Green's function method is used. Its numerical performance of the gauge fixing
algorithm is presented. Performance of the smeared gauge fixing in SU(3) is
also investigated.


title: The Landau gauge lattice QCD simulation and the gluon propagator

abstract:
  The gluon propagator in the Landau gauge lattice QCD simulation of quenched
8^3 x 16 lattice is measured. The data suggests the confinement mechanism of
the Gribov-Zwanziger theory.


title: On weak coupling expansion in models with unbroken symmetry

abstract:
  An investigation of the weak coupling region of 2D SU(N) spin models is
presented. An expansion of the free energy and correlation functions at low
temperatures is performed in the link formulation with periodic boundary
conditions (BC). The resulting asymptotics is shown to be nonuniform in the
volume for the free energy.


title: Spectator Effects in Inclusive Decays of Beauty Hadrons

abstract:
  We evaluate the matrix elements of the four-quark operators which contribute
to the lifetimes of $B$-mesons and the $\Lambda_b$-baryon. We find that the
spectator effects are not responsible for the discrepancy between the
theoretical prediction and experimental measurement of the ratio of lifetimes
$\tau(\Lambda_b)/\tau(B)$.


title:
Confinement, Chiral Symmetry Breaking and Continuum Limits in Quantum
  Link Models

abstract:
  Using the example of compact U(1) lattice gauge theory we argue that quantum
link models can be used to reproduce the physics of conventional Hamiltonian
lattice gauge theories. In addition to the usual gauge coupling $g$, these
models have a new parameter $j$ which naturally cuts-off large electric flux
quanta on each link while preserving exact U(1) gauge invariance. The
$j\to\infty$ limit recovers the conventional Hamiltonian. At strong couplings,
the theory shows confinement and chiral symmetry breaking for all non-trivial
values of $j$. The phase diagram of the 3+1 dimensional theory suggests that a
coulomb phase is present at large but finite $j$. Setting $g=0$, a new approach
to the physics of compact U(1) gauge theory on the lattice emerges. In this
case the parameter $j$ takes over the role of the gauge coupling, and $j\to
\infty$ describes free photons.


title: Exactly massless fermions on the lattice

abstract:
  The salient features of the Ginsparg-Wilson fermion in topologically
nontrivial background gauge fields are outlined. The R-invariance of the zero
modes, the indices and the index theorem on a finite lattice are illustrated.
The role of R in converting the nonlocal D_c into a sequence of highly local D
is demonstrated.

categories: hep-lat astro-ph cond-mat.str-el hep-ph hep-th


title: Scaling Analysis of Improved Actions for Pure SU(3) Gauge Theory

abstract:
  We have explored the behaviour of some improved actions based on a
nonperturbative renormalization group (RG) analysis in coupling space. We
calculate the RG flow in two-coupling space $(\boneone,\bonetwo)$ and examine
the restoration of rotational invariance and the scaling of physical quantities
$(T_c/\sqrt{\sigma})$.


title: Exotic meson spectroscopy from the clover action at beta = 5.85 and 6.15

abstract:
  We repeat our original simulations of the hybrid meson spectrum using the
clover action, as a check on lattice artifacts. Our results for the 1-+ masses
do not substantially change. We present preliminary results for the wave
function of the 1-+ state in Coulomb gauge.


title: The Strong-Coupling Expansion in Simplicial Quantum Gravity

abstract:
  We construct the strong-coupling series in 4d simplicial quantum gravity up
to volume 38. It is used to calculate estimates for the string susceptibility
exponent gamma for various modifications of the theory. It provides a very
efficient way to get a first view of the phase structure of the models.


title: Ginzburg Criterion for the Chiral Transition

abstract:
  This report is based on the work done together with J.B. Kogut and C.G.
Strouthos. We study a Yukawa theory with spontaneous chiral symmetry breaking
and with a large number N of fermions near the finite temperature phase
transition. Critical properties in such a system can be described by the mean
field theory very close to the transition point. We show that the width of the
window of non-trivial scaling is suppressed by a certain power of 1/N. Our
Monte Carlo simulations confirm these analytical results. We discuss
implications for the chiral phase transition in QCD.


title: Perturbative Matching of Heavy-Light Currents with NRQCD Heavy Quarks

abstract:
  We present further results for one-loop matching of heavy-light axial and
vector currents between continuum QCD and a lattice theory with NRQCD heavy
quarks and massless clover quarks.


title: Heavy quark potential in the instanton liquid model

abstract:
  We study the heavy quark potential in the instanton liquid model by carefully
measuring Wilson loops out to a distance of order 3$fm$. A random instanton
ensemble with a fixed radius $\rho$ = 1/3$fm$ generates a potential $V(R)$
growing very slowly at large $R$. In contrast, a more realistic size
distribution growing as $\rho^6$ at small $\rho$ and decaying as $\rho^{-5}$ at
large $\rho$, leads to a potential which grows linearly with $R$. The string
tension, however, is only about 1/10 of the phenomenological value.


title:
A New Exact Method for Dynamical Fermion Computations with Non-Local
  Actions

abstract:
  We introduce a new algorithm which we call the {Rational Hybrid Monte Carlo}
Algorithm (RHMC). This method uses a rational approximation to the fermionic
kernel together with a noisy Kennedy-Kuti acceptance step to give an efficient
algorithm with no molecular dynamics integration step-size errors.


title: The static potential beyond screening in the 3d SU(2) Higgs model

abstract:
  The static potential in the 3d SU(2) Higgs model is computed by a variational
calculation employing Wilson loops and two-meson operators. String breaking is
demonstrated numerically, the breaking scale is determined and the results are
compared with a quenched calculation.


title: Confinement studies in lattice QCD

abstract:
  We describe the current search for confinement mechanisms in lattice QCD. We
report on a recent derivation of a lattice Ehrenfest-Maxwell relation for the
Abelian projection of SU(2) lattice gauge theory. This gives a precise lattice
definition of field strength and electric current due to static sources,
charged dynamical fields, gauge fixing and ghosts. In the maximal Abelian gauge
the electric charge is anti-screened analogously to the non-Abelian charge.


title: Negative-Parity Baryon Spectroscopy

abstract:
  Results are reported for the first calculation of the low-lying spin-1/2
odd-parity octet baryon masses using ${\cal O}(a^2)$ improved gluon and fermion
actions. Methods for removing even-parity ground-state contaminations from the
two-point correlation functions at zero and finite momenta are outlined. We
investigate the properties of two odd-parity interpolating fields based on the
established interpolating fields for the nucleon ground state. Isolation of the
lowest-lying odd-parity state appears to be sufficient to begin exploring
odd-parity $N \to N^*$ electromagnetic transition form factors.


title:
Gauge model at finite temperature with massive quarks and at finite
  density on anisotropic lattice

abstract:
  Critical properties of QCD and the chiral condensate at finite density are
analytically studied on an anisotropic lattice in the approximation SU(N)
\simeq Z(N). Asymptotic behavior of the partition function and its continuum
limit are discussed.


title: Optimizing the Chiral Properties of Lattice Fermions

abstract:
  We describe a way to optimize the chiral behavior of Wilson-type lattice
fermion actions by studying the low energy real eigenmodes of the Dirac
operator. We find a candidate action, the clover action with fat links with a
tuned clover term. The action shows good scaling behavior at Wilson gauge
coupling beta=5.7.


title: Where is the string limit in QCD?

abstract:
  The energies of glue in the presence of a static quark-antiquark pair are
calculated for separations r ranging from 0.1 fm to 4 fm and for various
quark-antiquark orientations on the lattice. Our simulations use an improved
gauge-field action on anisotropic space-time lattices. Discretization errors
and finite volume effects are studied. We find that the spectrum does not
exhibit the expected onset of the universal pi/r Goldstone excitations of the
effective QCD string, even for r as large as 4 fm. Our results cast serious
doubts on the validity of treating glue in terms of a fluctuating string for r
below 2 fm. Retardation effects in the Upsilon system are also studied by
comparing level splittings from the Born-Oppenheimer approximation with those
directly obtained in simulations.


title: Exceptional Configurations with the Clover Action

abstract:
  We study exceptional modes of both the Wilson and the clover action in order
to understand why quenched clover spectroscopy suffers so severely from
exceptional configurations. We show that a large clover coefficient can make
the exceptional modes extremely localized and thus very sensitive to short
distance fluctuations. We contrast this with the case of the Wilson action
where exceptional modes correspond to large instantons. These modes are broadly
extended and suffer much less from discretization errors.


title: Operator product expansion and non-perturbative renormalization

abstract:
  It has been recently proposed to use the operator product expansion to
evaluate the expectation values of renormalized operators without the need of a
direct computation of the relevant renormalization constants. We test the
viability of this idea in the two-dimensional non-linear sigma-model discussing
the non-perturbative renormalization of the energy-momentum tensor.


title: Crossover scaling from classical to non-classical critical behaviour

abstract:
  Interacting physical systems in the neighborhood of criticality (and massive
continuum field theories) can often be characterized by just two physical
scales: a (macroscopic) correlation length and a (microscopic) interaction
range, related to the coupling and measured by the Ginzburg number $G$. A
critical crossover limit can be defined when both scales become large while
their ratio stays finite. The corresponding scaling functions are universal,
and they are related to the standard field-theory renormalization-group
functions. The critical crossover describes the unique flow from the Gaussian
to the nonclassical fixed point.


title:
Phase structure of lattice QCD at finite temperature for 2+1 flavors of
  Kogut-Susskind quarks

abstract:
  We report on a study of the finite-temperature chiral transition on an
$N_t=4$ lattice for 2+1 flavors of Kogut-Susskind quarks. We find the point of
physical quark masses to lie in the region of crossover, in agreement with
results of previous studies. Results of a detailed examination of the
$m_{u,d}=m_s$ case indicate vanishing of the screening mass of $\sigma$ meson
at the end point of the first-order transition.


title: New issues for Numerical Stochastic Perturbation Theory

abstract:
  First attempts in the application of Numerical Stochastic Perturbation Theory
(NSPT) to the problem of pushing one loop further the computation of SU(3)
(SU(2)) pertubative beta function (in different schemes) are reviewed and the
relevance of such a computation is discussed. Other issues include the proposal
of a different strategy for gauge-fixed NSPT computations in lattice QCD.


title: Applications of Partially Quenched Chiral Perturbation Theory

abstract:
  Partially quenched theories are theories in which the valence- and sea-quark
masses are different. Here, we will discuss the nonanalytic one-loop
corrections to some physical quantities, using partially quenched chiral
perturbation theory. In particular, we will focus on the results for Goldstone
boson masses to illustrate the general features of our calculation.


title: String breaking in Lattice QCD

abstract:
  The separation of a heavy quark and antiquark pair leads to the formation of
a tube of flux, or string, which should break in the presence of light
quark-antiquark pairs. This expected zero temperature phenomenon has proven
elusive in simulations of lattice QCD. We present simulation results that show
that the string does break in the confining phase at nonzero temperature.


title: Simulating 4D Simplicial Gravity including Degenerate Triangulations

abstract:
  We extend simulations of simplicial gravity in four dimensions to include
{\it degenerate} triangulations and demonstrate that using this ensemble the
geometric finite-size effects are much reduced. We provide strong numerical
evidence for the existence of an exponential bound on the entropy of the model
and establish that the phase structure is identical to that of a corresponding
model restricted to an ensemble of combinatorial triangulations.


title: Dynamical linke cluster expansions: Algorithmic aspects and applications

abstract:
  Dynamical linked cluster expansions are linked cluster expansions with
hopping parameter terms endowed with their own dynamics. They amount to a
generalization of series expansions from 2-point to point-link-point
interactions. We outline an associated multiple-line graph theory involving
extended notions of connectivity and indicate an algorithmic implementation of
graphs. Fields of applications are SU(N) gauge Higgs systems within variational
estimates, spin glasses and partially annealed neural networks. We present
results for the critical line in an SU(2) gauge Higgs model for the electroweak
phase transition. The results agree well with corresponding high precision
Monte Carlo results.


title: Ginsparg-Wilson Relation and Spin Chains

abstract:
  The Baxter 8-vertex model is equivalent to a particular lattice formulation
of a self-interacting, massive Dirac fermion theory. In the time-continuum
limit, the lattice Hamiltonian (XYZ spin chain) can be explicitly transformed
to a lattice Dirac Hamiltonian. We show that the kernel describing the
quadratic part of this Hamiltonian satisfies a one-dimensional version of the
Ginsparg-Wilson relation. The corresponding conserved charge is derived and
compared with the conserved arrow number of the 8-vertex model.


title: Heavy-Light Decay Constants: Conclusions from the Wilson Action

abstract:
  We report on the results of a MILC collaboration calculation of $f_B$,
$f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios. We discuss the most important
errors in more detail than we have elsewhere.


title: New Analytical Results on Anisotropic Membranes

abstract:
  We report on recent progress in understanding the tubular phase of
self-avoiding anisotropic membranes. After an introduction to the problem, we
sketch the renormalization group arguments and symmetry considerations that
lead us to the most plausible fixed point structure of the model. We then
employ an epsilon-expansion about the upper critical dimension to extrapolate
to the physical interesting 3-dimensional case. The results are $\nu=0.62$ for
the Flory exponent and $\zeta=0.80$ for the roughness exponent. Finally we
comment on the importance that numerical tests may have to test these
predictions.


title: Quenched Supersymmetry

abstract:
  We study the effects of quenching in Super-Yang-Mills theory. While
supersymmetry is broken, the lagrangian acquires a new flavour $U(1 \mid 1)$
symmetry. The anomaly structure thus differs from the unquenched case. We
derive the corresponding low-energy effective lagrangian. As a consequence, we
predict the mass splitting expected in numerical simulations for particles
belonging to the lowest-lying supermultiplet.


title: Anisotropic Membranes

abstract:
  We describe the statistical behavior of anisotropic crystalline membranes. In
particular we give the phase diagram and critical exponents for phantom
membranes and discuss the generalization to self-avoiding membranes.


title: Free energy of an SU(2) monopole-antimonopole pair

abstract:
  We induce an external ${Z}_2$ monopole-antimonopole pair in an SU(2) lattice
gauge system and measure its free energy as a way to probe the vacuum
structure. We discuss the motivation and computational methodology of the
investigation and illustrate our preliminary results.


title: Dynamics of the Conformal Mode and Simplicial Gravity

abstract:
  We review the derivation of the Liouville action in 2DQG via the trace
anomaly and emphasize how a similar approach can be used to derive an effective
action describing the long wavelength dynamics of the conformal factor in 4D.
In 2D we describe how to make an explicit connection between dynamical
triangulations and this continuum theory, and present results which confirm the
equivalance of the two approaches. By reconstructing a lattice conformal mode
from DT simulations it should be possible to test this equivalence in 4D also.


title: Delta I=1/2 rule from staggered fermions

abstract:
  We present our latest results for the Delta I=1/2 rule, obtained on quenched
ensembles with beta=6.0 and 6.2, and a set of N_f=2 configurations with
beta=5.7. The statistical noise is quite under control. We observe an
enhancement of the Delta I=1/2 amplitude consistent with experiment, although
the systematic errors are still large. We also present a non-perturbative
determination of Z_P, Z_S and the strange quark mass. We briefly discuss our
progress in calculating epsilon-prime.


title: Mean link versus average plaquette tadpoles in lattice NRQCD

abstract:
  We compare mean-link and average plaquette tadpole renormalization schemes in
the context of the quarkonium hyperfine splittings in lattice NRQCD.
Simulations are done for the three quarkonium systems $c\bar c$, $b\bar c$, and
$b\bar b$. The hyperfine splittings are computed both at leading and at
next-to-leading order in the relativistic expansion. Results are obtained at a
large number of lattice spacings. A number of features emerge, all of which
favor tadpole renormalization using mean links. This includes much better
scaling of the hyperfine splittings in the three quarkonium systems. We also
find that relativistic corrections to the spin splittings are smaller with
mean-link tadpoles, particularly for the $c\bar c$ and $b\bar c$ systems. We
also see signs of a breakdown in the NRQCD expansion when the bare quark mass
falls below about one in lattice units (with the bare quark masses turning out
to be much larger with mean-link tadpoles).


title: Matching the High Momentum Modes in a Truncated Determinant Algorithm

abstract:
  Within a truncated determinant algorithm, two alternatives are discussed for
including systematically the remaining ultraviolet modes. Evidence is presented
that these modes are accurately described by an effective action involving only
small Wilson loops.


title: Heavy Quark Physics in Nf=2 QCD

abstract:
  We present a preliminary analysis of the heavy-heavy spectrum and heavy-light
decay constants in full QCD, using a tadpole-improved SW quark action and an
RG-improved gauge action on a 16^3 x 32 lattice with four sea quark masses
corresponding to m_pi/m_rho = 0.8, 0.75, 0.7, 0.6 and a^-1 = 1.3 GeV. We focus
particularly on the effect of sea quarks on these observables.


title: Improved Lattice QCD Actions for Hadron Phenomenology

abstract:
  The masses and dispersions of light hadrons are calculated in lattice QCD
using an order a^2 tadpole-improved gluon action and the Dchi34 action, an
order a^2 tadpole-improved next-nearest-neighbor fermion action originally
proposed by Hamber and Wu. Two lattices of constant volume with lattice
spacings of approximately 0.40 fm and 0.24 fm are considered. The results
reveal some scaling violations at the coarser lattice spacing on the order of
5%. At the finer lattice spacing, the calculated N/rho mass ratio reproduces
state-of-the-art results using unimproved actions. Good dispersion and
rotational invariance up to momenta p*a the order of 1 are also found. The
relative merit of alternative choices for improvement operators is assessed
through close comparisons with other plaquette-based tadpole-improved actions.


title: Full QCD light hadron spectrum from the CP-PACS

abstract:
  We report on an on-going two-flavor full QCD study on CP-PACS using an
RG-improved gauge action and a tadpole-improved SW quark action. Runs are made
for three lattice spacings $a^{-1}\approx 0.9$, 1.3, and 2.5 GeV on
$12^3\times24$, $16^3\times32$, and $24^3\times48$ lattices. Four sea quark
masses having $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.6 are simulated, for each
of which hadron masses are evaluated for valence quark masses corresponding to
$m_{\rm PS}/m_{\rm V} \approx 0.8$--0.5. Results for hadron and light quark
masses are presented and compared with those obtained in quenched QCD.


title: The Ising model universality of the electroweak theory

abstract:
  Lattice simulations have shown that the first order electroweak phase
transition turns into a regular cross-over at a critical Higgs mass m_{H,c}. We
have developed a method which enables us to make a detailed investigation of
the critical properties of the electroweak theory at m_{H,c}. We find that the
transition falls into the 3d Ising universality class. The continuum limit
extrapolation of the critical Higgs mass is m_{H,c} = 72(2) GeV, which implies
that there is no electroweak phase transition in the Standard Model.


title:
The end point of the first-order phase transition of the SU(2)
  gauge-Higgs model on a four-dimensional isotropic lattice

abstract:
  We report results of a study of the end point of the electroweak phase
transition of the SU(2) gauge-Higgs model defined on a four-dimensional
isotropic lattice with N_t=2. Finite-size scaling study of Lee-Yang zeros
yields lambda_c=0.00116(16) for the end point. Combined with a zero-temperature
measurement of Higgs and W boson masses, this leads to M_{H,c}=68.2+-6.6 GeV
for the critical Higgs boson mass. An independent analysis of Binder cumulant
gives a consistent value lambda_c=0.00102(3) for the end point.


title:
Symmetry and Symmetry Restoration of Lattice Chiral Fermion in the
  Overlap Formalism

abstract:
  Three aspects of symmetry structure of lattice chiral fermion in the overlap
formalism are discussed. By the weak coupling expansion of the overlap Dirac
operator, the axial anomaly associated to the chiral transformation proposed by
Luescher is evaluated and is shown to have the correct form of the topological
charge density for perturbative backgrounds. Next we discuss the exponential
suppression of the self-energy correction of the lightest mode in the
domain-wall fermion/truncated overlap. Finally, we consider a supersymmetric
extension of the overlap formula in the case of the chiral multiplet and
examine the symmetry structure of the action.


title:
Non-perturbative renormalization factors of bilinear quark operators for
  Kogut-Susskind fermions and light quark masses in quenched QCD

abstract:
  Light quark masses are computed for Kogut-Susskind fermions by evaluating
non-perturbatively the renormalization factor for bilinear quark operators.
Calculations are carried out in the quenched approximation at \beta=6.0, 6.2,
and 6.4. For the average up and down quark mass we find $m_{\bar MS}(2 GeV)=
4.15(27) MeV$ in the continuum limit, which is significantly larger than
$3.51(20) MeV$ ($q^*=1/a$) or $3.40(21) MeV$ ($q^*=\pi/a$) obtained with the
one-loop perturbative renormalization factor.


title: On tadpole improvement for staggered fermions

abstract:
  An explanation is proposed for the fact that Lepage--Mackenzie tadpole
improvement does not work well for staggered fermions. The idea appears to work
for all renormalization constants which appear in the staggered fermion
self-energy. Wilson fermions are also discussed.


title: Laplacian Abelian Projection: Abelian dominance and Monopole dominance

abstract:
  A comparative study of Abelian and Monopole dominance in the Laplacian and
Maximally Abelian projected gauges is carried out. Clear evidence for both
types of dominance is obtained for the Laplacian projection. Surprisingly, the
evidence is much more ambiguous in the Maximally Abelian gauge. This is
attributed to possible ``long-distance imperfections'' in the maximally abelian
gauge fixing.


title: Putting centre dominance under the microscope

abstract:
  We make various short points on the phenomenon of centre dominance in SU(2).
The Z(2) dominance seen in Wilson loops is related to the loop distribution and
to half-odd-integer representations of the group. The distributions also make
it clear that, in this picture, the requirement of vortices for confinement is
essentially trivial. We confirm that the same effect appears in the positive
plaquette model. The simple random vortex picture is shown to give a
substantial fraction of the string tension.


title: Do Large Abelian Monopole Loops Survive the Continuum Limit?

abstract:
  An analysis of the monopole loop length distribution is performed in
Wilson-action SU(2) lattice gauge theory. A pure power law in the inverse
length is found, at least for loops of length, $l$, less than the linear
lattice size $N$. This power shows a definite $\beta$ dependence, passing 5
around $\beta =2.9$, and appears to have very little finite lattice size
dependence. It is shown that when this power exceeds 5, no loops any finite
fraction of the lattice size will survive the infinite lattice limit. This is
true for any reasonable size distribution for loops larger than N. The apparent
lack of finite size dependence in this quantity would seem to indicate that
abelian monopole loops large enough to cause confinement do not survive the
continuum limit. Indeed they are absent for all $\beta > 2.9$.


title:
Light hadron spectroscopy on the lattice with the non-perturbatively
  improved Wilson action

abstract:
  We present results for the light meson masses and decay constants as obtained
from calculations with the non-perturbatively improved (`Alpha') action and
operators on a 24^3 \times 64 lattice at beta = 6.2, in the quenched
approximation. The analysis was performed in a way consistent with O(a)
improvement. We obtained: reasonable agreement with experiment for the
hyperfine splitting; f_K=156(17) MeV, f_pi =139(22) MeV, f_K/f_pi = 1.13(4) ;
f_{K*}=219(7) MeV, f_rho =199(15) MeV, f_phi =235(4) MeV; f_{K*}^{T}(2 GeV) =
178(10) MeV, f_rho^{T}(2 GeV) =165(11) MeV, where f_V^{T} is the coupling of
the tensor current to the vector mesons; the chiral condensate
<\bar{q}q>^\bar{MS} (2 GeV)= - (253 +/- 25 MeV)^3. Our results are compared to
those obtained with the unimproved Wilson action. We also verified that the
free-boson lattice dispersion relation describes our results very accurately
for a large range of momenta.


title: An Estimate of alpha_S from Bottomonium in Unquenched QCD

abstract:
  We estimate the strong coupling constant from the perturbative expansion of
the plaquette. The scale is set by the 2S-1S and 1P-1S splittings in
bottomonium which are computed in NRQCD on dynamical gauge configurations with
nf=2 degenerate Wilson quarks at intermediate masses. We have increased the
statistics of our spectrum calculation in order to reliably extrapolate in the
sea-quark mass. We find a value of alpha_MS(m_Z) = 0.1118(26) which is somewhat
lower than previous estimates within NRQCD.


title: Lattice Gravity and Random Surfaces

abstract:
  I review recent progress in simplicial quantum gravity in three and four
dimensions, in particular new results on the phase structure of modified models
of dynamical triangulations, the application of a strong-coupling expansion,
and the benefits provided by including degenerate triangulations. In addition,
I describe some recent numerical and analytical results on anisotropic
crystalline membranes.


title:
Study of Instanton Contributions to Moments of Nucleon Spin-Dependent
  Structure Functions

abstract:
  Instantons are the natural mechanism in non-perturbative QCD to remove
helicity from valence quarks and transfer it to gluons and quark-antiquark
pairs. To understand the extent to which instantons explain the so-called "spin
crisis" in the nucleon, we calculate moments of spin-dependent structure
functions in quenched QCD and compare them with the results obtained with
cooled configurations from which essentially all gluon contributions except
instantons have been removed. Preliminary results are presented.


title:
Low-temperature expansion and perturbation theory in 2D models with
  unbroken symmetry: a new approach

abstract:
  A new method of constructing a weak coupling expansion of two dimensional
(2D) models with an unbroken continuous symmetry is developed. The method is
based on an analogy with the abelian XY model, respects the Mermin-Wagner (MW)
theorem and uses a link representation of the partition and correlation
functions. An expansion of the free energy and of the correlation functions at
small temperatures is performed and first order coefficients are calculated
explicitly. They are shown to coincide with the results of the conventional
perturbation theory. We discuss an applicability of our method to analysis of
uniformity of the low-temperature expansion.


title: Domain wall fermions at finite temperature

abstract:
  We investigate the properties of domain wall fermions on a set of quenched
configurations at non-zero temperature. In particular, we compute the low lying
eigenvalues of the DWF operator and study their relation with topology, level
crossings and chiral symmetry breaking. We also measure the screening
correlators and discuss the dependence on the extent of the extra dimension and
the quark mass.


title: 2d quantum gravity with discrete edge lengths

abstract:
  An approximation of the Standard Regge Calculus (SRC) was proposed by the
$Z_2$-Regge Model ($Z_2$RM). There the edge lengths of the simplicial complexes
are restricted to only two possible values, both always compatible with the
triangle inequalities. To examine the effect of discrete edge lengths, we
define two models to describe the transition from the $Z_2$RM to the SRC. These
models allow to choose the number of possible link lengths to be $n =
{4,8,16,32,64,...}$ and differ mainly in the scaling of the quadratic link
lengths. The first extension, the $X^1_n$-Model, keeps the edge lengths limited
and still behaves rather similar to the "spin-like" $Z_2$RM. The vanishing
critical cosmological constant is reproduced by the second extension, the
$X^C_n$-Model, which allows for increasing edge lengths. In addition the area
expectation values are consistent with the scaling relation of the SRC.


title:
Monte Carlo Renormalization of 2d Simplicial Quantum Gravity Coupled to
  Gaussian Matter

abstract:
  We extend a recently proposed real-space renormalization group scheme for
dynamical triangulations to situations where the lattice is coupled to
continuous scalar fields. Using Monte Carlo simulations in combination with a
linear, stochastic blocking scheme for the scalar fields we are able to
determine the leading eigenvalues of the stability matrix with good accuracy
both for c = 1 and c = 10 theories.


title: The string tensions of SU(3) representations

abstract:
  I report on the status of a computation of fundamental and some higher
representation string tensions in pure gauge SU(3). An order a^2 tadpole
improved action and an anisotropic lattice are used. At present, the static
quark potentials and the string tensions are calculated by measuring Wilson
loops on an 8^3 x 24 lattice. Wilson loops for higher representations are
measured in terms of Wilson loops of the fundamental representation. At the
small and intermediate distances available, rough agreement with Casimir
scaling is observed, and no color screening for the 8 representation is seen.


title: Finite Size Effects in Quark-Gluon Plasma Formation

abstract:
  Using lattice simulations of quenched QCD we estimate the finite size effects
present when a gluon plasma equilibrates in a slab geometry, i.e., finite width
but large transverse dimensions. Significant differences are observed in the
free energy density for the slab when compared with bulk behavior. A small
shift in the critical temperature is also seen. The free energy required to
liberate heavy quarks relative to bulk is measured using Polyakov loops; the
additional free energy required is on the order of $30-40 MeV$ at $2-3 T_c$.


title: Phase structure of CP(N-1) model with topological term

abstract:
  CP(N-1) model with topological term is numerically studied. The topological
charge distribution P(Q) is calculated and then transformed to the partition
function Z($\theta$) as a function of $\theta$ parameter. In the strong
coupling region, P(Q) shows a gaussian behavior, which indicates a first order
phase transition at $\theta =\pi$. In the weak coupling region,
  P(Q) deviates from gaussian. A bending behavior of resulting F($\theta$) at
$\theta \neq \pi$, which might be a signal of a first order phase transition,
could be misled by large errors coming from the fourier transform of P(Q).
Results are shown mainly for CP(3) case.


title: Spectroscopy of Hadrons with b Quarks from Lattice NRQCD

abstract:
  Preliminary results from an extensive lattice calculation of the B, B_c, and
\Upsilon spectrum at quenched \beta = 6.0 are presented. The study includes
radially and orbitally excited mesons, and baryons containing b quarks. The b
quarks are formulated using NRQCD; for light and c quarks, a tadpole-improved
clover action is used.


title: Continuous space-time symmetries in a lattice field theory

abstract:
  For purposes of regularization as well as numerical simulation, the
discretization of Lorentz invariant continuum field theories on a space-time
lattice is often convenient. In general, this discretization destroys the
rotational or Lorentz-frame independence of the theory, which is only recovered
in the continuum limit. The Baxter 8-vertex model may be interpreted as a
particular discretization of a self-interacting massive Dirac fermion theory in
two dimensions (the massive Thirring model). Here it is shown that, in the
8-vertex/massive Thirring model, the Lorentz frame independence of the theory
remains undisturbed on the lattice. The only effect of the discretization is to
compactify the manifold of Lorentz frames. The relationship between this
lattice Lorentz symmetry and the Yang-Baxter relations is discussed.


title: Delta S=2 and Delta I=3/2 Matrix Elements in Quenched QCD

abstract:
  We present preliminary results for B_K, B_7^{3/2} and B_8^{3/2} from two
high-statistics lattice computations. These calculations are performed at
beta=6.0 and 6.2 in the quenched approximation, using mean-field-improved
Sheikholeslami-Wohlert fermionic actions.


title: Evolutionary Algorithms Applied to Landau-Gauge Fixing

abstract:
  Current algorithms used to put a lattice gauge configuration into Landau
gauge either suffer from the problem of critical slowing-down or involve an
additional computational expense to overcome it. Evolutionary Algorithms (EAs),
which have been widely applied to other global optimisation problems, may be of
use in gauge fixing. Also, being global, they should not suffer from critical
slowing-down as do local gradient based algorithms. We apply EA's and also a
Steepest Descent (SD) based method to the problem of Landau Gauge Fixing and
compare their performance.


title: Truncated Determinant Approach to Light Dynamical Quarks

abstract:
  Virtual quark effects in lattice QCD are studied in an approach where the
infrared modes are included in a precise and gauge-invariant manner. At fixed
physical volume the required number of modes does not increase in the continuum
limit, and the acceptance is tolerable even for very light quark masses.
Topological charge distributions at varying quark mass, and the static quark
potential, showing the onset of string-breaking, are presented in both QED2 and
QCD4.


title: UV-filtered fermionic Monte Carlo

abstract:
  The short-range modes of the fermionic determinant can be absorbed in the
gauge action using the loop expansion. The coefficients of this expansion and
the zeroes of the polynomial approximating the remainder can be optimized by a
simple, practical method. When the multiboson approach is used, this
optimization results in a faster simulation with fewer auxiliary fields.


title:
Quenched Light Hadron Spectrum with the Wilson Quark Action: Final
  Results from CP-PACS

abstract:
  We report the final results of the CP-PACS calculation for the quenched light
hadron spectrum with the Wilson quark action. Our data support the presence of
quenched chiral singularities, and this motivates us to use mass formulae based
on quenched chiral perturbation theory in order to extrapolate hadron masses to
the physical point. Hadron masses and decay constants in the continuum limit
show unambiguous systematic deviations from experiment. We also report the
results for light quark masses.


title: Evidence for quenched chiral logs

abstract:
  Using the pole shifting procedure of the modified quenched approximation
(MQA) to cure the exceptional configuration problem, accurate hadron hadron
spectrum calculations can be obtained at very light quark mass. Here we use the
MQA to extend and improve our previous investigation of chiral logs in the pion
mass. At beta=5.7 for Wilson fermion, we see clear evidence for quenched chiral
logarithms in the pion mass as a function of quark mass. The size of the
observed chiral log exponent delta is in good agreement with the value obtained
from a direct calculation of the eta' hairpin diagram.


title: Tests of Improved Kogut-Susskind Fermion Actions

abstract:
  Improved Kogut-Susskind quark actions containing repeatedly smeared links are
studied to address the issue of flavor symmetry restoration. As a measure of
the flavor symmetry restoration the mass spectrum of all the pions is computed.
We present results for several variants of the "fat" actions that are suitable
for full QCD simulations.


title: Lattice Effective Actions and Light-Quark Confinement

abstract:
  The positive-plaquette Manton action at weak coupling is a reasonable action
for short-distance phenomena. We propose an iterative scheme for evolving this
action into an effective action for longer distance scales. We report on the
first step of this scheme in which we have measured ``blocked'' Creutz ratios
with lattice spacing 2a at beta = 16 on a 32^4 lattice and have searched for an
effective action that yields the same ratios on a 16^4 lattice.
  We also suggest a mechanism for quark confinement that relies upon the
lightness of the u and d quarks and formulate a way of testing it in lattice
simulations of QCD.


title: Search for Lambda^2/p^2 corrections to the QCD running coupling

abstract:
  We investigate the occurrence of power terms $(Lambda^2/p^2$ in the running
QCD coupling by analysing non-perturbative measurements of $\alpha_s(p)$ at
quite low momenta obtained from the lattice three-gluon vertex. Our study
provides some evidence for such a contribution. The phenomenological
implications of such a presence are reviewed.


title: Hadron matrix elements for nucleon decay with the Wilson quark action

abstract:
  We report preliminary results of our study of matrix elements of baryon
number violating operators which appear in the low-energy effective Lagrangian
of (SUSY-)Grand Unified Theories. The calculation is performed on a
$32^{3}\times80$ lattice at $\beta=6.1$ using Wilson fermions in the quenched
approximation. Our calculation is independent of details of (SUSY-)GUT models
and covers all interesting decay modes.


title: Scaling behavior of $f_{B}$ with NRQCD

abstract:
  We investigate the scaling behavior of the $B$ meson decay constant $f_B$ and
$f_{B_{s}}$ at $\beta$$=$$5.7, 5.9, 6.1$, employing the NRQCD heavy quark
action and the clover light quark action. Mixing effect from dimension-4
operator in the heavy-light axial-vector current is studied, and we find that
the $a$ dependence of $f_B$ is significantly reduced. Our preliminary result
for the decay constants in the quenched approximation is
$f_{B}$$=$$162(^{+35}_{-18})$ MeV, $f_{B_{s}}$$=$$190(^{+40}_{-19})$ MeV, and
$f_{B_{s}}/f_{B}$$=$$1.18(^{+6}_{-6})$.


title: Gauge invariant properties of Abelian monopoles

abstract:
  Using a renormalization group motivated smoothing technique, we investigate
the large scale structure of lattice configurations at finite temperature,
concentrating on Abelian monopoles identified in the maximally Abelian, the
Laplacian Abelian, and the Polyakov gauge. Monopoles are mostly found in
regions of large action and topological charge, rather independent of the gauge
chosen to detect them. Gauge invariant properties around Abelian monopoles, the
local non-Abelian action and topological density, are studied. We show that the
local averages of these densities along the monopole trajectories are clearly
above the background, which supports the existence of monopoles as physical
objects. Characteristic changes of the vacuum structure at the deconfinement
transition can be attributed to the corresponding Abelian monopoles, to an
extent that depends on the gauge chosen for Abelian projection. All three
Abelian projections reproduce the full SU(2) string tension within 10 percent
which is preserved by smoothing.


title:
Abelian monopoles in finite temperature lattice gauge fields:
  Classically perfect action, smoothing and various Abelian gauges

abstract:
  Using the renormalization group motivated smoothing technique, the large
scale structure of lattice configurations at finite temperature is
characterized in terms of Abelian monopoles identified in the maximally
Abelian, the Laplacian Abelian, and the Polyakov gauge. Abundance and
anisotropy of monopoles at deconfinement and gauge invariant properties like
local non-Abelian action and topological density are studied. Monopoles are
predominantly found in regions of large action and topological charge, rather
independent of the chosen gauge.


title: Chiral condensate, quark charge and chiral density

abstract:
  We study the topological and fermionic vacuum structure of four-dimensional
QCD on the lattice by means of correlators of fermionic observables and
topological densities. We show the existence of strong local correlations
between the topological charge density and the quark condensate, charge and
chiral density. By analysis of individual gauge configurations, we visualize
that instantons (antiinstantons) carry positive (negative) chirality, whereas
the quark charge density fluctuates in sign within instantons.


title: Preliminary study of $B_B$ parameter using Lattice NRQCD

abstract:
  We present the preliminary result of the calculation of $B_B$ parameter using
lattice NRQCD. The calculation is performed on a $16^3 \times 48$ quenched
lattice at $\beta=5.9$ with clover light quark. The use of lattice NRQCD
enables us to investigate the $1/m_Q$ correction from the static limit. The
observed mass dependence is well described by the vacuum saturation.


title:
Flavor-Symmetry Restoration and Symanzik Improvement for Staggered
  Quarks

abstract:
  We resolve contradictions in the literature concerning the origins and size
of unphysical flavor-changing strong interactions generated by the
staggered-quark discretization of QCD. We show that the leading contributions
are tree-level in $\order(a^2)$ and that they can be removed by adding three
correction terms to the link operator in the standard action. These corrections
are part of the systematic Symanzik improvement of the staggered-quark action.
We present a new improved action for staggered quarks that is accurate up to
errors of $\order(a^4,a^2\alpha_s)$ --- more accurate than most, if not all,
other discretizations of light-quark dynamics.


title:
Aharonov-Bohm effect, Center Monopoles and Center Vortices in SU(2)
  Lattice Gluodynamics

abstract:
  SU(2) gluodynamics is investigated numerically and analytically in the
(Indirect) Maximal Center gauge at finite temperature. The center vortices are
shown to be condensed in the confinement phase and dilute in the deconfinement
phase. A new physical object, center monopole, is constructed. We show that the
center monopole condensate is the order parameter of deconfinement phase
transition. The linking of the vortex worldsheets and quark trajectories is
identified with the Aharonov-Bohm interaction in an effective Abelian Higgs
theory. We conclude that the confinement in the Maximal Center gauge can be
explained by a new mechanism called "the real superconductor mechanism".


title: Dynamical QCD thermodynamics with domain wall fermions

abstract:
  We present results from numerical simulations of full, two flavor QCD
thermodynamics at N_t=4 with domain wall fermions. For the first time a
numerical simulation of the full QCD phase transition displays a low
temperature phase with spontaneous chiral symmetry breaking but intact flavor
symmetry and a high temperature phase with the full SU(2) x SU(2) chiral flavor
symmetry.


title: Multicanonical Hybrid Monte Carlo: Boosting Simulations of Compact QED

abstract:
  We demonstrate that substantial progress can be achieved in the study of the
phase structure of 4-dimensional compact QED by a joint use of hybrid Monte
Carlo and multicanonical algorithms, through an efficient parallel
implementation. This is borne out by the observation of considerable speedup of
tunnelling between the metastable states, close to the phase transition, on the
Wilson line. We estimate that the creation of adequate samples (with order 100
flip-flops) becomes a matter of half a year's runtime at 2 Gflops sustained
performance for lattices of size up to 24^4.


title: Numerical Studies of the Double Scaling Limit in Large N Reduced Model

abstract:
  We study the two-dimensional Eguchi-Kawai model as a toy model of the IIB
matrix model, which has been recently proposed as a nonperturbative definition
of the type IIB superstring theory. While the planar limit of the model is
known to reproduce the two-dimensional Yang-Mills theory, we find through Monte
Carlo simulation that the model allows a different large $N$ limit, which can
be considered as the double scaling limit in matrix models.


title: B-parameters for $\Delta S = 2$ SUSY Operators

abstract:
  We present the first lattice measurement, using Non Perturbative
Renormalization Method, of the B-parameters of the dimension-six four-fermion
operators relevant for the supersymmetric corrections to the $\Delta S=2$
transitions.


title: Monopoles and instantons in SU(2) lattice gauge theory

abstract:
  We investigate the monopole-instanton correlation in SU(2) lattice gauge
theory using a renormalisation group inspired smoothing technique. We look at
the properties of monopole clusters and their correlation with instantons.
Since the action of the smoothed configurations is dominated by instantons we
compare the smoothed Monte Carlo lattices to artificially reconstructed
configurations with the same instanton content but no other fluctuations. Both
parallel and randomly rotated (in group space) instanton ensembles are
considered.


title:
Mean field analysis of the SO(3) lattice gauge theory at finite
  temperature

abstract:
  We study the finite temperature properties of the SO(3) lattice gauge theory
using mean field theory. The main result is the calculation of the effective
action at finite temperature. The form of the effective action is used to
explain the behaviour of the adjoint Wilson line in numerical simulations.
Numerical simulations of the SO(3) lattice gauge theory show that the adjoint
Wilson line has a very small value at low temperatures; at high temperatures,
metastable states are observed in which the adjoint Wilson line takes positive
or negative values. The effective action is able to explain the origin of these
metastable states. A comparison of the effective actions of the SU(2) and the
SO(3) lattice gauge theories explains their different behaviour at high
temperatures. The mean field theory also predicts a finite temperature phase
transition in the SO(3) lattice gauge theory.


title: Resolving Exceptional Configurations in Quenched Lattice QCD

abstract:
  Quenched lattice QCD calculations with Wilson-type fermions at small quark
masses are impeded by exceptional configurations. We show how this problem can
be resolved in a practicable way without changing the physics in the chiral
limit.


title: New possibilities for QCD at finite density

abstract:
  I review the growing theoretical indications that at high densities color
SU(3) gauge symmetry is spontaneously broken by the formation of a quark pair
condensate. This leads to a rich phase structure for QCD as a function of
temperature and chemical potential.
  I also discuss the prospects for lattice QCD calculations at finite density,
including the Glasgow algorithm and imaginary chemical potential.


title: Analytical Results for Abelian Projection

abstract:
  Analytic methods for Abelian projection are developed, and a number of
results related to string tension measurements are obtained. It is proven that
even without gauge fixing, Abelian projection yields string tensions of the
underlying non-Abelian theory. Strong arguments are given for similar results
in the case where gauge fixing is employed. The subgroup used for projection
need only contain the center of the gauge group, and need not be Abelian. While
gauge fixing is shown to be in principle unnecessary for the success of Abelian
projection, it is computationally advantageous for the same reasons that
improved operators, e.g., the use of fat links, are advantageous in Wilson loop
measurements.


title: An Improvement to the Linear Accept/Reject Algorithm

abstract:
  We study the improvement of Kennedy-Kuti's linear accept/reject algorithm
with different ordering criterion and modified Bhanot-Kennedy estimator of
$e^{\Delta H}$ to reduce probability-bound violation. A new stochastic Monte
Carlo algorithm to accommodate the probability-bound violation is proposed.


title: Sphaleron rate at high temperature in 1+1 dimensions

abstract:
  We resolve the controversy in the high temperature behavior of the sphaleron
rate in the abelian Higgs model in 1+1 dimensions. The $T^2$ behavior at
intermediate lattice spacings is found to change into $T^{2/3}$ behavior in the
continuum limit. The results are supported by analytic arguments that the
classical approximation is good for this model.


title: NRQCD on an anisotropic lattice

abstract:
  We present preliminary results for the Upsilon spectrum on an anisotropic
lattice using the improved O(mv^6) NRQCD Hamiltonian. We find accurate results
can be obtained in moderate computer times and that they agree with earlier
results on an isotropic lattice.


title: Towards a Non-Perturbative Calculation of DIS Wilson Coefficients

abstract:
  We verify the operator product expansion (OPE) of deep inelastic scattering
(DIS) on the lattice and present first results of a non-perturbative
calculation of the Wilson coefficients.


title: Nucleon form factors and O(a) Improvement

abstract:
  Nucleon form factors have been extensively studied both experimentally and
theoretically for many years. We report here on new results of a high
statistics quenched lattice QCD calculation of vector and axial-vector nucleon
form factors at low momentum transfer within the Symanzik improvement
programme. The simulations are performed at three kappa and three beta values
allowing first an extrapolation to the chiral limit and then an extrapolation
in the lattice spacing to the continuum limit. The computations are all fully
non-perturbative. A comparison with experimental results is made.


title: Finite Temperature QCD on Anisotropic Lattices

abstract:
  We present results for mesonic propagators in temporal and spatial direction
and for topological properties at T below and above the deconfining transition
in quenched QCD. We use anisotropic lattices and Wilson fermions.


title: Non-Perturbative Improvement of the Anisotropic Wilson QCD Action

abstract:
  We describe the first steps in the extension of the Symanzik O($a$)
improvement program for Wilson-type quark actions to anisotropic lattices, with
a temporal lattice spacing smaller than the spatial one. This provides a fully
relativistic and computationally efficient framework for the study of heavy
quarks. We illustrate our method with accurate results for the quenched
charmonium spectrum.


title:
Two-Loop Computation of the Schroedinger Functional in Pure SU(3)
  Lattice Gauge Theory

abstract:
  We compute the Schroedinger functional (SF) for the case of pure SU(3) gauge
theory at two-loop order in lattice perturbation theory. This allows us to
extract the three-loop beta-function in the SF-scheme. These results are
required to compute the running coupling, the Lambda-parameter and quark masses
by finite size techniques with negligible systematic errors. In addition, we
can now implement two-loop O(a) improvement in simulations and extend and study
series in alternative ("tadpole-improved") bare couplings.


title:
Hopping expansion as a tool for handling dual variables in lattice
  models

abstract:
  The hopping expansion of 8-vertex models in their Grassmann representation is
studied. We use the functional similarity of the Ising model in this expansion
with the hopping expansion of 2-D Wilson fermions to show that the lattice
fermions are equivalent to the Self-avoiding Loop Model at bending rigidity
1/sqrt{2}.


title: Bottom and Charm quark masses from lattice NRQCD

abstract:
  We present new values for the $\bar{MS}$ masses of $b$ and $c$ quarks based
on lattice NRQCD simulations of the $\Upsilon (b\bar{b})$ and $\psi (c\bar{c})$
systems. These include three measurements of the $b$ mass based on quenched
simulations with lattice spacings ranging from 0.05fm to 0.15fm, which we find
to be largely independent of lattice spacing. In addition, we find a consistent
value from an unquenched simulation at 0.08fm.


title: Renormalization of four-fermion operators for higher twist calculations

abstract:
  The evaluation of the higher twist contributions to Deep Inelastic Scattering
amplitudes involves a non trivial choice of operator bases for the higher
orders of the OPE expansion of the two hadronic currents. In this talk we
discuss the perturbative renormalization of the four-fermion operators that
appear in the above bases.


title:
Computation of the improvement coefficient $c_{sw}$ to 1-loop with
  improved gluon actions

abstract:
  The clover coefficient $\csw$ is computed at one loop order of perturbation
theory for improved gluon actions including six-link loops. The O(a)
improvement coefficients for the dimension three isovector composite operators
bilinear in the quark fields are also calculated.


title:
A lattice potential investigation of quark mass and volume dependence of
  the $\Upsilon$ spectrum

abstract:
  We investigate bottomonia splittings by solving a Schrodinger-Pauli-type
equation with parametrisations of QCD potentials around those that have been
determined previously in lattice simulations. This is done both, in the
continuum and on finite lattices with resolutions ranging from a=0.2 fm down to
a=0.025 fm and extent of up to 12 fm or 144^3 lattice points. We find a strong
dependence of some splittings, in particular the 2S-1S and 1P-1S splittings, on
both the quark mass and the short range form of the static potential in the
neighbourhood of the bottom quark mass, while splittings such as 3S-2S and
2P-2S show reduced dependence on the short distance potential. We conclude that
the quenched quarkonium spectrum cannot be matched to experiment with a simple
redefinition of the lattice spacing. We investigate the size of relativistic
corrections as a function of the quark mass. Finite size effects are shown to
die out rather rapidly as the volume is increased, and we demonstrate the
restoration of rotational symmetry as the continuum limit is taken.


title: Hamilton-Jacobi Equation and the Tree Formula for Proper Vertices

abstract:
  The tree formula, which relates proper and connected vertices, is shown to be
the solution to a Hamilton-Jacobi equation.


title: Light hadron spectroscopy with O(a) improved dynamical fermions

abstract:
  We present results for the hadron spectrum and static quark potential from a
simulation with two flavours of $O(a)$ improved dynamical Wilson fermions at
$\beta=5.2$. We address the issues of sea quark dependence of observables and
finite-size effects.


title: Improvement, dynamical fermions, and heavy quark screening in QCD_3

abstract:
  First results from simulations of improved actions for both gauge fields and
staggered fermion fields in three dimensional QCD are presented. This work
provides insight into some issues of relevance to lattice theories in four
dimensions. In particular, the renormalization of the bare lattice coupling is
dramatically reduced when the tree-level $O(a^2)$ improved action is used. Naik
improvement of the staggered fermion action produces little reduction in
scaling violations of the rho meson mass. String breaking in the heavy quark
potential in the unquenched theory is also clearly resolved, using Wilson loops
to bound the ground state energy.


title: Chiral limit of light hadron mass in quenched staggered QCD

abstract:
  We discuss chiral limit of light hadron mass from our quenched staggered
calculations with a high lattice cutoff of (a^{-1})(\sim)3.7 GeV at (\beta)=6.5
and a large lattice volume of (48^3\times 64). We added six heavier quark mass
values of (m_qa)=0.0075, 0.015, 0.02, 0.03, 0.04 and 0.05 to the previously
existing 0.01, 0.005, 0.0025, and 0.00125. An interesting curvature is observed
in the (m_\pi^2/m_q) to (m_q) plot near (m_qa)=0.01.


title: The static quark potential in full QCD

abstract:
  We report results on the static quark potential in two-flavor full QCD. The
calculation is performed for three values of lattice spacing $a^{-1}\approx
0.9, 1.3$ and 2.5 GeV on $12^3{\times}24, 16^3{\times}32$ and $24^3{\times}48$
lattices respectively, at sea quark masses corresponding to $m_\pi/m_\rho
\approx 0.8-0.6$. An RG-improved gauge action and a tadpole-improved SW clover
quark action are employed. We discuss scaling of $m_{\rho}/\sqrt{\sigma}$ and
effects of dynamical quarks on the potential.


title: Finite density QCD with heavy quarks

abstract:
  In the large fermion mass limit of QCD at finite density the structure of the
partition function greatly simplifies and can be studied analytically. We show
that, contrary to general wisdom, the phase of the Dirac determinant is
relevant only at finite temperature and can be neglected for zero temperature
fields.


title: New results from APE with non-perturbatively improved Wilson fermions

abstract:
  We present the results for light hadron spectrum, decay constants and the
quark masses obtained with non-perturbatively improved Wilson fermions. We also
give our preliminary results for the heavy-light decay constants.


title:
Correlation Functions from Quantum Cluster Algorithms: Application to
  U(1) Quantum Spin and Quantum Link Models

abstract:
  We demonstrate how correlation functions for non-diagonal operators can be
measured with the loop-cluster algorithm for quantum spin models. We introduce
the U(1) quantum link model and present the construction of a cluster algorithm
for the model. We further show how an improved estimator for Wilson loops can
be realized with the flux-cluster algorithm.


title: Topological Phases in Neuberger-Dirac operator

abstract:
  The response of the Neuberger-Dirac fermion operator $D=\Id + V$ in the
topologically nontrivial background gauge field depends on the negative mass
parameter $m_0$ in the Wilson-Dirac fermion operator $D_w$ which enters $D$
through the unitary operator $V = D_w (D_w^{\dagger} D_w)^{-1/2}$. We classify
the topological phases of $D$ by comparing its index to the topological charge
of the smooth background gauge field. An exact discrete symmetry in the
topological phase diagram is proved for any gauge configurations. A formula for
the index of D in each topological phase is derived by obtaining the total
chiral charge of the zero modes in the exact solution of the free fermion
propagator.


title:
Evidence for fractional topological charge in SU(2) pure Yang-Mills
  theory

abstract:
  We investigate the spectral flows of the hermitian Wilson-Dirac operator in
the fundamental and adjoint representations on two ensembles of pure SU(2)
gauge field configurations at the same physical volume. We find several
background gauge field configurations where the index of the hermitian
Wilson-Dirac operator in the adjoint representation is not four times the index
in the fundamental representation. This could imply a topological basis for the
existence of degenerate vacua in supersymmetric Yang-Mills theories.


title: Status of the QCDSP project

abstract:
  We describe the completed 8,192-node, 0.4Tflops machine at Columbia as well
as the 12,288-node, 0.6Tflops machine assembled at the RIKEN Brookhaven
Research Center. Present performance as well as our experience in commissioning
these large machines is presented. We outline our on-going physics program and
explain how the configuration of the machine is varied to support a wide range
of lattice QCD problems, requiring a variety of machine sizes. Finally a brief
discussion is given of future prospects for large-scale lattice QCD machines.


title: Nucleon Magnetic Moments Beyond the Perturbative Chiral Regime

abstract:
  The quark mass dependence of nucleon magnetic moments is explored over a wide
range. Quark masses currently accessible to lattice QCD, which lie beyond the
regime of chiral perturbation theory (chiPT), are accessed via the cloudy bag
model (CBM). The latter reproduces the leading nonanalytic behavior of chiPT,
while modeling the internal structure of the hadron under investigation. We
find that the predictions of the CBM are succinctly described by the simple
formula, \mu_N(m_\pi) = \mu^{(0)}_N / (1 + \alpha m_\pi + \beta m_\pi^2), which
reproduces the lattice data, as well as the leading nonanalytic behavior of
chiPT. As this form also incorporates the anticipated Dirac moment behavior in
the limit m_\pi \to \infty, it constitutes a powerful method for extrapolating
lattice results to the physical mass regime.


title: Mass spectrum and decay constants in the continuum limit

abstract:
  We present first results for light hadron masses, quark masses and decay
constants in the continuum limit using O(a) improved fermions at three
different values of the gauge coupling \beta.


title: Ginsparg-Wilson Fermions: A study in the Schwinger Model

abstract:
  Qualitative features of Ginsparg-Wilson fermions, as formulated by Neuberger,
coupled to two dimensional U(1) gauge theory are studied. The role of the
Wilson mass parameter in changing the number of massless flavors in the theory
and its connection with the index of the Dirac operator is studied. Although
the index of the Dirac operator is not related to the geometric definition of
the topological charge for strong couplings, the two start to agree as soon as
one goes to moderately weak couplings. This produces the desired singularity in
the quenched chiral condensate which appears to be very difficult to reproduce
with staggered fermions. The fermion determinant removes the singularity and
reproduces the known chiral condensate and the meson mass within understandable
errors.


title: Center Projection With and Without Gauge Fixing

abstract:
  We consider projections of SU(2) lattice link variables onto Z(2) center and
U(1) subgroups, with and without gauge-fixing. It is shown that in the absence
of gauge-fixing, and up to an additive constant, the static quark potential
extracted from projected variables agrees exactly with the static quark
potential taken from the full link variables; this is an extension of recent
arguments by Ambjorn and Greensite, and by Ogilvie. Abelian and center
dominance is essentially trivial in this case, and seems of no physical
relevance. The situation changes drastically upon gauge fixing. In the case of
center projection, there are a series of tests one can carry out, to check if
vortices identified in the projected configurations are physical objects. All
these criteria are satisfied in maximal center gauge, and we show here that
they all fail in the absence of gauge fixing. The non-triviality of center
projection is due entirely to the maximal center gauge-fixing, which pumps
information about the location of extended physical objects into local Z(2)
observables.


title: Magnetic Monopole Content of Hot Instantons

abstract:
  We study the Abelian projection of an instanton in $R^3 \times S^1$ as a
function of temperature (T) and non-trivial holonomic twist ($\omega$) of the
Polyakov loop at infinity. These parameters interpolate between the circular
monopole loop solution at T=0 and the static 't Hooft-Polyakov
monopole/anti-monopole pair at high temperature.