title: A strategy to compute the b-quark mass with non-perturbative accuracy

abstract:
  We describe a strategy for a non-perturbative computation of the b-quark mass
to leading order in 1/m in the Heavy Quark Effective Theory (HQET). The
approach avoids the perturbative subtraction of power law divergencies, and the
continuum limit may be taken. First numerical results in the quenched
approximation demonstrate the potential of the method with a preliminary result
m_b(4GeV)=4.56(2)(7) GeV. In principle, the idea may also be applied to the
matching of composite operators or the computation of 1/m corrections in HQET.


title: Finite-size scaling and deconfinement transition in gauge theories

abstract:
  A new method is proposed for determining the critical indices of the
deconfinement transition in gauge theories, based on the finite-size scaling
analysis of simple lattice operators, such as the plaquette. A precise
determination of the critical index $\nu$, in agreement with the prediction of
the Svetitsky-Yaffe conjecture, is obtained for SU(3) gauge theory in
(2+1)-dimension. Preliminary results for SU(2) in (3+1)-dimension are also
given.


title: Novel Quantum Monte Carlo Algorithms for Fermions

abstract:
  Recent research shows that the partition function for a class of models
involving fermions can be written as a statistical mechanics of clusters with
positive definite weights. This new representation of the model allows one to
construct novel algorithms. We illustrate this through models consisting of
fermions with and without spin. A Hubbard type model with both attractive and
repulsive interactions becomes tractable using the new approach. Precision
results in the two dimensional attractive model confirm a superfluid phase
transition in the Kosterlitz-Thouless universality class.


title: The Lattice Fermi Surface

abstract:
  The Nambu - Jona-Lasinio model in 2+1 dimensions is simulated for non-zero
baryon chemical potential with a diquark source term. No evidence for a BCS
condensate or gap is seen at high density; rather, critical behaviour with
novel exponents is observed, suggesting that 2d superfluidity as first
described by Kosterlitz and Thouless is realised, but with the universality
class determined by the presence of relativistic fermions.


title: Branes in the 5D Abelian Higgs Model

abstract:
  We find 3-brane Higgs and Coulomb phases in the 5D Abelian Higgs Model and
determine the transition surfaces that separate them from the usual bulk
phases.


title: Improved non-perturbative renormalization without $c_{NGI}$

abstract:
  Recently, a method for O(a) improvement of composite operators has been
proposed which uses the large momentum behavior of fixed gauge quark and gluon
correlation functions (G. Martinelli et al., hep-lat/0106003). A practical
problem with this method is that a particular improvement coefficient,
$c_{NGI}$, which has a gauge non-covariant form, is difficult to determine.
Here I work out the size of the errors made in improvement coefficients and
physical quantities if one does not include the $c_{NGI}$ term.


title: Lattice QCD at finite isospin density

abstract:
  We have simulated QCD at a finite chemical potential $\mu_I$ for isospin
($I_3$) to probe part of the phase diagram for nuclear matter. Preliminary
results suggest that for $\mu_I > \mu_c$, this theory forms a charged pion
condensate which spontaneously breaks $I_3$, and the isospin density is non
zero.


title: Properties of a New Class of Lattice Dirac Operators

abstract:
  A new class of lattice Dirac operators $D$ have been recently proposed on the
basis of the generalized Ginsparg-Wilson relation, $\gamma_5(\gamma_5 D) +
(\gamma_5 D)\gamma_5 =2a^{2k+1}(\gamma_5 D)^{2k+2}$, where $k$ is a
non-negative integer. We discuss the index theorem and locality properties for
this general class of lattice Dirac operators.


title:
Gauge potential singularities and the gluon condensate at finite
  temperatures

abstract:
  The continuum limit of SU(2) lattice gauge theory is carefully investigated
at zero and at finite temperatures. It is found that the continuum gauge field
has singularities originating from center degrees of freedom being discovered
in Landau gauge. Our numerical results show that the density of these
singularities properly extrapolates to a non-vanishing continuum limit. The
action density of the non-trivial Z_2 links is tentatively identified with the
gluon condensate. We find for temperatures larger than the deconfinement
temperature that the thermal fluctuations of the embedded Z_2 gauge theory
result in an increase of the gluon condensate with increasing temperature.


title: Manifestation of Confinement in the Gluon propagator

abstract:
  The gluon propagator in Landau gauge is calculated on the lattice for SU(2)
gauge theory. In particular the manifestation of confinement in the gluon
propagator is studied. Removing the confining center vortices from the
Yang-Mills ensemble leads to a drastic reduction of the gluonic form factor in
the intermediate momentum regime.


title: A lattice study of the Faddeev-Niemi effective action

abstract:
  We perform a lattice analysis of the Faddeev-Niemi effective action
conjectured to describe the low energy sector of SU(2) Yang-Mills theory. We
generalize the effective action such that it contains all operators built from
a unit color vector field n with O(3)-symmetry and maximally four derivatives.
To avoid the presence of Goldstone bosons, we include explicit symmetry
breaking terms parametrized by an external field h of mass-dimension two. We
find a mass gap of the order of 1.5 GeV.


title:
Correlations for non-Hermitian Dirac operators: chemical potential in
  three-dimensional QCD

abstract:
  In the presence of a non-vanishing chemical potential the eigenvalues of the
Dirac operator become complex. We use a random matrix model approach to
calculate analytically all correlation functions at weak and strong
non-Hermiticity for three-dimensional QCD with broken flavor symmetry and
four-dimensional QCD in the bulk.


title:
Patterns of Spontaneous Chiral Symmetry Breaking in Vectorlike Gauge
  Theories

abstract:
  It has been conjectured that spontaneous chiral symmetry breaking in strongly
coupled vectorlike gauge theories falls into only three different classes,
depending on the gauge group and the representations carried by the fermions.
We test this proposal by studying SU(2), SU(3) and SU(4) lattice gauge theories
with staggered fermions in different irreducible representations. Staggered
fermions away from the continuum limit should, for all complex representations,
still belong to the continuum class of spontaneous symmetry breaking. But for
all real and pseudo-real representations we show that staggered fermions should
belong to incorrect symmetry breaking classes away from the continuum, thus
generalizing previous results. As an unambiguous signal for whether chiral
symmetry breaks, and which breaking pattern it follows, we look at the smallest
Dirac eigenvalue distributions. We find that the patterns of symmetry breaking
are precisely those conjectured.


title:
Light hadron spectrum using an O(a)-improved Wilson action with two
  dynamical quark flavours

abstract:
  I present results of recent work for the UKQCD Collaboration on the light
hadron spectrum using a non-perturbatively O(a)-improved Wilson action with two
degenerate flavours of dynamical quarks on a 16^3x32 lattice. Values of the
bare gauge coupling and bare dynamical quark mass were chosen to keep the
lattice spacing fixed at two distinct values in physical units as determined
through the Sommer scale parameter, r0. I also include results for a quenched
ensemble with a lattice spacing matching one of these dynamical sets and
results from an exploratory run at lighter bare quark mass.


title: Thermodynamics with 2+1 and 3 Flavors of Improved Staggered Quarks

abstract:
  We present preliminary results from exploring the phase diagram of finite
temperature QCD with three degenerate flavors and with two light flavors and
the mass of the third held approximately at the strange quark mass. We use an
order $\alpha_s^2 a^2, a^4$ Symanzik improved gauge action and an order
$\alpha_s a^2, a^4$ improved staggered quark action. The improved staggered
action leads to a dispersion relation with diminished lattice artifacts, and
hence better thermodynamic properties. It decreases the flavor symmetry
breaking of staggered quarks substantially, and we estimate that at the
transition temperature for an $N_t=8$ to $N_t=10$ lattice {\em all} pions will
be lighter than the lightest kaon. Preliminary results on lattices with
$N_t=4$, 6 and 8 are presented.


title: Heavy Baryons from Lattice NRQCD

abstract:
  The mass spectrum of heavy quark baryons has been computed on anisotropic
lattices using quenched lattice nonrelativistic QCD. The mass splittings
between spin-1/2 and spin-3/2 baryons are also calculated. Results are compared
to those obtained by using a Dirac-Wilson action of the D234 type. Color
hyperfine effects in heavy baryons are also discussed.


title: Susceptibilities and screening masses in two flavor QCD

abstract:
  We studied QCD with two flavors of dynamical staggered quarks at finite
temperature, with a bare sea quark mass of about 17 MeV. We report
investigations of baryon, isospin, charge and strangeness susceptibilities, as
well as screening masses obtained from correlators of local and one-link
separated meson operators. These were studied as functions of valence quark
mass at several temperatures. Our results for susceptibilities deviate
significantly from ideal gas values, and even more from the weak coupling
series. We also report the first measurement of off-diagonal quark number
susceptibilities below the transition temperature, Tc, where they are the main
contribution to charge fluctuations. We present evidence for a close connection
between the susceptibilities and the screening masses.


title: The Quest for Light Sea Quarks: Algorithms for the Future

abstract:
  As part of a systematic algorithm study, we present first results on a
performance comparison between a multibosonic algorithm and the hybrid Monte
Carlo algorithm as employed by the SESAM collaboration. The standard Wilson
fermion action is used on 32*16^3 lattices at beta=5.5.


title: The dual of non-Abelian Lattice Gauge Theory

abstract:
  Non-Abelian Lattice Gauge Theory in Euclidean space-time of dimension d>=2
whose gauge group is any compact Lie group is related to a Spin Foam Model by
an exact strong-weak duality transformation. The group degrees of freedom are
integrated out and replaced by combinatorial expressions involving irreducible
representations and intertwiners of the gauge group. This transformation is
available for the partition function, for the expectation value of observables
(spin networks), and for the correlator of centre monopoles which is a ratio of
partition functions in the original model and an ordinary expectation value in
the dual formulation.


title: Gribov Copies and Gauge Fixing in Lattice Gauge Theories

abstract:
  We address the problem of the gauge fixing versus Gribov copies in lattice
gauge theories. For the Landau gauge, results show that a suitable combination
of evolutionary algorithms with traditional steepest descent methods identifies
the global maximum of the optimisation function. We discuss the performance of
the combined algorithm on small cubic lattices for SU(2) and SU(3).


title: The $U_A(1)$ Problem on the Lattice

abstract:
  If the expression of the topological charge density operator, suggested by
fermions obeying the Ginsparg--Wilson relation, is employed, it is possible to
prove on the lattice the validity of the Witten--Veneziano formula for the
$\eta'$ mass. Recent numerical results from simulations with overlap fermions
in 2 (abelian Schwinger model) and 4 (QCD) dimensions give values for the mass
of the lightest pseudo-scalar flavour-singlet state that agree with theoretical
expectations and/or experimental data.


title: Topological Charge Fluctuations and Low-Lying Dirac Eigenmodes

abstract:
  We discuss the utility of low-lying Dirac eigenmodes for studying the nature
of topological charge fluctuations in QCD. The implications of previous results
using the local chirality histogram method are discussed, and the new results
using the overlap Dirac operator in Wilson gauge backgrounds at lattice
spacings ranging from a~0.04 fm to a~0.12 fm are reported. While the degree of
local chirality does not change appreciably closer to the continuum limit, we
find that the size and density of local structures responsible for chiral
peaking do change significantly. The resulting values are in disagreement with
the assumptions of the Instanton Liquid Model. We conclude that the
fluctuations of topological charge in the QCD vacuum are not locally quantized.


title:
Monopoles, confinement and deconfinement in lattice compact QED in
  (2+1)D with external fields

abstract:
  Finite temperature compact electrodynamics in (2+1) dimensions is studied in
the presence of external electromagnetic fields. The deconfinement temperature
is found to be insensitive to the external fields. This result corroborates our
observation that external fields create additional small--size magnetic dipoles
from the vacuum which do not spoil the confining properties of the model at low
temperature. However, the Polyakov loop is not an order parameter of
confinement. It can vanish in deconfinement in the presence of external field.
This does not mean the restoration of confinement for certain external field
fluxes. As a next step in the study of (2+1)D QED, the influence of monopoles
on the photon propagator is studied. First results are presented showing this
connection in the confining phase (without external field).


title: The Chiral Critical Point in 3-Flavour QCD

abstract:
  We determine the second order endpoint of the line of first order phase
transitions, which occur in the light quark mass regime of 3-flavour QCD at
finite temperature, and analyze universal properties of this chiral critical
point. A detailed analysis of Binder cumulants and the joint probability
distributions of energy like and ordering-field like observables confirms that
the chiral critical point belongs to the universality class of the 3d Ising
model. From a calculation with improved gauge and staggered fermion actions we
estimate that the transition is first order for pseudo-scalar meson masses less
than about 200 MeV.


title: Quark and Gluon Propagators in Covariant Gauges

abstract:
  We present data for the gluon and quark propagators computed in the standard
lattice Landau's gauge and for three values of the covariant gauge-fixing
parameter lambda=0,8,16. Our results are obtained using the SU(3) Wilson action
in the quenched approximation at beta=6.0 and volume=16^3x32.


title:
A new method for Monte Carlo simulation of theories with Grassmann
  variables

abstract:
  A new algorithm for simulation of theories with dynamical fermions is
presented. The algorithm is based on obtaining the new configuration U' from
the old one U by solving the equation M(U')\eta= \omega M(U)\eta, where M is
fermionic operator, \eta is random Gaussian vector, and \omega is random real
number close to unity. This algorithm can be used for acceleration of current
simulations in theories with fermions.


title:
Clear Evidence of a Continuum Theory of 4D Euclidean Simplicial Quantum
  Gravity

abstract:
  Four-dimensional (4D) simplicial quantum gravity coupled to both scalar
fields (N_X) and gauge fields (N_A) has been studied using Monte-Carlo
simulations. The matter dependence of the string susceptibility exponent
gamma^{(4)} is estimated. Furthermore, we compare our numerical results with
Background-Metric-Independent (BMI) formulation conjectured to describe the
quantum field theory of gravity in 4D. The numerical results suggest that the
4D simplicial quantum gravity is related to the conformal gravity in 4D.
Therefore, we propose a phase structure in detail with adding both scalar and
gauge fields and discuss the possibility and the property of a continuum theory
of 4D Euclidean simplicial quantum gravity.


title: Investigation of gauge-fixed pure U(1) theory at strong coupling

abstract:
  We numerically investigate the phase diagram of pure U(1) gauge theory with
gauge fixing at strong gauge coupling. The FM-FMD phase transition, which
proved useful in defining Abelian lattice chiral gauge theory, persists also at
strong gauge coupling. However, there the transition seems no to be longer
continuous. At large gauge couplings we find evidences for confinement.


title: Quenched Chiral Behavior of Hadrons with Overlap Fermions

abstract:
  We study the quenched chiral behavior of hadrons with the pseudoscalar mass
as low as $\approx 280$ MeV. We look for quenched chiral logs in the pion mass,
determine the renormalized quark mass, and observe quenched artifacts in the
$a_0$ and $N^*$ propagators. The calculation is done on a quenched lattice of
size $20^4$ and $a = 0.148(2)$ fm using overlap fermions and an improved gauge
action.


title: Mass renormalisation for improved staggered quarks

abstract:
  Improved staggered quark actions are designed to suppress flavour changing
strong interactions. We discuss the perturbation theory for this type of
actions and show the improvements to reduce the quark mass renormalisation
compared to naive staggered quarks. The renormalisations are of similar size as
for Wilson quarks.


title: Zero-modes of the QED Neuberger Dirac operator

abstract:
  We consider $4d$ compact lattice QED in the quenched approximation. First, we
briefly summarize the spectrum of the staggered Dirac operator and its
connection with random matrix theory. Afterwards we present results for the
low-lying eigenmodes of the Neuberger overlap-Dirac operator. In the strong
coupling phase we find exact zero-modes. Subsequently we discuss possibly
related topological excitations of the U(1) lattice gauge theory.


title:
Instabilities in Molecular Dynamics Integrators used in Hybrid Monte
  Carlo Simulations

abstract:
  We discuss an instability in the leapfrog integration algorithm, widely used
in current Hybrid Monte Carlo (HMC) simulations of lattice QCD. We demonstrate
the instability in the simple harmonic oscillator (SHO) system where it is
manifest. We demonstrate the instability in HMC simulations of lattic QCD with
dynamical Wilson-Clover fermions and discuss implications for future
simulations of lattice QCD.


title:
Lowest eigenvalues of the Dirac operator for two color QCD at nonzero
  chemical potential

abstract:
  We investigate the eigenvalue spectrum of the staggered Dirac matrix in SU(3)
and U(1) gauge theory as well as in full QCD with two colors and finite
chemical potential. Along the strong-coupling axis up to the phase transition,
the low-lying Dirac spectrum of these quantum field theories is well described
by random matrix theory and exhibits universal behavior. Related results for
gauge theories with minimal coupling are discussed in the chirally symmetric
phase and no universality is seen for the microscopic spectral densities.


title:
Lowest eigenvalues of the Dirac operator for two color QCD at finite
  density

abstract:
  We investigate the eigenvalue spectrum of the staggered Dirac matrix in full
QCD with two colors and finite chemical potential. Along the strong-coupling
axis up to the temperature phase transition, the low-lying Dirac spectrum is
well described by random matrix theory (RMT) and exhibits universal behavior.
The situation is discussed in the chirally symmetric phase and no universality
is seen for the microscopic spectral density.


title: Spins coupled to a $Z_2$-Regge lattice in 4d

abstract:
  We study an Ising spin system coupled to a fluctuating four-dimensional
$Z_2$-Regge lattice and compare with the results of the four-dimensional Ising
model on a regular lattice. Particular emphasis is placed on the phase
transition of the spin system and the associated critical exponents. We present
results from finite-size scaling analyses of extensive Monte Carlo simulations
which are consistent with mean-field predictions.


title:
Second Order Perturbation Theory for Improved Gluon and Staggered Quark
  Actions

abstract:
  We present the results of our perturbative calculations of the static quark
potential, small Wilson loops, the static quark self energy, and the mean link
in Landau gauge. These calculations are done for the one loop Symanzik improved
gluon action, and the improved staggered quark action.


title: Lattice study of nucleon properties with domain wall fermions

abstract:
  Domain wall fermions (DWF) are a new fermion discretization scheme with
greatly improved chiral symmetry. Our final goal is to study the nucleon spin
structure through lattice simulation using DWF. In this paper, we present our
current progress on two topics toward this goal: 1) the mass spectrum of the
nucleon excited states and 2) the iso-vector vector and axial charges, $g_{V}$
and $g_{A}$, of the nucleon.


title:
Nucleon axial charge from quenched lattice QCD with domain wall fermions
  and improved gauge action

abstract:
  In our previous DWF calculation with the Wilson gauge action at $\beta=6.0$
($a^{-1}\simeq$ 1.9 GeV) on a $16^3 \times 32 \times 16$ lattice, we found that
$\Ga$ had a fairly strong dependence on the quark mass. A simple linear
extrapolation of $\Ga$ to the chiral limit yielded a value that was almost a
factor of two smaller than the experimental one. Here we report our recent
study of this issue. In particular, we investigate possible errors arising from
finite lattice volume, especially in the lighter quark mass region. We employ a
RG-improved gauge action (DBW2), which maintains very good chiral behavior even
on a coarse lattice ($a^{-1}\simeq$ 1.3 GeV), in order to perform simulations
at large physical volume ($> (2{\rm fm})^3$). Our preliminary results suggest
that the finite volume effect is significant.


title: The Deconfinement Transition in SU(4) Lattice Gauge Theory

abstract:
  The deconfinement transition in SU(4) lattice gauge theory is studied on
N_s^3 X N_t lattices with N_s = 8-16 and N_t = 4-8 using a modified Wilson
action which is expected to have no bulk transitions. The peak of
susceptibility \chi_{|L|} is found to increase linearly with spatial volume for
N_t = 4, 5, and 6, indicating a first order deconfinement phase transition. The
latent heat is estimated to be approximately 2/3 of the corresponding ideal gas
energy density at T_c.


title: Singular gauge potentials and the gluon condensate at zero temperature

abstract:
  We consider a new cooling procedure which separates gluon degrees of freedom
from singular center vortices in SU(2) LGT in a gauge invariant way. Restricted
by a cooling scale $\kappa^4/\sigma^2$ fixing the residual SO(3) gluonic action
relative to the string tension, the procedure is RG invariant. In the limit
$\kappa \to 0$ a pure Z(2) vortex texture is left. This {\it minimal} vortex
content does not contribute to the string tension. It reproduces, however, the
lowest glueball states. With an action density scaling like $a^4$ with $\beta$,
it defines a finite contribution to the action density at T=0 in the continuum
limit. We propose to interpret this a mass dimension 4 condensate related to
the gluon condensate. Similarly, this vortex texture is revealed in the Landau
gauge.


title:
Hamiltonian Monte Carlo simulation of the two-dimensional Wess-Zumino
  model

abstract:
  We study a Hamiltonian lattice version of the two-dimensional Wess-Zumino
model. Preliminary results obtained by Quantum Monte Carlo with a
many-parameter guiding wave function are presented. We analyze the pattern of
supersymmetry breaking by measuring the ground state energy and a set of
supersymmetric Ward identities. The algorithm is quite effective and allows
very precise measurements.


title: The spin structure of the Lambda hyperon in quenched lattice QCD

abstract:
  It has been suggested to use the production of Lambda hyperons for
investigating the nucleon spin structure. The viability of this idea depends
crucially on the spin structure of the Lambda. Using nonperturbatively O(a)
improved Wilson fermions in the quenched approximation we have studied matrix
elements of two-quark operators in the Lambda. We present results for the axial
vector current, which give us the contributions of the u, d, and s quarks to
the Lambda spin.


title: Dual Superconductivity and Chiral Symmetry in Full QCD

abstract:
  A disorder parameter detecting dual superconductivity of the vacuum is
measured across the chiral phase transition in full QCD with two flavours of
dynamical staggered fermions. The observed behaviour is similar to the quenched
case.


title: Topics of monopole dynamics in gluodynamics

abstract:
  Three topics of monopole dynamics in gluodynamics are presented. 1)Gauge
(in)dependence of the monopole effective action (S.Ito, T.W.Park, T.Suzuki):
Four different abelian projections are studied. MA and Laplacian abelian gauges
show almost the same renormalization flow and renormalized trajectory. 2)The
quantized dual abelian Higgs model (DAH) derived from SU(2) gluodynamics and
its vacuum structure (Y.Koma, E.-M.Ilgenfritz, T.Suzuki,M.I.Polikarpov):
Monte-Carlo analysis of DAH is done. The quantum average of the dual field
strength shows a flux tube profile similar to the color-electric field profile
measured in SU(2) gluodynamics. 3)Lattice instanton action from 3D SU(2)
Georgi-Glashow model (GG)$_3$ (T.Yazawa, T.Suzuki): (GG)$_3$ is studied on the
lattice in the London limit. We determine an effective instanton action both in
unitary and MA gauges. For some range of parameters, we obtain almost perfect
actions which look the same in both gauges (gauge independence) and which
reproduce well the string tension.


title: The N_f=0 heavy quark potential and perturbation theory

abstract:
  The potential of a static quark-antiquark pair is studied in the range 0.05
fm $<$ r $<$ 0.8 fm, employing a sequence of lattices up to 64^4. The continuum
quantities are evaluated by extrapolation of the data at finite lattice
spacing. The results are compared with the perturbation theory predictions
obtained from the solution of the renormalization group equation for the
coupling. The renormalization scheme must be chosen carefully. No evidence for
large non-perturbative effects at short distances is seen.


title:
Confinement and monopole condensation: some properties of the disorder
  parameter

abstract:
  We demonstrate that the disorder parameter $<\mu>$ to detect dual
superconductivity in the confining phase of QCD is the v.e.v. of a magnetically
charged, Dirac like, gauge invariant operator $\mu$. We also show that the
abelian projection on the lattice is determined up to terms O(a^2) (a = lattice
spacing).


title: Critical behaviour of the Ginzburg-Landau model in the type II region

abstract:
  We study the critical behaviour of the three-dimensional U(1) gauge+Higgs
theory (Ginzburg-Landau model) at large scalar self-coupling \lambda (``type II
region'') by measuring various correlation lengths as well as the
Abrikosov-Nielsen-Olesen vortex tension. We identify different scaling regions
as the transition is approached from below, and carry out detailed comparisons
with the criticality of the 3d O(2) symmetric scalar theory.


title: Dirac operator and Ising model on a compact 2D random lattice

abstract:
  Lattice formulation of a fermionic field theory defined on a randomly
triangulated compact manifold is discussed, with emphasis on the topological
problem of defining spin structures on the manifold. An explicit construction
is presented for the two-dimensional case and its relation with the Ising model
is discussed. Furthermore, an exact realization of the Kramers-Wannier duality
for the two-dimensional Ising model on the manifold is considered. The global
properties of the field are discussed. The importance of the GSO projection is
stressed. This projection has to be performed for the duality to hold.


title: String breaking mechanisms induced by magnetic and electric condensates

abstract:
  The normal confining phase of gauge theories is characterised by the
condensation of magnetic monopoles and center vortices. Sometimes in coupled
gauge system one finds another phase with simultaneous condensation of electric
and magnetic charges. In both phases the confining string breaks down at a
given scale because of pair creation, however the mechanism is different. In
the former case the string breaking is a mixing phenomenon which is invisible
in the Wilson loop. On the contrary, in presence of both electric and magnetic
condensates the string breaking can be observed even in the Wilson loops.
Numerical experiments on a 3D $Z_2$ gauge-Higgs system neatly show this new
phenomenon.


title: Infrared Yang-Mills theory as a spin system. A lattice approach

abstract:
  To verify the conjecture that Yang-Mills theory in the infrared limit is
equivalent to a spin system whose excitations are knot solitons, a numerical
algorithm based on the inverse Monte Carlo method is proposed. To investigate
the stability of the effective spin field action, numerical studies of the
renormalization group flow for the coupling constants are suggested. A
universality of the effective spin field action is also discussed.


title: Susceptibility of Monte-Carlo Generated Projected Vortices

abstract:
  We determine the topological susceptibility from center projected vortices
and demonstrate that the topological properties of the SU(2) Yang-Mills vacuum
can be extracted from the vortex content. We eliminate spurious ultraviolet
fluctuations by two different smoothing procedures. The extracted
susceptibility is comparable to that obtained from full field configurations.


title: Thermodynamics with 3 and 2+1 Flavors of Improved Staggered Quarks

abstract:
  We present preliminary results from exploring the phase diagram of finite
temperature QCD with three degenerate flavors and with two light flavors and
the mass of the third held approximately at the strange quark mass. We use an
order $\alpha_s^2 a^2, a^4$ Symanzik improved gauge action and an order
$\alpha_s a^2, a^4$ improved staggered quark action. The improved staggered
action leads to a dispersion relation with diminished lattice artifacts, and
hence better thermodynamic properties. It decreases the flavor symmetry
breaking of staggered quarks substantially, and we estimate that at the
transition temperature for an $N_t=8$ to $N_t=10$ lattice {\em all} pions will
be lighter than the lightest kaon. Preliminary results on lattices with
$N_t=4$, 6 and 8 are presented.


title:
High-accuracy two-loop computation of the critical mass for Wilson
  fermions

abstract:
  We test an algebraic algorithm based on the coordinate-space method,
evaluating with high accuracy the critical mass for Wilson fermions in lattice
QCD at two loops. We test the results by using different types of infrared
regularization.


title: Spin models on Platonic solids and asymptotic freedom

abstract:
  We consider a two-dimensional sigma-model with discrete
icosahedral/dodecahedral symmetry. We present high-precision finite-size
numerical results that show that the continuum limit of this model is different
from the continuum limit of the rotationally invariant O(3) sigma-model.


title: The overlap operator as a continued fraction

abstract:
  We use a continued fraction expansion of the sign-function in order to obtain
a five dimensional formulation of the overlap lattice Dirac operator. Within
this formulation the inverse of the overlap operator can be calculated by a
single Krylov space method where nested conjugate gradient procedures are
avoided. We show that the five dimensional linear system can be made well
conditioned using equivalence transformations on the continued fractions. This
is of significant importance when dynamical overlap fermions are simulated.


title: A Two-Dimensional Lattice Model with Exact Supersymmetry

abstract:
  Starting from a simple discrete model which exhibits a supersymmetric
invariance we construct a local, interacting, two-dimensional Euclidean lattice
theory which also admits an exact supersymmetry. This model is shown to
correspond to the Wess-Zumino model with extended N=2 supersymmetry in the
continuum. We have performed dynamical fermion simulations to check the
spectrum and supersymmetric Ward identities and find good agreement with
theory.


title: Heavy-light decay constants with three dynamical flavors

abstract:
  We present preliminary results for the heavy-light leptonic decay constants
in the presence of three light dynamical flavors. We generate dynamical
configurations with improved staggered and gauge actions and analyze them for
heavy-light physics with tadpole improved clover valence quarks. When the scale
is set by $m_\rho$, we find an increase of approximately 23% in $f_B$ with
three dynamical flavors over the quenched case. Discretization errors appear to
be small (of order 3% or less) in the quenched case but have not yet been
measured in the dynamical case.


title:
Continuum versus periodic lattice Monte Carlo approach to classical
  field theory

abstract:
  We compare the momentum space with the standard periodic lattice approach to
Monte Carlo calculations in classical $\phi^4$ field theory. We show that the
mismatch in the initial value of $\phi^2_{\text{cl}}(t)$, results in a shift in
the ``thermalized'' value, at large times. The two approaches converge to the
same result in the continuum limit.


title: Chiral properties of domain wall fermions with improved gauge actions

abstract:
  We study the chiral properties of quenched domain wall fermions with several
gauge actions. We demonstrate that the nearly translationally invariant modes
in the fifth dimension that dominate the residual mass for Wilson gauge action
can be substantially suppressed using improved gauge actions. In particular, we
study the Symanzik action, the Iwasaki action, the DBW2 action and compare them
to the Wilson action.


title:
Kaon Matrix Elements and CP-violation from Quenched Lattice QCD: (I) the
  3-flavor case

abstract:
  We report the results of a calculation of the K --> pi pi matrix elements
relevant for the $\DIhalf$ rule and $\epe$ in quenched lattice QCD using domain
wall fermions at a fixed lattice spacing $a^{-1} \sim 2$ GeV. Working in the
three-quark effective theory, where only the u, d and s quarks enter and which
is known perturbatively to next-to-leading order, we calculate the lattice K
--> pi and K --> |0> matrix elements of dimension six, four-fermion operators.
Through lowest order chiral perturbation theory these yield K --> pi pi matrix
elements, which we then normalize to continuum values through a
non-perturbative renormalization technique. For the ratio of isospin amplitudes
|A_0|/|A_2| we find a value of $25.3 \pm 1.8$ (statistical error only) compared
to the experimental value of 22.2, with individual isospin amplitudes 10-20%
below the experimental values. For $\epe$, using known central values for
standard model parameters, we calculate $(-4.0 \pm 2.3) \times 10^{-4}$
(statistical error only) compared to the current experimental average of $(17.2
\pm 1.8) \times 10^{-4}$. Because we find a large cancellation between the I =
0 and I = 2 contributions to $\epe$, the result may be very sensitive to the
approximations employed. Among these are the use of: quenched QCD, lowest order
chiral perturbation theory and continuum perturbation theory below 1.3 GeV. We
have also calculated the kaon B parameter, B_K and find $B_{K,\bar{MS}}(2 {\rm
GeV}) = 0.532(11)$. Although currently unable to give a reliable systematic
error, we have control over statistical errors and more simulations will yield
information about the effects of the approximations on this first-principles
determination of these important quantities.


title:
Efficient computation of low-lying eigenmodes of non-Hermitian
  Wilson-Dirac type matrices

abstract:
  A polynomial transformation for non-Hermitian matrices is presented, which
provides access to wedge-shaped spectral windows. For Wilson-Dirac type
matrices this procedure not only allows the determination of the physically
interesting low-lying eigenmodes but also provides a substantial acceleration
of the eigenmode algorithm employed.


title: A New Approach to eta' on the Lattice

abstract:
  We perform an eta' mass analysis based on a total of 1130 dynamical gauge
field configurations, with 5 different quark mass values on lattices of size
16^3*32 (SESAM) and 24^3*40 (TkL) at beta = 5.6. We employ the stochastic
estimator technique and spectral methods to deal with the disconnected piece of
the flavour singlet correlation function. We demonstrate that very early
plateau formation in the local eta' mass can be achieved by first ground state
projecting the connected piece of its correlator.


title: The Berry Phase and Monopoles in Gluodynamics

abstract:
  We introduce a gauge invariant definition of a monopole on the lattice. The
construction is based on the observation that for each Wilson loop there exists
an extra U(1) group which leaves the loop invariant. Since the lattice
formulation utilizes the language of Wilson loops, the definition of the
monopole charge in terms of this plaquette dependent U(1) is gauge invariant.
The explicit construction of gauge invariant monopoles is presented both in
continuum and on the lattice.


title:
A Simulation of the 't Hooft Model at finite N_c with the Overlap Dirac
  Operator

abstract:
  We present some results of a numerical investigation of the 't Hooft model
with 2,3 and 4 colors, regularized on the lattice with overlap fermions.


title:
Aspects of the thermal phase transition of QCD with small chemical
  potential

abstract:
  We propose a new method to investigate the thermal properties of QCD with a
small chemical potential $(\mu)$. The derivatives of the phase transition point
with respect to $\mu$ are computed for 2 flavors of p4-improved staggered
fermions. We moreover comment on the complex phase of the fermion determinant
in finite-density QCD.


title: Lattice Quark Propagator in Landau and Laplacian Gauges

abstract:
  We present results for the lattice quark propagator in both Landau and
Laplacian gauges using standard and improved staggered quark actions. The
standard Kogut-Susskind action has errors of \oa{2} while the improved
``Asqtad'' action has \oa{4}, \oag{2}{2} errors. This improvement is seen in
the quark propagator. We demonstrate the application of tree-level corrections
to these actions and see that Landau and Laplacian gauges produce very similar
results.


title: Super Yang-Mills Theory on Lattice and the Transformation

abstract:
  We present a new lattice super Yang-Mills theory and its SUSY transformation.
After our formulation of the model in a fundamental lattice, it is extended to
the whole lattice with a substructure of modulo 2.


title: The Index and Axial Anomaly of a lattice Dirac operator

abstract:
  A remarkable feature of a lattice Dirac operator is discussed. Unlike the
Dirac operator for massless fermions in the continuum, this Ginsparg-Wilson
lattice Dirac operator does not possess topological zero modes for any
topologically-nontrivial background gauge fields, even though it is
exponentially-local, doublers-free, and reproduces correct axial anomaly for
topologically-trivial gauge configurations.


title: Heavy monopole potential in gluodynamics

abstract:
  We discuss predictions for the interaction energy of the fundamental
monopoles in gluodynamics introduced via the 't Hooft loop. At short distances,
the heavy monopole potential is calculable from first principles. At larger
distances, we apply the Abelian dominance models. We discuss the measurements
which would be crucial to distinguish between various models. Non-zero
temperatures are also considered. Our predictions are in qualitative agreement
with the existing lattice data. We discuss further measurements which would be
crucial to check the model.


title: One-loop renormalization of heavy-light currents

abstract:
  We calculate the mass dependent renormalization factors of heavy-light
bilinears at one-loop order of perturbation theory, when the heavy quark is
treated with the Fermilab formalism.
  We present numerical results for the Wilson and Sheikholeslami-Wohlert
actions, with and without tree-level rotation.
  We find that in both cases our results smoothly interpolate from the static
limit to the massless limit.
  We also calculate the mass dependent Brodsky-Lepage-Mackenzie scale $q^*$,
with and without tadpole-improvement.


title: Improved Hamiltonian Lattice Gauge Theory

abstract:
  We derive an improved lattice Hamiltonian for pure gauge theory, coupling
arbitrarily distant links in the kinetic term. The level of improvement
achieved is examined in variational calculations of the SU(2) specific heat in
2+1 dimensions.


title: B meson B-parameters and the decay constant in two-flavor dynamical QCD

abstract:
  We present a two-flavor dynamical QCD calculation of the B meson B parameters
and decay constant. We use NRQCD for heavy quark and the nonperturbatively
O(a)-improved Wilson action for light quark at $\beta$=5.2 on a $20^3\times 48$
lattice. We confirm that the sea quark effect increases the heavy-light decay
constant, while estimate of its magnitude depends significantly on the fitting
form in the chiral extrapolation. For the B parameters, on the other hand, we
do not find a significant sea quark effect. The chiral extrapolation with
logarithmic term is examined for both quantities and compared with the
prediction of ChPT.


title:
Non-trivial phase structure of $N_f=3$ QCD with $O(a)$-improved Wilson
  fermion at zero temperature

abstract:
  JLQCD collaboration recently started the $N_f=3$ QCD simulations with the
$O(a)$-improved Wilson fermion action employing an exact fermion algorithm
developed for odd number of quark flavors. It is found that this theory has an
unexpected non-trivial phase structure in the $(\beta,\kappa)$ plane even at
zero temperature. A detailed study is made to understand the nature of the
observed phase transitions and to find the way of avoiding untolerably large
lattice artifacts associated with the phase transition.


title:
Chemical potential response of pseudoscalar meson masses in the
  Nambu--Jona-Lasinio model

abstract:
  Using the Nambu--Jona-Lasinio (NJL) model we study chemical potential
response of the pion and kaon masses as a function of temperature and chemical
potential, i.e., dm/d\mu (T, \mu). First, we obtain the responses assuming the
vector-axial vector coupling is zero (g_V=0). Then, we include a non-zero g_V
and study the effects of g_V on the responses. We find that the behavior of
dm/d\mu for the pion is quite different from that for the kaon. It means that
dm/d\mu is much dependent on the mass difference between the two quarks, i.e.,
the u and s quarks (or even between the u and d quarks). Our results may give a
clue to future studies of dm/d\mu on the lattice.


title: Diquark condensation in dense SU(2) matter

abstract:
  We report on a lattice study of two-color QCD with adjoint staggered fermions
at high density. We find that the model has no early onset and we report on
results for diquark condensation, from simulations with and without a diquark
source term.


title:
B-parameters of the complete set of matrix elements of (Delta B = 2)
  operators from the lattice

abstract:
  We compute on the lattice the ``bag'' parameters of the five (Delta B = 2)
operators of the supersymmetric basis, by combining their values determined in
full QCD and in the static limit of HQET. The extrapolation of the QCD results
from the accessible heavy-light meson masses to the B-meson mass is constrained
by the static result. The matching of the corresponding results in HQET and in
QCD is for the first time made at NLO accuracy in the MSbar(NDR)
renormalization scheme. All results are obtained in the quenched approximation.


title: Real--time dynamics of a hot Yang-Mills theory: a numerical analysis

abstract:
  We discuss recent results obtained from simulations of high temperature,
classical, real time dynamics of SU(2) Yang-Mills theory at temperatures of the
order of the electroweak scale. Measurements of gauge covariant and gauge
invariant autocorrelations of the fields indicate that the ASY-Bodecker
scenario is irrelevant at these temperatures.


title: New Initial Conditions for Quantum Field Simulations after a Quench

abstract:
  We investigate a new way of using the quantum fluctuations in the vacuum as
initial conditions for subsequent classical field dynamics. This method avoids
problems with renormalization and leads to better thermalization.


title: On the Quantum Geometry of String Theory

abstract:
  The IKKT or IIB matrix model has been proposed as a non-perturbative
definition of type IIB superstring theories. It has the attractive feature that
space--time appears dynamically. It is possible that lower dimensional
universes dominate the theory, therefore providing a dynamical solution to the
reduction of space--time dimensionality. We summarize recent works that show
the central role of the phase of the fermion determinant in the possible
realization of such a scenario.


title: Equation of state for pure SU(3) gauge theory on anisotropic lattices

abstract:
  We present results for the equation of state for pure SU(3) gauge theory
obtained on anisotropic lattices with the anisotropy $\xi \equiv a_s/a_t = 2$.
The pressure and energy density are calculated on $N_t / \xi = 4, 5$ and 6
lattices with the integral method. They are found to satisfy the leading
$1/N_t^2$ scaling from our coarsest lattice $N_t/\xi=4$. This enables us to
carry out well controlled continuum extrapolations. We find that the pressure
and energy density agree with those obtained using the isotropic plaquette
action, but have smaller and more reliable errors.


title: An explicit example of HQET at one-loop order of perturbation theory

abstract:
  As an explicit example of HQET, we construct correlation functions containing
a heavy-light axial current, both in the static approximation and in full QCD.
This enables us to investigate the size of finite mass effects. As we use the
lattice regularisation, we can also check the mass dependence of discretisation
errors.


title: K0-K0bar mixing from the Schroedinger functional and twisted mass QCD

abstract:
  We describe how the Schroedinger functional and twisted mass QCD can be used
to compute the kaon B-parameter B_K on the lattice with Wilson fermions. This
new approach is expected to reduce the systematic uncertainties on B_K through
a better control of its (nonperturbative) renormalisation. Preliminary results
for the bare matrix element in a physical volume of (1.5^3 x 4.5) fm^4 are
presented. The renormalisation of the matrix element in a Schroedinger
functional scheme is also discussed.


title:
Vortices in the SU(2)-Higgs model -- Vortices and the covariant adjoint
  Laplacian

abstract:
  Vortices in the SU(2)--Higgs model: The presence of a fundamental Higgs in
the SU(N)-Higgs model yields color screening at some finite distance. Whereas
the transition to the Higgs "phase" is accompanied by a suppression of
projected center vortices, there is nearly no influence of color screening on
the vortex properties in the confined "phase". Hence the behavior of the Wilson
loop can be described in both phases within the vortex picture of confinement.
  Vortices and the covariant adjoint Laplacian: Laplacian center gauge is a
method to localize center vortices in SU(N) gauge theory. We show that the
eigenvectors of the covariant adjoint Laplacian identify vortices for a special
class of gauge field configurations. However, for Monte Carlo generated
configurations, modified approaches are required.


title: Constrained fitting of three-point functions

abstract:
  We determine matrix elements for $B \to D$ semileptonic decay. The use of the
constrained fitting method and multiple smearings for both two- and three-point
correlators allows an improved calculation of the form factors.


title: Fat and Thin Fisher Zeroes

abstract:
  We show that it is possible to determine the locus of Fisher zeroes in the
thermodynamic limit for the Ising model on planar (``fat'') phi4 random graphs
and their dual quadrangulations by matching up the real part of the high- and
low-temperature branches of the expression for the free energy. Similar methods
work for the mean-field model on generic, ``thin'' graphs. Series expansions
are very easy to obtain for such random graph Ising models.


title: Spectrum of k-string tensions in SU(N) gauge theories

abstract:
  We compute, for the four-dimensional SU(4) and SU(6) gauge theories
formulated on a lattice, the string tensions sigma_k related to sources with
Z_N charge k, using Monte Carlo simulations. Our results are compatible with
sigma_k \propto sin (k pi/N), and show sizeable deviations from Casimir
scaling.


title: Lattice QCD at finite T and \mu and the critical point of QCD

abstract:
  We propose a method to study lattice QCD at finite T and \mu. We compare it
with direct results and with the Glasgow method by using n_f=4 QCD at
Im(\mu)\neq 0. We locate the critical endpoint (E) of QCD on the Re(\mu)-T
plane. In this study we use n_f=2+1 dynamical staggered quarks with
semi-realistic masses on L_t=4 lattices.


title: Short distance physics with heavy quark potentials

abstract:
  We present lattice studies of heavy quark potentials in the quenched
approximation of QCD at finite temperatures. Both, the color singlet and color
averaged potentials are calculated. While the potentials are well known at
large distances, we give a detailed analysis of their short distance behavior
(from 0.015 fm to 1 fm) near the critical temperature. At these distances we
expect that the T-dependent potentials go over into the zero temperature
potential. Indeed, we find evidences that the temperature influence gets
suppressed and the potentials starts to become a unique function of the
underlying distance scale. We use this feature to normalize the heavy quark
potentials at short distances and extract the free energy of the quark system
in a gluonic heat bath.


title: Quenched charmonium near the continuum limit

abstract:
  We study relativistic charmonium on very fine quenched lattices (beta=6.4 and
6.6). We concentrate on the calculation of the hyperfine splitting between
eta_c and J/psi, aiming for a controlled continuum extrapolation of this
quantity. Results for the eta_c and J/psi wave functions are also presented.


title: Where do perturbative and non-perturbative QCD meet?

abstract:
  We computed the static potential and Wilson loops to $O(\alpha^2)$ in
perturbation theory for different lattice quark and gluon actions. In general,
we find short distance lattice data to be well described by ``boosted
perturbation theory''. For Wilson-type fermions at present-day quark masses and
lattice spacings agreement within 10% between measured ``$\beta$-shifts'' and
those predicted by perturbation theory is found. We comment on prospects for a
determination of the real world QCD running coupling.


title: An new order parameter with renormalized Polyakov loops

abstract:
  It is well established that physical quantities like the heavy quark
potentials get temperature independent at sufficiently short distances. As a
first application of this feature we suggest a new order parameter for the
confinement/deconfinement phase transition. Our investigations are based on
recent lattice studies.


title:
An exact algorithm for three-flavor QCD with $O(a)$-improved Wilson
  fermions

abstract:
  We present an exact dynamical QCD simulation algorithm for the
$O(a)$-improved Wilson fermion with odd number of flavors. Our algorithm is an
extension of the non-Hermitian polynomials HMC algorithm proposed by Takaishi
and de Forcrand previously. In our algorithm, the systematic errors caused by
the polynomial approximation of the inverse of Dirac operator is removed by a
noisy-Metropolis test. For one flavor quark it is achieved by taking the square
root of the correction matrix explicitly. We test our algorithm for the case of
$N_f=1+1$ on a moderately large lattice size ($16^3\times48$). The $N_f=2+1$
case is also investigated.


title: Hadron spectroscopy of twisted mass lattice QCD at beta = 6.0

abstract:
  Simulations that use the clover action in quenched QCD calculations have a
lower limit to the quark mass that can be reached, because of the fluctuations
caused by exceptional configurations. From this low statistics study, we find
that the twisted clover action, recently introduced by the ALPHA collaboration,
can be used to simulate quenched QCD at quark masses below those attainable by
simulations that use the clover action.


title: Nonequilibrium Aspects of Quantum Field Theory

abstract:
  We have developed a method for extracting equilibrium observables from
non-equilibrium simulations by rapidly changing the temperature and recording
the subsequent evolution of the Polyakov loop. Both nucleation and spinodal
decomposition are observed to occur. In the latter case the Polyakov loop
correlation function shows exponential growth for wavenumbers less than or
equal to the critical wavenumber k_c. We have constructed the bare as wee as
the effective potential for the Polyakov loop, from which k_c and m_D/k_c can
be extracted as a function of temperature. The shift from spinodal
decomposition to nucleation as the dominant equilibration mechanism occurs at
the spinodal temperature that separates these two regimes.


title: Lattice supersymmetric Ward identities

abstract:
  SUSY Ward identities for the N=1 SU(2) SUSY Yang-Mills theory are studied on
the lattice in a non-perturbative numerical approach. As a result a
determination of the subtracted gluino mass is obtained.


title: Temporal quark and gluon propagators: measuring the quasiparticle masses

abstract:
  We calculate the Coulomb gauge temporal quark and gluon propagators in
quenched QCD. From the temporal quark and gluon propagators, dispersion
relations and quasiparticle masses are determined by means of the Maximum
Entropy Method.


title: Is the Up Quark Massless?

abstract:
  Several lattice calculations of a combination of the low energy constants of
the chiral Lagrangian, 2\alpha_8-\alpha_5, are presented. This combination is
critical for the preclusion of a massless up quark. The result found is
2\alpha_8-\alpha_5 = 0.115 \pm 0.051^{stat} \pm 0.25^{syst}, which is well
outside of the range allowed by a massless up quark.


title: SUSY Ward identities in 1-loop perturbation theory

abstract:
  We present preliminary results of a study of the supersymmetric (SUSY) Ward
identities (WIs) for the N=1 SU(2) SUSY Yang-Mills theory in the context of
one-loop lattice perturbation theory. The supersymmetry on the lattice is
explicitly broken by the gluino mass and the lattice artifacts. However, the
renormalization of the supercurrent can be carried out in a scheme that
restores the nominal continuum WIs. The perturbative calculation of the
renormalization constants and mixing coefficients for the local supercurrent is
presented.


title: Non-perturbative parton mass for the gluon

abstract:
  A gauge invariant, non-local observable is constructed in pure gauge theory,
which is identical to the gluon propagator in a particular gauge, permitting to
define a non-perturbative parton mass for the gluon. This mass can be shown to
be related to the 1P-1S mass splitting of heavy quarkonia. Preliminary
numerical results for 3d SU(2) yield m_A=0.37(6)g^2, while from the \bar{b}b
spectrum one infers m_A\approx 420 MeV for QCD.


title: Static three- and four-quark potentials

abstract:
  We present results for the static three- and four-quark potentials in SU(3)
and SU(4) respectively. Using a variational approach, combined with multi-hit
for the time-like links, we determine the ground state of the baryonic string
with sufficient accuracy to test the $Y-$ and $\Delta-$ ans\"atze for the
baryonic Wilson area law. Our results favor the $\Delta$ ansatz, where the
potential is the sum of two-body terms.


title: FermiQCD: A tool kit for parallel lattice QCD applications

abstract:
  We present here the most recent version of FermiQCD, a collection of C++
classes, functions and parallel algorithms for lattice QCD, based on Matrix
Distributed Processing. FermiQCD allows fast development of parallel lattice
applications and includes some SSE2 optimizations for clusters of Pentium 4
PCs.


title: Combined Relativistic and static analysis for all Delta B=2 operators

abstract:
  We analyse matrix elements of Delta B=2 operators by combining QCD results
with the ones obtained in the static limit of HQET. The matching of all the QCD
operators to HQET is made at NLO order. To do that we have to include the
anomalous dimension matrix up to two loops, both in QCD and HQET, and the one
loop matching for all the Delta B=2 operators. The matrix elements of these
operators are relevant for the prediction of the B-\bar B mixing, B_s meson
width difference and supersymmetric effects in Delta B=2 transitions.


title: The Static Potential to O(\alpha^2) in Lattice Perturbation Theory

abstract:
  We present a calculation of Wilson loops, and the static inter-quark
potential to $O(\alpha^2)$ in lattice perturbation theory. This is carried out
with the Wilson, Symanzik-Weisz, and Iwasaki gauge actions and the Wilson,
Sheikholeslami-Wohlert, and Kogut-Susskind dynamical fermion action for small
Wilson loops, and with the Wilson gauge action and each of the dynamical quark
actions in the case of the static potential.


title: Finite-size scaling of interface free energies in the 3d Ising model

abstract:
  We perform a study of the universality of the finite size scaling functions
of interface free energies in the 3d Ising model. Close to the hot/cold phase
transition, we observe very good agreement with the same scaling functions of
the 4d SU(2) Yang--Mills theory at the deconfinement phase transition.


title: Nonperturbative tuning of $O(a^2)$ improved staggered fermions

abstract:
  We perform a nonperturbative tuning of the coefficients in the $O(a^2)$
improved action for staggered fermions. The mass splitting for the pions of
different doubler flavor is used as a measure of the symmetry breaking effects
introduced by $O(a^2)$ discretization errors. We find that the flavor
nondegeneracy can be somewhat reduced but not eliminated by such a tuning,
indicating the need for new terms in the action to reduce the nondegeneracy.


title: Physical Observables from Lattice QCD at Fixed Topology

abstract:
  Because present Monte Carol algorithms for lattice QCD may become trapped in
a given topological charge sector when one approaches the continuum limit, it
is important to understand the effect of calculating at fixed topology. In this
work, we show that although the restriction to a fixed topological sector
becomes irrelevant in the infinite volume limit, it gives rise to
characteristic finite size effects due to contributions from all
$\theta$-vacua. We calculate these effects and show how to extract physical
results from numerical data obtained at fixed topology.


title: Measuring infrared contributions to the QCD pressure

abstract:
  For the pressure (or free energy) of QCD, four-dimensional (4d) lattice data
is available at zero baryon density up to a few times the critical temperature
$T_c$. Perturbation theory, on the other hand, has serious convergence problems
even at very high temperatures. In a combined analytical and three-dimensional
(3d) lattice method, we show that it is possible to compute the QCD pressure
from about $2 T_c$ to infinity. The numerical accuracy is good enough to
resolve in principle, e.g., logarithmic contributions related to 4-loop
perturbation theory.


title: Vortex waistlines and vortex gas

abstract:
  We investigate the manner in which a linear potential arises from
fluctuations due to vortices linked with the Wilson loop. In particular, the
customary naive picture is critically reexamined.


title: Status of the QCDOC project

abstract:
  A status report is given of the QCDOC project, a massively parallel computer
optimized for lattice QCD using system-on-a-chip technology. We describe
several of the hardware and software features unique to the QCDOC architecture
and present performance figures obtained from simulating the current VHDL
design of the QCDOC chip with single-cycle accuracy.


title: Superconductivity and Chiral Symmetry Breaking with Fermion Clusters

abstract:
  Cluster variables have recently revolutionized numerical work in certain
models involving fermionic variables. This novel representation of fermionic
partition functions is continuing to find new applications. After describing
results from a study of a two dimensional Hubbard type model that confirm a
superconducting transition in the Kosterlitz-Thouless universality class, we
show how a cluster type algorithm can be devised to study the chiral limit of
strongly coupled lattice gauge theories with staggered fermions.


title:
Chiral property of domain-wall fermion from eigenvalues of 4D
  Wilson-Dirac Operator

abstract:
  We investigate a chiral property of the domain-wall fermion (DWF) system
using the four-dimensional hermitian Wilson-Dirac operator $H_W$. A formula
expressing the Ward-Takahashi identity quark mass $m_{5q}$ with eigenvalues of
this operator is derived, which well explains the $N_5$ dependence of $m_{5q}$
observed in previous numerical simulations. We further discuss the chiral
property of DWF in the large volume in terms of the spectra of $H_W$.


title:
Maximum entropy analysis of hadron spectral functions and excited states
  in quenched lattice QCD

abstract:
  Employing the maximum entropy method we extract the spectral functions from
meson correlators at four lattice spacings in quenched QCD with the Wilson
quark action. We confirm that the masses and decay constants, obtained from the
position and the area of peaks, agree well with the results from the
conventional exponential fit. For the first excited state, we obtain $m_{\pi_1}
= 660(590)$ MeV, $m_{\rho_1} = 1540(570)$ MeV, and $f_{\rho_1} = 0.085(36)$ in
the continuum limit.


title:
Non-perturbative renormalization for a renormalization group improved
  gauge action

abstract:
  Renormalization constants of vector ($Z_V$) and axial-vector ($Z_A$) currents
are determined non-perturbatively in quenched QCD for a renormalization group
improved gauge action and a tadpole improved clover quark action using the
Schr\"odinger functional method. Non-perturbative values of $Z_V$ and $Z_A$
turn out to be smaller than the one-loop perturbative values by $O(10%)$ at
$a^{-1}\approx 1$ GeV. A sizable scaling violation of meson decay constants
$f_\pi$ and $f_\rho$ observed with the one-loop renormalization factors remains
even with non-perturbative renormalization.


title: Charmonium spectrum from quenched QCD on anisotropic lattices

abstract:
  We present our final results of the charmonium spectrum in quenched QCD on
anisotropic lattices. Simulations are made with the plaquette gauge action and
a tadpole improved clover quark action employing $\xi = a_s/a_t = 3$. We
calculate the spectrum of S- and P-states and their excitation, and study the
scaling behavior of mass splittings. Comparison is made with the experiment and
previous lattice results. The issue of hyperfine splitting for different
choices of the clover coefficients obtained by Klassen is discussed.


title: QCD spectroscopy with three light quarks

abstract:
  We report about a simulation using three dynamical Wilson quarks and on the
progress in going to small quark masses.


title: The Charm Quark Mass to Two-Loop Order

abstract:
  The truncation of the perturbative series at one loop order for the mass
renormalization constants remain a significant systematic uncertainty in the
determination of heavy quark masses in lattice QCD. We present here a high beta
Monte Carlo calculation of the two loop mass renormalization constant for
clover-improved fermions near the charm mass in the Fermilab heavy quark
formalism. A preliminary value for the charm quark mass in the MS-bar scheme at
two loop order is reported.


title: Meson Spectral Functions at finite Temperature

abstract:
  The Maximum Entropy Method provides a Bayesian approach to reconstruct the
spectral functions from discrete points in Euclidean time. The applicability of
the approach at finite temperature is probed with the thermal meson correlation
function. Furthermore the influence of fuzzing/smearing techniques on the
spectral shape is investigated. We present first results for meson spectral
functions at several temperatures below and above $T_c$. The correlation
functions were obtained from quenched calculations with Clover fermions on
large isotropic lattices of the size $(24-64)^3 \times 16$. We compare the
resulting pole masses with the ones obtained from standard 2-exponential fits
of spatial and temporal correlation functions at finite temperature and in the
vacuum. The deviation of the meson spectral functions from free spectral
functions is examined above the critical temperature.


title:
Larger physical volume with a noncompact lattice regularization of SU(N)
  theories

abstract:
  Recently it has been found that in a noncompact formulation of the SU(2)
gauge theory on a lattice the physical volume is larger than in the Wilson
theory with the same number of sites. In its original formulation such
noncompact regularization is directly applicable to U(N) theories for any N and
to SU(N) theories for N=2 only. In this work we extend it to SU(N) for any N
and investigate some of its properties.


title: Light Quark Masses with $N_f=2$ Wilson Fermions

abstract:
  We present new data on the mass of the light and strange quarks from
SESAM/T$\chi$L. The results were obtained on lattice-volumes of $16^3\times 32$
and $24^3\times 40$ points, with the possibility to investigate finite-size
effects. Since the SESAM/T$\chi$L ensembles at $\beta=5.6$ have been
complemented by configurations with $\beta=5.5$, moreover, we are now able to
attempt the continuum extrapolation (CE) of the quark masses with standard
Wilson fermions.


title: 't Hooft loops and consistent order parameters for confinement

abstract:
  We study ratios of partition functions in two types of sectors of SU(2), with
fixed temporal center flux and with static fundamental charge. Both can be used
as bona fide order parameters for the deconfinement transition.


title: Application of Maximum Entropy Method to Dynamical Fermions

abstract:
  The Maximum Entropy Method is applied to dynamical fermion simulations of the
(2+1)-dimensional Nambu-Jona-Lasinio model. This model is particularly
interesting because at T=0 it has a broken phase with a rich spectrum of
mesonic bound states and a symmetric phase where there are resonances, and
hence the simple pole assumption of traditional fitting procedures breaks down.
We present results extracted from simulations on large lattices for the
spectral functions of the elementary fermion, the pion, the sigma, the massive
pseudoscalar meson and the symmetric phase resonances.


title:
Evidence for a BKT transition and a pseudogap phase in three-dimensional
  Gross-Neveu model at nonzero temperature

abstract:
  We present results from Monte Carlo simulations of the three-dimensional
Gross-Neveu model with a U(1) chiral symmetry at nonzero temperature. We
provide evidence that the model undergoes a Berezinskii-Kosterlitz-Thouless
transition in accordance with the dimensional reduction scenario. We also
identify a regime in the high temperature phase in which the fermions acquire
nonzero dynamical mass, analogous to the pseudogap behaviour observed in
cuprate superconductors.


title: Testing Dimensional Reduction in SU(2) Gauge Theory

abstract:
  At high temperature, every $(d+1)$-dimensional theory can be reformulated as
an effective theory in $d$ dimensions. We test the numerical accuracy of this
Dimensional Reduction for (3+1)-dimensional SU(2) by comparing perturbatively
determined effective couplings with lattice results as the temperature is
progressively lowered. We observe an increasing disagreement between numerical
and perturbative values from $T=4 T_c$ downwards, which may however be due to
somewhat different implementations of dimensional reduction in the two cases.


title:
Finite temperature phase transition, adjoint Polyakov loop and topology
  in SU(2) LGT

abstract:
  We investigate the phase structure of pure SU(2) LGT at finite temperature in
the mixed fundamental and adjoint representation modified with a Z2 monopole
chemical potential. The decoupling of the finite temperature phase transition
from unphysical zero temperature bulk phase transitions is analyzed with
special emphasis on the continuum limit. The possible relation of the adjoint
Polyakov loop to an order parameter for the finite temperature phase transition
and to the topological structure of the theory is discussed.


title: Some remarks on O(a) improved twisted mass QCD

abstract:
  Twisted mass QCD (tmQCD) has been introduced as a solution to the problem of
unphysical fermion zero modes in lattice QCD with quarks of the Wilson type. We
here argue that O(a) improvement of the tmQCD action and simple quark bilinear
operators can be more economical than in the standard framework. In particular,
an improved and renormalized estimator of the pion decay constant in
two-flavour QCD is available, given only the Sheikholeslami-Wohlert coefficient
c_sw and an estimate of the critical mass m_c.


title: Hadronic Correlators from All-point Quark Propagators

abstract:
  A method for computing all-point quark propagators is applied to a variety of
processes of physical interest in lattice QCD. The method allows, for example,
efficient calculation of disconnected parts and full momentum-space 2 and 3
point functions. Examples discussed include: extraction of chiral Lagrangian
parameters from current correlators, the pion form factor, and the unquenched
eta-prime.


title:
Calculation of $K\to\pi\pi$ decay amplitudes from $K\to\pi$ matrix
  elements in quenched domain-wall QCD

abstract:
  We present a calculation of the $K\to\pi\pi$ decay amplitudes from the
$K\to\pi$ matrix elements using leading order relations derived in chiral
perturbation theory. Numerical simulations are carried out in quenched QCD with
the domain-wall fermion action and the renormalization group improved gluon
action. Our results show that the I=2 amplitude is reasonably consistent with
experiment whereas the I=0 amplitude is sizably smaller. Consequently the
$\Delta I=1/2$ enhancement is only half of the experimental value, and
$\epsilon'/\epsilon$ is negative.


title: Hadron Spectrum for Quenched Domain-Wall Fermions with DBW2 Gauge Action

abstract:
  We investigate basic physical quantities for quenched simulation with
domain-wall fermions and the DBW2 gauge action. Masses and decay constant of
pseudoscalar mesons are measured. Scaling properties are tested.


title: Re $A_0$ and Re $A_2$ from Quenched Lattice QCD

abstract:
  We have used domain wall fermions to calculate $K \to \pi$ and $K \to 0$
matrix elements which can be used to study the $\Delta I = 1/2$ rule for K
decays in the Standard Model. Nonlinearities in the $\Delta I = 3/2$ matrix
elements due to chiral logarithms are explored and the subtractions needed for
the $\Delta I = 1/2$ matrix elements are discussed. Using renormalization
factors calculated using non-perturbative renormalization then yields values
for real $A_0$ and $A_2$. We present the details of our quenched $16^3 \times
32 \times 16$, $\beta = 6.0$, $M_5 = 1.8$ simulation, where a previous
calculation showed that the finite $L_s$ chiral symmetry breaking effects are
small ($m_{\rm res} \approx 4 \rm MeV$).


title: 1/M correction to quenched QCD with non-zero baryon density

abstract:
  We study the \kappa^2 corrections to the quenched limit of \mu>0 QCD. We use
an improved reweighting procedure.


title: Large Field Cutoffs Make Perturbative Series Converge

abstract:
  For lambda phi^4 problems, convergent perturbative series can be obtained by
cutting off the large field configurations. The modified series converge to
values exponentially close to the exact ones. For lambda larger than some
critical value, the method outperforms Pade approximants and Borel summations.
We discuss some aspects of the semi-classical methods used to calculate the
modified Feynman rules and estimate the error associated with the procedure. We
provide a simple numerical example where the procedure works despite the fact
that the Borel sum has singularities on the positive real axis.


title: Highly Improved Naive and Staggered Fermions

abstract:
  We present a new action for highly improved staggered fermions. We show that
perturbative calculations for the new action are well-behaved where those of
the conventional staggered action are badly behaved. We discuss the effects of
the new terms in controlling flavor mixing, and discuss the design of operators
for the action.


title: Quantum Link Models with Many Rishon Flavors and with Many Colors

abstract:
  Quantum link models are a novel formulation of gauge theories in terms of
discrete degrees of freedom. These degrees of freedom are described by quantum
operators acting in a finite-dimensional Hilbert space. We show that for
certain representations of the operator algebra, the usual Yang-Mills action is
recovered in the continuum limit. The quantum operators can be expressed as
bilinears of fermionic creation and annihilation operators called rishons.
Using the rishon representation the quantum link Hamiltonian can be expressed
entirely in terms of color-neutral operators. This allows us to study the large
N_c limit of this model. In the 't Hooft limit we find an area law for the
Wilson loop and a mass gap. Furthermore, the strong coupling expansion is a
topological expansion in which graphs with handles and boundaries are
suppressed.


title:
Thermodynamic properties of QCD with two flavors of Wilson-type lattice
  quarks

abstract:
  I report on a study of finite temperature QCD by the CP-PACS Collaboration
toward a precise determination of the equation of state with dynamical u,d
quarks. Based on a systematic simulation using improved Wilson-type quarks on
lattices with temporal size $N_t=4$ and 6, the energy density and pressure are
calculated as functions of temperature and renormalized light quark mass in the
range $T/T_c \approx 0.7$--2.5 and $m_{\rm PS}/m_{\rm V} = 0.65$--0.95. Results
for $N_t=4$ are found to contain significant scaling violations, while results
for $N_t=6$ are suggested to be not far from the continuum limit. On the other
hand, the quark mass dependence in the EOS turned out to be small for $m_{\rm
PS}/m_{\rm V} \simlt 0.8$.


title: Numerical study of Frohlich and Marchetti monopole creation operator

abstract:
  The monopole creation operator proposed recently by Frohlich and Marchetti is
investigated in the Abelian Higgs model with compact gauge field. We show
numerically that the creation operator detects the condensation of monopoles in
the presence of the dynamical matter field.


title: I=2 Pion Scattering Length and Phase Shift with Wilson Fermions

abstract:
  We present preliminary results of scattering length and phase shift for I=2
S-wave $\pi\pi$ system with the Wilson fermions in the quenched approximation.
The finite size method presented by L\"uscher is employed, and calculations are
carried out at $\beta=5.9$ on a $24^3\times 60$ and $32^3\times 60$ lattice.


title: Quasi particles in hot QCD

abstract:
  We show at very high temperature how the behaviour of the spatial 't Hooft
loop in the QCD plasma is simply related to the chromo electric flux of the
gluons. This simple picture is vindicated by a systematic quasi classical
approach. The spatial Wilson loop 's behaviour is computed by a similar nearly
free plasma of magnetic quasiparticles. This model predicts unambiguously
ratios of multiply charged Wilson loops. Recent simulations confirm these
predictions accurately.


title: Status of APEmille

abstract:
  This paper presents the status of the APEmille project, which is essentially
completed, as far as machine development and construction is concerned. Several
large installations of APEmille are in use for physics production runs leading
to many new results presented at this conference. This paper briefly summarizes
the APEmille architecture, reviews the status of the installations and presents
some performance figures for physics codes.


title: The monopole mass in the three-dimensional Georgi-Glashow model

abstract:
  We study the three-dimensional Georgi-Glashow model to demonstrate how
magnetic monopoles can be studied fully non-perturbatively in lattice Monte
Carlo simulations, without any assumptions about the smoothness of the field
configurations. We examine the apparent contradiction between the conjectured
analytic connection of the `broken' and `symmetric' phases, and the
interpretation of the mass (i.e., the free energy) of the fully quantised 't
Hooft-Polyakov monopole as an order parameter to distinguish the phases. We use
Monte Carlo simulations to measure the monopole free energy and its first
derivative with respect to the scalar mass. On small volumes we compare this to
semi-classical predictions for the monopole. On large volumes we show that the
free energy is screened to zero, signalling the formation of a confining
monopole condensate. This screening does not allow the monopole mass to be
interpreted as an order parameter, resolving the paradox.


title: The Consequences of Non-Normality

abstract:
  The non-normality of Wilson-type lattice Dirac operators has important
consequences - the application of the usual concepts from the textbook
(hermitian) quantum mechanics should be reconsidered. This includes an
appropriate definition of observables and the refinement of computational
tools. We show that the truncated singular value expansion is the optimal
approximation to the inverse operator D^{-1} and we prove that due to the
gamma_5-hermiticity it is equivalent to gamma_5 times the truncated eigenmode
expansion of the hermitian Wilson-Dirac operator.


title: Simulating dynamical fermions with smeared links

abstract:
  Smearing the gauge links of dynamical configurations removes small scale
unphysical vacuum fluctuations and thus improves the chiral properties of
lattice fermions. Recently we proposed the hypercubic smearing (HYP) that
improves the flavor symmetry of staggered fermions by an order of magnitude
with only minimal distortions at small distances. We describe a new algorithm
to simulate dynamical HYP fermions based on the standard pure gauge
overrelaxation and heatbath updates. The algorithm has been used to simulate
four and two flavors of staggered fermions. Unlike standard dynamical
simulation techniques, this algorithm does not loose efficiency at small quark
masses.


title: The QCD String Spectrum and Conformal Field Theory

abstract:
  The low energy excitation spectrum of the critical Wilson surface is
discussed between the roughening transition and the continuum limit of lattice
QCD. The fine structure of the spectrum is interpreted within the framework of
two-dimensional conformal field theory.


title:
Exploiting finite-size-effects to simulate full QCD with light quarks -
  a progress report

abstract:
  We present a report on the status of the GRAL project (Going Realistic And
Light), which aims at simulating full QCD with two dynamical Wilson quarks
below the vector meson decay threshold, m_ps/m_v < 0.5, making use of
finite-size-scaling techniques.


title:
A nonperturbative determination of the O(a) improvement coefficient c_A
  and the scaling of f_pi and m^{MSbar}

abstract:
  We report on an investigation of the LANL method for determining the O(a)
improvement coefficient c_A nonperturbatively. We find we are able to extract
reliable estimates for the coefficient using this method. However, our study of
systematic errors shows that for very accurate determinations of c_A, the
smearing function must be tuned and the volume fixed to keep the O(a) ambiguity
in c_A fixed as beta varies. Consistency was found with previous results from
the LANL group and (within fairly large errors) 1-loop perturbation theory; c_A
does not change significantly over the range beta=5.93-6.2. The big difference
between our results and those of the ALPHA collaboration, around beta=6.0, show
that the O(a) differences in c_A between the different methods can be large. We
find that the lattice spacing dependence of f_pi and the renormalised quark
mass is much smaller using our values of the coefficient compared to those of
the ALPHA collaboration.


title:
Bound states in the 3d Ising model and implications for QCD at finite
  temperature and density

abstract:
  We study the spectrum of bound states of the three dimensional Ising model in
the (h,beta) plane near the critical point. We show the existence of an
unbinding line, defined as the boundary of the region where bound states exist.
Numerical evidence suggests that this line coincides with the beta=beta_c axis.
When the 3D Ising model is considered as an effective description of hot QCD at
finite density, we conjecture the correspondence between the unbinding line and
the line that separates the quark-gluon plasma phase from the superconducting
phase. The bound states of the Ising model are conjectured to correspond to the
diquarks of the latter phase of QCD.


title: Heavy-light physics using NRQCD-staggered actions

abstract:
  One leading source of uncertainty in the lattice computation of semi-leptonic
form factors in B decay, and to a lesser extent B meson decay constants, comes
from the extrapolation of the light quark mass to the physical up/down mass.
This talk presents first explorations of simulating the light quark with
staggered fermion actions, which are free of the spurious zero modes that
effect Wilson-like Dirac operators and are less costly. Methods for fitting to
Euclidean-time NRQCD-staggered meson propagators are discussed, and some
preliminary spectrum results are presented.


title: Monopoles and hybrids in Abelian projection of lattice QCD

abstract:
  We study topological defects constructed from diagonal and non-diagonal
gluons in Abelian projection of zero temperature lattice QCD. We compare
results obtained in the quenched and non-quenched vacuum field configurations
and show that the density of hybrids is higher than the density of monopoles.
The density of some hybrids is sensitive to the presence of the virtual
fermions.


title: Spectral density calculations in a heavy-light meson-meson system

abstract:
  A system of two static quarks, at fixed distances r, and two light quarks is
studied on an anisotropic lattice. Excitations by operators emphasizing quark
or gluon degrees of freedom are examined. The maximum entropy method is applied
in the spectral analysis. These simulations ultimately aim at learning about
mechanisms of hadronic interaction.


title: N* Masses from an Anisotropic Lattice QCD Action

abstract:
  We report N* masses in the spin 3/2 sector from a highly-improved anisotropic
action. States with both positive and negative parity are isolated via a parity
projection method. The extent to which spin projection is needed is examined.
The gross features of the splittings from the nucleon ground state show a trend
consistent with experimental results at the quark masses explored.


title: The Maximal Abelian Gauge in SU(3) Lattice Gauge Theory

abstract:
  We gauge fix 600 SU(3) beta=6.0 configurations on a 16^4 lattice to a simple
form of the maximal abelian gauge. We project the SU(3) valued links to the
U(1)xU(1) subgroup, and extract U(1)xU(1) and monopole string tensions. After
gauge fixing to the indirect center gauge, the U(1)xU(1) links are projected to
Z(3) and a vortex string tension is measured. The vortex and magnetic current
densities are measured.


title: Quenched twisted mass QCD at small quark masses and in large volume

abstract:
  As a test of quenched lattice twisted mass QCD, we compute the
non-perturbatively O($a$) improved pseudoscalar and vector meson masses and the
pseudoscalar decay constant down to $M_{\rm PS}/M_{\rm V} = 0.467(13)$ at
$\beta=6$ in large volume. We check the absence of exceptional configurations
and -- by further data at $\beta=6.2$ -- the size of scaling violations. The
CPU time cost for reaching a given accuracy is close to that with ordinary
Wilson quarks at $M_{\rm PS}/M_{\rm V} \simeq 0.6$ and grows smoothly as
$M_{\rm PS}/M_{\rm V}$ decreases.


title: Glueballs and topology with O(a)-improved lattice QCD

abstract:
  We present evidence for unquenching effects in N_f=2, 16^3 32 ensembles by
comparing with `equivalent' quenched data at r_0~5.0. A (small) VEV for
torelons signals (weak) string breaking. A 15-20 % reduction in the scalar
glueball mass relative to quenched is argued to be (in part at least) a
discretisation effect. We find a chiral suppression of the topological
susceptibility consistent with expectations, and agreement between fermionic
and gluonic methods for measuring the topological charge.


title: The Static Potential with Hypercubic Blocking

abstract:
  We measure the static potential from Wilson loops constructed using
hypercubic blocked (HYP) links. The HYP potential agrees with the potential
measured using thin links for distances r/a>=2. We calculated the lowest order
perturbative expansion of the lattice Coulomb potential of HYP links. These
results are used in analyzing the static potential both on quenched and
dynamical lattices. The statistical accuracy of the potential with HYP links
improves by about an order of magnitude, giving a reliable scale even with
limited statistics both on quenched and dynamical lattices.


title: Extraction of K-->pipi Matrix Elements with Wilson Fermions

abstract:
  We present the status of a lattice calculation for the K-->pipi matrix
elements of the (delta S=1) effective weak Hamiltonian, directly with two pion
in the final state. We study the energy shift of two pion in a finite volume
both in the I=0 and I=2 channels. We explain a method to avoid the Goldstone
pole contamination in the computation of renormalization constants for (delta
I=3/2) operators. Finally we show some preliminary results for the matrix
elements of (delta I=1/2) operators. Our quenched simulation is done at
beta=6.0, with Wilson fermions, on a (24^3 X 64) lattice.


title: Finite-volume meson propagators in quenched chiral perturbation theory

abstract:
  We compute meson propagators in finite-volume quenched chiral perturbation
theory.


title: Anisotropic Lattices and Dynamical Fermions

abstract:
  We report results from full QCD calculations with two flavors of dynamical
staggered fermions on anisotropic lattices. The physical anisotropy as
determined from spatial and temporal masses, their corresponding dispersion
relations, and spatial and temporal Wilson loops is studied as a function of
the bare gauge anisotropy and the bare velocity of light appearing in the Dirac
operator. The anisotropy dependence of staggered fermion flavor symmetry
breaking is also examined. These results will then be applied to the study of
2-flavor QCD thermodynamics.


title: Staggered domain wall fermions

abstract:
  Staggered Domain Wall Fermions (SDWF) combine the attractive chiral
properties of staggered fermions with those of domain wall fermions. SDWF
describe four flavors with exact U(1)xU(1) flavor chiral symmetry. An extra
lattice dimension is introduced and the full SU(4)xSU(4) flavor chiral symmetry
is recovered as its size is increased. Here, the free theory of SDWF is
described and a preliminary discussion of the interacting case is presented.
SDWF may be well suited for numerical simulation of lattice QCD thermodynamics.


title: Phenomenological Models of the Quark-Gluon Plasma Equation of State

abstract:
  Two phenomenological models describing an SU(N) quark-gluon plasma are
presented. The first is obtained from high temperature expansions of the free
energy of a massive gluon, while the second is derived by demanding color
neutrality over a certain length scale. Each model has a single free parameter,
exhibits behavior similar to lattice simulations over the range T_d-5T_d, and
has the correct blackbody behavior for large temperatures. The N=2
deconfinement transition is second order in both models, while N=3,4, and 5 are
first order. Both modelsappear to have a smooth large-N limit. In both models,
the confined phase is characterized by a mutual repulsion of Polyakov loop
eigenvalues that makes the Polyakov loop expectation value zero. In the
deconfined phase, the rotation of the eigenvalues in the complex plane towards
1 is responsible for the approach to the blackbody limit over the range
T_d-5T_d. The addition of quarks in SU(3) breaks Z(3) symmetry weakly and
eliminates the deconfining phase transition for sufficiently light quarks.


title: Phenomenological Equations of State for SU(N) Gauge Theories

abstract:
  Two phenomenological models describing an SU(N) gluon plasma are presented
using the eigenvalues of the Polyakov loop as the order parameters of the
deconfinement transition. Each model has a single free parameter and exhibits
behavior similar to lattice simulations over the range T_d-5T_d. The N=2
deconfinement transition is second order in both models, while N=3,4, and 5 are
first order. Both models appear to have a smooth large-N limit. The confined
phase is characterized by a mutual repulsion of Polyakov loop eigenvalues that
makes the Polyakov loop expectation value zero. The motion of the eigenvalues
is responsible for the approach to the blackbody limit over the range T_d-5T_d.


title: Constrained Curve Fitting

abstract:
  We survey techniques for constrained curve fitting, based upon Bayesian
statistics, that offer significant advantages over conventional techniques used
by lattice field theorists.


title: O(a) improved Wilson quark action on anisotropic lattice

abstract:
  The $O(a)$ improved Wilson quark action on the anisotropic lattice is
investigated. We carry out numerical simulations in the quenched approximation
at three values of lattice spacing ($a_{\sigma}^{-1}=1$--2 GeV) with the
anisotropy $\xi=a_{\sigma}/a_{\tau}=4$, where $a_{\sigma}$ and $a_{\tau}$ are
the spatial and the temporal lattice spacings, respectively. Using the
dispersion relation of mesons, the bare anisotropy $\gamma_F$ in the quark
action is numerically tuned below the charm quark mass region with the
statistical accuracy of 1 % level. The systematic uncertainties in the
calibration are examined and found to be under control in the continuum limit.
Then we compute the light hadron masses and find that they are consistent with
the result of the UKQCD Collaboration on the isotropic lattice. The effect of
the uncertainty in the calibration on the hadron spectrum for physical quark
masses is also found to be under control.


title: Anisotropic Lattice and Its Application to Quark Gluon Plasma

abstract:
  We have studied the link-integration method for the improved actions. With
this method the $\eta$ parameter in the medium to strong coupling regions is
obtained. Effects of the self-energy terms for the $\eta$ parameters are small
in the regions of $\beta$ and $\eta$ studied. After these investigations, the
anisotropic lattice is used for the calculation of transport coefficients of
the quark gluon plasma.


title: Heavy quark expansion parameters from lattice NRQCD

abstract:
  Using the lattice NRQCD action for heavy quark, we calculate the heavy quark
expansion parameters $\mu_{\pi}^2$ and $\mu_G^2$ for heavy-light mesons and
heavy-light-light baryons. The results are compared with the mass differences
among heavy hadrons to test the validity of HQET relations on the lattice.


title:
Exploration of sea quark effects in two-flavor QCD with the
  O(a)-improved Wilson quark action

abstract:
  We explore sea quark effects in the light hadron mass spectrum in a
simulation of two-flavor QCD using the nonperturbatively O(a)-improved Wilson
fermion action. In order to identify finite-size effects, light meson masses
are measured on 12^3x48, 16^3x48 and 20^3x48 lattices with a~0.1 fm. On the
largest lattice, where the finite-size effect is negligible, we find a
significant increase of the strange vector meson mass compared to the quenched
approximation. We also investigate the quark mass dependence of pseudoscalar
meson masses and decay constants and test the consistency with (partially
quenched) chiral perturbation theory.


title: Speeding up the Hybrid-Monte-Carlo algorithm for dynamical fermions

abstract:
  We propose a modification of the Hybrid-Monte-Carlo algorithm that allows for
a larger step-size of the integration scheme at constant acceptance rate. The
key ingredient is the splitting of the pseudo-fermion action into two parts. We
test our proposal at the example of the two-dimensional lattice Schwinger model
and four-dimensional lattice QCD with two degenerate flavours of Wilson-
fermions.


title:
The Pion Light-Cone Wave Function Phi_pi on the lattice: a partonic
  signal?

abstract:
  We determine the conditions required to study the pion light-cone wave
function Phi_pi with a new method: a direct display of the partons constituting
the pion. We present the preliminary results of a lattice computation of Phi_pi
following this direction. An auxiliary scalar-quark is introduced. The
spectroscopy of its bound states is studied. We observe some indications of a
partonic behavior of the system of this scalar-quark and the anti-quark.


title:
Lattice QCD at finite temperature: Evidence for calorons from the
  eigenvectors of the Dirac operator

abstract:
  We analyze the eigenvalues and eigenvectors of the staggered Dirac operator
in quenched lattice QCD in the vicinity of the deconfinement phase transition
using the L\"uscher-Weisz gauge action. The spectral and localization
properties of the low-lying eigenmodes show characteristic differences between
the Z_3 sectors above the critical temperature T_c. These findings can be
interpreted in terms of calorons.


title:
Effects of Quenching and Partial Quenching on QCD Penguin Matrix
  Elements

abstract:
  We point out that chiral transformation properties of penguin operators
change in the transition from unquenched to (partially) quenched QCD. The way
in which this affects the lattice determination of weak matrix elements can be
understood in the framework of (partially) quenched chiral perturbation theory.


title: Quenched Results for Light Quark Physics with Overlap Fermions

abstract:
  We present results of a quenched QCD simulation with overlap fermions on a
lattice of volume V = 16^3X32 at beta=6.0, which corresponds approximatively to
a lattice cutoff of 2 GeV and an extension of 1.4 fm. From the two-point
correlation functions of bilinear operators we extract the pseudoscalar meson
masses and the corresponding decay constants. From the GMOR relation we
determine the chiral condensate and, by using the K-meson mass as experimental
input, we compute the sum of the strange and average up-down quark masses (m_s
+ \hat m). The needed logarithmic divergent renormalization constant Z_S is
computed with the RI/MOM non-perturbative renormalization technique. Since the
overlap preserves chiral symmetry at finite cutoff and volume, no divergent
quark mass and chiral condensate additive renormalizations are required and the
results are O(a) improved.


title: Im$A_0$, Im$A_2$, and $\epsilon^\prime$ from quenched lattice QCD

abstract:
  We present results for the imaginary parts of the I=0 and 2 $K\to\pi\pi$
decay amplitudes, Im$A_{0,2}$, and the ratio of CP violation parameters,
$\epsilon^\prime/\epsilon$. Our calculation is done in the quenched
approximation at $a^{-1}\approx 2$ GeV, lattice size $16^3\times 32$, using
domain wall fermions with $L_s=16$. We study the three flavor case (charm is
not an active flavor) and find $\epsilon^\prime/\epsilon$ is small and slightly
negative.


title: The Low-lying Dirac Eigenmodes from Domain Wall Fermions

abstract:
  We calculate the low-lying eigenvalues and eigenvectors of the hermitian
domain wall Dirac operator on various gauge backgrounds by Ritz minimization.
The mass dependence of these eigenvalues is studied to extract the physical 4
dimensional $\lambda$, whose spectral density is related to $<\bar{\psi} \psi>$
through the Banks-Casher relation, and $\delta m$, which represents the effects
of the residual chiral symmetry breaking in domain wall formalism on a per
eigenmode basis. The topological structure of the underlying gauge field is
examined by measuring the $\Gamma_5$ matrix elements between the low-lying
eigenmodes.


title: Chiral Loop Effects in the Quenched Scalar Isovector Propagator

abstract:
  The scalar isovector meson propagator is studied in quenched QCD. For the
lightest quark masses used, this propagator is dominated by a quenched chiral
loop effect associated with the $\eta'$-$\pi$ two-meson intermediate state.
Both the time dependence and the pion mass dependence of the effect are
well-described by quenched chiral perturbation theory.


title:
SU(2) Running Coupling Constant and Confinement in Minimal Coulomb and
  Landau Gauges

abstract:
  We present a numerical study of the space-space and time-time components of
the gluon propagator at equal time in the minimal Coulomb gauge, and of the
gluon and ghost propagators in the minimal Landau gauge. This work allows a
non-perturbative evaluation of the running coupling constant and a numerical
check of Gribov's confinement scenarios for these two gauges. Our simulations
are done in pure SU(2) lattice gauge theory at $\beta = 2.2$. We consider
several lattice volumes in order to control finite-volume effects and
extrapolate our results to infinite lattice volume.


title: Confinement made simple in the Coulomb gauge

abstract:
  In Gribov's scenario in Coulomb gauge, confinement of color charge is due to
a long-range instantaneous color-Coulomb potential V(R). This may be determined
numerically from the instantaneous part of the gluon propagator D_{44, inst} =
V(R) \delta(t). Confinement of gluons is reflected in the vanishing at k = 0 of
the equal-time three-dimensionally transverse would-be physical gluon
propagator D^{tr}(k). We present exact analytic results on D_{44} and D^{tr}
(which have also been investigated numerically, A. Cucchieri, T. Mendes, and D.
Zwanziger, this conference), in particular the vanishing of D^{tr}(k) at k = 0,
and the determination of the running coupling constant from x_0 g^2(k) = k^2
D_{44, inst}, where x_0 = 12N/(11N-2N_f).