title: Colour confinement and dual superconductivity of the vacuum - I

abstract:
  We study dual superconductivity of the ground state of SU(2) gauge theory, in
connection with confinement. We do that measuring on the lattice a disorder
parameter describing condensation of monopoles. Confinement appears as a
transition to dual superconductor, independent of the abelian projection
defining monopoles. Some speculations are made on the existence of a more
appropriate disorder parameter. A similar study for SU(3) is presented in a
companion paper.


title: Colour confinement and dual superconductivity of the vacuum - II

abstract:
  The dual superconductivity of the vacuum in SU(3) gauge theory is
investigated by constructing a disorder parameter which signals monopole
condensation in various abelian projections and by studying numerically on the
lattice its behaviour at finite temperature. We find that the vacuum is a dual
superconductor with respect to each U(1) of the residual gauge group after
abelian projection independently of the abelian projection chosen. Like in the
SU(2) case (discussed in a companion paper) a finite size scaling analysis
enables us to extract the indices of the phase transition and our analysis is
consistent with independent determinations.


title:
One loop calculation of SUSY Ward-Takahashi identity on lattice with
  Wilson fermion

abstract:
  One loop correction to the SUSY Ward-Takahashi identity is calculated on
lattice with Wilson fermion. The supersymmetry on lattice is broken explicitly
by the gluino mass and the lattice artifact. We should fine tune parameters in
the theory to the point given by the additive mass correction in order to
eliminate the breaking effect of lattice artifact. It is shown that the
additive mass correction appearing from the SUSY Ward-Takahashi identity
coincide with that from the axial $U(1)_R$ symmetry as was suggested by Curci
and Veneziano. Two important symmetries of the super Yang-Mills theory can be
recovered simultaneously in the continuum with a single fine tuning.
  Operator mixing of the supercurrent are also investigated. We find that the
supercurrent mixes only with a gauge invariant current $T_\mu$ which is related
to the gamma-trace anomaly.


title: Baryon Masses from Lattice QCD: Beyond the Perturbative Chiral Regime

abstract:
  Consideration of the analytic properties of pion-induced baryon self-energies
leads to new functional forms for the extrapolation of light baryon masses.
These functional forms reproduce the leading non-analytic behavior of chiral
perturbation theory, the correct non-analytic behavior at the $N \pi$ threshold
and the appropriate heavy-quark limit. They involve only three unknown
parameters, which may be obtained by fitting to lattice data. Recent dynamical
fermion results from CP-PACS and UKQCD are extrapolated using these new
functional forms. We also use these functions to probe the limit of
applicability of chiral perturbation theory to the extrapolation of lattice QCD
results.


title: Statistical mechanics of vortices from field theory

abstract:
  We study with lattice Monte Carlo simulations the interactions and
macroscopic behaviour of a large number of vortices in the 3-dimensional U(1)
gauge+Higgs field theory, in an external magnetic field. We determine
non-perturbatively the (attractive or repelling) interaction energy between two
or more vortices, as well as the critical field strength H_c, the
thermodynamical discontinuities, and the surface tension related to the
boundary between the Meissner phase and the Coulomb phase in the type I region.
We also investigate the emergence of vortex lattice and vortex liquid phases in
the type II region. For the type I region the results obtained are in
qualitative agreement with mean field theory, except for small values of H_c,
while in the type II region there are significant discrepancies. These findings
are relevant for superconductors and some models of cosmic strings, as well as
for the electroweak phase transition in a magnetic field.


title: Efficiency of the UV-filtered Multiboson algorithm

abstract:
  We study the efficiency of an improved Multiboson algorithm with two flavours
of Wilson fermions in a realistic physical situation ($\beta = 5.60$, $\kappa =
0.156$ on a $16^3 \times 24$ lattice). The performance of this exact algorithm
is compared with that of a state-of-the-art HMC algorithm: a considerable
improvement is obtained for the plaquette auto-correlation time, while the two
algorithms appear similarly efficient at decorrelating the topological charge.


title: Scaling property of domain-wall QCD in perturbation theory

abstract:
  We estimate the lattice artifacts in loop correction perturbatively for
domain-wall QCD with infinite number of extra flavors. We find that there
appear no ${\cal O}(a)$ errors in renormalization factors of quark wave
function, mass and quark bilinear operators at one and two loop level with
off-shell quark momentum. Our proof is based on even or oddness of the quantum
correction in terms of the quark external momentum and mass, and it can be
extended to any loop level.


title:
An Exploratory Lattice Study of Spectator Effects in Inclusive Decays of
  the Lambda_b Baryon

abstract:
  A possible explanation of the apparent disrepency between the theoretical
prediction and experimental measurement of the ratio of lifetimes
$\tau(\Lambda_b)/\tau(B_d)$ is that ``spectator effects'', which appear at
$O(1/m_b^3)$ in the heavy quark expansion, contribute significantly. We
investigate this possibility by computing the corresponding operator matrix
elements in a lattice simulation. We find that spectator effects are indeed
significant, but do not appear to be sufficiently large to account for the full
discrepency. We stress, however, that this is an exploratory study, and it is
important to check our conclusions on a larger lattice and using a larger
sample of gluon configurations.


title: The Conformal Mode in 2D Simplicial Gravity

abstract:
  We verify that summing 2D DT geometries correctly reproduces the Polyakov
action for the conformal mode, including all ghost contributions, at large
volumes. The Gaussian action is reproduced even for c=10, well into the
branched polymer phase, which confirms the expectation that the DT measure is
indeed correct in this regime as well.


title: Non-Perturbative Fine-Tuning in Approximately Supersymmetric Models

abstract:
  We present two Fermi-Bose models with an approximate supersymmetry and which
can be solved with great accuracy using the renormalization group method. The
bosonic parts of these models consist in Dyson's hierarchical model with one
and two scalar components respectively. We discuss the question of the
perturbative cancellation of divergences and compare with the non-perturbative
fine-tunings necessary to keep the renormalized mass small in cut-off units. We
show evidence for non-perturbative cancellations of quantum corrections,
however, we were not able to achieve exact cancellations without fine-tuning.


title: Flavor singlet phenomena in lattice QCD

abstract:
  Flavor singlet combinations of quark operators ${\cal{O}}_S^{\Gamma} =
\bar{u}\Gamma u + \bar{d}\Gamma d + \bar{s}\Gamma s$ contribute to many
important physical observables in the low energy region of QCD. Experimentally
one finds the values of some of these observables to be in sharp contrast to
the naive (perturbative) theoretical expectations. This indicates that non
perturbative vacuum properties might play a major role in the comprehension of
these phenomena. An example of such a vacuum contribution is the axial anomaly,
which appears in the divergence of the flavor singlet axial current and which
is connected to the topological properties of QCD. From a field theoretical
point of view flavor singlet matrix elements differ from non singlet amplitudes
in the occurrence of so called disconnected insertions. These are correlations
of hadron propagators with quark-antiquark loops or correlations between
quark-antiquark loops, which are mediated by vacuum fluctuations. According to
their respective flavor composition, the disconnected insertions cancel largely
in non singlet processes, but add in flavor singlet amplitudes. The lattice
approach provides an ideal tool to study flavor singlet phenomena. Being a
first principle method it should be capable to uncover non perturbative vacuum
contributions and to yield, on the long run, reliable results for the size of
such contributions in QCD. The present article reviews the status of flavor
singlet matrix element calculations in lattice QCD with respect to methods,
results and reliability. Special emphasis is paid to the discussion of state of
the art calculations of the pion nucleon sigma term $\sigma_{\pi N}$, the
flavor singlet axial coupling of the proton $G_A^1$, and the $\eta'$ mass.


title:
Stochastic Estimator Techniques and Their Implementation on Distributed
  Parallel Computers

abstract:
  The calculation of physical quantities by lattice QCD simulations requires in
some important cases the determination of the inverse of a very large matrix.
In this article we describe how stochastic estimator methods can be applied to
this problem, and how such techniques can be efficiently implemented on
parallel computers.


title: The basis of the physical Hilbert space of lattice gauge theories

abstract:
  Non-linear Fourier analysis on compact groups is used to construct an
orthonormal basis of the physical (gauge invariant) Hilbert space of
Hamiltonian lattice gauge theories. In particular, the matrix elements of the
Hamiltonian operator involved are explicitly computed. Finally, some
applications and possible developments of the formalism are discussed.


title: Ergodic Properties of Classical SU(2) Lattice Gauge Theory

abstract:
  We investigate the relationship between the Lyapunov exponents of periodic
trajectories, the average and fluctuations of Lyapunov exponents of ergodic
trajectories, and the ergodic autocorrelation time for the two-dimensional
hyperbola billiard. We then study the fluctuation properties of the ergodic
Lyapunov spectrum of classical SU(2) gauge theory on a lattice. Our results are
consistent with the notion that this system is globally hyperbolic. Among the
many powerful theorems applicable to such systems, we discuss one relating to
the fluctuations in the entropy growth rate.

categories: hep-lat chao-dyn cond-mat hep-ph nlin.CD nucl-th


title: On the continuum limit of the lattice chiral anomaly trace relation

abstract:
  Different aspects concerning the rigorous definition of the traces and
determinants of the operators involved in a procedure ---proposed by Neuberger
and others--- for avoiding fermion doublers on the lattice, are considered. A
result of the analysis is that it seems unclear that the consequences derived
from the independent treatment of the traces of the two operators contributing
to the index relation on the lattice, as carried out in recent manuscripts, can
be given rigorous mathematical footing, in particular, that these treatments
can commute with the continuum limit ---the lattice regularized trace being
additive all the way through the limit, while the otherwise regularized trace
in the continuum is not so.


title: Exact fermion zero-mode for the new calorons

abstract:
  We construct the fermion zero-mode for arbitrary charge one SU(n) calorons
with non-trivial holonomy, both in the finite temperature context
(anti-periodic boundary conditions in time) and in the Kaluza-Klein
compactification context (periodic boundary conditions in time). The zero-mode
is localised on one of the constituent monopoles and we discuss a relation to
the Callias index theorem.


title: Dynamic relaxation of SU(2) lattice gauge theory in (3+1) dimensions

abstract:
  We investigate the dynamic relaxation for SU(2) gauge theory at finite
temperatures in (3+1) dimensions. Using the Hybrid Monte Carlo algorithm, we
examine the time dependence of the system in the short-time regime. Starting
from the ordered state, the critical exponents beta, nu and z are calculated
from the power law behaviour of the Polyakov loop and the cumulant at or near
the critical point. The results for the static exponents are in agreement with
those obtained from simulations in equilibrium and those of the
three-dimensional Ising model. The value for the dynamic critical exponent was
determined with z=2.0(1).


title: Chiral Fermions and Multigrid

abstract:
  Lattice regularization of chiral fermions is an important development of the
theory of elementary particles. Nontheless, brute force computer simulations
are very expensive, if not prohibitive. In this letter I exploit the
non-interacting character of the lattice theory in the flavor space and propose
a multigrid approach for the simulation of the theory. Already a two-grid
algorithm saves an order of magnitude of computer time for fermion propagator
calculations.


title: The role of the Polyakov loop in finite density QCD

abstract:
  We study the behavior of the fermion determinant at finite temperature and
chemical potential, as a function of the Polyakov loop. The phase of the
determinant is correlated with the imaginary part of the Polyakov loop. This
correlation and its consequences are considered in static QCD, in a toy model
of free quarks in a constant $A_0$ background, and in simulations constraining
the imaginary part of the Polyakov loop to zero.


title: General bounds on the Wilson-Dirac operator

abstract:
  Lower bounds on the magnitude of the spectrum of the Hermitian Wilson-Dirac
operator H(m) have previously been derived for 0<m<2 when the lattice gauge
field satisfies a certain smoothness condition. In this paper lower bounds are
derived for 2p-2<m<2p for general p=1,2,...,d where d is the spacetime
dimension. The bounds can alternatively be viewed as localisation bounds on the
real spectrum of the usual Wilson-Dirac operator. They are needed for the
rigorous evaluation of the classical continuum limit of the axial anomaly and
index of the overlap Dirac operator at general values of m, and provide
information on the topological phase structure of overlap fermions. They are
also useful for understanding the instanton size-dependence of the real
spectrum of the Wilson-Dirac operator in an instanton background.


title: Lattice Yang-Mills theory at finite densities of heavy quarks

abstract:
  SU(N_c) Yang-Mills theory is investigated at finite densities of N_f heavy
quark flavors. The calculation of the (continuum) quark determinant in the
large-mass limit is performed by analytic methods and results in an effective
gluonic action. This action is then subject to a lattice representation of the
gluon fields and computer simulations. The approach maintains the same number
of quark degrees of freedom as in the continuum formulation and a physical
heavy quark limit (to be contrasted with the quenched approximation N_f -> 0).
The proper scaling towards the continuum limit is manifest. We study the
partition function for given values of the chemical potential as well as the
partition function which is projected onto a definite baryon number. First
numerical results for an SU(2) gauge theory are presented. We briefly discuss
the breaking of the color-electric string at finite densities and shed light
onto the origin of the overlap problem inherent in the Glasgow approach.


title: Running coupling for Wilson bermions

abstract:
  A non perturbative finite size scaling technique is used to study a running
coupling in lattice Yang-Mills theory coupled to a bosonic Wilson spinor field
in the Schr\"odinger functional scheme. This corresponds to two negative
flavours. The scaling behaviour in this case is compared to quenched results
and to QCD with two flavours. The continuum limit is confronted with
renormalized perturbation theory.


title:
Quantum Spin-1/2 Antiferromagnetic Chains and Strongly Coupled
  Multiflavor Schwinger Models

abstract:
  We review the correspondence between strongly coupled lattice multiflavor
Schwinger models and SU(N) antiferromagnetic chains. We show that finding the
low lying states of the gauge models is equivalent to solving an SU(N)
Heisenberg antiferromagnetic chain. For the two-flavor lattice Schwinger model
the massless excitations correspond to gapless states of the Heisenberg chain,
while the massive states are created by fermion transport in the ground state
of the spin chain. Our analysis shows explicitly how spinons may arise in
lattice gauge theories.


title: Real Time Simulations in Lattice Gauge Theory

abstract:
  I review the study of real (Minkowski) time correlators in hot, weakly
coupled Yang-Mills theory via lattice methods. I concentrate on the Minkowski
time topological susceptibility, which is related to the efficiency of baryon
number violation at high temperature. It can be computed by approximating the
IR fields as classical and solving their dynamics nonperturbatively on the
lattice. However it is essential to include the UV degrees of freedom. Their
influence can be computed perturbatively and included in the lattice model by
the addition of auxiliary fields.


title: What we do understand of Colour Confinement

abstract:
  A review is presented of what we understand of colour confinement in QCD.
Lattice formulation provides evidence that QCD vacuum is a dual superconductor:
the chromoelectric field of a $q\bar q$ pair is constrained by dual Meissner
effect into a dual Abrikosov flux tube and the static potential energy is
proportional to the distance.


title: Comparing lattice Dirac operators with Random Matrix Theory

abstract:
  We study the eigenvalue spectrum of different lattice Dirac operators
(staggered, fixed point, overlap) and discuss their dependence on the
topological sectors. Although the model is 2D (the Schwinger model with
massless fermions) our observations indicate possible problems in 4D
applications. In particular misidentification of the smallest eigenvalues due
to non-identification of the topological sector may hinder successful
comparison with Random Matrix Theory (RMT).


title: Random manifolds and quantum gravity

abstract:
  The non-perturbative, lattice field theory approach towards the quantization
of Euclidean gravity is reviewed. Included is a tentative summary of the most
significant results and a presentation of the current state of art.


title: Fermions on random lattices

abstract:
  We put fermions and define the Dirac operator and spin structures on a
randomly triangulated 2d manifold.


title: Random Matrix Theory, Chiral Perturbation Theory, and Lattice Data

abstract:
  Recently, the chiral logarithms predicted by quenched chiral perturbation
theory have been extracted from lattice calculations of hadron masses. We argue
that the deviations of lattice results from random matrix theory starting
around the so-called Thouless energy can be understood in terms of chiral
perturbation theory as well. Comparison of lattice data with chiral
perturbation theory formulae allows us to compute the pion decay constant. We
present results from a calculation for quenched SU(2) with Kogut-Susskind
fermions at \beta=2.0 and 2.2.


title:
Green Function Simulation of Hamiltonian Lattice Models with Stochastic
  Reconfiguration

abstract:
  We apply a recently proposed Green Function Monte Carlo to the study of
Hamiltonian lattice gauge theories. This class of algorithms computes quantum
vacuum expectation values by averaging over a set of suitable weighted random
walkers. By means of a procedure called Stochastic Reconfiguration the long
standing problem of keeping fixed the walker population without a priori
knowledge on the ground state is completely solved. In the $U(1)_2$ model,
which we choose as our theoretical laboratory, we evaluate the mean plaquette
and the vacuum energy per plaquette. We find good agreement with previous works
using model dependent guiding functions for the random walkers.


title:
Universal Scaling of the Chiral Condensate in Finite-Volume Gauge
  Theories

abstract:
  We confront exact analytical predictions for the finite-volume scaling of the
chiral condensate with data from quenched lattice gauge theory simulations.
Using staggered fermions in both the fundamental and adjoint representations,
and gauge groups SU(2) and SU(3), we are able to test simultaneously all of the
three chiral universality classes. With overlap fermions we also test the
predictions for gauge field sectors of non-zero topological charge. Excellent
agreement is found in most cases, and the deviations are understood in the
others.


title: On the Spectrum of Lattice Dirac Operators

abstract:
  With the Schwinger model as example I discuss properties of lattice Dirac
operators, with some emphasis on Monte Carlo results for topological charge,
chiral fermions and eigenvalue spectra.


title: Non-perturbative states in the three-dimensional phi^4 theory

abstract:
  We study the spectrum of massive excitations of the three-dimensional phi^4
and Ising models, in the broken-symmetry phase. Using a variational method, we
show that the spectrum contains all the 0+ states that one expects from duality
with the glueball spectrum of the Z(2) gauge model. From the point of view of
continuum phi^4 theory, we show that at least one of the states we find has a
non-perturbative origin.


title: Staggered Fermions and Gauge Field Topology

abstract:
  Based on a large number of smearing steps, we classify SU(3) gauge field
configurations in different topological sectors. For each sector we compare the
exact analytical predictions for the microscopic Dirac operator spectrum of
quenched staggered fermions. In all sectors we find perfect agreement with the
predictions for the sector of topological charge zero, showing explicitly that
the smallest Dirac operator eigenvalues of staggered fermions at presently
realistic lattice couplings are insensitive to gauge field topology. On the
smeared configurations, $4\nu$ eigenvalues clearly separate out from the rest
on configurations of topological charge $\nu$, and move towards zero in
agreement with the index theorem.


title: The Gluon Propagator

abstract:
  We discuss the current state of what is known non-perturbatively about the
gluon propagator in QCD, with emphasis on the information coming from lattice
simulations. We review the specification of the lattice Landau gauge and the
procedure for calculating the gluon propagator on the lattice. We also discuss
some of the difficulties in non-perturbative calculations, especially Gribov
copy issues. We trace the evolution of lattice simulations over the past dozen
years, emphasizing how the improvement in computations has led not only to more
precise determinations of the propagator, but has allowed more detailed
information about it to be extracted.


title:
Vortex Structure vs. Monopole Dominance in Abelian-Projected Gauge
  Theory

abstract:
  We find that Polyakov lines, computed in abelian-projected SU(2) lattice
gauge theory in the confined phase, have finite expectation values for lines
corresponding to two units of the abelian electric charge. This means that the
abelian-projected lattice has at most Z(2), rather than U(1), global symmetry.
We also find a severe breakdown of the monopole dominance approximation, as
well as positivity, in this charge-2 case. These results imply that the
abelian-projected lattice is not adequately represented by a monopole Coulomb
gas; the data is, however, consistent with a center vortex structure. Further
evidence is provided, in lattice Monte Carlo simulations, for collimation of
confining color-magnetic flux into vortices.


title: Finite-size scaling of the quark condensate in quenched lattice QCD

abstract:
  We confront the finite volume and small quark mass behaviour of the scalar
condensate, determined numerically in quenched lattice QCD using Neuberger
fermions, with predictions of quenched chiral perturbation theory. We find that
quenched chiral perturbation theory describes the numerical data well, allowing
us to extract the infinite volume, chiral limit scalar condensate, up to a
multiplicative renormalization constant.


title: When QCD strings can break

abstract:
  The confining string in presence of dynamical quarks can behave in different
ways, depending on the quark masses and on the number N_f N_c of charge
species. For light masses and large N_f N_c the creation of quark pairs
produces microscopic holes in the world- sheet swept by the string; as a
consequence string breaking is invisible in the Wilson loop, while is manifest
in operators composed of disjoint sources, as observed in many numerical
experiments. Similar arguments apply also to the adjoint string breaking. For
larger quark masses it is possible that the string world-sheet undergoes a
transition to a tearing phase, characterized by macroscopic holes, which
manifest themselves through a visible string breaking effect also in the Wilson
loop, as observed in 2+1 D SU(2) gauge theory with two flavors.


title: SU(3) vortex-like configurations in the maximal center gauge

abstract:
  A new algorithm for fixing the gauge to (direct) maximal center gauge in
SU(N) lattice gauge theory is presented. We check how this method works on
SU(3) configurations which are vortex-like, and show how these configurations
look like when center projected.


title:
Interquark potential, susceptibilities and particle density of two color
  QCD at finite chemical potential and temperature

abstract:
  We explore the phase diagram of SU(2) Lattice Gauge Theory with dynamical
fermions in the temperature, mass, chemical potential space. We observe
qualitative changes of the dependence of the particle density on $\mu$ and $T$,
which is compatible with that expected of a gas of free massless quarks $n
\propto \mu^3$ only for $T \simeq T_c$. At the onset for thermodynamics the
interquark potential flattens at large separations, indicating enhanced fermion
screening and the transition to a deconfined phase. Temporal and spatial
Polyakov loops behave in different ways, the latter being nearly insensitive to
the chemical potential. The rotation of the chiral condensate to a baryonic
condensate, as inferred from the susceptibilities, might occur together with a
reduction of its magnitude in the chiral limit, possibly leading to a critical
temperature for diquark condensation smaller than the deconfinement
temperature. We further asses the r\^ole of the chemical potential into the
gauge dynamics by carrying out a partial quenched calculation. We speculate on
the relevance, or lack thereof, of our findings to real QCD.


title: Ising and Potts Models on Quenched Random Gravity Graphs

abstract:
  We report on single-cluster Monte Carlo simulations of the Ising, 4-state
Potts and 10-state Potts models on quenched ensembles of planar, tri-valent
random graphs. We confirm that the first-order phase transition of the 10-state
Potts model on regular 2D lattices is softened by the quenched connectivity
disorder represented by the random graphs and that the exponents of the Ising
and 4-state Potts models are altered from their regular lattice counterparts.
The behaviour of spin models on such graphs is thus more analogous to models
with quenched bond disorder than to Poisonnian random lattices, where regular
lattice critical behaviour persists.
  Using a wide variety of estimators we measure the critical exponents for all
three models, and compare the exponents with predictions derived from taking a
quenched limit in the KPZ formula for the Ising and 4-state Potts models.
Earlier simulations suggested that the measured values for the 10-state Potts
model were very close to the predicted quenched exponents of the {\it
four}-state Potts models. The analysis here, which employs a much greater range
of estimators and also benefits from greatly improved statistics, still
supports these numerical values.


title: Abelian gauge fields coupled to simplicial quantum gravity

abstract:
  We study the coupling of Abelian gauge theories to four-dimensional
simplicial quantum gravity. The gauge fields live on dual links. This is the
correct formulation if we want to compare the effect of gauge fields on
geometry with similar effects studied so far for scalar fields. It shows that
gauge fields couple equally weakly to geometry as scalar fields, and it offers
an understanding of the relation between measure factors and Abelian gauge
fields observed so-far.


title: The relevance of center vortices

abstract:
  We show remnants of chiral symmetry breaking in the center-projected theory.
We construct and study an unambiguous definition of center vortices.


title: Confinement in QCD

abstract:
  The guiding lines of lattice investigations on colour confinement are
reviewed, together with recent results.


title: Perturbative Subtraction Methods

abstract:
  The effects of an automated, tenth order in $\kappa$ subtraction scheme on
the noise variance of various Wilson QCD disconnected matrix elements are
examined. It is found that there is a dramatic reduction in the variance of the
lattice point-split electromagnetic currents and that this reduction persists
at small quark mass.


title: The Infrared Limit of the QCD Dirac Spectrum

abstract:
  The distribution of the low-lying QCD Dirac spectrum is analyzed by means of
partial quenched chiral perturbation theory. We identify an energy scale below
which the valence quark mass dependence of the QCD partition function is given
by chiral Random Matrix Theory. This is the the domain where the low-energy QCD
partition function is dominated by the fluctuations of the mass term of the
Goldstone bosons. In mesoscopic physics this domain is known the ergodic domain
and the corresponding energy scale is the Thouless energy.


title: Efficiencies and optimization of HMC algorithms in pure gauge theory

abstract:
  As a prerequisite to dynamical fermion simulations a detailed study of
optimal parameters and scaling behavior is conducted for the quenched
Schr\"odinger functional at fixed renormalized coupling. We compare standard
hybrid overrelaxation techniques with local and global hybrid Monte Carlo. Our
efficiency measure is designed to be directly relevant for the strong coupling
constant as used by the ALPHA collaboration.


title: Using lattice methods in non-canonical quantum statistics

abstract:
  We define a natural coarse-graining procedure which can be applied to any
closed equilibrium quantum system described by a density matrix ensemble and we
show how the coarse-graining leads to the Gaussian and canonical ensembles.
After this motivation, we present two ways of evaluating the Gaussian
expectation values with lattice simulations. The first one is computationally
demanding but general, whereas the second employs only canonical expectation
values but it is applicable only for systems which are almost thermodynamical.


title: A Lattice Determination of Light Quark Masses

abstract:
  A fully non-perturbative lattice determination of the up/down and strange
quark masses is given for quenched QCD using both, $O(a)$ improved Wilson
fermions and ordinary Wilson fermions. For the strange quark mass with $O(a)$
improved fermions we obtain $m^{\msbar}_s(\mu=2 {GeV}) = 105(4) {MeV}$, using
the interquark force scale $r_0$. Due to quenching problems fits are only
possible for quark masses larger than the strange quark mass. If we extrapolate
our fits to the up/down quark mass we find for the average mass
$m^{\msbar}_l(\mu=2 {GeV}) = 4.4(2) {MeV}$.


title: Finite density (might well be easier) at finite temperature

abstract:
  Experiments with imaginary chemical potential and Glasgow method carried out
in two interrelated models - four dimensional QCD in the infinite coupling
limit, and one dimensional QCD - support the point of view expressed by the
title.


title: Aspects of determining fBs: scaling and power-law divergences

abstract:
  We present preliminary results for the decay constant of the Bs meson, fBs,
at three values of beta=5.7, 6.0 and 6.2 using NRQCD and clover fermions for
the heavy and light quarks respectively. As a consistency check the decay
constant has also been extracted from the axial-vector current at finite
momentum. In addition, we discuss the cancellation of O(alpha/(aM0)) terms and
the remaining uncertainty in fBs from higher order divergences.


title: Critical Behavior in Nt = 4 Staggered Fermion Thermodynamics

abstract:
  Quantum chromodynamics with two zero-mass flavors is expected to exhibit a
phase transition with O(4) critical behavior. Fixing the universality class is
important for phenomenology and for facilitating the extrapolation of
simulation data to physical quark mass values. Other groups have reported
results from lattice QCD simulations with dynamical staggered quarks at Nt = 4,
which suggest a departure from the expected critical behavior. We have pushed
simulations to the largest volumes and smallest quark mass to date. Strong
discrepancies in critical exponents and the scaling equation of state persist.


title: Comment on "Valence QCD: Connecting QCD to the Quark Model"

abstract:
  I criticize certain conclusions about the physics of hadrons drawn from a
"valence QCD" approximation to QCD.


title: Heavy Quark Potentials in Quenched QCD at High Temperature

abstract:
  Heavy quark potentials are investigated at high temperatures. The temperature
range covered by the analysis extends from $T$ values just below the
deconfinement temperature up to about $4 T_c$ in the deconfined phase. We
simulated the pure gauge sector of QCD on lattices with temporal extents of 4,
6 and 8 with spatial volumes of $32^3$. On the smallest lattice a tree level
improved action was employed while in the other two cases the standard Wilson
action was used. Below $T_c$ we find a temperature dependent logarithmic term
contributing to the confinement potential and observe a string tension which
decreases with rising temperature but retains a finite value at the
deconfinement transition. Above $T_c$ the potential is Debye-screened, however
simple perturbative predictions do not apply.


title: Higher-Twist Contribution to Pion Structure Function: 4-Fermi Operators

abstract:
  We present quenched lattice QCD results for the contribution of higher-twist
operators to the lowest non-trivial moment of the pion structure function. To
be specific, we consider the combination $F_2^{\pi^+} + F_2^{\pi^-} - 2
F_2^{\pi^0}$ which has $I = 2$ and receives contributions from 4-Fermi
operators only. We introduce the basis of lattice operators. The
renormalization of the operators is done perturbatively in the $\bar{\rm{MS}}$
scheme using the 't Hooft-Veltman prescription for $\gamma_5$, taking
particular care of mixing effects. The contribution is found to be of
$O(f_\pi^2/Q^2)$, relative to the leading contribution to the moment of
$F_2^{\pi^+}$.


title: Improved Overlap Fermions

abstract:
  We test exact and approximate Ginsparg-Wilson fermions with respect to their
chiral and scaling behavior in the 2-flavor Schwinger model. We first consider
explicit approximate GW fermions in a short range, then we proceed to their
chiral correction by means of the ``overlap formula'', and finally we discuss a
numerically efficient perturbative chiral correction. In this way we combine
very good chiral and scaling properties with a relatively modest computational
effort.


title:
Renormalization of lattice gauge theories with massless Ginsparg Wilson
  fermions

abstract:
  Using functional techniques, we prove, to all orders of perturbation theory,
that lattice vector gauge theories with Ginsparg Wilson fermions are
renormalizable. For two or more massless fermions, they satisfy a flavour
mixing axial vector Ward identity. It involves a lattice specific part that is
quadratic in the vertex functional and classically irrelevant. We show that it
stays irrelevant under renormalization. This means that in the continuum limit
the (standard) chiral symmetry becomes restored. In particular, the flavour
mixing current does not require renormalization.


title: Lattice QED and Universality of the Axial Anomaly

abstract:
  We give a perturbative proof that U(1) lattice gauge theories generate the
axial anomaly in the continuum limit under very general conditions on the
lattice Dirac operator. These conditions are locality, gauge covariance and the
absense of species doubling. They hold for Wilson fermions as well as for
realizations of the Dirac operator that satisfy the Ginsparg-Wilson relation.
The proof is based on the lattice power counting theorem. The results
generalize to non-abelian gauge theories.


title: Improving the sign problem in QCD at finite density

abstract:
  If the fermion mass is large enough, the phase of the fermion determinant of
QCD at finite density is strongly correlated with the imaginary part of the
Polyakov loop. This fact can be exploited to reduce the fluctuations of the
phase significantly, making numerical simulations feasible in regions of
parameters where the naive brute force method does not work.


title:
Can lattice data for two heavy-light mesons be understood in terms of
  simply two-quark potentials?

abstract:
  By comparing lattice data for the two heavy-light meson system (Q^2 qbar^2)
with a standard many-body approach employing only interquark potentials, it is
shown that the use of unmodified two-quark potentials leads to a gross
overestimate of the binding energy.


title: Vortex Structure in Abelian-Projected Lattice Gauge Theory

abstract:
  We report on a breakdown of both monopole dominance and positivity in
abelian-projected lattice Yang-Mills theory. The breakdown is associated with
observables involving two units of the abelian charge. We find that the
projected lattice has at most a global $Z_2$ symmetry in the confined phase,
rather than the global U(1) symmetry that might be expected in a dual
superconductor or monopole Coulomb gas picture. Implications for monopole and
center vortex theories of confinement are discussed.


title:
Random Matrices and the Convergence of Partition Function Zeros in
  Finite Density QCD

abstract:
  We apply the Glasgow method for lattice QCD at finite chemical potential to a
schematic random matrix model (RMM). In this method the zeros of the partition
function are obtained by averaging the coefficients of its expansion in powers
of the chemical potential. In this paper we investigate the phase structure by
means of Glasgow averaging and demonstrate that the method converges to the
correct analytically known result. We conclude that the statistics needed for
complete convergence grows exponentially with the size of the system, in our
case, the dimension of the Dirac matrix. The use of an unquenched ensemble at
$\mu=0$ does not give an improvement over a quenched ensemble.
  We elucidate the phenomenon of a faster convergence of certain zeros of the
partition function. The imprecision affecting the coefficients of the
polynomial in the chemical potential can be interpeted as the appearance of a
spurious phase. This phase dominates in the regions where the exact partition
function is exponentially small, introducing additional phase boundaries, and
hiding part of the true ones. The zeros along the surviving parts of the true
boundaries remain unaffected.


title: Improved Transfer-Matrix Schemes of Phenomenological Renormalization

abstract:
  Different phenomenological RG transformations based on scaling relations for
the derivatives of the inverse correlation length and singular part of the
free-energy density are considered. These transformations are tested on the 2D
square Ising and Potts models as well as on the 3D simple-cubic Ising model.
Variants of RG equations yielding more accurate results than Nightingale's RG
scheme are obtained. In the 2D case the finite-size equations which give the
{\it exact} values of the critical point or the critical exponent are found.


title: Some Insights into the Method of Center Projection

abstract:
  We present several new results which pertain to the successes of center
projection in maximal center gauge (MCG). In particular, we show why any center
vortex, inserted "by hand" into a thermalized lattice configuration, will be
among the set of vortices found by the center projection procedure. We show
that this "vortex-finding property" is lost when gauge-field configurations are
fixed to Landau gauge prior to the maximal center gauge fixing; this fact
accounts for the loss of center dominance in the corresponding projected
configurations. Variants of maximal center (adjoint Landau) gauge are proposed
which correctly identify relevant center vortices.


title: Casimir scaling or flux counting?

abstract:
  Potentials between two static sources in various representations of the SU(3)
gauge group are determined on anisotropic 3+1 dimensional lattices. Strong
evidence in favour of "Casimir scaling" is found.


title:
Decorrelation of the topological charge in tempered Hybrid Monte Carlo
  simulations of QCD

abstract:
  We study the improvement of simulations of QCD with dynamical Wilson fermions
by combining the Hybrid Monte Carlo algorithm with parallel tempering. As an
indicator for decorrelation we use the topological charge.


title: A construction of chiral fermion action

abstract:
  According to the necessary requirements for a chirally symmetric Dirac
operator, we present a systematic construction of such operators. We formulate
a criterion for the hermitian operator which enters the construction such that
the doubled modes are decoupled even at finite lattice spacing.


title: Message passing on the QCDSP supercomputer

abstract:
  The QCDSP machines were designed for lattice gauge calculations. For planning
it is crucial to explore this architecture for other computationally intensive
tasks. Here I describe an implementation of a simple message passing scheme.
With the objective being simplicity, I introduce a small number of generic
functions for manipulating a large data set spread over the machine. I test the
scheme on three applications: a fast Fourier transform, arbitrary dimension
SU(N) pure lattice gauge theory, and the manipulation of Fermionic Fock states
through a distributed hash table. These routines compile both on QCDSP and a
Unix workstation.


title:
A first study of epsilon'/epsilon on the lattice using domain wall
  fermions

abstract: This paper has been withdrawn.


title: Quantum gauge fixing and vortex dominance

abstract:
  We introduce quantum gauge fixing (QGF) as a new class of gauge fixings.
While the maximal center gauge might not show vortex dominance, the confining
properties of the vortices observed in past lattice calculations are argued to
have been obtained in a gauge more akin to QGF than to the strict maximal
center gauge.


title: Magnetic Monopoles, Center Vortices and Topology of Gauge Fields

abstract:
  The topological properties of magnetic monopoles and center vortices arising,
respectively, in Abelian and center gauges are studied in continuum Yang-Mills
Theory. For this purpose the continuum analog of the maximum center gauge is
constructed.


title: Light quark masses from the lattice

abstract:
  A completely non-perturbative estimate is given for the u/d and strange quark
masses in quenched QCD using O(a) improved fermions and, for comparison, Wilson
fermions. For improved fermions we find m_{u/d}^MSbar(\mu=2 GeV) = 4.4(2) MeV,
m_s^MSbar(\mu=2 GeV) = 105(4) MeV when using r_0 to set the physical scale.


title: Operator improvement for Ginsparg-Wilson fermions

abstract:
  The improvement of fermionic operators for Ginsparg-Wilson fermions is
investigated. We present explicit formulae for improved Green's functions,
which apply both on-shell and off-shell.


title: U(1) staggered Dirac operator and random matrix

abstract:
  We investigate the spectrum of the staggered Dirac operator in 4d quenched
U(1) lattice gauge theory and its relationship to random matrix theory. In the
confined as well as in the Coulomb phase the nearest-neighbor spacing
distribution of the unfolded eigenvalues is well described by the chiral
unitary ensemble. The same is true for the distribution of the smallest
eigenvalue and the microscopic spectral density in the confined phase. The
physical origin of the chiral condensate in this phase deserves further study.


title: Bound on the string tension by the excitation probability for a vortex

abstract:
  A lower bound on the string tension for large beta in SU(2) LGT is derived.
The derivation is from first principles and bounds the string tension from
below by the expectation for the excitation of a single `tagged' thick vortex
winding around the lattice. Thus confinement follows if this expectation
remains nonvanishing at large beta. Numerical simulations are presented to show
that this is indeed the case.


title: Interactions of heavy-light mesons

abstract:
  The potential between static-light mesons forming a meson-meson or a
meson-antimeson system is calculated in quenched and unquenched SU(3) gauge
theory. We use the Sheikholeslami-Wohlert action and statistical estimators of
light quark propagators with maximal variance reduction. The dependence of the
potentials on the light quark spin and isospin and the effect of meson exchange
is investigated. Our main motivation is exploration of bound states of two
mesons and string breaking. The latter also involves the two-quark potential
and the correlation between two-quark and two-meson states.


title: Percolation and Deconfinement in SU(2) Gauge Theory

abstract:
  We show that deconfinement in SU(2) gauge theory can be described by the
percolation of site-bond clusters of like-sign Polyakov loops. In particular,
we find that in 2+1 dimensions the percolation variables coincide with those of
the 2-dimensional Ising model.


title: Dirac operator normality and chiral properties

abstract:
  Normality and $\ga$-hermiticity are what gives rise to chiral properties and
rules. The Ginsparg-Wilson (GW) relation is only one of the possible spectral
constraints. The sum rule for chiral differences of real modes has important
consequences. The alternative transformation of L\"uscher gives the same Ward
identity as the usual chiral one (if zero modes are properly treated). Imposing
normality on a general function of the hermitean Wilson-Dirac operator $H$
leads at the same time to the GW relation and to the Neuberger operator.


title: Light-cone QCD on the lattice

abstract:
  Ideas and recent results for light-front Hamiltonian quantisation of lattice
gauge theories.


title: Topology and chiral symmetry in finite temperature QCD

abstract:
  We investigate the realization of chiral symmetry in the vicinity of the
deconfinement transition in quenched QCD using overlap fermions. Via the index
theorem obeyed by the overlap fermions, we gain insight into the behavior of
topology at finite temperature. We find small eigenvalues, clearly separated
from the bulk of the eigenvalues, and study the properties of their
distribution. We compare the distribution with a model of a dilute gas of
instantons and anti-instantons and find good agreement.


title: Ginsparg-Wilson Games

abstract:
  I implement a set of tricks for constructing lattice fermion actions which
approximately realize the Ginsparg-Wilson relation, with very promising results
from simulations.


title:
Higher-twist contributions to the Structure Functions coming from
  4-fermion operators

abstract:
  We evaluate the contribution of a class of higher-twist operators to the
lowest moment of the Structure Functions, by computing appropriate matrix
elements of six four-fermion operators in the quenched approximation. Their
perturbative renormalization constants and mixing coefficients are calculated
in the 't Hooft-Veltman scheme of dimensional regularization, using codes
written in the algebraic manipulation computer language FORM.


title: Renormalization of the static-light axial current

abstract:
  We discuss the determination of the heavy-light axial current renormalization
in the static approximation, using a new method based on the Schr\"odinger
Functional (SF). Previous perturbative results for the renormalization constant
are confirmed.


title: Impact of Z_2 monopoles and vortices on the deconfinement transition

abstract:
  The impact of Z_2-monopoles and vortices on the bulk and the deconfinement
phase transitions of the SU(2) lattice gauge theory with a mixed Villain form
of action is investigated by varying their numbers with appropriate chemical
potentials. Suppressing the former shifts the line of deconfinement transitions
in the coupling plane but it continues to behave also like the bulk transition
line. We find separate deconfinement and bulk phase transitions on the same
lattice, suggesting the two to be indeed coincident at higher adjoint
couplings. Universality is restored when both monopoles and vortices are
suppressed.


title:
The spectrum of the three-dimensional adjoint Higgs model and hot SU(2)
  gauge theory

abstract:
  We compute the mass spectrum of the SU(2) adjoint Higgs model in 2+1
dimensions at several points located in the (metastable) confinement region of
its phase diagram. We find a dense spectrum consisting of an almost unaltered
repetition of the glueball spectrum of the pure gauge theory, and additional
bound states of adjoint scalars. For the parameters chosen, the model
represents the effective finite temperature theory for pure SU(2) gauge theory
in four dimensions, obtained after perturbative dimensional reduction.
Comparing with the spectrum of screening masses obtained in recent simulations
of four-dimensional pure gauge theory at finite temperature, for the low lying
states we find quantitative agreement between the full and the effective theory
for temperatures as low as T = 2 Tc. This establishes the model under study as
the correct effective theory, and dimensional reduction as a viable tool for
the description of thermodynamic properties. We furthermore compare the
perturbative contribution O(g.T) with the non-perturbative contributions
O(g^2.T) and O(g^3.T) to the Debye mass. The latter turns out to be dominated
by the scale g^2.T, whereas higher order contributions are small corrections.


title: Analytic approach to confinement and monopoles in lattice SU(2)

abstract:
  We extend the approach of Banks, Myerson, and Kogut for the calculation of
the Wilson loop in lattice U(1) to the non-abelian SU(2) group. The original
degrees of freedom of the theory are integrated out, new degrees of freedom are
introduced in several steps. The centre group $Z_2$ enters automatically
through the appearance of a field strength tensor $f_{\mu \nu}$, which takes on
the values 0 or 1 only. It obeys a linear field equation with the loop current
as source. This equation implies that $f_{\mu \nu}$ is non vanishing on a
two-dimensional surface bounded by the loop, and possibly on closed surfaces.
The two-dimensional surfaces have a natural interpretation as strings moving in
euclidean time. In four dimensions we recover the dual Abrikosov string of a
type II superconductor, i.e. an electric string encircled by a magnetic
current. In contrast to other types of monopoles found in the literature, the
monopoles and the associated magnetic currents are present in every
configuration. With some plausible, though not generally conclusive, arguments
we are directly led to the area law for large loops.


title: Beyond the Thouless energy

abstract:
  The distribution and the correlations of the small eigenvalues of the Dirac
operator are described by random matrix theory (RMT) up to the Thouless energy
$E_c\propto 1/\sqrt{V}$, where $V$ is the physical volume. For somewhat larger
energies, the same quantities can be described by chiral perturbation theory
(chPT). For most quantities there is an intermediate energy regime, roughly
$1/V<E<1/\sqrt{V}$, where the results of RMT and chPT agree with each other. We
test these predictions by constructing the connected and disconnected scalar
susceptibilities from Dirac spectra obtained in quenched SU(2) and SU(3)
simulations with staggered fermions for a variety of lattice sizes and coupling
constants. In deriving the predictions of chPT, it is important to take into
account only those symmetries which are exactly realized on the lattice.


title:
Two loop lattice expansion of the Schroedinger functional coupling in
  improved QCD

abstract:
  The contributions of the improved fermion action of Sheikholeslami and
Wohlert to the two loop coefficient of the expansion of the Schroedinger
functional coupling in terms of the lattice coupling are calculated for the
gauge group SU(3). These coefficients are required for the second order
relation of lattice data to the MSbar-coupling. By taking into account all
improvement coefficients we are able to improve the Schroedinger functional to
two loop order.


title: Spontaneous CP violation on the lattice

abstract:
  At finite temperatures around the electroweak phase transition, the
thermodynamics of the MSSM can be described by a three-dimensional two Higgs
doublet effective theory. This effective theory has a phase where CP is
spontaneously violated. We study spontaneous CP violation with non-perturbative
lattice simulations, and analyse whether one could end up in this phase for any
physical MSSM parameter values.


title: The non-zero baryon number formulation of QCD

abstract:
  We discuss the non-zero baryon number formulation of QCD in the quenched
limit at finite temperature. This describes the thermodynamics of gluons in the
background of static quark sources. Although a sign problem remains in this
theory, our simulation results show that it can be handled quite well
numerically. The transition region gets shifted to smaller temperatures and the
transition region broadens with increasing baryon number. Although the action
is in our formulation explicitly Z(3) symmetric the Polyakov loop expectation
value becomes non-zero already in the low temperature phase and the heavy quark
potential gets screened at non-vanishing number density already this phase.


title: Monte Carlo Hamiltonian

abstract:
  We suggest how to construct an effective low energy Hamiltonian via Monte
Carlo starting from a given action. We test it by computing thermodynamical
observables like average energy and specific heat for simple quantum systems.


title: Phase Transition of 4D Simplicial Quantum Gravity with U(1) Gauge Field

abstract:
  The phase transition of 4D simplicial quantum gravity coupled to U(1) gauge
fields is studied using Monte-Carlo simulations. The phase transition of the
dynamical triangulation model with vector field ($N_{V}=1$) is smooth as
compared with the pure gravity($N_{V}=0$). The node susceptibility ($\chi$) is
studied in the finite size scaling method. At the critical point, the node
distribution has a sharp peak in contrast to the double peak in the pure
gravity. From the numerical results, we expect that 4D simplicial quantum
gravity with U(1) vector fields has higher order phase transition than 1st
order, which means the possibility to take the continuum limit at the critical
point.


title: Numerical Simulations of d=3 SU(2) LGT in the Dual Formulation

abstract:
  We have developed the techniques necessary for a numerical simulation of d=3
SU(2) Lattice Gauge theories in the dual formulation as originally developed by
Anishetty et al . These include updating techniques that preserve the
constrained configuration space, efficient evaluation of 6-j symbols and a
certain problem associated with the positive indefiniteness of the weight
factors.


title: The lattice gluon propagator into the next millennium

abstract:
  We evaluate numerically the momentum-space gluon propagator in the lattice
Landau gauge, for three- and four-dimensional pure SU(2) lattice gauge theory.
Although there are large finite-size effects, we always observe, in the limit
of large lattice volumes, a gluon propagator decreasing in the infrared limit.
This result can be interpreted in a straightforward way, by considering the
proximity of the so-called first Gribov horizon in the infrared directions. We
also consider the problem of discretization errors introduced by the lattice
regularization, and their effect on the ultraviolet behavior of the gluon
propagator.


title: Short Strings and Gluon Propagator in the Infrared Region

abstract:
  We discuss how infrared region influence on short distance physics via new
object, called ``short string''. This object exists in confining theories and
violates the operator product expansion. Most analytical results are obtained
for the dual Abelian Higgs theory, while phenomenological arguments are given
for QCD.


title: Proton Spin Content From Lattice QCD

abstract:
  We calculate the form factor of the quark energy momentum tensor and thereby
extract the quark orbital angular momentum of the nucleon. The calculation is
done on a quenched $16^3 \times 24$ lattice at $\beta = 6.0$ and with Wilson
fermions at $\kappa$ = 0.148, 0.152, 0.154 and 0.155. We calculate the
disconnected insertion stochastically which employs the $Z_2$ noise with an
unbiased subtraction. This proves to be an efficient method of reduce the error
from the noise. We find that the total quark contribution to the proton spin is
$0.29 \pm 0.07$. From this we deduce that the quark orbital angular momentum is
$0.17 \pm 0.08$ and predict the gluon spin to be $0.21 \pm 0.07$, i.e. about
40% of the proton spin is due to the glue.


title:
Some effects of the anisotropy in a simple lattice gauge model at finite
  temperature

abstract:
  Monte Carlo simulations are carried out on the (3+1)-dimensional Z(2)
anisotropic lattice model, and a new method to simulate extremely anisotropic
lattice systems with discrete symmetries is proposed. Dependence of the
temporal and spatial average plaquette, Wilson loops on the anisotropy
parameter is presented.


title: On the phase diagram of 2d Lorentzian Quantum Gravity

abstract:
  The phase diagram of 2d Lorentzian quantum gravity (LQG) coupled to conformal
matter is studied. A phase transition is observed at $c=c_{\rm crit}$
($1/2<c_{\rm crit}<4$) which can be thought of as the analogue of the $c=1$
barrier of Euclidean quantum gravity (EQG). The non--trivial properties of the
quantum geometry are discussed.


title: Instanton Effects in Hadron Spectroscopy Revisited

abstract:
  We use an optimised clover action to study spectroscopy on an instanton
ensemble reconstructed from smoothed Monte Carlo configurations. Due to the
better chirality of the clover action, the artificial configurations show a
marked difference from the free field behaviour obtained with the Wilson
action. They however still fail to reproduce the physics observed on the
smoothed configurations. The presence of freely propagating quark modes is
found to be responsible for this.


title: Gluon propagator, triple gluon vertex and the QCD coupling constant

abstract:
  We study the UV-scaling of the flavorless gluon propagator in the Landau
gauge in an energy window up to 9 GeV. Dominant hypercubic lattice artifacts
are eliminated. A large set of renormalization schemes is used to test
asymptotic scaling. We compare with our results obtained directly from the
triple gluon vertex. We end-up with \Lambda_{\bar{\rm{MS}}} = 318(12)(5) MeV
and 292(5)(15) MeV respectively for these two methods, compatible which each
other but significantly above the Schrodinger method estimate.


title: Modelling the Quark Determinant in Full QCD Simulations

abstract:
  The computational requirements and dynamics of Monte Carlo simulations of
unquenched QCD incorporating the infrared quark eigenmodes (up to $\approx
\Lambda_{QCD}$) exactly and UV modes via a loop representation are discussed.
The accuracy of such a loop representation is studied for a variety of lattice
volumes and quark masses. The method has been successfully applied for lattices
up to 10$^3$x20 at $a \simeq$0.17F with improved (clover) action, and allows
simulations at or near kappa critical.


title: Semi-leptonic decays heavy-light to heavy light

abstract:
  We present results for the QCD matrix elements involved in semi-leptonic
decays of B-mesons into pseudo scalar heavy light states. The application of
NRQCD heavy quarks allows for quark masses around the physical b-quark. We
investigate the dependence of the form factors on the external momenta and
looked at the mass dependence at zero recoil. For the first time, results for
radially excited decay products are presented.


title: Vortex profiles and vortex interactions at the electroweak crossover

abstract:
  Local correlations of Z-vortex operators with gauge and Higgs fields (lattice
quantum vortex profiles) as well as vortex two-point functions are studied in
the crossover region near a Higgs mass of 100 GeV within the 3D SU(2) Higgs
model. The vortex profiles resemble certain features of the classical vortex
solutions in the continuum. The vortex-vortex interactions are analogous to the
interactions of Abrikosov vortices in a type-I superconductor.


title:
The Structure of Projected Center Vortices at Zero and Finite
  Temperature

abstract:
  We investigate the structure of center projected vortices of SU(2) lattice
gauge theory at zero and finite temperature. At zero temperature we find, in
agreement with the area law behaviour of Wilson loops, that most of the
P-vortex plaquettes are parts of a single huge vortex. This vortex is an
unorientable surface and has a very irregular structure with many handles.
Small P-vortices, and short-range fluctuations of the large vortex surface, do
not contribute to the string tension. At finite temperature P-vortices exist
also in the deconfined phase. However, they form cylindric objects which extend
in time direction and consist only of space-space plaquettes.


title: A local formulation of lattice QCD without unphysical fermion zero modes

abstract:
  The problem of unphysical zero modes in lattice QCD with Wilson fermions can
be solved in a clean way by including a mass term proportional to $i \psibar
\gamma_5 \tau^3 \psi$ in the standard lattice theory with Nf=2 mass degenerate
Wilson quarks. We argue that up to cutoff effects, this lattice theory is
equivalent to standard lattice QCD, for suitable choices of the mass parameters
and with a natural re-interpretation of observables. On-shell O(a) improvement
can be implemented in a straightforward way.


title: Improved Multiboson Algorithm

abstract:
  We compare the performance of an UV-filtered Multiboson algorithm, including
a global quasi-heatbath update, to the standard Hybrid Monte Carlo algorithm in
full QCD with two flavours of Wilson fermions.


title: The Role of Center Vortices in QCD

abstract:
  Center vortices are unambiguously identified after Laplacian Center Gauge
fixing and their influence on confinement and chiral symmetry breaking is
investigated on a sample of SU(2) configurations at zero and finite
temperature.


title: Lattice QCD at Finite Temperature and Density

abstract:
  We review recent results on QCD at finite temperature and non-vanishing
baryon number density. We focus on observables which are of immediate interest
to experimental searches for the Quark Gluon Plasma, i.e. the phase transition
temperature, the equation of state in two and three flavour QCD and thermal
effects on hadron masses. Some new developments in finite density QCD are also
presented.


title: Fermion Cluster Algorithms

abstract:
  Cluster algorithms have been recently used to eliminate sign problems that
plague Monte-Carlo methods in a variety of systems. In particular such
algorithms can also be used to solve sign problems associated with the
permutation of fermion world lines. This solution leads to the possibility of
designing fermion cluster algorithms in certain cases. Using the example of
free non-relativistic fermions we discuss the ideas underlying the algorithm.


title: Test of the Kugo-Ojima Confinement Criterion in the Lattice Landau Gauge

abstract:
  We present the first results of numerical test of the Kugo-Ojima confinement
criterion in the lattice Landau gauge. The Kugo-Ojima criterion of colour
confinement in the BRS formulation of the continuum gauge theory is given by
$u_b^a(p^2)=-\delta_b^a$, where $u_b^a$ is defined by the two point function of
the Faddeev-Popov ghost fields $c, \bar c$ and the gauge field $A_\mu$. We
measured the lattice version of $u_b^a(0)$ in use of $1/(-\partial D(A))$ where
$D_\mu(A)$ is a lattice covariant derivative in the new definition of the gauge
fields as $U=e^A$. We obtained that $u_b^a(0)$ is consistent with
$-c\delta_b^a, c=0.7$ in SU(3) quenched simulation data of $\beta=5.5$ on $8^4$
and $12^4$. We report the $\beta$ dependence and finite-size effect of c.


title: Finite-Volume Scaling of the Quenched Chiral Condensate

abstract:
  In the large-volume limit $V\to\infty$ with $V << 1/m_{\pi}^4$ the
mass-dependent chiral condensate is predicted to satisfy exact finite-volume
scaling laws that fall into three major universality classes. We test these
analytical predictions with staggered fermions and overlap fermions in gauge
field sectors of fixed topological charge $\nu$.


title: Even flavor QED3 in an external magnetic field

abstract:
  The magnetically induced fermionic condensate is studied at zero and finite
temperatures. The effects of a non-homogeneous external magnetic fields is
briefly considered.


title:
Discretization effects and gauge independence for the electric and
  magnetic screening masses

abstract:
  We evaluate the electric and magnetic screening masses from the long-distance
behavior of the (temporal and spatial) gluon correlation functions, for pure
SU(2) gauge theory at finite temperature. In order to investigate the gauge
dependence of the screening masses we consider seven different gauges. We also
evaluate these masses using different definitions of the lattice gluon field,
corresponding to discretization errors of different orders.


title: Chiral Anomaly and Index Theorem on a finite lattice

abstract:
  The condition for a lattice Dirac operator D to reproduce correct chiral
anomaly at each site of a finite lattice for smooth background gauge fields is
that D possesses exact zero modes satisfying the Atiyah-Singer index theorem.
This is also the necessary condition for D to have correct fermion determinant
(ratio) which plays the important role of incorporating dynamical fermions in
the functional integral.


title:
Numerical evidence for Goldstone-mode effects in the three-dimensional
  O(4)-model

abstract:
  We investigate the three-dimensional O(4)-model on 24^3--96^3 lattices as a
function of the magnetic field H. Below the critical point, in the broken
phase, we confirm explicitly the H^{1/2} dependence of the magnetization and
the corresponding H^{-1/2} divergence of the longitudinal susceptibility, which
are predicted from the existence of Goldstone modes. At the critical point the
magnetization follows the expected finite-size-scaling behavior, with critical
exponent delta = 4.87(1).


title: Resummation of Cactus Diagrams in Lattice QCD, to all Orders

abstract:
  We show how to perform a resummation, to all orders in perturbation theory,
of a certain class of gauge invariant tadpole-like diagrams in Lattice QCD.
These diagrams are often largely responsible for lattice artifacts.
  Our resummation leads to an improved perturbative expansion. Applied to a
number of cases of interest, e.g. the lattice renormalization of some
two-fermion operators, this expansion yields results remarkably close to
corresponding nonperturbative estimates.
  We consider in our study both the Wilson and the clover action for fermions.


title: Folding and Design in Coarse-Grained Protein Models

abstract:
  Recent advances in coarse-grained lattice and off-lattice protein models are
reviewed. The sequence dependence of thermodynamical folding properties are
investigated and evidence for non-randomness of the binary sequences of good
folders are discussed. Similar patterns for non-randomness are found for real
proteins. Dynamical parameter MC methods, such as the tempering and
multisequence algorithms, are essential in order to obtain these results. Also,
a new MC method for design, the inverse of folding, is presented. Here, one
maximizes conditional probabilities rather than minimizing energies. By
construction, this method ensures that the designed sequences represent good
folders thermodynamically.


title: Nahm transformation on the lattice

abstract:
  The Nahm transformation is a duality mapping between self-dual Yang-Mills
configurations on the torus, which exchanges the number of colours with the
topological charge. We show how lattice gauge theory techniques can be used to
implement it numerically. The method is presented and its precision illustrated
with some applications.


title:
Looking for Effects of Topology in the Dirac Spectrum of Staggered
  Fermions

abstract:
  We classify SU(3) gauge field configurations in different topological sectors
by the smearing technique. In each sector we compute the distribution of low
lying eigenvalues of the staggered Dirac operator. In all sectors we find
perfect agreement with the predictions for the sector of topological charge
zero. The smallest Dirac operator eigenvalues of staggered fermions at
presently realistic lattice couplings are thus insensitive to gauge field
topology. On the smeared configurations, $4\nu$ eigenvalues go to zero in
agreement with the index theorem.


title: Topological properties of QCD with two dynamical fermions

abstract:
  We investigate the topological susceptibility of the QCD vacuum with two
flavours of dynamical staggered fermions on the lattice both at zero and finite
temperature. At zero temperature we study the dependence of the signal on the
fermion mass and at finite temperature we analyze the behaviour across the
phase transition.


title:
Four loop results for the 2D O(n) nonlinear sigma model with 0-loop and
  1-loop Symanzik actions

abstract:
  We present complete three loop results and preliminary four loop results for
the 2D O(n) nonlinear sigma model with 0-loop and 1-loop Symanzik improved
actions. This calculation aims to test the improvement in the numerical
precision that the combination of Symanzik actions and effective couplings can
give in Monte Carlo simulations.


title: Simulation of QCD and other similar theories

abstract:
  In QCD one can change the representation of the gauge group for quarks and/or
the gauge group itself. Examples of such generalizations are: (a)
supersymmetric Yang-Mills theory with gauge group SU(2) or SU(3); (b) QCD with
SU(2) colour and quarks in the adjoint representation; (c) QCD with three
equal-mass quarks. Experience and perspectives in simulations of these theories
by applying the two-step multi-bosonic algorithm is described. As an example of
an interesting physical problem in these theories the expected spontaneous
CP-violation in QCD with three equal-mass quarks is discussed.


title: Abelian hard thermal loops on a lattice

abstract:
  In Abelian theories, one can write for the hard thermal loop equations of
motions a local formulation that is more economical than the traditional Vlasov
formulation and is in explicitly canonical form. I show how this formulation
can be used for simulating non-equilibrium dynamics in the Abelian Higgs model.


title: Centre vortices and their friends

abstract:
  We report two probes of centre vortices in pure SU(2). First, we attempt to
generate plaquette-size Z(2) vortices in a quasi-random way to compare the
structure with those of projected centre vortices from the full theory; our
prescription is, however, not completely random. Second, we test the effect of
centre vortices on Wilson loops as a function of position. This shows clearly
that the major effect is the piercing of the Wilson loop regardless of the
position of the vortex inside.


title:
Potential between external monopole and antimonopole in SU(2) lattice
  glu odynamics

abstract:
  We present the results of a study of the free energy of a monopole pair in
pure
  SU(2) theory at finite temperature, both below and above the deconfinement
tran sition. We find a Yukawa potential between monopoles in both phases. At
low temp erature, the screening mass is compatible with the lightest glueball
mass. At hi gh temperature, we observe an increased screening mass with no
apparent disconti nuity at the phase transition.


title: Overlap Dirac Operator, Eigenvalues and Random Matrix Theory

abstract:
  The properties of the spectrum of the overlap Dirac operator and their
relation to random matrix theory are studied. In particular, the predictions
from chiral random matrix theory in topologically non-trivial gauge field
sectors are tested.


title:
The chiral limit of the two-flavor lattice Schwinger model with Wilson
  fermions

abstract:
  We study the 2-flavor lattice Schwinger model with Wilson fermions in the
chiral limit. The quark mass is determined using the PCAC definition. We
numerically compute the masses of the iso-triplet (pi) and iso-singlet
particles (eta) for different quark masses and compare our results with
analytical formulas.


title: Chiral symmetry breaking from Ginsparg-Wilson fermions

abstract:
  We calculate the large-volume and small-mass dependences of the quark
condensate in quenched QCD using Neuberger's operator. We find good agreement
with the predictions of quenched chiral perturbation theory, enabling a
determination of the chiral lagrangian parameter \Sigma, up to a multiplicative
renormalization.


title: Strongly coupled 't Hooft model on the lattice

abstract:
  A lattice strong coupling calculation of the spectrum and chiral condensate
of the 't Hooft model is presented. The agreement with the results of the
continuum theory is strikingly good even at the fourth order in the strong
coupling expansion.


title: U(1) Chiral Gauge Theory with Domain Wall Fermions and Gauge Fixing

abstract:
  We investigate a U(1) lattice chiral gauge theory with the waveguide
formulation of the domain wall fermions and with compact gauge fixing. In the
reduced model limit, there seems to be no mirror chiral modes at the waveguide
boundary.


title: Cooling, Physical Scales and the Vacuum Structure of Y-M Theories

abstract:
  We present a cooling method controlled by a physical cooling radius that
defines a scale below which fluctuations are smoothed out while leaving physics
unchanged at all larger scales. This method can be generally used as a gauge
invariant low pass filter to extract the physics from noisy MC configurations.
Here we apply this method to study topological properties of lattice gauge
theories where it allows to retain instanton--anti-instanton pairs.


title: Lattice QCD on a Beowulf Cluster

abstract:
  Using commodity component personal computers based on Alpha processor and
commodity network devices and a switch, we built an 8-node parallel computer.
GNU/Linux is chosen as an operating system and message passing libraries such
as PVM, LAM, and MPICH have been tested as a parallel programming environment.
We discuss our lattice QCD project for a heavy quark system on this computer.


title:
Differential equation for spectral flows of hermitean Wilson-Dirac
  operator

abstract:
  Establishing an exact relation for the derivative we show that the eigenvalue
flows of the hermitean Wilson-Dirac operator obey a differential equation. We
obtain a complete overview of the characteristic features of its solutions. The
underlying mathematical aspects are fully clarified.


title: Equivalent of a Thouless energy in lattice QCD Dirac spectra

abstract:
  Random matrix theory (RMT) is a powerful statistical tool to model spectral
fluctuations. In addition, RMT provides efficient means to separate different
scales in spectra. Recently RMT has found application in quantum chromodynamics
(QCD). In mesoscopic physics, the Thouless energy sets the universal scale for
which RMT applies. We try to identify the equivalent of a Thouless energy in
complete spectra of the QCD Dirac operator with staggered fermions and
$SU_c(2)$ lattice gauge fields. Comparing lattice data with RMT predictions we
find deviations which allow us to give an estimate for this scale.


title: Five Dimensional Dynamical Triangulations

abstract:
  The dynamical triangulations approach to quantum gravity is investigated in
detail for the first time in five dimensions. In this case, the most general
action that is linear in components of the f-vector has three terms. It was
suspected that the corresponding space of couplings would yield a rich phase
structure. This work is primarily motivated by the hope that this new viewpoint
will lead to a deeper understanding of dynamical triangulations in general.
Ultimately, this research programme may give a better insight into the
potential application of dynamical triangulations to quantum gravity. This
thesis serves as an exploratory study of this uncharted territory.
  The five dimensional (k,l) moves used in the Monte Carlo algorithm are proven
to be ergodic in the space of combinatorially equivalent simplicial
5-manifolds. A statement is reached regarding the possible existence of an
exponential upper bound on the number of combinatorially equivalent
triangulations of the 5-sphere. Monte Carlo simulations reveal non-trivial
phase structure which is analysed in some detail. Further investigations deal
with the geometric and fractal nature of triangulations. This is followed by a
characterisation of the weak coupling limit in terms of stacked spheres. Simple
graph theory arguments are used to reproduce and generalise a well-known result
in combinatorial topology. Finally, a comprehensive study of singular
structures in dynamical triangulations is presented. It includes a new
understanding of their existence, which appears to be consistent with the
non-existence of singular vertices in three dimensions. The thesis is concluded
with an overview of results, general discussion and suggestions for future
work.


title:
Topology in CP(N-1) models: a critical comparison of different cooling
  techniques

abstract:
  Various cooling methods, including a recently introduced one which smoothes
out only quantum fluctuations larger than a given threshold, are applied to the
study of topology in 2d CP(N-1) models. A critical comparison of their
properties is performed.


title: Gross-Neveu model with overlap fermions

abstract:
  We investigate the chiral properties of overlap lattice fermion by using two
dimensional Gross-Neveu model coupled with a gauge field. Chiral properties of
this model are similar to those of QCD$_4$, that is, the chiral symmetry is
spontaneously broken in the presence of small but finite fermion mass and also
there appears the chiral anomaly because of the coupling with the gauge field.
In order to respect L\"uscher's extended chiral symmetry we insert overlap
Dirac operator even in the interaction terms so that the whole action including
them are invariant under the extended chiral transformation at {\em finite
lattice spacing}, though the interaction terms become nonlocal. We calculate
mass of the quasi-Nambu-Goldstone boson as a function of the bare fermion mass
and two parameters in the overlap formalism, and find that the
quasi-Nambu-Goldstone boson has desired properties as a result of the extended
chiral symmetry. We furthermore examine the PCAC relation and find that it is
satisfied at {\em finite lattice spacing}. Relationship between the anomaly
term in the PCAC relation and the U(1) problem is also discussed.


title: Flavour-singlet pseudoscalar and scalar mesons

abstract:
  We measure correlations appropriate for favour-singlet mesons using dynamical
quark configurations from UKQCD. Improved methods of evaluating the
disconnected quark diagrams are presented. The scalar and pseudoscalar meson
channels are explored, with special reference to the mixing of scalar mesons
with scalar glueballs.


title: Further Evidence for an unstable H-Dibaryon?

abstract:
  We present preliminary results for the mass of the 6q flavor-singlet state
($J^P=0^+$, $S=-2$) called H-dibaryon, calculated in quenched QCD on $16^3$x30
and $24^3$x30 lattices with improved gauge and fermion actions (Symanzik
improvement, Clover action). For both lattice sizes we applied the fuzzing
technique to enhance the overlap with the ground state. We observe a H-mass
above the $\Lambda\Lambda$ threshold for strong decay. The difference in mass,
$m_H - 2m_\Lambda$, increases with increasing lattice size.


title: Exotic Quarkonia from Anisotropic Lattices

abstract:
  We study in detail the spectrum of heavy quarkonia with different orbital
angular momentum along with their radial and gluonic excitations. Using an
anisotropic formulation of Lattice QCD we achieved an unprecedented control
over statistical errors and were able to study systematic errors such as
lattice spacing artefacts, finite volume effects and relativistic corrections.
First results on the spin structure in heavy hybrids are also presented.


title:
Quark Masses and Renormalization Constants from Quark Propagator and
  3-point Functions

abstract:
  We have computed the light and strange quark masses and the renormalization
constants of the quark bilinear operators, by studying the large-p^2 behaviour
of the lattice quark propagator and 3-point functions. The calculation is
non-perturbatively improved, at O(a), in the chiral limit. The method used to
compute the quark masses has never been applied so far, and it does not require
an explicit determination of the quark mass renormalization constant.


title: Real-time dynamics in the 1+1 D abelian Higgs model with fermions

abstract:
  In approximate dynamical equations, inhomogenous classical (mean) gauge and
Higgs fields are coupled to quantized fermions. The equations are solved
numerically on a spacetime lattice. The fermions appear to equilibrate
according to the Fermi-Dirac distribution with time-dependent temperature and
chemical potential.


title: Matrix Elements without Quark Masses on the Lattice

abstract:
  We introduce a new parameterization of four-fermion matrix elements which
does not involve quark masses and thus allows a reduction of systematic
uncertainties in physical amplitudes. As a result the apparent quadratic
dependence of e'/e on m_s is removed. To simplify the matching between lattice
and continuum renormalization schemes, we express our results in terms of
Renormalization Group Invariant B-parameters which are renormalization-scheme
and scale independent. As an application of our proposal, matrix elements of
DeltaI=3/2 and SUSY DeltaF=2 ($F=S,C,B$) four-fermion operators have been
computed.


title: Chiral fermions on the lattice

abstract:
  Chiral fermions resisted being put on the lattice for twenty years. This
raised the suspicion that asymptotically free chiral gauge theories were not
renormalizable outside perturbation theory and therefore could not be
mathematically extended to infinite energies. During the last several years the
situation has reversed itself. Today we believe that all the essential
ingredients for a full lattice definition of non-anomalous chiral gauge
theories are in place within the overlap construction. This construction is
based on earlier work by Callan and Harvey, by Kaplan and by Frolov and
Slavnov. It can be reinterpreted as coming from the Ginsparg-Wilson relation,
but, at the moment, it is a unique construction and therefore might also be the
way by which Nature itself regularizes chiral fermions. This is yet another
instance in which lattice field theory makes a potentially important
contribution to fundamental particle physics.


title: Tricks to implement the overlap Dirac operator

abstract:
  I present several tricks to help implement the overlap Dirac operator
numerically.


title: Stochastic Split Determinant Algorithms

abstract:
  I propose a large class of stochastic Markov processes associated with
probability distributions analogous to that of lattice gauge theory with
dynamical fermions. The construction incorporates the idea of approximate
spectral split of the determinant through local loop action, and the idea of
treating the infrared part of the split through explicit diagonalizations. I
suggest that exact algorithms of practical relevance might be based on the
Markov processes so constructed.


title: Eta meson mass and topology in QCD with two light flavors

abstract:
  We present results for the mass of the flavor singlet meson calculated on
two-flavor full QCD configurations generated by the CP-PACS full QCD project.
We also investigate topological charge fluctuations and their dependence on the
sea quark mass.


title:
Prospects of `Topologically Unquenched QCD' from a study of the
  analogous importance sampling method in the massive Schwinger model

abstract:
  I give a quick summary of my proposal for simulating an improvement on
quenched QCD with dynamical fermions which interact with the gluon
configuration only via the topological index of the latter. It amounts to
include only the topological part of the functional determinant into the
measure, thereby absorbing a correction factor into the observable. I discuss
the prospects of this concept from a study in the massive $N_f$-flavour
Schwinger model, where the correction factor is indeed found to be of order
$O(1)$.


title: Theoretical Aspects of Topologically Unquenched QCD

abstract:
  I give an outline of my proposal to take the QCD functional determinant in
lattice simulations partially into account: The determinant is split into two
factors, the factor referring to a standard background in each topological
sector is kept exactly, the factor describing the effect of the smooth
deviation of the actual configuration from the reference background is replaced
by one. The issue of how to choose the reference configurations is discussed
and it is argued that ``topologically unquenched QCD'' is an interesting
starting point to study full QCD in lattice simulations as it gets the main
qualitative features right from the beginning.


title:
Perturbative renormalization factors of quark operators for domain-wall
  QCD

abstract:
  We calculate one-loop renormalization factors of several quark operators
including bilinear, three- and four-quark operator for domain-wall fermion
action. Since Green functions are constructed for external physical quark
fields, our renormalization method is simple and can be easily applied to
calculation of any quark operators. Our results show that these renormalized
quark operators preserve several chiral properties of continuum massless QCD,
which can be understood by the property of external quark line propagator.


title: Quenched QCD with domain-wall fermions on coarse lattices

abstract:
  We investigate the existence of chiral zero modes at a^{-1} \simeq 1 GeV in
quenched domain-wall QCD. Simulations are carried out for the plaquette and an
RG-improved gauge actions on a 12^3x24xN_s lattice with N_s=10-50. We find that
the pion mass in the chiral limit remains non-vanishing as N_s\to\infty for
both gauge actions. Possible origins of this non-vanishing pion mass are
discussed.


title:
Light hadron spectrum and quark masses in QCD with two flavors of
  dynamical quarks

abstract:
  We present updated results of the CP-PACS calculation of the light hadron
spectrum in $N_{\rm f}=2$ full QCD. Simulations are made with an RG-improved
gauge action and a tadpole-improved clover quark action for sea quark masses
corresponding to $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.6 and the lattice
spacing $a=0.22$--0.09 fm. A comparison of the full QCD spectrum with new
quenched results, obtained with the same improved action, shows clearly the
existence of sea quark effects in vector meson masses. Results for light quark
masses in $N_{\rm f}=2$ QCD are also presented.


title: Lattice chiral fermions in the background of non-trivial topology

abstract:
  We address the problem of numerical simulations in the background non-trivial
topology in the chiral Schwinger model. An effective fermionic action is
derived which is in accord with established analytical results, and which
satisfies the anomaly equation. We describe a numerical evaluation of baryon
number violating amplitudes, specifically the 't Hooft vertex.


title:
Heavy-light decay constants from clover heavy quark action in QCD with
  two flavors of dynamical quarks

abstract:
  We present results on an analysis of the decay constants f_B and f_Bs with
two flavours of sea quark. The calculation has been carried out on 3 different
bare gauge couplings and 4 sea quark masses at each gauge coupling, with
m_pi/m_rho ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform
calculations with heavy quarks whose mass is in the range of the b-quark. A
detailed comparison with a quenched calculation using the same action is made
to elucidate the effects due to the sea quarks.


title: A new mechanism of mass protection for fermions

abstract:
  We present a way of protecting a Dirac fermion interacting with a scalar
(Higgs) field from getting a mass from the vacuum. It is obtained through an
implementation of translational symmetry when the theory is formulated with a
momentum cutoff, which forbids the usual Yukawa term. We consider that this
mechanism can help to understand the smallness of neutrino masses without a
tuning of the Yukawa coupling. The prohibition of the Yukawa term for the
neutrino forbids at the same time a gauge coupling between the right-handed
electron and neutrino. We prove that this mechanism can be implemented on the
lattice.


title: Hard Thermal Loops and the Sphaleron Rate on the Lattice

abstract:
  We measure the sphaleron rate (topological susceptibility) of hot SU(2) gauge
theory, using a lattice implementation of the hard thermal loop (HTL) effective
action. The HTL degrees of freedom are implemented by an expansion in spherical
harmonics and truncation. Our results for the sphaleron rate agree with the
parametric prediction of Arnold, Son and Yaffe: Gamma ~ \alpha^5 T^4.


title:
Large rescaling of the Higgs condensate: theoretical motivations and
  lattice results

abstract:
  In the Standard Model the Fermi constant is associated with the vacuum
expectation value of the Higgs field, `the condensate', usually believed to be
a cutoff-independent quantity. General arguments related to the `triviality' of
$\Phi^4$ theory in 4 space-time dimensions suggest, however, a dramatic
renormalization effect in the continuum limit that is clearly visible on the
relatively large lattices available today. The result can be crucial for the
Higgs phenomenology and in any context where spontaneous symmetry breaking is
induced through scalar fields.


title: Abelian monopole condensation in lattice gauge theories

abstract:
  We investigate the dynamics of lattice gauge theories in an Abelian monopole
background field. By means of the gauge-invariant lattice Schrodinger
functional we study the Abelian monopole condensation in U(1) lattice gauge
theory at zero temperature and in SU(3) lattice gauge theory at finite
temperature.


title: Truncated Overlap Fermions

abstract:
  In this talk I propose a new computational scheme with overlap fermions and a
fast algorithm to invert the corresponding Dirac operator.


title: Fermion decoupling and the Axial Anomaly on the Lattice

abstract:
  In the axial Ward identity of lattice QED we show that in the limit of
infinite fermion mass m the pseudoscalar density term exactly cancels the
Adler-Bell-Jackiw anomaly. Using this result we calculate the U(1) axial
anomaly in a non-abelian gauge theory.


title:
Feasibility study of using the overlap-Dirac operator for hadron
  spectroscopy

abstract:
  We investigate a number of algorithms that calculate the quark propagators
for the overlap-Dirac fermion operator. The QCD simulations were performed at
beta = 5.9 with a lattice volume of 16**3*32.


title: Chiral Disorder in Two-Color QCD with Abelian External Fluxes

abstract:
  We investigate the effects of several Abelian external fluxes $\phi$, on the
Euclidean Dirac spectrum of light quarks in QCD with two colors. Our results
provide for a novel way of assessing the pion weak decay constant directly from
spectral fluctuations, and discriminating a flux-rich from a flux-poor vacuum,
using QCD lattice simulations.


title: Hadron Masses and Quark Condensate from Overlap Fermions

abstract:
  We present results on hadron masses and quark condensate from Neuberger's
overlap fermion. The scaling and chiral properties and finite volume effects
from this new Dirac operator are studied. We find that the generalized
Gell-Mann-Oakes-Renner relation is well satisfied down to the physical u and d
quark mass range. We find that in the range of the lattice spacing we consider,
the $\pi$ and $\rho$ masses at a fixed $m_{\pi}/m_{\rho}$ ratio have weak
$O(a^2)$ dependence.


title: Center Vortices, Instantons, and Confinement

abstract: We study the relation between center vortices and instantons in lattice QCD.


title:
Genetic Algorithm for Lattice Gauge Theory. on SU(2) and U(1) on 4
  dimensional lattice, how to hitchhike to thermal equilibrium state

abstract:
  Applying Genetic Algorithm for the Lattice Gauge Theory is formed to be an
effective method to minimize the action of gauge field on a lattice. In 4
dimensions, the critical point and the Wilson loop behaviour of SU(2) lattice
gauge theory as well as the phase transition of U(1) theory have been studied.
The proper coding methodi has been developed in order to avoid the increase of
necessary memory and the overload of calculation for Genetic Algorithm. How
hichhikers toward equlibrium appear against kidnappers is clarified.


title: Landau Gauge Fixing supported by Genetic Algorithm

abstract:
  A class of algorithms for the Landau gauge fixing is proposed, which makes
the steepest ascent (SA) method be more efficient by concepts of genetic
algorithm. Main concern is how to incorporate random gauge transformation (RGT)
%, mutation in genetic algorithm (GA) terminology, to gain higher achievement
of the minimal Landau gauge fixing, and to keep lower time consumption. One of
these algorithms uses the block RGT, and another uses RGT controlled by local
fitness density, and the last uses RGT determined by Ising Monte Carlo process.
We tested these algorithms on SU(2) lattice gauge theory in 4 dimension with
small $\beta$s, 2.0, 1.75 and 1.5, and report improvements in hit rate and/or
in time consumption, compared to other methods.


title:
Low energy effective action of domain-wall fermion and the
  Ginsparg-Wilson relation

abstract:
  We derive the effective action of the light fermion field of the domain-wall
fermion, which is referred as q(x) and \bar q(x) by Furman and Shamir. The
inverse of the effective Dirac operator turns out to be identical to the
inverse of the truncated overlap Dirac operator except a local contact term,
which would give the chiral symmetry breaking in the Ginsparg-Wilson relation.
We argue that there are direct relations between the low energy observables of
the domain-wall QCD and observables of the Ginsparg-Wilson fermion described by
the (truncated) overlap Dirac operator.


title:
UKQCD's latest results for the static quark potential and light hadron
  spectrum with O(a) improved dynamical fermions

abstract:
  We present UKQCD's latest results for the static quark potential and light
hadron spectrum obtained from matched simulations using two flavours of
dynamical quarks. We report that using matched ensembles helps disentangle
screening effects from discretisation errors in the static quark potential.


title: Hamiltonian LGT in the complete Fourier analysis basis

abstract:
  The main problem in the Hamiltonian formulation of Lattice Gauge Theories is
the determination of an appropriate basis avoiding the over-completeness
arising from Mandelstam relations. We short-cut this problem using Harmonic
analysis on Lie-Groups and intertwining operators formalism to explicitly
construct a basis of the Hilbert space. Our analysis is based only on
properties of the tensor category of Lie-Group representations. The Hamiltonian
of such theories is calculated yielding a sparse matrix whose spectrum and
eigenstates could be exactly derived as functions of the coupling $g^2$


title:
Gauge-invariant nonlocal quark condensates in QCD: a new interpretation
  of the lattice results

abstract:
  We study the asymptotic short-distance behaviour as well as the asymptotic
large-distance behaviour of the gauge-invariant quark-antiquark nonlocal
condensates in QCD. A comparison of some analytical results with the available
lattice data is performed.


title:
On $K\to\pi\pi$ Decays in Quenched and Unquenched Chiral Perturbation
  Theory

abstract:
  We calculate the logarithmic corrections to the matrix elements for
$K^+\to\pi^+$ and $K\to$vacuum (which are used on the lattice to determine
$K\to\pi\pi$ amplitudes), in one-loop quenched and unquenched Chiral
Perturbation Theory. We find that these corrections can be large. We also
discuss, and present some results for, the direct determination of $K\to\pi\pi$
amplitudes. In particular, we address effects from choosing $m_s=m_d$ and
vanishing external spatial momenta, finite volume and quenching. In the
quenched octet case, we find enhanced finite-volume contributions which may
make numerical estimates of this matrix element unreliable for large volumes.


title:
Numerical simulations of dynamical gluinos in SU(3) Yang-Mills theory:
  first results

abstract:
  In a numerical Monte Carlo simulation of SU(3) Yang-Mills theory with
dynamical gluinos we have investigated the behaviour of the expectation value
of the scalar and pseudoscalar gluino condensates in order to determine the
phase structure. Preliminary results are presented as a function of the hopping
parameter.


title: Low-energy features of SU(2) Yang-Mills theory with light gluinos

abstract:
  We report on the latest results of the low-lying spectrum of bound states in
SU(2) Yang-Mills theory with light gluinos. The behavior of the disconnected
contributions in the critical region is analyzed. A first investigation of a
three-gluino state is also discussed.


title: The topological susceptibility in `full' (UK)QCD

abstract:
  We report first calculations of the topological susceptibility measured using
the field theoretic method on SU(3) gauge configurations produced by the UKQCD
collaboration with two flavours of dynamical, improved, Wilson fermions. Using
three ensembles with matched lattice spacing but differing sea quark mass we
find that hybrid Monte Carlo simulation appears to explore the topological
sectors efficiently, and a topological susceptibility consistent with
increasing linearly with the quark mass.