title: Topology and pion correlators -- a study in the N_f=2 Schwinger model

abstract:
  I readdress the issue whether the topological charge of the gauge background
has an influence on a hadronic observable. To this end pion correlators in the
Schwinger model with 2 dynamical flavours are determined on subensembles with a
fixed topological charge. It turns out that the answer depends on a specific
function of the sea-quark mass and the box volume which is in close analogy to
the Leutwyler-Smilga parameter in full QCD.


title: Theta term instead of the Higgs field in Electroweak theory

abstract:
  We consider the electroweak theory without fundamental scalar field. The
topological excitation of the SU(2)*U(1) theory (the monopole) plays the role
of the Higgs field, it carries the SU(2)*U(1) topological charge due to the
theta--term of the special type.


title: The Microscopic Dirac Operator Spectrum

abstract:
  We review the exact results for microscopic Dirac operator spectra based on
either Random Matrix Theory, or, equivalently, chiral Lagrangians. Implications
for lattice calculations are discussed.


title:
Monopole fields from vortex sheets reconciling Abelian and center
  dominance

abstract:
  We describe a new order parameter for the confinement-deconfinement
transition in lattice SU(2) Yang-Mills theory. It is expressed in terms of
magnetic monopole field correlators represented as sums over sheets of center
vortices. Our construction establishes a link between "abelian" and "center
dominance". It avoids an inconsistency in the treatment of small scales present
in earlier definitions of monopole fields by respecting Dirac's quantization
condition for magnetic fluxes.


title:
The anti-B --> D* lepton anti-neutrino form factor at zero recoil and
  the determination of V(cb)

abstract:
  We summarize our lattice QCD study of the form factor at zero recoil in the
decay anti-B --> D* lepton anti-neutrino. After careful consideration of all
sources of systematic uncertainty, we find,
  h_A1(1) = 0.913(+0.024-0.017)(+0.017-0.030), where the first uncertainty is
from statistics and fitting while the second combined uncertainty is from all
other systematic effects.


title: Dynamical Fermions in Hamiltonian Lattice Gauge Theory

abstract:
  We describe a first attempt to understand dynamical fermions within a
Hamiltonian framework. As a testing ground we study compact QED3 which shares
some important features of QCD4 such as confinement, glueballs, mesons, and
chiral symmetry breaking. We discuss the methods used and show data for the
chiral condensate.


title:
The Maximal Abelian Gauge, Monopoles, and Vortices in SU(3) Lattice
  Gauge Theory

abstract:
  We report on calculations of the heavy quark potential in SU(3) lattice gauge
theory. Full SU(3) results are compared to three cases which involve
gauge-fixing and projection. All of these start from the maximal abelian gauge
(MAG), in its simplest form. The first case is abelian projection to U(1)xU(1).
The second keeps only the abelian fields of monopoles in the MAG. The third
involves an additional gauge-fixing to the indirect maximal center gauge
(IMCG), followed by center projection to Z(3). At one gauge
fixing/configuration, the string tensions calculated from MAG U(1)xU(1), MAG
monopoles, and IMCG Z(3) are all less than the full SU(3) string tension. The
projected string tensions further decrease, by approximately 10%, when account
is taken of gauge ambiguities. Comparison is made with corresponding results
for SU(2). It is emphasized that the formulation of the MAG is more subtle for
SU(3) than for SU(2), and that the low string tensions may be caused by the
simple MAG form used. A generalized MAG for SU(3) is formulated.


title: The APENEXT project

abstract:
  APENEXT is a new generation APE processor, optimized for LGT simulations. The
project follows the basic ideas of previous APE machines and develops simple
and cheap parallel systems with multi T-Flops processing power. This paper
describes the main features of this new development.


title:
A comparative study of numerical methods for the overlap Dirac
  operator--a status report

abstract:
  Improvements of various methods to compute the sign function of the hermitian
Wilson-Dirac matrix within the overlap operator are presented. An optimal
partial fraction expansion (PFE) based on a theorem of Zolotarev is given.
Benchmarks show that this PFE together with removal of converged systems within
a multi-shift CG appears to approximate the sign function times a vector most
efficiently. A posteriori error bounds are given.


title: Scalar condensate and light quark masses from overlap fermions

abstract:
  We have studied pseudoscalar correlation functions computed using the overlap
operator. Within the accuracy of our calculation we find that the quark mass
dependence agrees with the prediction of lowest-order Chiral Perturbation
Theory (ChPT) for quark masses in the range of m ~ m_s/2-2m_s. We present the
results of an analysis which assumes lowest-order ChPT to be valid to extract
the low-energy constants Sigma and f_P, as well as the strange quark mass.
Non-perturbative renormalization is implemented via a matching procedure with
data obtained using Wilson fermions in the Schroedinger functional set-up. We
find that the scalar condensate computed here agrees with the one obtained
previously through a finite-size scaling analysis.


title: PJLZ--gauge fixing approach in SU(2) lattice gauge theory

abstract:
  We study the SU(2) gauge theory with the interpolating gauge {\it a la}
Parrinello--Jona-Lasinio--Zwanziger (PJLZ) with the gauge fixing functional
$F=\sum_{x\mu} {1/2}\tr (U_{x\mu}\sigma_3U_{x\mu}^{\dagger}\sigma_3)$. We find
a strong indication of the non--analiticity with respect to the interpolating
parameter $\lambda$ at $\lambda_c \sim 0.8$.


title: The Schroedinger functional coupling in quenched QCD at low energies

abstract:
  Existing non-perturbative computations of the running coupling of quenched
QCD in the Schroedinger functional scheme are extended to scales mu lying much
deeper in the low-energy regime. We are able to reach 1/mu ~ 0.9 fm, where a
significant deviation from its perturbative evolution is observed.


title: Nonstandard Cutoff Effects in the Nonlinear Sigma Model

abstract:
  High precision measurements of the renormalized zero-momentum 4-point
coupling g_R and of the Luscher-Weisz-Wolff running coupling gbar(L) = L*m(L)
performed with two different lattice actions in the non-perturbative region
confirm the earlier observations, that the cutoff effects look linear, in
contrast to perturbative considerations. The use of different actions allows
one to make a more reliable estimate on the continuum limit. The measurements
were done for infinite volume correlation length up to 350.


title:
Numerical Quantum Field Theory on the Continuum and a New Look at
  Perturbation Theory

abstract:
  The Source Galerkin method finds approximate solutions to the functional
differential equations of field theories in the presence of external sources.
While developing this process, it was recognized that approximations of the
spectral representations of the Green's functions by Sinc function expansions
are an extremely powerful calculative tool. Specifically, this understanding
makes it not only possible to apply the Source Galerkin method to higher
dimensional field theories, but also leads to a new approach to perturbation
theory calculations in scalar and fermionic field theories. This report
summarizes the methodologies for solving quantum field theories with the Source
Galerkin method and for performing perturbation theory calculations using Sinc
approximations.


title:
Study of spatial meson correlators at finite temperature in quenched
  anisotropic lattice QCD

abstract:
  We analyze the meson correlator in the spatial direction at finite
temperature. To achieve fine resolution in the spatial direction, we use an
anisotropic lattice with the standard Wilson plaquette gauge action and the
$O(a)$ improved Wilson quark action. Below and above $T_c$, properties of
correlators are investigated by two methods: fits with ansatz for the spectral
function, and direct reconstruction of the spectral function using the maximum
entropy method.


title: Generalized ensemble algorithm for U(1) gauge theory

abstract:
  Hybrid Monte Carlo simulations of the pure compact U(1) gauge theory are
performed with the Tsallis weight. The simulations show that the use of the
Tsallis weight enhances the tunneling rate between metastable states.


title: $K\to\pi\pi$ matrix elements beyond the leading-order chiral expansion

abstract:
  We propose an approach for calculating $K\to\pi\pi$ decays to the
next-to-leading order in chiral expansion. A detailed numerical study of this
approach is being performed.


title: Relativistic bottomonium spectrum from anisotropic lattices

abstract:
  We report on our results from a fully relativistic simulation of the quenched
bottomonium spectrum. Using an anisotropic formulation of Lattice QCD, we were
able to retain a very fine resolution into the temporal direction for a range
of different lattice spacings. At fixed renormalized anisotropy we study the
scaling properties of the spectrum and compare our results with
non-relativistic calculations.


title: A Lattice Calculation of Thermal Dilepton Rates

abstract:
  Using clover improved Wilson fermions we calculate thermal vector meson
correlation functions above the deconfinement phase transition of quenched QCD.
At temperatures 1.5 Tc and 3Tc they are found to differ by less than 15% from
that of a freely propagating quark anti-quark pair. This puts severe
constraints on the dilepton production rate and in particular rules out a
strong divergence of the dilepton rate at low energies. The vector spectral
function, which has been reconstructed using the Maximum Entropy Method, yields
an enhancement of the dilepton rate over the Born rate of at most a factor two
in the energy interval 4 < E/T < 8 and suggests that the spectrum is cut-off at
low energies by a thermal mass threshold of about (2-3)T.


title: Continuum limit in abelian projected SU(2) lattice gauge theory

abstract:
  We study the continuum limit of the abelian string tension and the density of
abelian monopoles calculated after carefully fixing the maximal abelian gauge
by employing the simulated annealing algorithm. We present the evidence that
the abelian string tension converges to the nonabelian one in the continuum
limit. For the monopole density we confirm earlier findings that the density of
the properly defined infrared monopoles has correct scaling while the total
density seems divergent in the continuum limit due to ultraviolate
contributions. We also compare with results obtained with the usual iterative
gauge fixing algorithm.


title:
Separating perturbative and non-perturbative contributions to the
  plaquette

abstract:
  We try to separate the perturbative and non-perturbative contributions to the
plaquette of pure SU(3) gauge theory. To do this we look at the large-n
asymptotic behaviour of the perturbation series in order to estimate the
contribution of the as-yet uncalculated terms in the series. We find no
evidence for the previously reported Lambda^2 contribution to the gluon
condensate. Attempting to determine the conventional Lambda^4 condensate gives
a value of approximately 0.03(2) GeV^4, in reasonable agreement with sum rule
estimates, though with very large uncertainties.


title: The three-loop beta-fuction of QCD with the clover action

abstract:
  We calculate, to 3 loops in perturbation theory, the bare $\beta$-function of
QCD, formulated on the lattice with the clover fermionic action. The dependence
of our result on the number of colors $N$, the number of fermionic flavors
$N_f$, as well as the clover parameter $c_{SW}$, is shown explicitly.
  A direct outcome of our calculation is the two-loop relation between the bare
coupling constant $g_0$ and the one renormalized in the MS-bar scheme.
  Further, we can immediately derive the three-loop correction to the relation
between the lattice $\Lambda$-parameter and $g_0$, which is important in checks
of asymptotic scaling. For typical values of $c_{SW}$, this correction is found
to be very pronounced.


title: Classical solutions with nontrivial holonomy in SU(2) LGT at T \ne 0

abstract:
  We generate SU(2) lattice gauge fields at finite temperature and cool them in
order to characterize the two phases by the occurrence of specific classical
solutions.We apply two kinds of spatial boundary conditions: fixed holonomy and
standard periodic b.c. For T < T_c our findings concerning classical
configurations semi-quantitatively agree for both types of boundary conditions.
We find in the confinement phase a mixture of undissociated calorons with lumps
of positive or negative half-integer topological charges.


title: Testing Asymptotic Scaling and Nonabelian Symmetry Enhancement

abstract:
  We determine some points on the finite size scaling curve for the correlation
length in the two dimensional O(3) and icosahedron spin models. The Monte Carlo
data are consistent with the two models possessing the same continuum limit.
The data also suggest that the continuum scaling curve lies above the estimate
of Kim and of Caracciolo et al and thus leads to larger thermodynamic values of
of the correlation length than previously reported.


title: Test of the Polyakov Loop Model

abstract:
  We discuss the two point functions for the real and imaginary parts of the
Polyakov loop in a pure SU(3) gauge theory. The behavior of these correlation
functions in the Polyakov Loop Model is markedly different from that in
perturbation theory.


title: From Spin Ladders to the 2-d O(3) Model at Non-Zero Density

abstract:
  The numerical simulation of various field theories at non-zero chemical
potential suffers from severe complex action problems. In particular, QCD at
non-zero quark density can presently not be simulated for that reason. A
similar complex action problem arises in the 2-d O(3) model -- a toy model for
QCD. Here we construct the 2-d O(3) model at non-zero density via dimensional
reduction of an antiferromagnetic quantum spin ladder in a magnetic field. The
complex action problem of the 2-d O(3) model manifests itself as a sign problem
of the ladder system. This sign problem is solved completely with a
meron-cluster algorithm.


title: Hadron Masses From Novel Fat-Link Fermion Actions

abstract:
  The hadron mass spectrum is calculated in lattice QCD using a novel fat-link
clover fermion action in which only the irrelevant operators in the fermion
action are constructed using smeared links. The simulations are performed on a
16^3 x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with
n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link
Irrelevant Clover (FLIC) action provides scaling which is superior to
mean-field improvement, and offers advantages over nonperturbative 0(a)
improvement, including a reduced exceptional configuration problem.


title:
Nonperturbative Lattice Simulation of High Multiplicity Cross Section
  Bound in $\phi^4_3$ on Beowulf Supercomputer

abstract:
  In this thesis, we have investigated the possibility of large cross sections
at large multiplicity in weakly coupled three dimensional $\phi^4$ theory using
Monte Carlo Simulation methods. We have built a Beowulf Supercomputer for this
purpose. We use spectral function sum rules to derive a bound on the total
cross section where the quantity determining the bound can be measured by Monte
Carlo simulation in Euclidean space. We determine the critical threshold energy
for large high multiplicity cross section according to the analysis of M.B.
Volosion and E.N. Argyres, R.M.P. Kleiss, and C.G. Papadopoulos. We compare the
simulation results with the perturbation results and see no evidence for large
cross section in the range where tree diagram estimates suggest they should
exist.


title: Ginsparg-Wilson fermions: practical aspects and applications

abstract:
  I review recent progress in the implementation of lattice fermions satisfying
the Ginsparg-Wilson relation and some physical applications.


title: Screening Masses in Dimensionally Reduced (2+1)D Gauge Theory

abstract:
  We discuss the screening masses and residue factorisation of the SU(3) (2+1)D
theory in the dimensional reduction formalism. The phase structure of the
reduced model is also investigated.


title: Pion Decay Constant, $Z_A$ and Chiral Log from Overlap Fermions

abstract:
  We report our calculation of the pion decay constant $f_\pi$, the axial
renormalization constant $Z_A$, and the quenched chiral logarithms from the
overlap fermions. The calculation is done on a quenched $20^4$ lattice at
$a=0.148$ fm using tree level tadpole improved gauge action. The smallest pion
mass we reach is about 280 MeV. The lattice size is about 4 times the Compton
wavelength of the lowest mass pion.


title: Discrete non-Abelian groups and asymptotically free models

abstract:
  We consider a two-dimensional $\sigma$-model with discrete
icosahedral/dodecahedral symmetry. Using the perturbative renormalization
group, we argue that this model has a different continuum limit with respect to
the O(3) $\sigma$ model. Such an argument is confirmed by a high-precision
numerical simulation.


title: Quantum Chaos in Physical Systems: from Super Conductors to Quarks

abstract:
  This article is the written version of a talk delivered at the Bexbach
Colloquium of Science 2000 and starts with an introduction into quantum chaos
and its relationship to classical chaos. The Bohigas-Giannoni-Schmit conjecture
is formulated and evaluated within random-matrix theory. Several examples of
physical systems exhibiting quantum chaos ranging from nuclear to solid state
physics are presented. The presentation concludes with recent research work on
quantum chromodynamics and the quark-gluon plasma. In the case of a chemical
potential the eigenvalue spectrum becomes complex and one has to deal with
non-Hermitian random-matrix theory.


title: Screening mass responses to the chemical potential at finite temperature

abstract:
  Responses to chemical potential of the pseudoscalar meson screening mass and
the chiral condensate in lattice QCD are investigated. On a $16 \times 8^2
\times \4$ lattice with two flavors of staggered quarks the first and second
responses below and above $T_c$ are evaluated. Different behavior in the low
and the high temperature phases are observed, which may be explained as a
consequence of the chiral symmetry breaking and restoration.


title: Schr\"odinger functional at N_f=-2

abstract:
  We study the Schr\"odinger functional coupling for lattice Yang-Mills theory
coupled to an improved bosonic spinor field, which corresponds to QCD with
minus two light flavors. This theory serves as a less costly testcase than QCD
for the scaling of the coupling.


title:
O(a) improved QCD: The 3-loop beta-function, and the critical hopping
  parameter

abstract:
  We calculate the 3-loop bare $\beta$-function of QCD, formulated on the
lattice with the clover fermionic action. The dependence of our result on the
number of colors $N$, the number of fermionic flavors $N_f$, and the clover
parameter $c_{SW}$, is shown explicitly. A direct outcome of our calculation is
the two-loop relation between the bare coupling constant $g_0$ and the one
renormalized in the MS-bar scheme. Further, we can immediately derive the
three-loop correction to the relation between the lattice $\Lambda$-parameter
and $g_0$, which turns out to be very pronounced.
  We also calculate the critical value of the hopping parameter, $\kappa_c$, in
the clover action, to two loops in perturbation theory. This quantity is an
additive renormalization; as such, it exhibits a linear divergence in the
lattice spacing. We compare our results to non perturbative evaluations of
$\kappa_c$ coming from MC simulations.


title: Vector condensation in QCD

abstract:
  The response of the QCD vacuum to quark chemical potentials on the order of
the pion mass is studied within the context of chiral perturbation theory. For
two colour QCD diquark condensation sets in when the baryon chemical potential
becomes larger than the pion mass. This leading order result is confirmed at
next to leading order. Next a set of massive spin-one vectors is included in
the effective Lagrangian and the vector masses are calculated at leading order.
Massless vector modes appear when the baryon chemical potential is equal to the
mass of the lightest vector at zero chemical potential. This suggest vector
condensation.


title: Scaling behavior of improvement and renormalization constants

abstract:
  This talk summarizes results for all the scale independent renormalization
constants for bilinear currents ($Z_A$, $Z_V$, and $Z_S/Z_P$), the improvement
constants ($c_A$, $c_V$, and $c_T$), the quark mass dependence of $Z_O$, and
the coefficients of the equation of motion operators for $O(a)$ improved
lattice QCD. Using data at $\beta=6.0$, 6.2 and 6.4 we study the scaling
behavior of these quantities and quantify residual discretization errors.


title: Renormalization constants using quark states in Landau gauge

abstract:
  We show that given one O(a) improvement constant, b_m, all the remaining
quantities needed to define the renormalized and O(a) improved dimension-3
quark bilinears can be obtained by studying the matrix elements of these
operators between external quark states in a fixed gauge.


title:
Chiral perturbation theory, dispersion relations and final state
  interactions in K -> pi pi

abstract:
  We discuss the recent literature on the treatment of final state interactions
in K -> pi pi. Various approaches are compared and particular emphasis is given
to the possibility of combining dispersive methods with lattice input. Recent
results on the dependence of various quantities on the quark masses at order
p^6 in the chiral expansion are presented and the relevance for the lattice
calculations is discussed.


title: Weak matrix elements for CP violation

abstract:
  We present preliminary results of matrix elements of four-fermion operators
relevant to the determination of e and e'/e using staggered fermions.


title: Light hadron spectrum and quark masses

abstract:
  Recent developments in lattice QCD calculations of the light hadron spectrum
and quark masses are reviewed.


title:
The strong coupling constant from lattice QCD with N_f=2 dynamical
  quarks

abstract:
  We compute $\Lambda_{\bar{MS}}$ for two flavors of light dynamical quarks
using non-perturbatively $O(a)$ improved Wilson fermions. We improve on a
recent calculation by employing Pad\'e-improved two-loop and three-loop
perturbation theory to convert the lattice numbers to the $\bar{MS}$ scheme.


title: Free fermionic propagators on a lattice

abstract:
  A method used recently to obtain a formalism for classical fields with
non-local actions preserving chiral symmetry and uniqueness of fermion fields
yields a discrete version of Huygens' principle with free discrete propagators
that recover their continuum forms in certain limit.


title: The supersymmetric Ward identities on the lattice

abstract:
  Supersymmetric (SUSY) Ward identities are considered for the N=1 SU(2) SUSY
Yang Mills theory discretized on the lattice with Wilson fermions (gluinos).
They are used in order to compute non-perturbatively a subtracted gluino mass
and the mixing coefficient of the SUSY current. The computations were performed
at gauge coupling $\beta$=2.3 and hopping parameter $\kappa$=0.1925, 0.194,
0.1955 using the two-step multi-bosonic dynamical-fermion algorithm. Our
results are consistent with a scenario where the Ward identities are satisfied
up to O(a) effects. The vanishing of the gluino mass occurs at a value of the
hopping parameter which is not fully consistent with the estimate based on the
chiral phase transition. This suggests that, although SUSY restoration appears
to occur close to the continuum limit of the lattice theory, the results are
still affected by significant systematic effects.


title: Topology and Low Lying Fermion Modes

abstract:
  Recent results concerning the relation of topology and low-lying fermion
modes are summarized.


title: Heavy quark physics from lattice QCD

abstract:
  I review the current status of lattice calculations of heavy quark
quantities. Particular emphasis is placed on leptonic and semileptonic decay
matrix elements.


title: Searching for dynamical fermion effects in UKQCD simulations

abstract:
  We present recent results from the UKQCD collaboration's dynamical QCD
simulations. This data has fixed lattice spacing but varying dynamical quark
mass. We concentrate on searching for an unquenching signal in the mesonic mass
spectrum where we do not find a significant effect at the quark masses
considered.


title:
Progress towards a lattice determination of (moments of) nucleon
  structure functions

abstract:
  Using unimproved and non-perturbatively O(a) improved Wilson fermions,
results are given for the three lowest moments of unpolarised nucleon structure
functions. Renormalisation, chiral extrapolation and the continuum limit of the
matrix elements are briefly discussed. The simulations are performed for both
quenched and two flavours of unquenched fermions. No obvious sign of deviation
from linearity in the chiral extrapolations are found. (This is most clearly
seen in our quenched unimproved data, which extends to lighter quark mass.)
Possible quenching effects also seem to be small. The lowest moment thus
remains too large, so it seems to be necessary to reach smaller quark masses in
numerical simulations.


title:
Study of 3-flavor QCD Finite Temperature Phase Transition with Staggered
  Fermions

abstract:
  We have studied the 3-flavor, finite temperature, QCD phase transition with
staggred fermions on an $ N_t=4$ lattice. By studying a variety of quark masses
we have located the critical point, $m_c$, where the first order 3-flavor
transition ends as lying in the region $0.32 \le m_c \le 0.35$ in lattice units


title:
Physics development of web-based tools for use in hardware clusters
  doing lattice physics

abstract:
  Jefferson Lab and MIT are developing a set of web-based tools within the
Lattice Hadron Physics Collaboration to allow lattice QCD theorists to treat
the computational facilities located at the two sites as a single
meta-facility. The prototype Lattice Portal provides researchers the ability to
submit jobs to the cluster, browse data caches, and transfer files between
cache and off-line storage. The user can view the configuration of the PBS
servers and to monitor both the status of all batch queues as well as the jobs
in each queue. Work is starting on expanding the present system to include job
submissions at the meta-facility level (shared queue), as well as multi-site
file transfers and enhanced policy-based data management capabilities.


title: Dynamical fermion algorithm for variable actions

abstract:
  A new version of the two-step multi-boson algorithm is developed with
different fermion actions in the multi-boson and noisy Metropolis steps.


title: Functional Forms for Lattice Correlators at Small Times

abstract:
  The analytic form of the lattice quark propagator is used to derive the
functional form for short distance mesonic correlators. These are then used to
calculate ``Continuum Model'' Ansatze which comprise of a pole, representing
the ground state, plus a contribution for the excited states, coming from the
short distance behaviour. These are compared to Monte Carlo data.


title: Dynamical suppression of large instantons

abstract:
  We investigate the distribution of instanton sizes in the framework of a
simplified model for ensembles of instantons. This model takes into account the
non-diluteness of instantons. The infrared problem for the integration over
instanton sizes is dealt with in a self-consistent manner by approximating
instanton interactions by a repulsive hard core potential. This leads to a
dynamical suppression of large instantons. The characteristic features of the
instanton size distribution are studied by means of analytic and Monte Carlo
methods. We find a power law behaviour for small sizes, consistent with the
semi-classical results. At large instanton sizes the distribution decays
exponentially. The results are compared with those from lattice simulations.


title: Glueball and gluelump spectrum in abelian projected QCD

abstract:
  We study glueball and gluelump spectra calculated after abelian projection in
both quenched and $N_f=2$ full QCD. The abelian projection is made after MA
gauge fixing. We demonstrate that both spectra can be recovered despite the
problem with positivity. We suggest the interpretation of some of the gluelump
states in the language of the abelian projected theory.


title: The Relationship of the Laplacian Gauge to the Landau Gauge

abstract:
  The Laplacian gauge for gauge group SU(N) is discussed in perturbation
theory. It is shown that to the lowest non-trivial order, O(g^1),
configurations in the Laplacian gauge automatically satisfy the (finite
difference) Landau gauge condition. Laplacian gauge fixed configurations are
examined numerically and it is seen that to O(g^2) they do not remain in the
Landau gauge.


title: Connection between Tomboulis vortices and projection vortices

abstract:
  By using the freedom of picking a representative we explore connections
between the Tomboulis SO(3)xZ(2) form of the partition function and the SU(2)
form. We are able to express the monopole and vortex observables of the former
in terms of configurations of the latter. Also we can measure Tomboulis and
projection vortex counters on the same configuration to search for
correlations.


title: Towards the topological susceptibility with overlap fermions

abstract:
  Using a reweighting technique combined with a low-mode truncation of the
fermionic determinant, we estimate the quark-mass dependence of the QCD
topological susceptibility with overlap fermions. In contrast to previous
lattice simulations which all used non-chiral fermions, our results appear to
be consistent with the simple continuum model of D\"urr. This indicates that at
current lattice spacings the use of the index theorem might not be justified
and the fermionic definition of the charge might be needed.


title:
Multi-Layer Structure in the Strongly Five Dimensional Abelian Higgs
  Model

abstract:
  We explore the phase diagram of the 5--D anisotropic Abelian Higgs model by
Monte Carlo simulations. In particular, we study the transition between the
confining phase and the four dimensional layered Higgs phase. We find that, in
a certain region of the lattice parameter space, this transition can be first
order and that each layer moves into the Higgs phase independently of the
others (decoupling of layers).


title: Lattice 2001: Reflections

abstract:
  A few subjects which strongly intertwine our field are discussed: K --> Pi Pi
decay, chiral symmetry on the lattice and a few other selected topics. Open
questions are touched also on perturbation theory, locality, Gribov copies, CP
symmetry in chiral gauge theories and cut-off effects.


title: Composite reweighting SU(2) QCD at Finite Temperature

abstract:
  The Glasgow reweighting method is evaluated for SU(2) lattice gauge theory at
nonzero \mu and finite T. We establish that the ' overlap problem' of SU(3)
measurements, in which the transition points determined from thermodynamic
observables have an unphysical dependence on the value of \mu used in the
reweighting persists for SU(2). By combining the information from different
lattice ensembles we alleviate sampling bias in the fugacity expansion, and
identify the Lee-Yang zeros associated with the transition to a high density
phase that can plausibly be associated with diquark condensation. We also
confirm the existence of a line of first order transitions above a critical
point in the T-\mu plane previously identified by effective chiral lagrangian
calculations.


title: Relativistic heavy quarks on the lattice

abstract:
  We investigate feasibility of relativistic approaches to the heavy quark
physics on both anisotropic and isotropic lattices. Our peturbative calculation
reveals that the anisotropic lattice is not theoretically adovantageous over
the isotropic one to control $m_Q a$ errors. We instead propose a new
relativistic approach to handle heavy quarks on the isotropic lattice.


title: Alternative to Domain Wall Fermions

abstract:
  An alternative to commonly used domain wall fermions is presented. Some
rigorous bounds on the condition number of the associated linear problem are
derived. On the basis of these bounds and some experimentation it is argued
that domain wall fermions will in general be associated with a condition number
that is of the same order of magnitude as the {\it product} of the condition
number of the linear problem in the physical dimensions by the inverse bare
quark mass. Thus, the computational cost of implementing true domain wall
fermions using a single conjugate gradient algorithm is of the same order of
magnitude as that of implementing the overlap Dirac operator directly using two
nested conjugate gradient algorithms. At a cost of about a factor of two in
operation count it is possible to make the memory usage of direct
implementations of the overlap Dirac operator independent of the accuracy of
the approximation to the sign function and of the same order as that of
standard Wilson fermions.


title: Fast evaluation and locality of overlap fermions

abstract:
  In order to construct improved overlap fermions, we start from a short ranged
approximate Ginsparg-Wilson fermion and insert it into the overlap formula. We
show that its polynomial evaluation is accelerated considerably compared to the
standard Neuberger fermion. In addition the degree of locality is strongly
improved.


title:
Perturbative expansions from Monte Carlo simulations at weak coupling:
  Wilson loops and the static-quark self-energy

abstract:
  Perturbative coefficients for Wilson loops and the static-quark self-energy
are extracted from Monte Carlo simulations at weak coupling. The lattice
volumes and couplings are chosen to ensure that the lattice momenta are all
perturbative. Twisted boundary conditions are used to eliminate the effects of
lattice zero modes and to suppress nonperturbative finite-volume effects due to
Z(3) phases. Simulations of the Wilson gluon action are done with both periodic
and twisted boundary conditions, and over a wide range of lattice volumes (from
$3^4$ to $16^4$) and couplings (from $\beta \approx 9$ to $\beta \approx 60$).
A high precision comparison is made between the simulation data and results
from finite-volume lattice perturbation theory. The Monte Carlo results are
shown to be in excellent agreement with perturbation theory through second
order. New results for third-order coefficients for a number of Wilson loops
and the static-quark self-energy are reported.


title:
Low-lying eigenmodes of the Wilson-Dirac operator and correlations with
  topological objects

abstract:
  The probability density of low-lying eigenvectors of the hermitian
Wilson-Dirac operator is examined. Comparisons in position and size between
eigenvectors, topological charge and action density are made. We do this for
standard Monte-Carlo generated SU(3) background fields and for single instanton
background fields. Both hot and cooled SU(3) background fields are considered.
An instanton model is fitted to eigenmodes and topological charge density and
the sizes and positions of these are compared.


title: Low-lying fermion modes of Nf=2 improved Wilson fermions

abstract:
  We present preliminary results for the topological charge and susceptibility
determined from the low-lying eigenmodes of the Wilson-Dirac operator. These
modes have been computed on dynamical configurations with Nf=2
non-perturbatively improved Wilson fermions. We compare our results with the
eigenmodes of fermions in the quenched approximation.


title:
Performance studies of the two-step multiboson algorithm in compact
  lattice QED

abstract:
  The performance of the two-step multiboson (TSMB) algorithm is investigated
in comparison with the hybrid Monte Carlo (HMC) method for compact lattice QED
with standard Wilson fermions both in the Coulomb and confinement phases. The
restriction to QED allows for extensive measurements of autocorrelation times.
Preliminary results show that the TSMB algorithm is at least competitive with
standard HMC.


title: Study of the SU(2) High Density System with Wilson Fermion

abstract:
  We investigate high density state of SU(2) QCD in the case of the Wilson
fermions with Iwasaki improved action. Based on the Woodbery formula, the ratio
of fermion determinants is evaluated at each step of the Metropolis link
update. At $\beta=0.7$, for $\kappa = 0.150$, and $\kappa = 0.175$, we
calculate thermodynamical quantities, such as, baryon number density, Polyakov
line, and the energy density of gluon sector with chemical potential $\mu$=0 to
0.9 on the $4^{3} \times 8$ lattice. The susceptibility of the Polyakov line to
the chemical potential shows peak at around $\mu = 0.7$ which indicates the
deconfinement phase transition. Behavior of the meson and diquark propagators
with finite chemical potential are also investigated at both side of the peak.


title: Finite Volume Effects in Weak Hadronic Decays

abstract:
  In this talk we discuss finite-volume computations of two-body hadronic
decays below the inelastic threshold (e.g. $K\to\pi\pi$ decays). In particular
we show how the relation between finite-volume matrix elements and physical
amplitudes, recently derived by Lellouch and L\"uscher, can be extended to all
elastic states under the inelastic threshold. We also provide a derivation of
the L\"uscher quantization condition directly in quantum field theory.


title: Towards the lattice study of M-theory (II)

abstract:
  We present new results of the quenched simulations of the reduced D=4
supersymmetric Yang - Mills quantum mechanics for larger gauge groups SU(N),
2<N<9. The model, studied at finite temperature, reveals existence of the two
distinct regions which may be precursors of a black hole and the elementary D0
branes phases of M-theory conjectured in the literature. Present results for
higher groups confirm the picture found already for N=2. Similar behaviour is
observed in the preliminary simulations for the D=6 and D=10 models.


title: Analytic progress on exact lattice chiral symmetry

abstract:
  Theoretical issues of exact chiral symmetry on the lattice are discussed and
related recent works are reviewed. For chiral theories, the construction with
exact gauge invariance is reconsidered from the point of view of domain wall
fermion. The issue in the construction of electroweak theory is also discussed.
For vector-like theories, we discuss unitarity (positivity), Hamiltonian
approach, and several generalizations of the Ginsparg-Wilson relation
(algebraic and odd-dimensional).


title: On the lattice construction of electroweak gauge theory

abstract:
  Based on the Ginsparg-Wilson relation, a gauge invariant formulation of
electroweak SU(2)xU(1) gauge theory on the lattice is considered. If the
hypercharge gauge coupling is turned off in the vacuum sector of the U(1) gauge
fields, the theory consists of four left-handed SU(2) doublets and it is
possible, as in vector-like theories, to make the fermion measure defined
globally in all topological sectors of SU(2). We then try to incorporate U(1)
gauge field, following L\"uscher's reconstruction theorem. The global
integrability condition is proved for ``gauge loops'' in the space of the U(1)
gauge fields with arbitrary SU(2) gauge field fixed in the background. For
``non-gauge loops'', however, the proof is given so far only for the classical
SU(2) instanton backgrounds.


title: Effective Theories of Confinement

abstract:
  We review some approaches to describe confinement in terms of effective
(model) field theories. After a brief discussion of the dual Abelian Higgs
model, we concentrate on a lattice analysis of the Faddeev-Niemi effective
action conjectured to describe the low-lying excitations of SU(2) gluodynamics.
We generalize the effective action such that it contains all operators built
from a unit color vector field n with O(3) symmetry and maximally four
derivatives. To avoid the presence of Goldstone bosons, we include explicit
symmetry breaking terms parametrized by an external field h of mass-dimension
two. We find a mass gap of the order of 1.5 GeV.


title: Parallel tempering in full QCD with Wilson fermions

abstract:
  We study the performance of QCD simulations with dynamical Wilson fermions by
combining the Hybrid Monte Carlo algorithm with parallel tempering on $10^4$
and $12^4$ lattices. In order to compare tempered with standard simulations,
covariance matrices between sub-ensembles have to be formulated and evaluated
using the general properties of autocorrelations of the parallel tempering
algorithm. We find that rendering the hopping parameter $\kappa$ dynamical does
not lead to an essential improvement. We point out possible reasons for this
observation and discuss more suitable ways of applying parallel tempering to
QCD.


title: Color-Flavor Transformation for the Special Unitary Group

abstract:
  We extend Zirnbauer's color-flavor transformation in the fermionic sector to
the case of the special unitary group. The transformation allows a certain
integral over SU(N_c) color matrices to be transformed into an integral over
flavor matrices which parameterize the coset space U(2N_f)/U(N_f)xU(N_f).
Integrals of the type considered appear, for example, in the partition function
of lattice gauge theory.


title: Zero temperature phase structure of multi-flavor QCD

abstract:
  To study continuum limit of lattice QCD with many light quark flavors, we
investigate the zero temperature phase structures of multi-flavor QCD.
Currently a series of exploratory simulations are being performed with the
number of quark flavors, $N_f $= 6, 8, and 10 on a set of lattice volumes for
various quark masses. Here, we report on the current status of our simulation
on a $8^4$ lattice.


title: Chiral Properties of Quenched and Full QCD

abstract:
  We extend a technique for the chiral extrapolation of hadron masses
calculated with dynamical fermions to those generated by quenched simulations.
The method ensures the correct leading and next-to-leading non-analytic
behaviour for either QCD or quenched QCD in the chiral limit, as well as the
correct large quark mass behaviour. We find that the primary difference between
quenched and dynamical baryon masses can be described by the meson loops which
give rise to the different leading and next-to-leading non-analytic behaviour.


title: On the dynamics of color magnetic monopoles in full QCD

abstract:
  We present first results on the dynamics of monopoles in full QCD with N_f=2
flavors of dynamical quarks. Among the quantities being studied are the
monopole density and the monopole screening length, the static potential as
well as the profile of the color electric flux tube. Furthermore, we derive the
low-energy effective monopole action.


title: Improving the Dirac Operator in Lattice QCD

abstract:
  Recently various new concepts for the construction of Dirac operators in
lattice Quantum Chromodynamics (QCD) have been introduced. These operators
satisfy the so-called Ginsparg-Wilson condition (GWC), thus obeying the
Atiyah-Singer index theorem and violating chiral symmetry only in a modest and
local form. Here we present studies in 4-d for SU(3) gauge configurations with
non-trivial topological content. We study the flow of eigenvalues and we
compare the numerical stability and efficiency of a recently suggested chirally
improved operator with that of others in this respect.


title: Finite-size scaling for two-flavor QCD and comparison with O(N) models

abstract:
  The chiral transition for two-flavor QCD is predicted to be in the same
universality class as the 3d O(4) model. This prediction is verified in the
Wilson case, but not for the staggered-fermion case. The comparison is usually
done assuming infinite-volume behavior. Here we make an analysis of existing
staggered-fermion data using finite-size scaling and normalizing the QCD data.
We find better agreement for larger quark masses.


title: Analytic calculation of the mass gap in U(1)_{2+1} lattice gauge theory

abstract:
  An analytic calculation of the photon mass gap M of compact U(1)_{2+1} in the
Hamiltonian formalism is performed utilizing the first four Hamiltonian moments
with respect to a one-plaquette mean field state in the plaquette expansion
method. Scaling of M is clearly evident at and beyond the transition from
strong to weak coupling. The scaling behaviour agrees well with the range of
results from numerical calculations.


title: Mesons in Transverse Lattice QCD at Strong Coupling and Large-N

abstract:
  Mesons in large-N QCD are analysed in light-front coordinates with a
transverse lattice at strong coupling. In this limit, their properties can be
expressed as simple renormalisations of the 't Hooft model results. The
integral eigenvalue equation for the mesons is derived. Spectrum, lightcone
wavefunctions and form factors of various mesons can be numerically calculated
from this equation.


title:
The Phase Diagram for the anisotropic SU(2) Adjoint Higgs Model in 5D:
  Lattice Evidence for Layered Structure

abstract:
  We explore, by Monte Carlo and Mean Field methods, the five--dimensional
SU(2) adjoint Higgs model. We allow for the possibility of different couplings
along one direction, describing the so--called anisotropic model. This study is
motivated by the possibility of the appearance of four--dimensional layered
dynamics. Actually, our results lead to the conclusion that the establishment
of a layered phase in four dimensions described by U(1) symmetry is possible,
the extra dimension being confined due to the SU(2) gauge symmetry. The
five-dimensional adjoint Higgs model turns out to have a layered phase, in
contradistinction with what is known about the pure SU(2) model.


title: A lattice approach to QCD in the chiral regime

abstract:
  Non-perturbative lattice studies of QCD in the chiral thermodynamic regime,
where chiral symmetry is spontaneously broken, require to deal with almost
quark zero modes in a theoretically clean and computationally efficient way. We
discuss the basic features and some realistic tests of a formulation, known as
lattice tmQCD, that fulfills these requirements. Based on a talk given by R.
Frezzotti at the conference HEP2001 (Budapest, July 2001)


title: Relativistic Bottomonium Spectrum from Anisotropic Lattices

abstract:
  We report on a first relativistic calculation of the quenched bottomonium
spectrum from anisotropic lattices. Using a very fine discretisation in the
temporal direction we were able to go beyond the non-relativistic approximation
and perform a continuum extrapolation of our results from five different
lattice spacings (0.04-0.17 fm) and two anisotropies (4 and 5). We investigate
several systematic errors within the quenched approximation and compare our
results with those from non-relativistic simulations.


title: Baryons in Partially Quenched Chiral Perturbation Theory

abstract:
  We include the lowest-lying octet- and decuplet-baryons into partially
quenched chiral perturbation theory. Perturbing about the chiral limit of the
graded SU(6|3)_L x SU(6|3)_R flavor group of partially quenched QCD, we compute
the leading one-loop contributions to the octet-baryon masses, magnetic moments
and matrix elements of isovector twist-2 operators. We work in the isospin
limit and keep two of the three sea quarks degenerate. The usefulness of the
non-unique extension of the electric charge matrix and the isovector twist-2
operators from QCD to partially quenched QCD is discussed.


title: Chiral Logs in the Presence of Staggered Flavor Symmetry Breaking

abstract:
  Chiral logarithms in $m_\pi^2$ are calculated at one loop, taking into
account the leading contributions to flavor symmetry breaking due to staggered
fermions. I treat both the full QCD case (2+1 light dynamical flavors) and the
quenched case; finite volume corrections are included. My starting point is the
effective chiral Lagrangian introduced by Lee and Sharpe. It is necessary to
understand the one-loop diagrams in the ``quark flow'' picture in order to
adjust the calculation to correspond to the desired number of dynamical quarks.


title: Glueball Properties at Finite Temperature

abstract:
  We study the glueball properties at finite temperature below T_c using SU(3)
anisotropic quenched lattice QCD with beta=6.25, the renormalized anisotropy
gamma = a_s/a_t = 4 and 20^3 \times N_t (N_t = 35, 36, 37, 38, 40, 43, 45, 50,
72). From the temporal correlation analysis with the smearing method, we
observe the mass reduction of about 20 % for the lowest 0^{++} glueball as
m_G(T) = 1.25 \pm 0.1 GeV for 0.8 T_c < T < T_c in comparison with m_G \simeq
1.5 \sim 1.7 GeV at T \sim 0.


title: Hadron Mass Extraction from Lattice QCD

abstract:
  The extraction of quantities from lattice QCD calculations at realistic quark
masses is of considerable importance. Whilst physical quark masses are some way
off, the recent advances in the calculation of hadron masses within full QCD
now invite improved extrapolation methods. We show that, provided the correct
chiral behaviour of QCD is respected in the extrapolation to realistic quark
masses, one can indeed obtain a fairly reliable determination of masses, the
sigma commutator and the J parameter. We summarise these findings by presenting
the nonanalytic behaviour of nucleon and rho masses in the standard Edinburgh
plot.


title: Unquenched Studies Using the Truncated Determinant Algorithm

abstract:
  A truncated determinant algorithm is used to study the physical effects of
the quark eigenmodes associated with eigenvalues below 420 MeV. This initial
high statistics study focuses on coarse ($6^4$) lattices (with O($a^2$)
improved gauge action), light internal quark masses and large physical volumes.
Three features of full QCD are examined: topological charge distributions,
string breaking as observed in the static energy and the eta prime mass.


title: Probing the QCD vacuum with overlap fermions

abstract:
  We use low lying eigenvectors of the overlap-Dirac operator as a probe of the
QCD vacuum. If instantons play a significant role one would expect the low
lying eigenmodes of the overlap-Dirac operator to consist mainly of the mixed
``would be zero modes''. Then, the eigenmodes should exhibit local chirality.
Studying a recently introduced local chirality parameter, we find evidence
supporting this picture.


title: The eta and eta' mesons from lattice QCD

abstract:
  Lattice QCD allows a first-principles study of QCD with the freedom to vary
the number and masses of the quarks. I present results on the flavour singlet
correlations (this illuminates OZI violating effects) for mesons. Concentrating
on the pseudoscalar mesons, the flavour singlet mass splitting ($\eta$, $\eta'$
mass splitting) appears naturally.
  I also present results on an investigation of decay constants for the $\eta$
and $\eta'$ ($f_{\eta}$) and discuss which quantities may be accessible in
future lattice studies.
  The Witten-Veneziano approach can also be explored by determining the
quenched topological susceptibility on a lattice.


title: A Fermion Doublet With Chiral Gauge Interaction On A Lattice

abstract:
  We present a new staggered discretization of the Dirac operator. Doubling
gives only a doublet of Dirac fermions which we propose to interpret as a
physical (lepton or quark) doublet. If coupled with gauge fields, an
$(1+\gamma^5)$ chiral interaction appears in a natural way. We define a
generalization for curved background which does not require tetrad variables.
The approach suggests a natural explanation for the three fermion families.


title:
Properties of the renormalized quark mass in the Schrodinger functional
  with a non-vanishing background field

abstract:
  We compute the current quark mass in the Schrodinger functional with a
non-vanishing background field at one loop order of perturbation theory. The
results are used to obtain the critical mass at which the renormalized quark
mass vanishes, and some lattice artefacts at one loop order.


title:
Common features of deconfining and chiral critical points in QCD and the
  three state Potts model in an external field

abstract:
  In the presented study we investigated the second order endpoints of the
lines of first order phase transitions which emerge for the QCD in the heavy
and light quark mass regime and for the three-dimensional three state Potts
model with an external field. We located the endpoints with Binder cumulants
and constructed the energy-like and ordering field like observables. The joint
probability distributions of these scaling fields and the values of the Binder
cumulant confirm that all three endpoints belong to the universality class of
the 3-dimensional Ising model.


title:
Numerical study of lattice index theorem usingimproved cooling and
  overlap fermions

abstract:
  We investigate topological charge and the index theorem on finite lattices
numerically. Using mean field improved gauge field configurations we calculate
the topological charge Q using the gluon field definition with ${\cal
O}(a^4)$-improved cooling and an ${\cal O}(a^4)$-improved field strength tensor
$F_{\mu\nu}$. We also calculate the index of the massless overlap fermion
operator by directly measuring the differences of the numbers of zero modes
with left- and right--handed chiralities. For sufficiently smooth field
configurations we find that the gluon field definition of the topological
charge is integer to better than 1% and furthermore that this agrees with the
index of the overlap Dirac operator, i.e., the Atiyah-Singer index theorem is
satisfied. This establishes a benchmark for reliability when calculating
lattice quantities which are very sensitive to topology.


title:
Reaching the continuum limit in lattice gauge theory - without a
  computer

abstract:
  The scaling slope of the anti-symmetric mass gap M of compact U(1)_{2+1}
lattice gauge theory is obtained analytically in the Hamiltonian formalism
using the plaquette expansion. Based on the first four moments of the
Hamiltonian with respect to a one-plaquette mean field state the results
demonstrate clear scaling of M at and beyond the transition from strong to weak
coupling. The scaling parameters determined agree well with the range of
numerical determinations available.


title: Overlap and domain wall fermions: what is the price of chirality?

abstract:
  In this contribution the costs of simulations employing domain wall and
overlap fermions are estimated. In the discussion we will stay within the
quenched approximation.


title: Investigating QCD Vacuum on the lattice

abstract:
  Investigations on the structure of QCD vacuum from first principles can be
done on the lattice. The mechanism of confinement is an example: results from
lattice on it are reviewed.


title: The critical point of lattice QCD on the \mu-T plane

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


title:
Antisymmetric and other subleading corrections to scaling in the local
  potential approximation

abstract:
  For systems in the universality class of the three-dimensional Ising model we
compute the critical exponents in the local potential approximation (LPA), that
is, in the framework of the Wegner-Houghton equation. We are mostly interested
in antisymmetric corrections to scaling, which are relatively poorly studied.
We find the exponent for the leading antisymmetric correction to scaling
$\omega_A \approx 1.691$ in the LPA. This high value implies that such
corrections cannot explain asymmetries observed in some Monte Carlo
simulations.


title: Confinement: Results and Perspectives

abstract:
  An updated review is presented of lattice investigations of colour
confinement.


title: Asymptotic freedom with discrete spin variables?

abstract:
  We study the critical behaviour of the 2d dodecahedron spin model and
investigate the conjecture that the discrete model describes the same continuum
theory as the O(3) non-linear sigma model. In particular, we found that the
anisotropy of the magnetization A(z) measured in a fixed physical volume
decreases with increasing correlation length, at least up to \xi \approx 1000.


title: Is the Graviton a Domain Wall Glueball?

abstract:
  Strong coupling calculations for the glueball spectrum in an $AdS^7$ black
hole are modified by introducing an UV cut-off at a Planck brane. A new
normalizable state in the tensor spectrum is found which reproduces
Einstein-Hilbert gravity up to exponentially small corrections due to off shell
mixing with massive glueballs.


title:
Non-perturbative renormalization in domain-wall QCD by Schr\"odinger
  functional scheme

abstract:
  We formulate and numerically test the Schr\"odinger functional scheme for
domain-wall QCD. We then apply it to a non-perturbative calculation of the
renormalization factors for vector and axial-vector currents in quenched
domain-wall QCD with plaquette and renormalization group improved gauge actions
at $a^{-1}\simeq 2$ GeV.


title: Domain-wall fermions and chiral symmetries

abstract:
  We investigate chiral properties of the domain-wall fermion (DWF) system.
After a brief introduction for the DWF, we summarize the recent numerical
results on the chiral properties of the domain-wall QCD (DWQCD), which seem
mutually inconsistent. We next derive a formula which connects a chiral
symmetry breaking term in the five dimensional DWF Ward-Takahashi identity with
the four-dimensional hermitian Wilson-Dirac operator. Based on this formula, we
propose a solution, which resolves the inconsistency among recent numerical
data, and give a consistent picture of the chiral properties of the DWQCD.


title: Supersymmetric Yang-Mills theory on the lattice

abstract:
  Recent development in numerical simulations of supersymmetric Yang-Mills
(SYM) theories on the lattice is reviewed.


title: Z(3) Symmetric Dimensional Reduction of (2+1)D QCD

abstract:
  Here we present a candidate for a Z(3)-symmetric reduced action for the
description of the (2+1)D SU(3) gauge theory


title:
Gauged Nambu-Jona Lasinio Studies of the Triviality of Quantum
  Electrodynamics

abstract:
  By adding a small, irrelevant four fermi interaction to the action of
noncompact lattice Quantum Electrodynamics (QED), the theory can be simulated
with massless quarks in a vacuum free of lattice monopoles. The lattice theory
possesses a second order chiral phase transition which we show is
logarithmically trivial, with the same systematics as the Nambu-Jona Lasinio
model. The irrelevance of the four fermi coupling is established numerically.
The widths of the scaling windows are examined in both the coupling constant
and bare fermion mass directions in parameter space. For vanishing fermion mass
we find a broad scaling window in coupling. By adding a small bare fermion mass
to the action we find that the width of the scaling window in the fermion mass
direction is very narrow. Only when a subdominant scaling term is added to the
leading term of the equation of state are adequate fits to the data possible.
The failure of past studies of lattice QED to produce equation of state fits
with adequate confidence levels to seriously address the question of triviality
is explained. The vacuum state of the lattice model is probed for topological
excitations, such as lattice Monopoles and Dirac strings, and these objects are
shown to be non-critical along the chiral transition line as long as the four
fermi coupling is nonzero.


title: Excitation Spectra in a Heavy-Light Meson-Meson System

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


title: Matrix Elements of Light Quarks

abstract:
  Lattice results for matrix elements of light quark operators are reviewed.
The discussion is focused on recent theoretical progress and new numerical
calculations which appeared after the Lattice 2000 Conference.


title: I=0 scalar channel

abstract:
  Using lattice QCD with dynamical Wilson fermions, we study I=0 and
$J^{P}=0^{+}$ channel which is constructed by
$\frac{1}{\sqrt{2}}(\bar{u}u+\bar{d}d)|0>$, in order to search for the $\sigma$
meson. Our preliminary result shows that the connected and disconnected
diagrams contribute to the $\sigma$ meson propagator in the same order.


title:
On the possibility of the critical behavior of LGT in the area of
  asymptotically large \beta

abstract:
  Coupling dependence on lattice spacing and size is estimated analytically at
\beta -> \infty region where for a->0 the critical area is shifted in
accordance with Callan-Symanzik relation. In considered approximation no trace
of critical behavior is found in this area.


title:
The extraction of the axial coupling from finite volume systems: The
  long and short of it

abstract:
  Due to a pion-pole contribution, the nucleon axial current matrix elements
can be visualized in position space as becoming delocalized as the chiral limit
is approached, with one-third of the current at distance of order the inverse
pion mass. However, this delocalization effect will not cause calculations of
the axial coupling in a finite system with standard boundary conditions
(periodic for boson fields, antiperiodic for fermions) to have large finite
volume effects. This is seen by calculating axial coupling using a nonstandard
current with axial quantum numbers. The matrix elements of this new current
lacks a pion pole and is not delocalized; however, its zero-momentum matrix
element is identical to that of the standard axial current both for infinite
and finite volumes.


title:
The Coupled Cluster Method in Hamiltonian Lattice Field Theory: SU(2)
  Glueballs

abstract:
  The glueball spectrum within the Hamiltonian formulation of lattice gauge
theory (without fermions) is calculated for the gauge group SU(2) and for two
spatial dimensions.
  The Hilbert space of gauge-invariant functions of the gauge field is
generated by its parallel-transporters on closed paths along the links of the
spatial lattice. The coupled cluster method is used to determine the spectrum
of the Kogut-Susskind Hamiltonian in a truncated basis. The quality of the
description is studied by computing results from various truncations, lattice
regularisations and with an improved Hamiltonian.
  We find consistency for the mass ratio predictions within a scaling region
where we obtain good agreement with standard lattice Monte Carlo results.


title: Finite-size Scaling of Meson Propagators

abstract:
  Using quenched chiral perturbation theory we compute meson correlation
functions at finite volume and fixed gauge field topology. We also present the
corresponding analytical predictions for the unquenched theory at fixed gauge
field topology. These results can be used to measure the low-energy parameters
of the chiral Langrangian from lattice simulations in volumes much smaller than
one pion Compton wavelength.


title: Fermions on tori in uniform abelian fields

abstract:
  We study Fermi fields defined on tori in the presence of gauge backgrounds
carrying non-trivial topology. We show that 2k dimensional field space can
alternatively be described by fields over a k-dimensional space. This dual
description is particularly natural when the background is uniform and abelian.
The reduction in number of dimensions carries over to the lattice. The lattice
ultraviolet regularization induces an infrared regularization of the lower
dimensional representations. We focus on k=1,2.


title: (1+1)-dimensional Baryons from the SU(N) Color-Flavor Transformation

abstract:
  The color-flavor transformation, an identity that connects two integrals,
each of which is over one of a dual pair of Lie groups acting in the fermionic
Fock space, is extended to the case of the special unitary group. Using this
extension, a toy model of lattice QCD is studied: N_f species of spinless
fermions interacting with strongly coupled SU(N_c) lattice gauge fields in 1+1
dimensions. The color-flavor transformed theory is expressed in terms of gauge
singlets, the meson fields, organized into sectors distinguished by the
distribution of baryonic flux. A comprehensive analytical and numerical search
is made for saddle-point configurations of the meson fields, with various
topological charges, in the vacuum and single-baryon sectors. Two definitions
of the static baryon on the square lattice, straight and zigzag, are
investigated. The masses of the baryonic states are estimated using the
saddle-point approximation for large N_c.


title: Glueballs, strings and topology in SU(N) gauge theory

abstract:
  I show how one can use lattice methods to calculate various continuum
properties of SU(N) gauge theories; in part to explore old ideas that N=3 might
be close to N=infinity. I describe calculations of the low-lying `glueball'
mass spectrum, of the string tensions of k-strings and of topological
fluctuations for N=2,3,4,5. We find that mass ratios appear to show a rapid
approach to the large-N limit, and, indeed, can be described all the way down
to SU(2) using just a leading O(1/NxN) correction. We confirm that the smooth
large-N limit we find is confining and is obtained by keeping a constant 't
Hooft coupling. We find that the ratio of the k=2 string tension to the k=1
fundamental string tension is much less than the naive (unbound) value of 2 and
is considerably greater than the naive bag model prediction; in fact we find
that it is consistent, within quite small errors, with either the
M(-theory)QCD-inspired conjecture or with `Casimir scaling'. Finally I describe
calculations of the topological charge of the gauge fields. We observe that, as
expected, the density of small-size instantons vanishes rapidly as N increases,
while the topological susceptibility appears to have a non-zero N=infinity
limit.


title: Charmonium Spectrum from Quenched Anisotropic Lattice QCD

abstract:
  We present a detailed study of the charmonium spectrum using anisotropic
lattice QCD. We first derive a tree-level improved clover quark action on the
anisotropic lattice for arbitrary quark mass. The heavy quark mass dependences
of the improvement coefficients, i.e. the ratio of the hopping parameters
$\zeta=K_t/K_s$ and the clover coefficients $c_{s,t}$, are examined at the tree
level. We then compute the charmonium spectrum in the quenched approximation
employing $\xi = a_s/a_t = 3$ anisotropic lattices. Simulations are made with
the standard anisotropic gauge action and the anisotropic clover quark action
at four lattice spacings in the range $a_s$=0.07-0.2 fm. The clover
coefficients $c_{s,t}$ are estimated from tree-level tadpole improvement. On
the other hand, for the ratio of the hopping parameters $\zeta$, we adopt both
the tree-level tadpole-improved value and a non-perturbative one. We calculate
the spectrum of S- and P-states and their excitations. The results largely
depend on the scale input even in the continuum limit, showing a quenching
effect. When the lattice spacing is determined from the $1P-1S$ splitting, the
deviation from the experimental value is estimated to be $\sim$30% for the
S-state hyperfine splitting and $\sim$20% for the P-state fine structure. Our
results are consistent with previous results at $\xi = 2$ obtained by Chen when
the lattice spacing is determined from the Sommer scale $r_0$. We also address
the problem with the hyperfine splitting that different choices of the clover
coefficients lead to disagreeing results in the continuum limit.


title: Quenched chiral perturbation theory for baryon form factors

abstract:
  A new intuitive method for the rapid calculation of the leading nonanalytic
behavior of hadronic observables in quenched chiral perturbation theory is
presented. After proving the technique in a consideration of baryon masses, the
quenched magnetic moments of octet baryons are addressed. The technique
provides a separation of magnetic moment contributions into full, sea, valence
and quenched valence contributions, the latter being the conventional view of
the quenched approximation. Both baryon mass and meson mass violations of
SU(3)-flavor symmetry are accounted for. A comprehensive examination of the
individual quark-sector contributions to octet baryon magnetic moments reveals
that the u-quark contribution to the proton magnetic moment provides an optimal
opportunity to directly view nonanalytic behavior associated with the quenched
meson cloud of baryons in the quenched approximation.


title: Effective Monopole Action at Finite Temperature in SU(2) Gluodynamics

abstract:
  Effective monopole action at finite temperature in SU(2) gluodynamics is
studied on anisotropic lattices. Using an inverse Monte-Carlo method and the
blockspin transformation for space directions, we determine 4-dimensional
effective monopole action at finite temperature. We get an almost perfect
action in the continuum limit under the assumption that the action is composed
of two-point interactions alone. It depends on a physical scale $b_s$ and the
temperature $T$. The temperature-dependence appears with respect to the
spacelike monopole couplings in the deconfinement phase, whereas the timelike
monopole couplings do not show any appreciable temperature-dependence. The
dimensional reduction of the 4-dimensional SU(2) gluodynamics ((SU(2))$_{4D}$)
at high temperature is the 3-dimensional Georgi-Glashow model ($(GG)_{3D}$).
The latter is studied at the parameter region obtained from the dimensional red
uction. We compare the effective instanton action of $(GG)_{3D}$ with the
timelike monopole action obtained from (SU(2))$_{4D}$. We find that both agree
very well for $T \ge 2.4T_c$ at large $b$ region. The dimensional reduction
works well also for the effective action.


title: Bayesian curve fitting for lattice gauge theorists

abstract:
  A new method of extracting the low-lying energy spectrum from Monte Carlo
estimates of Euclidean-space correlation functions which incorporates Bayesian
inference is described and tested. The procedure fully exploits the information
present in the correlation functions at small temporal separations and uses
this information in a way consistent with fundamental probabilistic hypotheses.
The computed errors on the best-fit energies include both statistical
uncertainties and systematic errors associated with the treatment of
contamination from higher-lying stationary states. Difficulties in performing
the integrals needed to compute these error estimates are briefly discussed.


title: Setting the scale for the Luescher-Weisz action

abstract:
  We study the quark-antiquark potential of quenched SU(3) lattice gauge theory
with the Luescher-Weisz action. After blocking the gauge fields with the
recently proposed hypercubic transformation we compute the Sommer parameter,
extract the lattice spacing a and set the scale at 6 different values of the
gauge coupling in a range from a = 0.084 fm to 0.136 fm.


title: Testing a Fourier Accelerated Hybrid Monte Carlo Algorithm

abstract:
  We describe a Fourier Accelerated Hybrid Monte Carlo algorithm suitable for
dynamical fermion simulations of non-gauge models. We test the algorithm in
supersymmetric quantum mechanics viewed as a one-dimensional Euclidean lattice
field theory. We find dramatic reductions in the autocorrelation time of the
algorithm in comparison to standard HMC.


title: Cost-Effective Clustering

abstract:
  Small Beowulf clusters can effectively serve as personal or group
supercomputers. In such an environment, a cluster can be optimally designed for
a specific problem (or a small set of codes). We discuss how theoretical
analysis of the code and benchmarking on similar hardware lead to optimal
systems.


title:
Quark propagator from an improved staggered action in Laplacian and
  Landau gauges

abstract:
  Studies of gauge dependent quantities are afflicted with Gribov copies, but
Laplacian gauge fixing provides one possible solution to this problem. We
present results for the lattice quark propagator in both Landau and Laplacian
gauges using standard and improved staggered quark actions. The standard
Kogut-Susskind action has errors of \oa{2} while the improved ``Asqtad'' action
has \oa{4}, \oag{2}{2} errors and this improvement is seen in the quark
propagator. We demonstrate the application of tree-level corrections to these
actions and see that Landau and Laplacian gauges produce very similar results.
In addition, we test an ansatz for the quark mass function, with promising
results. In the chiral limit, the infrared quark mass, $M(q^2 = 0)$ is found to
be $260\pm 20$ MeV.


title: Improved Pseudofermion Approach for All-Point Propagators

abstract:
  Quark propagators with arbitrary sources and sinks can be obtained more
efficiently using a pseudofermion method with a mode-shifted action.
Mode-shifting solves the problem of critical slowing down (for light quarks)
induced by low eigenmodes of the Dirac operator. The method allows the full
physical content of every gauge configuration to be extracted, and should be
especially helpful for unquenched QCD calculations. The method can be applied
for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert,
Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The
statistical properties of the method are examined and examples of physical
processes under study are presented.


title: Is strong CP invariance due to a massless up quark?

abstract:
  A standing mystery in the Standard Model is the unnatural smallness of the
strong CP violating phase. A massless up quark has long been proposed as one
potential solution. A lattice calculation of the constants of the chiral
Lagrangian essential for the determination of the up quark mass, 2 alpha_8 -
alpha_5, is presented. We find 2 alpha_8 - alpha_5 = 0.29 +/- 0.18, which
corresponds to m_u / m_d = 0.410 +/- 0.036. This is the first such calculation
using a physical number of dynamical light quarks, N_f = 3.


title: Vortex fermion on the lattice

abstract:
  The domain wall fermion formalism in lattice gauge theory is much
investigated recently. This is set up by reducing 4+1 dimensional theory to low
energy effective 4 dimensional one. In order to look around other possibilities
of realizing chiral fermion on the lattice, we construct vortex fermion by
reducing 4+2 dimensional theory to low energy effective 4 dimensional one on
the lattice. In extra 2 dimensions we propose a new lattice regularization
which has a discrete rotational invariance but not a translational one. In
order to eliminate doubling species in the naive construction we introduce the
extended Wilson term which is appropriate to our model. We propose two models
for convenience and show that a normalizable zero mode solution appears at the
core of the vortex.


title:
Excited nucleon spectrum using a non-perturbatively improved clover
  fermion action

abstract:
  We discuss the extraction of negative-parity baryon masses from lattice QCD
calculations. The mass of the lowest-lying negative-parity $J = 1/2^{-}$ state
is computed in quenched lattice QCD using an ${\cal O}(a)$-improved clover
fermion action, and a splitting found with the nucleon mass. The calculation is
performed on two lattice volumes, and three lattice spacings enabling a study
of both finite-volume and finite-lattice-spacing uncertainties. A measurement
of the first excited radial excitation of the nucleon finds a mass considerably
larger than that of the negative-parity ground state, in accord with other
lattice determinations but in disagreement with experiment. Results are also
presented for the lightest negative-parity $I=3/2$ state.


title: Phase transition strengths from the density of partition function zeroes

abstract:
  We report on a new method to extract thermodynamic properties from the
density of partition function zeroes on finite lattices. This allows direct
determination of the order and strength of phase transitions numerically.
Furthermore, it enables efficient distinguishing between first- and
second-order transitions, elucidates crossover between them and illuminates the
origins of finite-size scaling. The power of the method is illustrated in
typical applications for both Fisher and Lee-Yang zeroes.


title: The Kentucky Noisy Monte Carlo Algorithm for Wilson Dynamical Fermions

abstract:
  We develop an implementation for a recently proposed Noisy Monte Carlo
approach to the simulation of lattice QCD with dynamical fermions by
incorporating the full fermion determinant directly. Our algorithm uses a
quenched gauge field update with a shifted gauge coupling to minimize
fluctuations in the trace log of the Wilson Dirac matrix. The details of tuning
the gauge coupling shift as well as results for the distribution of noisy
estimators in our implementation are given. We present data for some basic
observables from the noisy method, as well as acceptance rate information and
discuss potential autocorrelation and sign violation effects. Both the results
and the efficiency of the algorithm are compared against those of Hybrid Monte
Carlo.
  PACS Numbers: 12.38.Gc, 11.15.Ha, 02.70.Uu Keywords: Noisy Monte Carlo,
Lattice QCD, Determinant, Finite Density, QCDSP


title: Cooling for instantons and the Wrath of Nahm

abstract:
  The dynamics of instantons and anti-instantons in lattice QCD can be studied
by analysing the action and topological charge of configurations as they
approach a self-dual or anti-self-dual state, i.e. a state in which S/S_0=|Q|.
We use cooling to reveal the semi-classical structure of the configurations we
study. Improved actions which eliminate discretization errors up to and
including O(a^4) are used to stabilise instantons as we cool for several
thousand sweeps. An analogously improved lattice version of the continuum
field-strength tensor is used to construct a topological charge free from
O(a^4) discretization errors. Values of the action and topological charge
obtained with these improved operators approach mutually-consistent integer
values to within a few parts in 10^4 after several hundred cooling sweeps.
Analysis of configurations with |Q| \approx 1 and |Q| \approx 2 supports the
hypothesis that a self-dual |Q|=1 configuration cannot exist on the 4-torus.


title: The Area Law in Matrix Models for Large N QCD Strings

abstract:
  We study the question whether matrix models obtained in the zero volume limit
of 4d Yang-Mills theories can describe large N QCD strings. The matrix model we
use is a variant of the Eguchi-Kawai model in terms of Hermitian matrices, but
without any twists or quenching. This model was originally proposed as a toy
model of the IIB matrix model. In contrast to common expectations, we do
observe the area law for Wilson loops in a significant range of scale of the
loop area. Numerical simulations show that this range is stable as N increases
up to 768, which strongly suggests that it persists in the large N limit. Hence
the equivalence to QCD strings may hold for length scales inside a finite
regime.


title:
Matching Current Correlators in Lattice QCD to Chiral Perturbation
  Theory

abstract:
  Chiral perturbation theory gives direct and unambiguous predictions for the
form of various two-point hadronic correlators at low momentum in terms of a
finite set of couplings in a chiral Lagrangian. In this paper we study the
feasibility of extracting the couplings in the chiral Lagrangian (through
1-loop order) by fitting two-point correlators computed in lattice QCD to the
predicted chiral form. The correlators are computed using a pseudofermion
technique yielding all-point quark propagators which allows the computation of
the full four-momentum transform of the two-point functions to be obtained
without sacrificing any of the physical content of the unquenched gauge
configurations used. Results are given for an ensemble of dynamical
configurations generated using the truncated determinant algorithm on a large
coarse lattice. We also present a new analysis of finite volume effects based
on a finite volume dimensional regularization scheme which preserves the
power-counting rules appropriate for a chiral Lagrangian.


title:
Exact finite-size scaling with corrections in the two-dimensional Ising
  model with special boundary conditions

abstract:
  The two-dimensional Ising model with Brascamp-Kunz boundary conditions has a
partition function more amenable to analysis than its counterpart on a torus.
This fact is exploited to exactly determine the full finite-size scaling
behaviour of the Fisher zeroes of the model. Moreover, exact results are also
determined for the scaling of the specific heat at criticality, for the
specific-heat peak and for the pseudocritical points. All corrections to
scaling are found to be analytic and the shift exponent $\lambda$ does not
coincide with the inverse of the correlation length exponent $1/\nu$.


title: Benchmarking and tuning the MILC code on clusters and supercomputers

abstract:
  Recently, we have benchmarked and tuned the MILC code on a number of
architectures including Intel Itanium and Pentium IV (PIV), dual-CPU Athlon,
and the latest Compaq Alpha nodes. Results will be presented for many of these,
and we shall discuss some simple code changes that can result in a very
dramatic speedup of the KS conjugate gradient on processors with more advanced
memory systems such as PIV, IBM SP and Alpha.


title: Cost of dynamical quark simulations with improved staggered quarks

abstract:
  The cost of dynamical quark simulations with improved staggered quarks is
estimated based on current and planned running by the MILC collaboration. I
find that a few 10s of Teraflop years should be sufficient to calculate down to
a lattice spacing of 0.045 fm.


title:
A Lattice Study of the Magnetic Moment and the Spin Structure of the
  Nucleon

abstract:
  Using an approach free from momentum extrapolation, we calculate the nucleon
magnetic moment and the fraction of the nucleon spin carried by the quark
angular momentum in the quenched lattice QCD approximation. Quarks with three
values of lattice masses, 210, 124 and 80 MeV, are formulated on the lattice
using the standard Wilson approach. At every mass, 100 gluon configurations on
16^3 x 32 lattice with \beta=6.0 are used for statistical averaging. The
results are compared with the previous calculations with momentum
extrapolation. The contribution of the disconnected diagrams is studied at the
largest quark mass using noise theory technique.


title: Accelerated Overlap Fermions

abstract:
  Numerical evaluation of the overlap Dirac operator is difficult since it
contains the sign function $\epsilon(H_w)$ of the Hermitian Wilson-Dirac
operator $H_w$ with a negative mass term. The problems are due to $H_w$ having
very small eigenvalues on the equilibrium background configurations generated
in current day Monte Carlo simulations. Since these are a consequence of the
lattice discretisation and do not occur in the continuum version of the
operator, we investigate in this paper to what extent the numerical evaluation
of the overlap can be accelerated by making the Wilson-Dirac operator more
continuum-like. Specifically, we study the effect of including the clover term
in the Wilson-Dirac operator and smearing the link variables in the irrelevant
terms. In doing so, we have obtained a factor of two speedup by moving from the
  Wilson action to a FLIC (Fat Link Irrelevant Clover) action as the overlap
kernel.


title: Improving the low-lying spectrum of the overlap kernel

abstract:
  The action of the overlap-Dirac operator on a vector is typically implemented
in directly through a multi-shift conjugate gradient solver. The compute-time
this takes to evaluate depends upon the condition number $\kappa$ of the matrix
that is used as the overlap kernel. We examine the low-lying spectra of various
candidate kernels in an effort to optimise $\kappa$, thereby speeding up the
overlap evaluation.


title: The Gluon Propagator without lattice Gribov copies on a finer lattice

abstract:
  We extend our study of the gluon propagator in quenched lattice QCD using the
Laplacian gauge to a finer lattice. We verify the existence of a pole mass as
we take the continuum limit and deduce a value of $\sim 600^{+150}_{-30}$ MeV
for this pole mass. We find a finite value of $(454(5){\rm MeV})^{-2}$ for the
renormalized zero-momentum propagator, in agreement with results on coarser
lattices.


title:
Application of heavy-quark effective theory to lattice QCD: II.
  Radiative corrections to heavy-light currents

abstract:
  We apply heavy-quark effective theory to separate long- and short-distance
effects of heavy quarks in lattice gauge theory. In this approach, the inverse
heavy-quark mass and the lattice spacing are treated as short distances, and
their effects are lumped into short-distance coefficients. We show how to use
this formalism to match lattice gauge theory to continuum QCD, order by order
in the heavy-quark expansion. In this paper, we focus on heavy-light currents.
In particular, we obtain one-loop results for the matching factors of lattice
currents, needed for heavy-quark phenomenology, such as the calculation of
heavy-light decay constants, and heavy-to-light transition form factors.
Results for the Brodsky-Lepage-Mackenzie scale $q^*$ are also given.


title:
Application of heavy-quark effective theory to lattice QCD: III.
  Radiative corrections to heavy-heavy currents

abstract:
  We apply heavy-quark effective theory (HQET) to separate long- and
short-distance effects of heavy quarks in lattice gauge theory. In this paper
we focus on flavor-changing currents that mediate transitions from one heavy
flavor to another. We stress differences in the formalism for heavy-light
currents, which are discussed in a companion paper, showing how HQET provides a
systematic matching procedure. We obtain one-loop results for the matching
factors of lattice currents, needed for heavy-quark phenomenology, such as the
calculation of zero-recoil form factors for the semileptonic decays $B\to
D^{(*)}l\nu$. Results for the Brodsky-Lepage-Mackenzie scale $q^*$ are also
given.


title: Numerical simulation of high quark densities in QCD with two colours

abstract:
  The DESY-Swansea Collaboration performed numerical simulations investigating
SU(2) lattice gauge theory at non-zero chemical potential with one staggered
quark flavour in the adjoint representation. This lattice model has similar
features to QCD itself and its study gives interesting insights into some open
problems of high density quark matter. In particular the role of the ``sign
problem'' can be clarified in connection with diquark condensation and the
phase diagram.


title: On the non-perturbative gluon mass and heavy quark physics

abstract:
  We study a recently proposed gauge invariant, non-local pure gauge
observable, which is equivalent to the gluon propagator in a certain gauge. The
correlator describes a gluon coupled to static sources and decays with
eigenvalues of the Hamiltonian, permitting a non-perturbative definition of a
gluonic parton mass. Detailed numerical tests of the observable are performed
in SU(2) gauge theories in 2+1 dimensions. In a Higgs model it reproduces the
physical W-boson mass, while in a confining theory its non-local nature results
in almost exclusive projection onto torelonic states. However, the gluon mass
can also be related to the mass difference between the lowest gluelumps, i.e.
gluon configurations bound to adjoint sources. Its value is computed in SU(2)
pure gauge theory in 2+1 dimensions to be m_A=0.360(19)g^2, which plays an
important role as "magnetic mass" of the four-dimensional theory at high
temperatures. The same quantity is found to determine the mass splitting
between vector and scalar mesons in the three-dimensional theory. In SU(3) pure
gauge theory in 3+1 dimensions the corresponding gluelump splitting yields
m_A\approx 370 MeV. Possible relations of this quantity with the QCD heavy
meson spectrum are discussed.


title:
Photon propagator, monopoles and the thermal phase transition in 3D
  compact QED

abstract:
  We investigate the gauge boson propagator in three dimensional compact
Abelian gauge model in the Landau gauge at finite temperature. The presence of
the monopole plasma in the confinement phase leads to appearance of an
anomalous dimension in the momentum dependence of the propagator. The anomalous
dimension as well as an appropriate ratio of photon wave function
renormalization constants with and without monopoles are observed to be order
parameters for the deconfinement phase transition. We discuss the relation
between our results and the confining properties of the gluon propagator in
non--Abelian gauge theories.


title:
Critical universality and hyperscaling revisited for Ising models of
  general spin using extended high-temperature series

abstract:
  We have extended through beta^{23} the high-temperature expansion of the
second field derivative of the susceptibility for Ising models of general spin,
with nearest-neighbor interactions, on the simple cubic and the body-centered
cubic lattices. Moreover the expansions for the nearest-neighbor correlation
function, the susceptibility and the second correlation moment have been
extended up to beta^{25}. Taking advantage of these new data, we can improve
the accuracy of direct estimates of critical exponents and of hyper-universal
combinations of critical amplitudes such as the renormalized four-point
coupling g_r or the quantity usually denoted by R^{+}_{xi}. We have used a
variety of series extrapolation procedures and, in some of the analyses, we
have assumed that the leading correction-to-scaling exponent theta is universal
and roughly known. We have also verified, to high precision, the validity of
the hyperscaling relation and of the universality property both with regard to
the lattice structure and to the value of the spin.


title: Lattice chiral symmetry, Yukawa couplings and the Majorana condition

abstract:
  It is shown that the conflict between lattice chiral symmetry and the
Majorana condition in the presence of Yukawa couplings, which was noted in our
previous paper, is related in an essential way to the basic properties of
Ginsparg-Wilson operators, namely, locality and species doubling.


title:
Polynomial Hybrid Monte Carlo algorithm for lattice QCD with an odd
  number of flavors

abstract:
  We present a polynomial hybrid Monte Carlo (PHMC) algorithm for lattice QCD
with odd numbers of flavors of O(a)-improved Wilson quark action. The algorithm
makes use of the non-Hermitian Chebyshev polynomial to approximate the inverse
square root of the fermion matrix required for an odd number of flavors. The
systematic error from the polynomial approximation is removed by a noisy
Metropolis test for which a new method is developed. Investigating the property
of our PHMC algorithm in the N_f=2 QCD case, we find that it is as efficient as
the conventional HMC algorithm for a moderately large lattice size (16^3 times
48) with intermediate quark masses (m_{PS}/m_V ~ 0.7-0.8). We test our
odd-flavor algorithm through extensive simulations of two-flavor QCD treated as
an N_f = 1+1 system, and comparing the results with those of the established
algorithms for N_f=2 QCD. These tests establish that our PHMC algorithm works
on a moderately large lattice size with intermediate quark masses (16^3 times
48, m_{PS}/m_V ~ 0.7-0.8). Finally we experiment with the (2+1)-flavor QCD
simulation on small lattices (4^3 times 8 and 8^3 times 16), and confirm the
agreement of our results with those obtained with the R algorithm and
extrapolated to a zero molecular dynamics step size.


title: Towards the Super Yang-Mills Theory on the Lattice

abstract:
  We present an entirely new approach towards a realization of the
supersymmetric Yang-Mills theory on the lattice. The action consists of the
staggered fermion and the plaquette variables distributed in the Euclidean
space with a particular pattern. The system is shown to have fermionic
symmetries relating the fermion and the link variables.


title: Monopoles and Chaos

abstract:
  We decompose U(1) gauge fields into a monopole and photon part across the
phase transition from the confinement to the Coulomb phase. We analyze the
leading Lyapunov exponents of such gauge field configurations on the lattice
which are initialized by quantum Monte Carlo simulations. It turns out that
there is a strong relation between the sizes of the monopole density and the
Lyapunov exponent.


title: Determinant Calculations with Random Walk Worldline Loops

abstract:
  We propose to calculate bosonic and fermionic determinants with some general
field background, and the corresponding 1-loop effective actions by evaluating
random walk worldline loops generated statistically on the lattice. This is
illustrated by some numerical calculations for constant gauge field backgrounds
and then discussed for the general case.


title: Progress in lattice algorithms

abstract:
  The development of Monte Carlo algorithms for generating gauge field
configurations with dynamical fermions and methods for extracting the most
information from ensembles are summarised.


title: Novel fat-link fermion actions

abstract:
  The hadron mass spectrum is calculated in lattice QCD using a novel fat-link
clover fermion action in which only the irrelevant operators of the fermion
action are constructed using smeared links. The simulations are performed on a
16^3 X 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with
n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat Link
Irrelevant Clover (FLIC) action provides scaling which is superior to
mean-field improvement, and offers advantages over nonperturbative O(a)
improvement.


title: Baryon resonances from a novel fat-link fermion action

abstract:
  We present first results for masses of positive and negative parity excited
baryons in lattice QCD using an O(a^2) improved gluon action and a Fat Link
Irrelevant Clover (FLIC) fermion action in which only the irrelevant operators
are constructed with fat links. The results are in agreement with earlier
calculations of N^* resonances using improved actions and exhibit a clear mass
splitting between the nucleon and its chiral partner, even for the Wilson
fermion action. The results also indicate a splitting between the lowest J^P =
1/2^- states for the two standard nucleon interpolating fields.


title: Hybrid meson decay from the lattice

abstract:
  We discuss the allowed decays of a hybrid meson in the heavy quark limit. We
deduce that an important decay will be into a heavy quark non-hybrid state and
a light quark meson, in other words, the de-excitation of an excited gluonic
string by emission of a light quark-antiquark pair.
  We discuss the study of hadronic decays from the lattice in the heavy quark
limit and apply this approach to explore the transitions from a spin-exotic
hybrid to $\chi_b \eta$ and $\chi_b S$ where $S$ is a scalar meson. We obtain a
signal for the transition emitting a scalar meson and we discuss the
phenomenological implications.


title:
Density Matrix Renormalization Group Approach to the Massive Schwinger
  Model

abstract:
  The massive Schwinger model is studied, using a density matrix
renormalization group approach to the staggered lattice Hamiltonian version of
the model. Lattice sizes up to 256 sites are calculated, and the estimates in
the continuum limit are almost two orders of magnitude more accurate than
previous calculations. Coleman's picture of `half-asymptotic' particles at
background field (theta = pi) is confirmed. The predicted phase transition at
finite fermion mass (m/g) is accurately located, and demonstrated to belong in
the 2D Ising universality class.


title:
Local Chirality of Low-Lying Dirac Eigenmodes and the Instanton Liquid
  Model

abstract:
  The reasons for using low-lying Dirac eigenmodes to probe the local structure
of topological charge fluctuations in QCD are discussed, and it is pointed out
that the qualitative double-peaked behavior of the local chiral orientation
probability distribution in these modes is necessary, but not sufficient for
dominance of instanton-like fluctuations. The results with overlap Dirac
operator in Wilson gauge backgrounds at lattice spacings ranging from a~0.04 fm
to a~0.12 fm are reported, and it is found that the size and density of local
structures responsible for double-peaking of the distribution are in
disagreement with the assumptions of the Instanton Liquid Model. More
generally, our results suggest that vacuum fluctuations of topological charge
are not effectively dominated by locally quantized (integer-valued) lumps in
QCD.


title: Flavour Singlet Mesons in Full QCD on the Lattice

abstract:
  We apply spectral methods to compute the OZI-rule suppressed loop-loop
correlators in the pseudoscalar meson flavour singlet channel. Using SESAM
configurations (obtained with two degenerate sea quark flavours on 16x16x16x32
lattices at beta = 5.6 with standard Wilson action), we find for the first time
clear evidence for mass plateau formation in the eta' channel of this theory.
As a consequence, we observe a clear signal of a mass gap persistent under
chiral extrapolation. This sets the stage for a more realistic two-channel
approach, where partially quenched strange quarks would be included, in
addition to u, d sea quarks.