title: Running quark mass in two flavor QCD

abstract:
  We present first results for the step scaling function sigma_P of the
renormalization factor Z_P of the pseudoscalar density. The simulations are
performed within the framework of the Schroedinger functional with two flavors
of O(a) improved Wilson fermions. The knowledge of sigma_P is required to
compute the renormalization group invariant quark masses. We also study the
performance of a variant of the HMC algorithm using two pseudofermion fields.


title: Dynamical fermions on anisotropic lattices

abstract:
  We report on our study of two-flavor full QCD on anisotropic lattices using
$O(a)$-improved Wilson quarks coupled with an RG-improved glue. The bare gauge
and quark anisotropies corresponding to the renormalized anisotropy
$\xi=a_s/a_t = 2$ are determined as functions of $\beta$ and $\kappa$, using
the Wilson loop and the meson dispersion relation at several lattice cutoffs
and quark masses.


title:
The phase diagram of the three-dimensional Z2 gauge Higgs system at zero
  and finite temperature

abstract:
  We study the effect of adding a matter field to the Z2 gauge model in three
dimensions at zero and finite temperature. Up to a given value of the parameter
regulating the coupling, the matter field produces a slight shift of the
transition line without changing the universality class of the pure gauge
theory, as seen by finite size scaling analysis or by comparison, in the finite
temperature case, to exact formulas of conformal field theory. At zero
temperature the critical line turns into a first-order transition. The fate of
this kind of transition in the finite temperature case is discussed.


title: On the Continuum Limit of the Discrete Regge Model in 4d

abstract:
  The Regge Calculus approximates a continuous manifold by a simplicial
lattice, keeping the connectivities of the underlying lattice fixed and taking
the edge lengths as degrees of freedom. The Discrete Regge model employed in
this work limits the choice of the link lengths to a finite number. This makes
the computational evaluation of the path integral much faster. A main concern
in lattice field theories is the existence of a continuum limit which requires
the existence of a continuous phase transition. The recently conjectured
second-order transition of the four-dimensional Regge skeleton at negative
gravity coupling could be such a candidate. We examine this regime with Monte
Carlo simulations and critically discuss its behavior.


title:
Confining string and P-vortices in the indirect Z(2) projection of SU(2)
  lattice gauge theory

abstract:
  We study the distribution of P-vortices near the confining string in the
indirect Z(2) projection of SU(2) lattice gauge theory. It occurs that the
density of vortices is constant at large distances and strongly suppressed near
the line connecting the test quark-antiquark pair. This means that the
condensate of P-vortices is broken inside the confining string. We also find
that the width of the P-vortex density distribution is proportional to the
logarithm of the distance between the quark and antiquark.


title: Vacuum Structure of the Ichimatsu-Decomposed Lattice Models

abstract:
  We proposed an `Ichimatsu'-decomposed lattice gauge theory with fermionic
symmetries. The vacuum structures of the gauge sector with two coupling
constants ($\beta_p,\beta_c$) are investigated for 3-dimensional Z$_2$ and
4-dimensional SU(2) cases using mean-field approximation and numerical
simulation. We found two phases on the ($\beta_p,\beta_c$) phase diagram for
3-dim. Z$_2$ case, while the diagram is a single phase for the latter.


title: Gluon propagators in maximal abelian gauge of SU(2) lattice gauge theory

abstract:
  We study propagators of diagonal and off-diagonal gluons in the momentum
space in maximal abelian gauge of SU(2) lattice gauge theory. Remaining U(1)
degrees of freedom are fixed using Landau gauge. We find substantial difference
between the propagator of the diagonal and the off-diagonal gluon in the
infrared region. The propagator of the off-diagonal gluon is suppressed in
comparison with that of the diagonal gluon at small momenta. In the ultraviolet
region both propagators behave as in nonabelian Landau gauge.


title: Non-commutative Solitons in Finite Quantum Mechanics

abstract:
  We construct the unitary evolution operators that realize the quantization of
linear maps of SL(2,R) over phase spaces of arbitrary integer discretization N
and show the non-trivial dependence on the arithmetic nature of N. We discuss
the corresponding uncertainty principle and construct the corresponding
coherent states, that may be interpreted as non-commutative solitons.


title: Transport coefficients from the lattice?

abstract:
  The prospects of extracting transport coefficients from euclidean lattice
simulations are discussed. Some general comments on the reconstruction of
spectral functions using the Maximal Entropy Method are given as well.


title: Fermionic Symmetry in Ichimatsu-Decomposed Lattice Models

abstract:
  We present the lattice models with exact fermionic symmetries relating
fermions and link variables. The plaquettes are distributed in an Ichimatsu
pattern (chequered). We explain this peculiar structure allows us to have a
translation in the algebra of the fermionic symmetries.


title: Comparing the R algorithm and RHMC for staggered fermions

abstract:
  The R algorithm is widely used for simulating two flavours of dynamical
staggered fermions. We give a simple proof that the algorithm converges to the
desired probability distribution to within O(dt^2) errors, but show that the
relevant expansion parameter is (dt/m)^2, m being the quark mass. The Rational
Hybrid Monte Carlo (RHMC) algorithm provides an exact (i.e., has no step size
errors) alternative for simulating the square root of the staggered Dirac
operator. We propose using it to test the validity of the R algorithm for
simulations carried out with dt m.


title:
Light quark masses from UKQCD's dynamical simulations with O(a)-improved
  Wilson fermions

abstract:
  I present preliminary results on the light quark masses from a partially
quenched analysis of UKQCD's dynamical datasets.


title:
Multiple molecular dynamics time-scales in Hybrid Monte Carlo fermion
  simulations

abstract:
  A scheme for separating the high- and low-frequency molecular dynamics modes
in Hybrid Monte Carlo (HMC) simulations of gauge theories with dynamical
fermions is presented. The algorithm is tested in the Schwinger model with
Wilson fermions.


title: Lattice QCD with light dynamical quarks

abstract:
  We report on the simulation of QCD with light dynamical quarks using the
two-step multi-boson (TSMB) algorithm.
  In an exploratory study with two flavours of quarks at lattice spacing about
0.27 fm and with quark mass down to one sixth of the strange quark mass
eigenvalue spectra and autocorrelations have been studied.
  Here we present results on the volume dependence as well as tests of possible
algorithmic improvements.


title: Lyapunov exponents in Minkowskian U(1) gauge theory

abstract:
  U(1) gauge fields are decomposed 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. We observe that the
monopole field carries the same Lyapunov exponent as the original U(1) field.
Evidence is found that monopole fields stay chaotic in the continuum whereas
the photon fields are regular.


title: Running coupling constant and propagators in SU(2) Landau gauge

abstract:
  We present a numerical study of the running coupling constant and of the
gluon and ghost propagators in minimal Landau gauge. Simulations are done in
pure SU(2) lattice gauge theory for several values of beta and lattice sizes.
We use two different lattice setups.


title: Composite reweighting with Imaginary Chemical Potentials in SU(3)

abstract:
  We review the overlap pathology of the Glasgow reweighting method for finite
density QCD, and discuss the sampling bias that effects the determination of
the ensemble-averaged fugacity polynomial expansion coefficients that form the
Grand Canonical Partition function. The expectation of the difference in free
energies between canonical partition functions generated with different
measures is presented as an indicator of a systematic quark number dependent
biasing in the reweighting approach. The advantages of building up an unbiased
polynomial expansion for the Grand Canonical Partition function through a
series of parallel ensembles generated by reweighting with imaginary chemical
potentials are then contrasted with addressing the overlap pathology through a
secondary reweighting.


title: The Paraldor Project

abstract:
  Paraldor is an experiment in bringing the power of categorical languages to
lattice QCD computations. Our target language is Aldor, which allows the
capture of the mathematical structure of physics directly in the structure of
the code using the concepts of categories, domains and their
inter-relationships in a way which is not otherwise possible with current
popular languages such as Fortran, C, C++ or Java. By writing high level
physics code portably in Aldor, and implementing switchable machine dependent
high performance back-ends in C or assembler, we gain all the power of
categorical languages such as modularity, portability, readability and
efficiency.


title: Electric Polarizability of Hadrons

abstract:
  The electric polarizability of a hadron allows an external electric field to
shift the hadron mass. We try to calculate the electric polarizability for
several hadrons from their quadratic response to the field at a=0.17fm using an
improved gauge field and the clover quark action. Results are compared to
experiment where available.


title: Residual mass effects in improved domain wall fermions

abstract:
  In order to improve simulations with domain wall fermions (DWFs), it has been
suggested to project out a number of low-lying eigenvalues of the 4-dimensional
Dirac operator that generates the transfer matrix of DWF. We investigate how
this projection method affects chiral properties of quenched DWF. In
particular, we study the behaviour of the residual mass as a function of the
size of the extra dimension.


title: Twisted mass QCD and the $\Delta I=1/2$ rule

abstract:
  We show that the application of twisted mass QCD (tmQCD) with four (Wilson)
quark flavours to the computation of lattice weak matrix elements relevant to
$\Delta I=1/2$ transitions has important advantages: the renormalisation of $K
\to \pi$ matrix elements does not require the subtraction of other dimension
six operators, the divergence arising from the subtraction of lower dimensional
operators is softened by one power of the lattice spacing and quenched
simulations do not suffer from exceptional configurations at small pion mass.
This last feature is also retained in the tmQCD computation of $K \to \pi\pi$
matrix elements, which, as far as renormalisation and power subtractions are
concerned, has properties analogous to the standard Wilson case.


title: Non-perturbative scale evolution of four-fermion operators

abstract:
  We apply the Schroedinger Functional (SF) formalism to determine the
renormalisation group running of four-fermion operators which appear in the
effective weak Hamiltonian of the Standard Model. Our calculations are done
using Wilson fermions and the parity-odd components of the operators.
Preliminary results are presented for the operator $O_{VA}=(\bar s \gamma_\mu
d)(\bar s \gamma_\mu \gamma_5 d)$.


title: Zone methods and the fermion sign problem

abstract:
  We review a recently proposed approach to the problem of alternating signs
for fermionic many body Monte Carlo simulations in finite temperature
simulations. We derive an estimate for fermion wandering lengths and introduce
the notion of permutation zones, special regions of the lattice where identical
fermions may interchange and outside of which they may not. Using successively
larger permutation zones, one can extrapolate to obtain thermodynamic
observables in regimes where direct simulation is impossible.


title:
Static Potential and Local Color Fields in Unquenched Three-Dimensional
  Lattice QCD

abstract:
  String breaking by dynamical quarks in (2+1)-d lattice QCD is demonstrated in
this project, by measuring the static potential and the local color-electric
field strength between a heavy quark and antiquark pair at large separations.
Simulations are done for unquenched SU(2) color with two flavors of staggered
quarks. An improved gluon action is used which allows simulations to be done on
coarse lattices, providing an extremely efficient means to access the quark
separations and propagation times at which string breaking occurs. The static
quark potential is extracted using only Wilson loop operators and hence no
valence quarks are present in the trial states. Results give unambiguous
evidence for string breaking as the static quark potential completely saturates
at twice the heavy-light meson mass at large separations. It is also shown that
the local color-electric field strength between the quark pair tends toward
vacuum values at large separations. Implications of these results for
unquenched simulations of QCD in 4-d are drawn.


title:
Hybrid mesons from anisotropic lattice QCD with the clover and improved
  gauge actions

abstract:
  We study hybrid mesons from the clover and improved gauge actions at
$\beta=2.6$ on the anisotropic $12^3\times36$ lattice using our PC cluster. We
estimate the mass of $1^{-+}$ light quark hybrid as well as the mass of the
charmonium hybrid. The improvement of both quark and gluonic actions, first
applied to the hybrid mesons, is shown to be more efficient in reducing the
lattice spacing and finite volume errors.


title: Topological susceptibility with the improved Asqtad action

abstract:
  As a test of the chiral properties of the improved Asqtad (staggered fermion)
action, we have been measuring the topological susceptibility as a function of
quark masses for 2 + 1 dynamical flavors. We report preliminary results, which
show reasonable agreement with leading order chiral perturbation theory for
lattice spacing less than 0.1 fm. The total topological charge, however, shows
strong persistence over Monte Carlo time.


title: Static hybrid quarkonium potential with improved staggered quarks

abstract:
  We are studying the effects of light dynamical quarks on the excitation
energies of a flux tube between a static quark and antiquark. We report
preliminary results of an analysis of the ground state potential and the
$\Sigma^{\prime+}_g$ and $\Pi_u$ potentials. We have measured these potentials
on closely matched ensembles of gauge configurations, generated in the quenched
approximation and with 2+1 flavors of Asqtad improved staggered quarks.


title: Chiral symmetry breaking in (2+1) dimensional QED

abstract:
  We study dynamical mass generation in QED in (2+1) dimensions using
Hamiltonian lattice methods. We use staggered fermions, and perform simulations
with explicit dynamical fermions in the chiral limit. We demonstrate that a
recently developed method to reduce the fermion sign problem can successfully
be applied to this problem. Our results are in agreement with both the strong
coupling expansion and with Euclidean lattice simulations.


title: Mollified Monte Carlo

abstract:
  Using a common technique for approximating distributions [generalized
functions], we are able to use standard Monte Carlo methods to compute QFT
quantities in Minkowski spacetime, under phase transitions, or when dealing
with coalescing stationary points.


title: Lattice QCD at finite isospin chemical potential and temperature

abstract:
  We simulate lattice QCD at a finite chemical potential $\mu_I$ for isospin
($I_3$) at zero and finite temperatures. At some $\mu_I=\mu_c$ QCD has a second
order transition with mean-field critical exponents to a state where ($I_3$) is
broken spontaneously by a charged pion condensate. Heating the system with
$\mu_I > \mu_c$ we find there is some temperature at which this condensate
evaporates. This transition appears to be second order and mean-field at lower
$\mu_I$ values, and first order for $\mu_I$ sufficiently large. We are
determining the dependence of the finite temperature crossover $T_c$ on $\mu_I$
for $\mu_I < \mu_c$. This is expected to be identical to $T_c$'s dependence on
quark-number chemical potential $\mu_q$ for small $\mu_q$.


title: Study of stochastic estimates of quark loops with unbiased subtraction

abstract:
  Stochastic noise estimator method is a powerful tool to calculate the
disconnected insertion involving quark loops. We study the variance reduction
technique with unbiased subtraction. We use the complex $Z_2$ noise to
calculate the quark loops on a $16^3 \times 24$ lattice with $\beta = 6.0$ and
$\kappa$ = 0.154. Unbiased subtraction method is performed by using hoping
parameter expansion. We report on the variance reduction for the point-split
vector current as a function of the number of subtraction terms and the number
of noise used.


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

abstract:
  We present results of phase shift for I=2 $S$-wave $\pi\pi$ system with the
Wilson fermions in the quenched approximation. The finite size method proposed
by L\"uscher is employed, and calculations are carried out at $\beta=5.9$
($a^{-1}=1.934(16)$ GeV from $m_\rho$) on $24^3 \times 60$, $32^3 \times 60$,
and $48^3 \times 60$ lattices.


title:
Light hadron spectrum with two flavors of $O(a)$ improved dynamical
  quarks : final results from JLQCD

abstract:
  We present the final results of the JLQCD calculation of the light hadron
spectrum and quark masses with two flavors of dynamical quarks using the
plaquette gauge action and fully $O(a)$-improved Wilson quark action at
$\beta=5.2$. We observe that sea quark effects lead to a closer agreement of
the strange meson and baryon masses with experiment and a reduction of quark
masses by about 25.


title:
Study of unstable particle through the spectral function in O(4)
  $\phi^4$ theory

abstract:
  We test application of the maximum entropy method to decompose the states
contributing to the unstable $\sigma$ correlation function through the spectral
function in the four dimensional O(4) $\phi^4$ theory. Reliable results are
obtained for the $\sigma$ mass and two-particle $\pi\pi$ state energy using
only the $\sigma$ correlation function. We also find that the property of the
$\sigma$ particle is different between the unstable ($m_{\sigma}/m_{\pi}>2$)
and stable ($m_{\sigma}/m_{\pi}<2$) cases.


title: Bayesian approach to the first excited nucleon state in lattice QCD

abstract:
  We present preliminary results from the first attempt to reconstruct the
spectral function in the nucleon and $\Delta$ channels from lattice QCD data
using the maximum entropy method (MEM). An advantage of the MEM analysis is to
enable us to access information of the excited state spectrum. Performing
simulations on two lattice volumes, we confirm the large finite size effect on
the first excited nucleon state in the lighter quark mass region.


title: Vortex free energies in SO(3) and SU(2) lattice gauge theory

abstract:
  Lattice gauge theories with gauge groups SO(3) and SU(2) are compared. The
free energy of electric twist, an order parameter for the
confinement-deconfinement transition which does not rely on centre-symmetry
breaking, is measured in both theories. The results are used to calibrate the
scale in SO(3).


title:
An exact Polynomial Hybrid Monte Carlo algorithm for dynamical
  Kogut-Susskind fermions

abstract:
  We present a polynomial Hybrid Monte Carlo (PHMC) algorithm as an exact
simulation algorithm with dynamical Kogut-Susskind fermions. The algorithm uses
a Hermitian polynomial approximation for the fractional power of the KS fermion
matrix. The systematic error from the polynomial approximation is removed by
the Kennedy-Kuti noisy Metropolis test so that the algorithm becomes exact at a
finite molecular dynamics step size. We performed numerical tests with
$N_f$$=$2 case on several lattice sizes. We found that the PHMC algorithm works
on a moderately large lattice of $16^4$ at $\beta$$=$5.7, $m$$=$0.02
($m_{\mathrm{PS}}/m_{\mathrm{V}}$$\sim$0.69) with a reasonable computational
time.


title: The ground state of three quarks

abstract:
  We measure the static three-quark potential in SU(3) lattice gauge theory
with improved accuracy, by using all available technical refinements, including
Luscher-Weisz exponential variance reduction. Together with insight gained from
3-state Potts model simulations, our results allow us to sort out the merits of
the Delta- and Y-ansaetze.


title: Masses of singlet and non-singlet 0++ particles

abstract:
  We compute the mass of the singlet 0++ state using both (psi_bar psi) and
Wilson loop operators from a N_f=2 lattice QCD calculation.


title: Recent results using all-point quark propagators

abstract:
  Pseudofermion methods for extracting all-point quark propagators are
reviewed, with special emphasis on techniques for reducing or eliminating
autocorrelations induced by low eigenmodes of the quark Dirac operator. Recent
applications, including high statistics evaluations of hadronic current
correlators and the pion form factor, are also described.


title: Spectrum of SU(2) SUSY Yang-Mills Theory with a light gluino

abstract:
  We report on new results for the low lying spectrum of N=1 SUSY Yang-Mills
Theory with SU(2) as the gauge group. Simulating on larger lattices at \kappa =
0.194 and \beta = 2.3, we slowly approach the supersymmetric limit at
m_{gluino} = 0.


title: Chiral logs with staggered fermions

abstract:
  We compute chiral logarithms in the presence of "taste" symmetry breaking of
staggered fermions. The lagrangian of Lee and Sharpe is generalized and then
used to calculate the logs in $\pi$ and $K$ masses. We correct an error in Ref.
[1] [C. Bernard, hep-lat/0111051]; the issue turns out to have implications for
the comparison with simulations, even at tree level. MILC data with three light
dynamical flavors can be well fit by our formulas. However, two new chiral
parameters, which describe order $a^2$ hairpin diagrams for taste-nonsinglet
mesons, enter in the fits. To obtain precise results for the physical
coefficients at order $p^4$, these new parameters will need to be bounded, at
least roughly.


title: Gauge-invariant two- and three- density correlators

abstract:
  Gauge-invariant spatial correlations between two and three quarks inside a
hadron are measured within quenched and unquenched QCD. These correlators
provide information on the shape and multipole moments of the pion, the rho,
the nucleon and the $\Delta$.


title: Gluon propagator and confinement scenario in Coulomb gauge

abstract:
  We present numerical results in SU(2) lattice gauge theory for the
instantaneous part of the gluon propagator in Coulomb gauge D_{44, inst} =
V_{coul}(R) \delta(t). Data are taken on lattice volumes 24^4 and 28^4 for 7
values of beta in the interval $2.2 \leq beta \leq 2.8$. The data are
confronted with the confinement scenario in Coulomb gauge. They are consistent
with a linearly rising color-Coulomb potential V_{coul}(R).


title: Staggered Fermion Thermodynamics using Anisotropic Lattices

abstract:
  Numerical simulations of full QCD on anisotropic lattices provide a
convenient way to study QCD thermodynamics with fixed physics scales and
reduced lattice spacing errors. We report results from calculations with
2-flavors of dynamical fermions where all bare parameters and hence the physics
scales are kept constant while the temperature is changed in small steps by
varying only the number of the time slices. The results from a series of
zero-temperature scale setting simulations are used to determine the Karsch
coefficients and the equation of state at finite temperatures.


title: Using Approximating Polynomials in Partial-Global Dynamical Simulations

abstract:
  Smeared link fermionic actions can be straightforwardly simulated with
partial-global updating. The efficiency of this simulation is greatly increased
if the fermionic matrix is written as a product of several near-identical
terms. Such a break-up can be achieved using polynomial approximations for the
fermionic matrix. In this paper we will focus on methods of determining the
optimum polynomials.


title:
Improving the Partial-Global Stochastic Metropolis Update for Dynamical
  Smeared Link Fermions

abstract:
  We discuss several methods that improve the partial-global stochastic
Metropolis (PGSM) algorithm for smeared link staggered fermions. We present
autocorrelation time measurements and argue that this update is feasible even
on reasonably large lattices.


title: Four-loop logarithms in 3d gauge + Higgs theory

abstract:
  We discuss the logarithmic contributions to the vacuum energy density of the
three-dimensional SU(3) + adjoint Higgs theory in its symmetric phase, and
relate them to numerical Monte Carlo simulations. We also comment on the
implications of these results for perturbative and non-perturbative
determinations of the pressure of finite-temperature QCD.


title: Exploring QCD at small sea quark masses with improved Wilson-type quarks

abstract:
  We explore the region of small sea quark masses below $m_{PS}/m_V=0.5$ in
two-flavor QCD using a mean-field improved clover quark action and an
RG-improved gauge action at $a \simeq 0.2$ fm on $12^3 \times 24$ and $16^3
\times 24$ lattices. We find that instability of the standard BiCGStab
algorithm at small quark masses can be mostly removed by the BiCGStab(DS-$L$)
algorithm, which employs $L$-th minimal residual polynomials with a dynamical
selection of $L$. We also find singular spikes of $\Delta H$ in the HMC
algorithm at moderate values of $\Delta\tau$. Nature of the spike is studied.
We also study finite-size effects and chiral properties of meson masses.


title: Calculation of the N to Delta electromagnetic transition matrix element

abstract:
  We present results on the ratio of electric quadrupole to magnetic dipole
amplitudes, $R_{EM}={\cal G}_{E2}/{\cal G}_{M1}$, for the transition $\gamma N
to \Delta$ from lattice QCD. We consider both the quenched and the 2-flavor
theory.


title: Geometry of percolating monopole clusters

abstract:
  We perform detailed measurements of the geometrical characteristics of the
percolating cluster of the magnetic monopole currents in the confining phase of
the lattice SU(2) gluodynamics. The Maximal Abelian projection is used to
define the monopoles. The use of the geometrical language is motivated by
recent observations that the full non-Abelian action associated with the
monopoles corresponds to point-like particles on the currently available
lattices. Scaling behavior of various quantities is observed.


title: Lattice simulations for the running coupling constant of QCD

abstract:
  The strong coupling constant alpha_s(mu_0), taken at a fixed reference scale
mu_0, is the single free parameter of QCD and should be known to the highest
available precision. The value of alpha_s should also be determined with good
accuracy over as large a range of scales as possible, in order to reveal
potential anomalous running in the strength of the strong interaction. Lattice
QCD is now able to calculate alpha_s with accuracy comparable to or better than
experiment. We review the status of such lattice calculations in quenched and
full QCD.


title: On the strange quark mass with improved staggered quarks

abstract:
  We present results on the sum of the masses of light and strange quark using
improved staggered quarks. Our calculation uses 2+1 flavours of dynamical
quarks. The effects of the dynamical quarks are clearly visible.


title: Non-perturbative determination of Z_A^{stat} in quenched QCD

abstract:
  We non-perturbatively calculate the renormalization factor of the static
axial vector current in O(a) improved quenched lattice QCD. Its scale
dependence is mapped out in the Schroedinger functional scheme by means of a
recursive finite-size scaling technique, taking the continuum limit in each
step. We also obtain Z_A^{stat} for Wilson fermions in order to renormalize
existing unimproved data on F_B^{bare} non-perturbatively.


title: High temperature QCD with three flavors of improved staggered quarks

abstract:
  We present an update of our study of high temperature QCD with three flavors
of quarks, using a Symanzik improved gauge action and the Asqtad staggered
quark action. Simulations are being carried out on lattices with Nt=4, 6 and 8
for the case of three degenerate quarks with masses less than or equal to the
strange quark mass, $m_s$, and on lattices with Nt=6 and 8 for degenerate up
and down quarks with masses in the range 0.2 m_s \leq m_{u,d} \leq 0.6 m_s, and
the strange quark fixed near its physical value. We also report on first
computations of quark number susceptibilities with the Asqtad action. These
susceptibilities are of interest because they can be related to event-by-event
fluctuations in heavy ion collision experiments. Use of the improved quark
action leads to a substantial reduction in lattice artifacts. This can be seen
already for free fermions and carries over into our results for QCD.


title: Color confinement and dual superconductivity in unquenched QCD

abstract:
  We report on evidence from lattice simulations that confinement is produced
by dual superconductivity of the vacuum in full QCD as in quenched QCD.
Preliminary information is obtained on the order of the deconfining phase
transition.


title:
Calorons and BPS monopoles with non-trivial holonomy in the confinement
  phase of SU(2) gluodynamics

abstract:
  With the help of the cooling method applied to SU(2) lattice gauge theory at
non-zero $T \le T_c$ we present numerical evidence for the existence of
superpositions of Kraan-van Baal caloron (or BPS monopole pair) solutions with
non-trivial holonomy, which might constitute an important contribution to the
semi-classical approximation of the partition function.


title: Deconfining transition in Full QCD

abstract:
  We present evidence that in full QCD with two dynamical quarks confinement is
produced by dual superconductivity of the vacuum as in the quenched theory.
Preliminary information is obtained on the nature of the deconfining
transition.


title: Remark on the Theoretical Uncertainty in $B^0$-$\bar{B}^0$ Mixing

abstract:
  We re-examine the theoretical uncertainty in the Standard Model expression
for $B^0$-$\bar{B}^0$ mixing. We focus on lattice calculations of the ratio
$\xi$, needed to relate the oscillation frequency of $B^0_s$-$\bar{B}^0_s$
mixing to $V_{td}$. We replace the usual linear chiral extrapolation with one
that includes the logarithm that appears in chiral perturbation theory. We find
a significant shift in the ratio $\xi$, from the conventional $1.15\pm0.05$ to
$\xi=1.32\pm0.10$.


title: QCD phase diagram for small densities from simulations at imaginary mu

abstract:
  We present results on the QCD phase diagram for small densities without
reweighting. Our simulations are performed with an imaginary chemical potential
mu_I for which the fermion determinant is positive. On an 8^3x4 lattice with 2
flavors of staggered quarks, we map out the pseudo-critical temperature
T_c(mu_I). For mu_I/T < pi/3, this is an analytic function whose Taylor
expansion converges rapidly, with truncation errors smaller than statistical
ones. The result is analytically continued to give the location of the
pseudo-critical line for real mu_B<500 MeV.


title: A study of large field configurations in MC simulations

abstract:
  We discuss a new approach of scalar field theory where the small field
contributions are treated perturbatively and the large field configurations
(which are responsible for the asymptotic behavior of the perturbative series)
are neglected. In two Borel summable lambda phi ^4 problems improved
perturbative series can be obtained by this procedure. The modified series
converge towards values exponentially close to the exact ones. For lambda
larger than some critical value, the method outperforms Pade approximants and
Borel summations. The method can also be used for series which are not Borel
summable such as the double-well potential series and provide a perturbative
approach of the instanton contribution. Semi-classical methods can be used to
calculate the modified Feynman rules, estimate the error and optimize the field
cutoff. We discuss Monte Carlo simulations in one and two dimensions which
support the hypothesis of dilution of large field configurations used in these
semi-classical calculations. We show that Monte Carlo methods can be used to
calculate the modified perturbative series.


title: Panel discussion on chiral extrapolation of physical observables

abstract:
  This is an approximate reconstruction of the panel discussion on chiral
extrapolation of physical observables. The session consisted of brief
presentations from panelists, followed by responses from the panel, and
concluded with questions and comments from the floor with answers from
panelists. In the following, the panelists have summarized their statements,
and the ensuing discussion has been approximately reconstructed from notes.


title: Topological flux sectors in extended U(1) gauge theory on T^4

abstract:
  We consider the 4d compact U(1) gauge theory with fundamental-adjoint action
on a hypertorus. We give a full characterization of the phase diagram of this
model in terms of topological flux sectors.


title: k-String Tensions and Center Vortices at Large N

abstract:
  We point out that there is a natural explanation, in terms of the center
vortex confinement mechanism, for the expected Casimir/Sine Law scaling of
k-string tensions in the large N limit. The crucial ingredient is the existence
of Z(N) center monopoles, which go over to U(1) monopoles in this limit. Vortex
densities leading to Casimir/Sine Law scaling at large-N are constructed; these
densities have no obvious pathologies and in particular do not grow with N. We
also note that center vortices are stable classical solutions of the Wilson
action, for all SU(N) gauge theories with N>4, and extend this old result to a
broad class of lattice actions motivated by the improved action program and the
renormalization group.


title: Topological Charge Correlators, Spectral Bounds, and Contact Terms

abstract:
  The structure of topological charge fluctuations in the QCD vacuum is
strongly restricted by the spectral negativity of the Euclidean 2-point
correlator for $x\neq 0$ and the presence of a positive contact term. Some
examples are considered which illustrate the physical origin of these
properties.


title: Heavy-light meson in anisotropic lattice QCD

abstract:
  We examine whether the $O(a)$ improved quark action on anisotropic lattices
can be used as a framework for the heavy quark, which enables precision
computation of matrix elements of heavy-light mesons. To this end, it is
crucial to verify that a mass independent and nonperturbative tuning of the
parameters is possible. As a first step, we observe the dispersion relation of
heavy-light mesons on a quenched lattice using the action which is
nonperturbatively tuned only for the leading terms. On a lattice with the
spatial cutoff $a_\sigma^{-1} \simeq$ 1.6 GeV and the anisotropy $\xi=4$, the
relativity relation holds within 2% accuracy in the quark mass region $a_\sigma
m_Q \leq 1.2$ with the bare anisotropy parameter tuned for the massless quark.
We also apply the action to a calculation of heavy-light decay constants in the
charm quark mass region.


title:
Chiral extrapolation of light-light and heavy-light decay constants in
  unquenched QCD

abstract:
  We test the one-loop chiral perturbation theory formula on unquenched lattice
data of pseudoscalar meson decay constants. The chiral extrapolation including
the effect of the chiral logarithm is attempted and its uncertainty is
discussed.


title: A lattice estimate of the g_{D^* D pi} coupling

abstract:
  We present the results of the first direct determination of the g_{D^* D pi}
coupling using lattice QCD. From our simulations in the quenched approximation,
we obtain g_{D^* D pi} = 18.8 +/- 2.3^{+1.1}_{-2.0} and hat(g) = 0.67 +/-
0.08^{+0.04}_{-0.06}. It is in agreement with a recent experimental result from
CLEO.


title: Confinement without a center: the exceptional group G(2)

abstract:
  We discuss theories with the exceptional centerless gauge group G(2), paying
attention to confinement and the pattern of chiral symmetry breaking.
Exploiting the Higgs mechanism to break the symmetry down to SU(3), we also
present how the familiar features of confinement and chiral symmetry breaking
of SU(3) gauge theories reemerge. G(2) gauge theories show up as an unusual
theoretical framework to study SU(3) gauge theories without the ``luxury'' of a
center.


title: String breaking with Wilson loops?

abstract:
  A convincing, uncontroversial observation of string breaking, when the static
potential is extracted from Wilson loops only, is still missing. This failure
can be understood if the overlap of the Wilson loop with the broken string is
exponentially small. In that case, the broken string ground state will only be
seen if the Wilson loop is long enough. Our preliminary results show string
breaking in the context of the 3d SU(2) adjoint static potential, using the
L\"uscher-Weisz exponential variance reduction approach. As a by-product, we
measure the fundamental SU(2) static potential with improved accuracy and see
clear deviations from Casimir scaling.


title:
Simulation of a modified Hubbard model with a chemical potential using a
  meron-cluster algorithm

abstract:
  We show how a variant of the Hubbard model can be simulated using a
meron-cluster algorithm. This provides a major improvement in our ability to
determine the behavior of these types of models. We also present some results
that clearly demonstrate the existence of a superconducting state in this
model.


title: B_s Mesons using Staggered Light Quarks

abstract:
  Last year we proposed using staggered fermions as the light quarks, combined
with nonrelativistic heavy quarks, in simulations of heavy-light mesons. A
first round of tests which focuses on the B_s meson has been completed using
quenched lattices, and results are presented here for the kinetic B_s mass, the
B_s^* - B_s splitting, and f_{B_s}. The next project, already underway, is to
compute the B and B_s decay constants and spectra on the n_f = 2+1 and 3 MILC
lattices. We report on progress with one set of these configurations.


title: Exotic hybrid mesons from improved Kogut-Susskind fermions

abstract:
  We summarize our measurement of the mass of the exotic $1^{-+}$ hybrid meson
using an improved Kogut-Susskind action. We show results from both quenched and
dynamical quark simulations and compare with results from Wilson quarks.
Extrapolation of these results to the physical quark mass allows comparison
with experimental candidates for the $1^{-+}$ hybrid meson.


title: On Witten's global anomaly for higher SU(2) representations

abstract:
  The spectral flow of the overlap operator is computed numerically along a
particular path in gauge field space. The path connects two gauge equivalent
configurations which differ by a gauge transformation in the non-trivial class
of pi_4(SU(2)). The computation is done with the SU(2) gauge field in the
fundamental, the 3/2, and the 5/2 representation. The number of eigenvalue
pairs that change places along this path is established for these three
representations and an even-odd pattern predicted by Witten is verified.


title: Quenched QCD with fixed-point and chirally improved fermion

abstract:
  In this contribution we present results from quenched QCD simulations with
the parameterized fixed-point (FP) and the chirally improved (CI) Dirac
operator. Both these operators are approximate solutions of the Ginsparg-Wilson
equation and have good chiral properties. We focus our discussion on
observables sensitive to chirality. In particular we explore pion masses down
to 210 MeV in light hadron spectroscopy, quenched chiral logs, the pion decay
constant and the pion scattering length. We discuss finite volume effects,
scaling properties of the FP and CI operators and performance issues in their
numerical implementation.


title: The radial distributions of a heavy-light meson on a lattice

abstract:
  In an earlier work, the charge (vector) and matter (scalar) radial
distributions of heavy-light mesons were measured in the quenched approximation
on a 16^3 times 24 lattice with a quark-gluon coupling of 5.7, a lattice
spacing of 0.17 fm, and a hopping parameter corresponding to a light quark mass
about that of the strange quark.
  Several improvements are now made: 1) The configurations are generated using
dynamical fermions with a quark-gluon coupling of 5.2 (a lattice spacing of
0.14 fm); 2) Many more gauge configurations are included (78 compared with the
earlier 20); 3) The distributions at many off-axis, in addition to on-axis,
points are measured; 4) The data-analysis is much more complete. In particular,
distributions involving excited states are extracted.
  The exponential decay of the charge and matter distributions can be described
by mesons of mass 0.9+-0.1 and 1.5+-0.1 GeV respectively - values that are
consistent with those of vector and scalar qqbar-states calculated directly
with the same lattice parameters.


title: Lattice QCD Results at Finite Temperature and Density

abstract:
  Recent lattice results on QCD at finite temperatures and densities are
reviewed. Two new and independent techniques give compatible results for
physical quantities. The phase line separating the hadronic and quark-gluon
plasma phases, the critical endpoint and the equation of state are discussed.


title: Numerical Exploration of the RI/MOM Scheme Gauge Dependence

abstract:
  The gauge dependence of some fermion bilinear RI/MOM renormalization
constants is studied by comparing data which have been gauge-fixed in two
different realizations of the Landau gauge and in a generic covariant gauge.
The very good agreement between the various sets of results and the theory
indicates that the numerical uncertainty induced by the lattice gauge-fixing
procedure is below the statistical errors of our data sample which is of the
order of (1-1.5)%.


title: The inverted XY universality of the superconductivity phase transition

abstract:
  It has been conjectured that the phase transition in the Ginzburg-Landau
theory is dual to the XY model transition. We study numerically a particular
limit of the GL theory where this duality becomes exact, clarifying some of the
problems encountered in standard GL theory simulations. This may also explain
the failure of the superconductor experiments to observe the XY model scaling.


title: Instantons and chiral symmetry breaking in SU(N) gauge theories

abstract:
  We address the question of whether the low modes of the Dirac operator are
caused by topological objects such as instantons in SU(N) gauge theories. We
study the pseudo-scalar density of these modes, finding the size distributions
of the instantons, and comparing it with the underlying gauge field. We find
that, although the near-zero modes of the Dirac operator depend on topology for
all N, their small instanton content decreases as N increases.


title: No confinement without Coulomb confinement

abstract:
  We compare the physical potential $V_D(R)$ of an external quark-antiquark
pair in the representation $D$ of SU(N), to the color-Coulomb potential $V_{\rm
coul}(R)$ which is the instantaneous part of the 44-component of the gluon
propagator in Coulomb gauge, $D_{44}(\vx,t) = V_{\rm coul}(|\vx|) \delta(t)$ +
(non-instantaneous). We show that if $V_D(R)$ is confining, $\lim_{R \to
\infty}V_D(R) = + \infty$, then the inequality $V_D(R) \leq - C_D V_{\rm
coul}(R)$ holds asymptotically at large $R$, where $C_D > 0$ is the Casimir in
the representation $D$. This implies that $ - V_{\rm coul}(R)$ is also
confining.


title: Stripes from (noncommutative) stars

abstract:
  We show that lattice regularization of noncommutative field theories can be
used to study non-perturbative vacuum phases. Specifically we provide evidence
for the existence of a striped phase in two-dimensional noncommutative scalar
field theory


title: Effects of Quenching in \Delta I=1/2 Kaon Decays

abstract:
  We present the inconsistencies which arise in quenched QCD in $\Delta I=1/2$
non-leptonic kaon decays using chiral perturbation theory (ChPT) to one loop.
In particular we discuss how the lack of unitarity of the quenched theory
invalidates the usual methods for the extraction of matrix elements from
correlation functions.


title: $K\to \pi\pi$ Decay Amplitude on the Lattice

abstract:
  Recent theoretical and numerical progresses of the lattice calculations of
$K\to\pi\pi$ decay amplitude are reviewed.


title: QCD String Spectrum 2002

abstract:
  Results from a comprehensive new analysis on the excitation spectrum of the
QCD string are presented. A rapid onset of string formation is observed in the
spectrum on a length scale of 2 fm, with Dirichlet boundary conditions. The
crossover from the short distance spectrum towards string excitations and an
observed fine structure in the 1--3 fm range are related to effective string
theory. The deficiencies of the Nambu-Goto bosonic string model in describing
the observed spectrum are briefly discussed.


title: Finite size effects on $M_\pi$ in QCD from Chiral Perturbation Theory

abstract:
  We present a determination of the shift $M_\pi(L)-M_\pi$ due to the finite
spatial box size $L$ by means of $N_f=2$ Chiral Perturbation Theory and
L\"uscher's formula. The range of applicability of the chiral prediction is
discussed.


title: Finite Size Effects in Nucleon Masses in Dynamical QCD

abstract:
  For lattice calculations with light dynamical quarks, finite size effects
have become an important aspect. We study finite size effects in nucleon masses
on N_f=2 dynamical lattices of 1-2 fm. Predictions for the finite size effects
are obtained in one-loop chiral perturbation theory.


title: The lattice scale at large beta in quenched QCD

abstract:
  In this paper we extend the estimate of the value of the lattice spacing a in
units of the r0 scale at values of the bare coupling larger than those
available. By using results from the computation of the renormalised coupling
in the Schroedinger functional formalism we find that from beta \simeq 7 onward
the behaviour predicted by asymptotic freedom at tree loop describes very well
the data if a value of (r0 Lambda) slightly lower then the latest available is
used. We also show that, by sticking to the current value, an effective four
loop term can describe as well the data. The systematic relative error on the
lattice spacing induced by the choice of the procedure is between 1% and 3% for
6.92 < beta < 8.5.


title: fB from finite size effects in lattice QCD

abstract:
  We discuss a novel method to calculate fB on the lattice based on the study
of the dependence of finite size effects upon the heavy quark mass of flavoured
mesons and on a non--perturbative recursive finite size technique. This method
avoids the systematic errors related to extrapolations from the static limit or
to the tuning of the coefficients of effective Lagrangian and the results admit
an extrapolation to the continuum limit. We show the results of a first
estimate at finite lattice spacing, but close to the continuum limit, giving fB
= 170(11)(5)(22)MeV. We also obtain fBs = 192(9)(5)(24)MeV. The first error is
statistical, the second is our estimate of the systematic error from the method
and the third the systematic error from the specific approximations adopted in
this first exploratory calculation. The method can be generalized to two--scale
problems in lattice QCD.


title: The QCD equation of state at finite T and \mu

abstract:
  We calculate the pressure (p), the energy density (\epsilon) and the baryon
density (n_B) of QCD at finite temperatures (T) and chemical potentials (\mu).
The recently proposed overlap improving multi-parameter reweighting technique
is used to determine observables at nonvanishing chemical potentials. Our
results are obtained by studying n_f=2+1 dynamical staggered quarks with
semi-realistic masses on N_t=4 lattices.


title: A scalable PC-based parallel computer for lattice QCD

abstract:
  A PC-based parallel computer for medium/large scale lattice QCD simulations
is suggested. The Eotvos Univ., Inst. Theor. Phys. cluster consists of 137
Intel P4-1.7GHz nodes. Gigabit Ethernet cards are used for nearest neighbor
communication in a two-dimensional mesh. The sustained performance for
dynamical staggered(wilson) quarks on large lattices is around 70(110) GFlops.
The exceptional price/performance ratio is below $1/Mflop.


title: Heavy to light vector meson semileptonic decays

abstract:
  New (preliminary) results for the form factors relevant for the semileptonic
decays of heavy pseudoscalar to a light vector meson are presented. In
particular, we discuss the form factors for D --> K* and B --> rho modes.


title: The eta ' signal from partially quenched Wilson fermions

abstract:
  We present new results from our ongoing study of flavor singlet pseudoscalar
mesons in QCD. Our approach is based on (a) performing truncated eigenmode
expansions for the hairpin diagram and (b) incorporating the ground state
contribution for the connected meson propagator. First, we explain how the
computations can be substantially improved by even-odd preconditioning. We
extend previous results on early mass plateauing in the eta' channel of
two-flavor full QCD with degenerate sea and valence quarks to the partially
quenched situation. We find that early mass plateau formation persists in the
partially quenched situation.


title: Monopole Condensation in full QCD using the Schroedinger Functional

abstract:
  We use a lattice thermal partition functional to study Abelian monopole
condensation in full QCD with $N_f=2$ staggered fermions. We present
preliminary results on $16^3\times4$ and $32^3\times4$ lattices.


title: Probing Confinement with Chromomagnetic Fields

abstract:
  Using the lattice Schr\"odinger functional we study vacuum dynamics of SU(3)
gauge theory at finite temperature. The vacuum is probed by means of an
external constant Abelian chromomagnetic field. We find that by increasing the
strength of the applied external field the deconfinement temperature decreases
towards zero. This implies that strong enough Abelian chromomagnetic fields
destroy confinement of color.


title: Determinant Calculations Using Random Walk Worldline Loops

abstract:
  We use statistical ensembles of worldline loops generated by random walk on
hypercubic lattices to calculate matter determinants in background Yang-Mills
fields.


title: International Lattice Data Grid

abstract:
  We propose the co-ordination of lattice QCD grid developments in different
countries to allow transparent exchange of gauge configurations in future,
should participants wish to do so. We describe briefly UKQCD's XML schema for
labelling and cataloguing the data. A meeting to further develop these ideas
will be held in Edinburgh on 19/20 December 2002, and will be available over
AccessGrid.


title:
The determination of alpha_s from lattice QCD with 2+1 flavors of
  dynamical quarks

abstract:
  We describe the first lattice determination of the strong coupling constant
with 3 flavors of dynamical quarks. The method follows previous analyses in
using a perturbative expansion for the plaquette and Upsilon spectroscopy to
set the scale. Using dynamical configurations from the MILC collaboration with
2+1 flavors of dynamical quarks we are able to avoid previous problems of
having to extrapolate to 3 light flavors from 0 and 2. Our results agree with
our previous work: alpha_s_MSbar(M_Z) = 0.121(3).


title: Unquenched QCD with Light Quarks

abstract:
  We present recent results in unquenched lattice QCD with two degenerate light
sea quarks using the truncated determinant approximation (TDA). In the TDA the
infrared modes contributing to the quark determinant are computed exactly up to
some cutoff in quark off-shellness (typically 2$\Lambda_{QCD}$). This approach
allows simulations to be performed at much lighter quark masses than possible
with conventional hybrid MonteCarlo techniques. Results for the static energy
and topological charge distributions are presented using a large ensemble
generated on very coarse (6$^4$) but physically large lattices. Preliminary
results are also reported for the static energy and meson spectrum on 10$^3$x20
lattices (lattice scale $a^{-1}$=1.15 GeV) at quark masses corresponding to
pions of mass $\leq$ 200 MeV. Using multiboson simulation to compute the
ultraviolet part of the quark determinant the TDA approach becomes an exact
with essentially no increase in computational effort. Some preliminary results
using this fully unquenched algorithm are presented.


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

abstract:
  We present a lattice QCD calculation of the scattering phase shift for the
I=2 $S$-wave two-pion system using the finite size method proposed by
L\"uscher. We work in the quenched approximation employing the standard
plaquette action at $\beta=5.9$ for gluons and the Wilson fermion action for
quarks. The phase shift is extracted from the energy eigenvalues of the
two-pion system, which are obtained by a diagonalization of the pion 4-point
function evaluated for a set of relative spatial momenta. In order to change
momentum of the two-pion system, calculations are carried out on $24^3\times
60$, $32^3\times 60$, and $48^3\times 60$ lattices. The phase shift is
successfully calculated over the momentum range $0 < p^2 < 0.3 {\rm GeV}^2$.


title: Locality and topology with fat link overlap actions

abstract:
  We study the locality and topological properties of fat link clover overlap
(FCO) actions. We find that a small amount of fattening (2-4 steps of APE or 1
step of HYP) already results in greatly improved properties compared to the
Wilson overlap (WO). We present a detailed study of the localisation of the FCO
and its connection to the density of low modes of $A^\dagger A$. In contrast to
the Wilson overlap, on quenched gauge backgrounds we do not find any dependence
of the localization of the FCO on the gauge coupling. This suggests that the
FCO remains local in the continuum limit. The FCO also faithfully reproduces
the zero mode wave functions of typical lattice instantons, not like the Wilson
overlap. After a general discussion of different lattice definitions of the
topological charge we also show that the FCO together with the Boulder charge
are likely to satisfy the index theorem in the continuum limit. Finally, we
present a high statistics computation of the quenched topological
susceptibility with the FCO action.


title: QCD simulations at small chemical potential

abstract:
  Within the reweighting approach, one has the freedom to choose the Monte
Carlo action so that it provides a good overlap with the finite-\mu measure but
remains simple to simulate. We explore several choices of action in the regime
of small \mu. Simulating with a finite isospin chemical potential \mu_I=\mu
gives a better overlap than the standard choice \mu=0, with no computational
overhead.


title: Alternative Numerical Techniques

abstract: Two new approaches to numerical QFT are presented.


title: Magnetic polarizability of hadrons from lattice QCD

abstract:
  We extract the magnetic polarizability from the quadratic response of a
hadron's mass shift in progressively small static magnetic fields. The
calculation is done on a 24x12x12x24 lattice at a = 0.17 fm with an improved
gauge action and the clover quark action. The results are compared to those
from experiments and models where available.


title: Modelling the quark propagator

abstract:
  The quark propagator is at the core of lattice hadron spectrum calculations
as well as studies in other nonperturbative schemes. We investigate the quark
propagator with an improved staggered action (Asqtad) and an improved gluon
action, which provides good quality data down to small quark masses. This is
used to construct ans\"{a}tze suitable for model hadron calculations as well as
adding to our intuitive understanding of QCD.


title: Lattice perturbation theory for gluonic and fermionic actions

abstract:
  We calculate the two loop Landau mean links and the one loop renormalisation
of the anisotropy for Wilson and improved SU(3) gauge actions, using twisted
boundary conditions as a gauge invariant infrared regulator. We show these
accurately describe simulated results, and outline a method for generating
Feynman rules for general lattice field theories, in a form suitable for
efficient numerical calculation of perturbative loop diagrams.


title:
Non-perturbative renormalisation of four fermion operators and B-bar B
  mixing with Wilson fermions

abstract:
  We present new results for the renormalisation and subtraction constants for
the four fermion Delta F=2 operators, computed non-perturbatively in the RI-MOM
scheme (in the Landau gauge). From our preliminary analysis of the lattice data
at beta=6.45, for the B-bar B mixing bag-parameter we obtain B_B^{RGI} =
1.46(7)(1).


title: Quenched scalar meson correlator with Domain Wall Fermions

abstract:
  We study the singlet and non-singlet scalar-meson masses using domain wall
fermions and the quenched approximation. The singlet mass is found to be
smaller than the non-singlet mass and indicates that the lowest singlet meson
state could be lighter than 1 GeV. The two-point functions for very small quark
masses are compared with expectations from the small-volume chiral perturbation
theory and the presence of fermionic zero modes.


title: The chiral limit of non-compact QED(3)

abstract:
  Non-compact QED(3) with four-component fermion flavor content larger than or
equal to two is studied numerically near the chiral limit to understand its
chiral symmetry breaking features. We monitor discretization and finite size
effects on the chiral condensate by simulating the model at different values of
the gauge coupling on lattices ranging in size from 10^3 to 50^3. Our upper
bound for the dimensionless condensate beta^2<psibarpsi> in the N_f=2 case is
5x10^{-5}.


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

abstract:
  We introduce a generalized Maximum Abelian Gauge (MAG). We work with this new
gauge on 12^4 lattices for beta=5.7,5.8 and 16^4 lattices for beta=5.9,6.0. We
also introduce a form of abelian projection related to the generalized MAG. We
measure U(1)xU(1) wilson loops and single color magnetic current densities.


title: Moving NRQCD for B Form Factors at High Recoil

abstract:
  We derive the continuum and lattice tree-level moving NRQCD (mNRQCD) through
order 1/m^2. mNRQCD is a generalization of NRQCD for dealing with hadrons with
nonzero velocity u_mu. The quark's total momentum is written as P^mu=Mu^mu+k^mu
where k^mu << Mu^mu is discretized and Mu^mu is treated exactly. Radiative
corrections to couplings on the lattice are discussed. mNRQCD is particularly
useful for calculating B->pi and B->D form factors since errors are similar at
low and high recoil.


title: Kaon Weak Matrix Elements with Wilson Fermions

abstract:
  We present results of several numerical studies with Wilson fermions relevant
for kaon physics. We compute the B_K parameter by using two different methods
and extrapolate to the continuum limit. Our preliminary result is B_K(2
GeV)=0.66(7). Delta I=3/2 K->pi pi matrix elements are obtained by using the
next-to-leading order expressions derived in chiral perturbation theory in
which the low energy constants are determined by the lattice results computed
at unphysical kinematics. From the simulation at beta=6.0 our (preliminary)
results read: <pi pi|O_7(2 GeV)|K>_{I=2}=0.14(1)(1) GeV^3 and <pi
pi|O_8(2GeV)|K>_{I=2}=0.69(6)(6) GeV^3.


title: Nucleon matrix elements with domain wall fermions

abstract:
  We present the status of our calculation of the first few moments of the
nucleon structure functions. Our calculations are done using domain wall
fermions in the quenched approximation with the DBW2 gauge action at 1.3GeV
inverse lattice spacing.


title: Center Vortices at N > 4 Colors

abstract:
  We discuss two issues related to the physics of center vortices in pure SU(N)
lattice gauge theory at large N: (1) Center vortices are stable classical
solutions of the Wilson action, as well as of a wide class of improved lattice
actions, for any N > 4. (2) The natural scaling of k-string tensions at large
N, in the vortex picture of confinement, is \sigma(k)=k \sigma(1). This is the
common large N limit of Casimir and Sine Law scaling. The crucial feature for
explaining this behavior is the existence of center monopoles.


title:
Temporal meson correlators at finite temperature on quenched anisotropic
  lattice

abstract:
  We study charmonium correlators at finite temperature in quenched anisotropic
lattice QCD. The smearing technique is applied to enhance the low energy part
of the correlator. We use two analysis procedures: the maximum entropy method
for extraction of the spectral function without assuming specific form, as an
estimate of the shape of spectral function, and the $\chi^2$ fit assuming
typical forms as quantitative evaluation of the parameters associated to the
forms. We find that at $T\simeq 0.9T_c$ the ground state peak has almost the
same mass as at T=0 and almost vanishing width. At $T\simeq 1.1T_c$, our result
suggests that the correlator still has nontrivial peak structure at almost the
same position as below $T_c$ with finite width.


title: Evidence for BCS Diquark Condensation in the 3+1d Lattice NJL Model

abstract:
  We present results of numerical simulations of the 3+1d Nambu - Jona-Lasinio
model with a non-zero baryon chemical potential mu, with particular emphasis on
the superfluid diquark condensate and associated susceptibilities. The results,
when extrapolated to the zero diquark source limit, are consistent with the
existence of a non-zero BCS condensate at high baryon density. The nature of
the infinite volume and zero temperature limits are discussed.


title: Gasser-Leutwyler coefficients: A progress report

abstract:
  Last year, we reported our first results on the determination of
Gasser-Leutwyler coefficients using partially quenched lattice QCD with three
flavors of dynamical staggered quarks. We give an update on our progress in
determining two of these coefficients, including an exhaustive effort to
estimate all sources of systematic error. At this conference, we have heard
about algorithmic techniques to reduce staggered flavor symmetry breaking and a
method to incorporate staggered flavor breaking into the partially quenched
chiral Lagrangian. We comment on our plans to integrate these developments into
our ongoing program.


title: On the price of light quarks

abstract:
  The computational cost of numerical simulations of QCD with light dynamical
Wilson-quarks is estimated. The qualitative behaviour of the pion mass and
coupling at small quark masses is discussed.


title: Phase diagram of the three-dimensional NJL model

abstract:
  With the exception of confinement the three-dimensional Nambu-Jona-Lasinio
(NJL_3) model incorporates many of the essential properties of QCD. We discuss
the critical properties of the model at nonzero temperature T and/or nonzero
chemical potential $\mu$. We show that the universality class of the thermal
transition is that of the d=2 classical spin model with the same symmetry. We
provide evidence for the existence of a tricritical point in the
($\mu$,temperature) plane. We also discuss numerical results by Hands et al.
which showed that the system is critical for $\mu>\mu_c$ and the diquark
condensate is zero.


title:
Monte Carlo studies of three-dimensional O(1) and O(4)
  \boldmath{$\phi^4$} theory related to BEC phase transition temperatures

abstract:
  The phase transition temperature for the Bose-Einstein condensation (BEC) of
weakly-interacting Bose gases in three dimensions is known to be related to
certain non-universal properties of the phase transition of three-dimensional
O(2) symmetric $\phi^4$ theory. These properties have been measured previously
in Monte Carlo lattice simulations. They have also been approximated
analytically, with moderate success, by large $N$ approximations to O($N$)
symmetric $\phi^4$ theory. To begin investigating the region of validity of the
large $N$ approximation in this application, I have applied the same Monte
Carlo technique developed for the O(2) model ([5]) to O(1) and O(4) theories.
My results indicate that there might exist some theoretically unanticipated
systematic errors in the extrapolation of the continuum value from lattice
Monte Carlo results. The final results show that the difference between
simulations and NLO large $N$ calculations does not improve significantly from
N=2 to N=4. This suggests one would need to simulate yet larger $N$'s to see
true large $N$ scaling of the difference. Quite unexpectedly (and presumably
accidentally), my Monte Carlo result for N=1 seems to give the best agreement
with the large $N$ approximation among the three cases.


title: Locality and Statistical Error Reduction on Correlation Functions

abstract:
  We propose a multilevel Monte-Carlo scheme, applicable to local actions,
which is expected to reduce statistical errors on correlation functions. We
give general arguments to show how the efficiency and parameters of the
algorithm are determined by the low-energy spectrum. As an application, we
measure the euclidean-time correlation of pairs of Wilson loops in SU(3) pure
gauge theory with constant relative errors. In this case the ratio of the new
method's efficiency to the standard one increases as exp{m_0t/2}, where m_0 is
the mass gap and t the time separation.


title: Finite density QCD via imaginary chemical potential

abstract:
  We study QCD at nonzero temperature and baryon density in the framework of
the analytic continuation from imaginary chemical potential. We carry out
simulations of QCD with four flavor of staggered fermions, and reconstruct the
phase diagram in the temperature-imaginary \mu plane. We consider ans\"atze for
the analytic continuation of the critical line and other observables motivated
both by theoretical considerations and mean field calculations in four fermion
models and random matrix theory. We determine the critical line, and the
analytic continuation of the chiral condensate, up to \mu_B approx. 500 MeV.
The results are in qualitative agreement with the predictions of model field
theories, and consistent with a first order chiral transition. The correlation
between the chiral transition and the deconfinement transition observed at
\mu=0 persists at nonzero density.


title:
Nucleon Magnetic Moments, their Quark Mass Dependence and Lattice QCD
  Extrapolations

abstract:
  We calculate the quark mass dependence of both isovector and isoscalar
anomalous magnetic moments of the nucleon in a chiral effective field theory
with explicit pion, nucleon and Delta(1232) degrees of freedom to
leading-one-loop order. In the isovector sector we fit 3 unknown couplings of
the effective Lagrangian to available lattice data and obtain a surprisingly
well-behaved extrapolation function connecting the chiral limit, experimental
data and the lattice simulations. We also discuss the polynomial quark mass
dependence in the isoscalar sector and finally compare with the Pade formula of
the Adelaide group.


title:
A non-perturbative determination of Z_V and b_V for O(a) improved
  quenched and unquenched Wilson fermions

abstract:
  By considering the local vector current between nucleon states and imposing
charge conservation we determine, for $O(a)$ improved Wilson fermions, its
renormalisation constant and quark mass improvement coefficient. The
computation is performed for both quenched and two flavour unquenched fermions.


title: Electric and Magnetic Fluxes in SU(2) Yang-Mills Theory

abstract:
  We measure the free energies in SU(2) of static fundamental charges and
center monopoles. Dual to temporal center fluxes, the former provide a
well-defined (dis)order parameter for deconfinement. In contrast, the monopole
free energies vanish in the thermodynamic limit at all temperatures and are
thus irrelevant for the transition.


title: A Relativistic $O(a^2)$ Improved Action for Heavy Quarks

abstract:
  We extend the Fermilab formalism for heavy quarks to develop an $O(a^2)$
improved relativistic action. We discuss our construction of the action,
including the identification of redundant operators and the calculation of the
improvement coefficients.


title: Structure functions near the chiral limit

abstract:
  We compute hadron masses and the lowest moments of unpolarized and polarized
nucleon structure functions down to pion masses of 300 MeV, in an effort to
make unambiguous predictions at the physical light quark mass.


title: Taste-Changing in Staggered Quarks

abstract:
  We present results from a systematic perturbative investigation of
taste-changing in improved staggered quarks. We show one-loop taste-changing
interactions can be removed perturbatively by an effective four-quark term and
calculate the necessary coefficients.


title: Optimal lattice domain-wall fermions

abstract:
  I show that the conventional formulations of lattice domain-wall fermion with
any finite N_s (in the fifth dimension) do not preserve the chiral symmetry
optimally and propose a new action which preserves the chiral symmetry
optimally for any finite N_s.


title: Generalised Spin Projection for Fermion Actions

abstract:
  The majority of compute time doing lattice QCD is spent inverting the fermion
matrix. The time that this takes increases with the condition number of the
matrix. The FLIC(Fat Link Irrelevant Clover) action displays, among other
properties, an improved condition number compared to standard actions and hence
is of interest due to potential compute time savings. However, due to its two
different link sets there is a factor of two cost in floating point
multiplications compared to the Wilson action. An additional factor of two has
been attributed due to the loss of the so-called spin projection trick. We show
that any split-link action may be written in terms of spin projectors, reducing
the additional cost to at most a factor of two. Also, we review an efficient
means of evaluating the clover term, which is additional expense not present in
the Wilson action.


title: FLIC Overlap Fermions

abstract:
  The action of the overlap-Dirac operator on a vector is typically implemented
indirectly through a multi-shift conjugate gradient solver. The compute-time
required depends upon the condition number, $\kappa$, of the matrix that is
used as the overlap kernel. While the Wilson action is typically used as the
overlap kernel, the FLIC (Fat Link Irrelevant Clover) action has an improved
condition number and provides up to a factor of two speedup in evaluating the
overlap action. We summarize recent progress on the use of FLIC overlap
fermions.


title: FLIC-Overlap Fermions and Topology

abstract:
  APE smearing the links in the irrelevant operators of clover fermions
(Fat-Link Irrelevant Clover (FLIC) fermions) provides significant improvement
in the condition number of the Hermitian-Dirac operator and gives rise to a
factor of two savings in computing the overlap operator. This report
investigates the effects of using a highly-improved definition of the lattice
field-strength tensor F_mu_nu in the fermion action, made possible through the
use of APE-smeared fat links in the construction of the irrelevant operators.
Spurious double-zero crossings in the spectral flow of the Hermitian-Wilson
Dirac operator associated with lattice artifacts at the scale of the lattice
spacing are removed with FLIC fermions composed with an O(a^4)-improved lattice
field strength tensor. Hence, FLIC-Overlap fermions provide an additional
benefit to the overlap formalism: a correct realization of topology in the
fermion sector on the lattice.


title: Thermodynamics and heavy quark potential in N_f=2 dynamical QCD

abstract:
  We study N_f=2 lattice QCD with nonperturbatively improved Wilson fermions at
finite temperature on 16^3 \cdot 8 lattices. We determine the transition
temperature at m_{\pi}/m_{\rho} \sim 0.8 and lattice spacing as small as
0.12fm. The string breaking at T < T_c is also studied. We find that the static
potential can be fitted by a simple expression involving string model potential
at finite temperature.


title: Stochastic field evolution of disoriented chiral condensates

abstract:
  I present a summary of recent work \cite{BRS} where we describe the
time-evolution of a region of disoriented chiral condensate via Langevin field
equations for the linear $\sigma$ model. We analyze the model in equilibrium,
paying attention to subtracting ultraviolet divergent classical terms and
replacing them by their finite quantum counterparts. We use results from
lattice gauge theory and chiral perturbation theory to fix nonuniversal
constants. The result is a ultraviolet cutoff independent theory that
reproduces quantitatively the expected equilibrium behavior of pion and
$\sigma$ quantum fields. We also estimate the viscosity $\eta(T)$, which
controls the dynamical timescale in the Langevin equation, so that the near
equilibrium dynamical response agrees with theoretical expectations.


title:
Path Integral Monte Carlo Approach to the U(1) Lattice Gauge Theory in
  (2+1) Dimensions

abstract:
  Path Integral Monte Carlo simulations have been performed for U(1) lattice
gauge theory in (2+1) dimensions on anisotropic lattices. We extractthe static
quark potential, the string tension and the low-lying "glueball" spectrum.The
Euclidean string tension and mass gap decrease exponentially at weakcoupling in
excellent agreement with the predictions of Polyakov and G{\" o}pfert and Mack,
but their magnitudes are five times bigger than predicted. Extrapolations are
made to the extreme anisotropic or Hamiltonian limit, and comparisons are made
with previous estimates obtained in the Hamiltonian formulation.


title: Calculation of Moments of Structure Functions

abstract:
  The progress on the lattice computation of low moments of both the
unpolarised and polarised nucleon structure functions is reviewed with
particular emphasis on continuum and chiral extrapolations and comparison
between quenched and unquenched fermions.


title: Mass gap in compact U(1) Model in (2+1) dimensions

abstract:
  A numerical study of low-lying glueball masses of compact U(1) lattice gauge
theory in (2+1) dimensions is performed using Standard Path integral Monte
Carlo techniques. The masses are extracted, at fixed (low) temperature, from
simulations on anisotropic lattices, with temporal lattice spacing much smaller
than the spatial ones. Convincing evidence of the scaling behaviour in the
antisymmetric mass gap is observed over the range $1.4<\beta <2.25$. The
observed behaviour is very consistent with asymptotic form predicted by G{\"
o}pfert and Mack. Extrapolations are made to the "Hamiltonian" limit, and the
results are compared with previous estimates obtained by many other Hamiltonian
studies.


title: Non-perturbative renormalization of HQET and QCD

abstract:
  We discuss the necessity of non-perturbative renormalization in QCD and HQET
and explain the general strategy for solving this problem. A few selected
topics are discussed in some detail, namely the importance of off-shell
improvement in the MOM-scheme on the lattice, recent progress in the
implementation of finite volume schemes and then particular emphasis is put on
the recent idea to carry out a non-perturbative renormalization of the Heavy
Quark Effective Theory.


title: Heavy-light meson decay constants with N_f=3

abstract:
  During the past year the MILC Collaboration has continued its study of
heavy-light meson decay constants with three dynamical quarks. Calculations
have been extended to a second lattice spacing of about 0.09 fm. At this
lattice spacing, there are results in the quenched approximation and for three
sets of dynamical quark mass: m_l=m_s; m_l=0.4 m_s and m_l=0.2 m_s, where m_l
is the light mass for the u and d quarks and m_s is the strange quark mass. At
the coarser lattice spacing, for which results were presented at Lattice 2001,
statistics have been increased for two sets of quark masses and three
additional sets of quark masses have been studied, giving a total of eight
combinations used to interpolate between the quenched and chiral limits. When
these calculations are completed, we can study the decay constants taking into
account both chiral and continuum extrapolations.


title:
Low Energy Chiral Lagrangian Parameters for Scalar and Pseudoscalar
  Mesons

abstract:
  We present results of a high-statistics study of scalar and pseudoscalar
meson propagators in quenched QCD at two values of lattice spacing, beta = 5.7
and 5.9, with clover-improved Wilson fermions. The study of the chiral limit is
facilitated by the pole-shifting ansatz of the modified quenched approximation.
Pseudoscalar masses and decay constants are determined as a function of quark
mass and quenched chiral log effects are estimated. A study of the flavor
singlet eta prime hairpin diagram yields a precise determination of the eta
prime mass insertion. The corresponding value of the quenched chiral log
parameter delta is compared with the observed QCL effects. Removal of QCL
effects from the scalar propagator allows a determination of the mass of the
lowest lying isovector scalar $q\bar{q}$ meson.


title: Excitations of the nucleon with dynamical fermions

abstract:
  We measure the spectrum of low-lying nucleon resonances using Bayesian
fitting methods. We compare the masses obtained in the quenched approximation
to those obtained with two flavours of dynamical fermions at a matched lattice
spacing. At the pion masses employed in our simulations, we find that the mass
of the first positive-parity nucleon excitation is always greater than that of
the parity partner of the nucleon.


title: Critical behavior in a quasi D dimensional spin model

abstract:
  We study a classical spin model (more precisely a class of models) with O(N)
symmetry that can be viewed as a simplified $D$ dimensional lattice model. It
is equivalent to a non-translationinvariant one dimensional model and contains
the dimensionality $D$ as a parameter that need not be an integer. The critical
dimension turns out to be 2, just as in the usual translation invariant models.
We study the phase structure, critical phenomena and spontaneous symmetry
breaking. Furthermore we compute the perturbation expansion to low order with
various boundary conditions. In our simplified models a number of questions can
be answered that remain controversial in the translation invariant models, such
as the asymptoticity of the perturbation expansion and the role of
super-instantons. We find that perturbation theory produces the right
asymptotic expansion in dimension $D\leq 2$ only with special boundary
conditions. Finally the model allows a test of the percolation ideas of
Patrascioiu and Seiler.

categories: hep-lat cond-mat.stat-mech math-ph math.MP


title: The CKM Lattice Working Group initiative

abstract:
  We present the CKM-LWG, a collection of working groups whose aim is to
compile world averages of lattice results relevant for high-energy
phenomenology.


title: Non-perturbative renormalization constants and light quark masses

abstract:
  We present the results of an extensive non-perturbative calculation of the
renormalization constants of bilinear quark operators for the
non-perturbatively O(a)-improved Wilson action. The results are obtained at
four values of the lattice coupling, by using the RI/MOM and the Ward
identities methods. A new non-perturbative renormalization technique, which is
based on the study of the lattice correlation functions at short distance in
x-space, is also numerically investigated. We then use our non-perturbative
determination of the quark mass renormalization constants to compute the values
of the strange and the average up/down quark masses. After performing an
extrapolation to the continuum limit, we obtain ms^msbar(2 GeV) = (106 +- 2 +-
8) MeV and ml^msbar(2 GeV)=(4.4 +- 0.1 +- 0.4) MeV.


title:
Calorons, instantons and constituent monopoles in SU(3) lattice gauge
  theory

abstract:
  We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge
configurations at non-zero temperature and compare periodic and anti-periodic
temporal boundary conditions for the fermions. It is demonstrated that for the
different boundary conditions often the modes are localized at different
space-time points and have different sizes. Our observations are consistent
with patterns expected for Kraan - van Baal solutions of the classical
Yang-Mills equations. These solutions consist of constituent monopoles and the
zero-modes are localized on different constituents for different boundary
conditions. Our findings indicate that the excitations of the QCD vacuum are
more structured than simple instanton-like lumps.


title: The Color--Flavor Transformation of induced QCD

abstract:
  The color-flavor transformation is applied to the U(N) lattice gauge model,
in which the gauge theory is induced by a heavy chiral scalar field sitting on
lattice sites. The flavor degrees of freedom can encompass several
`generations' of the auxiliary field, and for each generation, remaining
indices are associated with the elementary plaquettes touching the lattice
site. The effective, color-flavor transformed theory is expressed in terms of
gauge singlet matrix fields carried by lattice links. The effective action is
analyzed for a hypercubic lattice in arbitrary dimension. The saddle points
equations of the model in the large-N limit are discussed.


title: K \to \pi\pi decay amplitudes from the lattice

abstract:
  In order to directly compute physical two-pion K-decay amplitudes using
lattice methods we must prepare a two-pion state with non-zero relative
momentum. Building upon a proposal of Lellouch and L\"uscher, we describe a
finite-volume method to realize such a state as the lowest energy state of two
pions.


title:
New proposal for numerical simulations of systems with a theta-vacuum
  term

abstract:
  A new approach to perform numerical simulations of systems with a
theta-vacuum term is proposed, tested, and applied to CP3 The main new
ingredient of this approach is the method used to compute the probability
distribution function of the topological charge at theta=0. We comment also on
the possibility of applying this approach to QCD at finite baryon density.


title: Light quark masses from Domain Wall Fermions

abstract:
  We present results for the renormalised light and strange quark masses
calculated using Domain Wall Fermions in quenched QCD. New results using the
DBW2 gauge action at inverse lattice spacings of approximately 2 GeV and 1.3
GeV will be presented and compared against existing results at 2 GeV using the
Wilson gauge action. This comparison allows a study of the uncertainties due to
both finite lattice spacing and residual chiral symmetry breaking effects.


title:
Nucleon axial charge from quenched lattice QCD with domain wall fermions
  and DBW2 gauge action

abstract:
  The domain wall fermion (DWF) method, with its almost perfectly preserved
chiral symmetry on the lattice, makes the calculation of the nucleon axial
charge particularly easy. By maintaining chiral symmetry and using the
Ward-Takahashi (WT) identity, one has Z_A = Z_V and the bare lattice
calculation yields the physical value without explicit renormalization. The
DBW2 improved gauge action provides further enhancement of the symmetry and
hence a more accurate WT identity at coarse lattice spacing. Taking advantage
of these methods, we confirmed a significant volume dependence of the nucleon
axial charge on (1.2 fm)^3 and (2.4 fm)^3 lattice volumes.


title: Wilson fermions with chirally twisted mass

abstract:
  Lattice formulations of QCD with Wilson fermions and a chirally twisted quark
mass matrix provide an attractive framework for non-perturbative numerical
studies. Owing to reparameterization invariance, the limiting continuum theory
is just QCD. No spurious quark zero modes, which are responsible for the
problem with exceptional configurations, can occur at finite values of the
quark mass. Moreover, the details of the lattice formulation can be adjusted so
as to simplify the renormalization and the O($a$) improvement of several
quantities of phenomenological relevance. The first exploratory studies in the
quenched approximation yield very encouraging results.


title: Nucleon Decay Matrix Elements for Domain-Wall Fermions

abstract:
  We report on the nucleon decay matrix elements with domain-wall fermions in
quenched approximation. Results from direct and indirect method are compared
with a focus on the process of a proton decaying to a pion and a lepton. We
discuss the renormalization necessary for the matching to the continuum theory.
Preliminary results for the renormalized chiral lagrangian parameters are
presented.


title: Simulations of Alice Electrodynamics on a Lattice

abstract:
  In this paper we present results of numerical simulations and some
(analytical) approximations of a compact $U(1)\ltimes\ZZ_2$ lattice gauge
theory, including an extra bare mass term for Alice fluxes. The subtle
interplay between Alice fluxes and (Cheshire) magnetic charges is analysed. We
determine the phase diagram and some characteristics of the model in three and
four dimensions. The results of the numerical simulations in various regimes,
compare well with some analytic approximations.


title: Compact QED under scrutiny: it's first order

abstract:
  We report new results from our finite size scaling analysis of 4d compact
pure U(1) gauge theory with Wilson action. Investigating several cumulants of
the plaquette energy within the Borgs-Kotecky finite size scaling scheme we
find strong evidence for a first-order phase transition and present a high
precision value for the critical coupling in the thermodynamic limit.


title: Lattice QCD with dynamical domain wall quarks

abstract:
  We study lattice QCD with two flavors of dynamical domain wall quarks. With
renormalization group motivated actions, we find chiral symmetry can be
preserved to a high degree at lattice cut off of a^{-1} \sim 2 GeV even for
fifth dimension size as small as L_s = 12. In addition two new steps are
introduced to improve the performance of the hybrid Monte Carlo simulation.


title: Lattice study of "f$_{0}$(600) or $\sigma$"

abstract:
  We investigate the propagator of "f$_{0}$(600) or the $\sigma$" by the
full-QCD simulation with Wilson fermions. We calculate the mesonic correlator
in the I=0, $J^P=0^{+}$ channel on the $8^{3} \times 16$ lattice. Plaquet
action and Wilson fermion action are adopted. A coupling constant $\beta$ is
set to 4.8 and three kinds of hopping parameter, $\kappa$=0.1846, 0.1874 and
0.1891 are assayed. The disconnected diagram in the propagator is evaluated
through taking average over 500 or 1000 Z2 noise. Simulations with the larger
hopping parameter provide us with less noisy results. Though the statistics is
not yet enough, our results indicate the existence of a pole with a mass in
almost the same order as that of the $\rho$.


title: Domain wall fermion and CP symmetry breaking

abstract:
  We examine the CP properties of chiral gauge theory defined by a formulation
of the domain wall fermion, where the light field variables $q$ and $\bar q$
together with Pauli-Villars fields $Q$ and $\bar Q$ are utilized. It is shown
that this domain wall representation in the infinite flavor limit $N=\infty$ is
valid only in the topologically trivial sector, and that the conflict among
lattice chiral symmetry, strict locality and CP symmetry still persists for
finite lattice spacing $a$. The CP transformation generally sends one
representation of lattice chiral gauge theory into another representation of
lattice chiral gauge theory, resulting in the inevitable change of propagators.
A modified form of lattice CP transformation motivated by the domain wall
fermion, which keeps the chiral action in terms of the Ginsparg-Wilson fermion
invariant, is analyzed in detail; this provides an alternative way to
understand the breaking of CP symmetry at least in the topologically trivial
sector. We note that the conflict with CP symmetry could be regarded as a
topological obstruction. We also discuss the issues related to the definition
of Majorana fermions in connection with the supersymmetric Wess-Zumino model on
the lattice.


title: A fresh look on the flux tube in Abelian-projected SU(2) gluodynamics

abstract:
  We reconsider the properties of the $Q\bar{Q}$ flux tube within
Abelian-projected SU(2) lattice gauge theory in terms of electric field and
monopole current. In the maximal Abelian gauge we assess the influence of the
Gribov copies on the apparent flux-tube profile. For the optimal gauge fixing
we study the independence of the profile on the lattice spacing for $\beta=$
2.3, 2.4, and 2.5115 on a $32^4$ lattice. We decompose the Abelian Wilson loop
into monopole and photon parts and compare the electric and monopole profile
emerging from different sources with the field strength and monopole current
within the dual Ginzburg-Landau theory.


title: Supersymmetry on the lattice

abstract:
  Lattice results in supersymmetry are summarized. Past, present and future
perspectives are discussed.


title: Dual Abrikosov vortex between confined charges

abstract:
  We show that the dual Abrikosov vortex between quark and antiquark in Abelian
Projected SU(2) gauge theory is insensitive to truncation of all loops except
the large monopole cluster noted by Hart and Teper. As the transverse distance
increases, the discrepancy decreases, suggesting that the London penetration
depth determined by the tail is invariant under the truncation of short loops.


title:
Lattice Perturbation Theory in Noncommutative Geometry and Parity
  Anomaly in 3D Noncommutative QED

abstract:
  We formulate lattice perturbation theory for gauge theories in noncommutative
geometry. We apply it to three-dimensional noncommutative QED and calculate the
effective action induced by Dirac fermions. In particular "parity invariance"
of a massless theory receives an anomaly expressed by the noncommutative
Chern-Simons action. The coefficient of the anomaly is labelled by an integer
depending on the lattice action, which is a noncommutative counterpart of the
phenomenon known in the commutative theory. The parity anomaly can also be
obtained using Ginsparg-Wilson fermions, where the masslessness is guaranteed
at finite lattice spacing. This suggests a natural definition of the
lattice-regularized Chern-Simons theory on a noncommutative torus, which could
enable nonperturbative studies of quantum Hall systems.


title: Effective Potential for Polyakov Loops in Lattice QCD

abstract:
  Toward the derivation of an effective theory for Polyakov loops in lattice
QCD, we examine Polyakov loop correlation functions using the multi-level
algorithm which was recently developed by Luscher and Weisz.


title:
Chiral 1/M^2 corrections to B^(*) -> D^(*) at Zero Recoil in Quenched
  Chiral Perturbation Theory

abstract:
  Heavy quark effective theory can be used to calculate the values of the
semileptonic B^(*) -> D^(*) decays in the limit that the heavy quark masses are
infinite. We calculate the lowest order chiral corrections, which are of
O(1/M^2), from the breaking of heavy quark symmetry at the zero recoil point in
quenched chiral perturbation theory. These results will aid in the
extrapolation of quenched lattice calculations from the light quark masses used
on the lattice down to the physical ones.


title: Observables of Lattice Gauge Theory in Minkowski Space

abstract:
  U(1) gauge fields are decomposed 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. We observe that the
monopole field carries the same Lyapunov exponent as the original U(1) field.
Evidence is found that monopole fields stay chaotic in the continuum whereas
the photon fields are regular. First results are presented for the full
spectrum of Lyapunov exponents of the U(1) gauge system.


title: Effective sigma models and lattice Ward identities

abstract:
  We perform a lattice analysis of the Faddeev-Niemi effective action
conjectured to describe the low-energy sector of SU(2) Yang-Mills theory. To
this end we generate an ensemble of unit vector fields ("color spins") n from
the Wilson action. The ensemble does not show long-range order but exhibits a
mass gap of the order of 1 GeV. From the distribution of color spins we
reconstruct approximate effective actions by means of exact lattice
Schwinger-Dyson and Ward identities ("inverse Monte Carlo"). We show that the
generated ensemble cannot be recovered from a Faddeev-Niemi action, modified in
a minimal way by adding an explicit symmetry-breaking term to avoid the
appearance of Goldstone modes.


title:
Analysis of unstable particle with the maximum entropy method in O(4)
  $\phi^4$ theory on the lattice

abstract:
  We explore applications of the maximum entropy method (MEM) to determine
properties of unstable particles using the four-dimensional O(4) $\phi^4$
theory as a laboratory. The spectral function of the correlation function of
the unstable $\sigma$ particle is calculated with MEM, and shown to yield
reliable results for both the mass of $\sigma$ and the energy of the two-pion
state. Calculations are also made for the case in which $\sigma$ is stable.
Distinctive differences in the volume dependence of the $\sigma$ mass and
two-pion energy for the stable and unstable cases are analyzed in terms of
perturbation theory.


title: String effects in Polyakov loop correlators

abstract:
  We compare the predictions of the effective string description of confinement
in finite temperature gauge theories to high precision Monte Carlo data for the
three-dimensional Z(2) gauge theory. We show that string interaction effects
become more relevant as the temperature is increased towards the deconfinement
one, and are well modeled by a Nambu-Goto string action.


title: The gluonic excitation of the three-quark system in SU(3) lattice QCD

abstract:
  We present the first study of the gluonic excitation in the three-quark (3Q)
system in SU(3) lattice QCD with $\beta$=5.8 and $16^3 \times 32 $ at the
quenched level. For the spatially-fixed 3Q system, we measure the gluonic
excited-state potential, which corresponds to the flux-tube vibrational energy
in the flux-tube picture. The lowest gluonic-excitation energy in the 3Q system
is found to be about 1GeV in the hadronic scale. This large gluonic-excitation
energy is expected to bring about the success of the simple quark model without
gluonic modes.


title: Chiral Effective Lagrangian and Quark Masses

abstract:
  The status of lattice determinations of quark masses is reviewed (with the
exception of m_b). Attempts to extract the low-energy constants in the
effective chiral Lagrangian are discussed, with special emphasis on those
couplings which are required to test the hypothesis of a massless up-quark.
Furthermore, the issue of quenched chiral logarithms is addressed.


title: Heavy Quarks on the Lattice

abstract:
  I review the basic ideas behind lattice QCD calculations that involve charm
and bottom quarks. I report on the progress in getting the correct hyperfine
splitting in charmonium from lattice QCD. Some of the basic technology behind
numerical lattice QCD calculations is explained by studying some specific
examples: computation of the charm quark mass, and the calculation of fB.


title: Baryon Spectroscopy on the Lattice

abstract: Recent lattice QCD calculations of the baryon spectrum are outlined.


title:
One loop matching coefficients for a variant overlap action--and some of
  its simpler relatives

abstract:
  I present one-loop perturbative calculations of matching coefficients between
matrix elements in continuum regulated QCD and lattice QCD with overlap
fermions, with emphasis a recently-proposed variant discretization of the
overlap. These fermions have extended (``fat link'') gauge connections. The
scale for evaluation of the running coupling constant (in the context of the
Lepage-Mackenzie fixing scheme) is also given.
  A variety of results (for additive mass renormalization, local currents, and
some non-penguin four-fermion operators) for naive, Wilson, clover, and overlap
actions are shown.


title: Moments of Isovector Quark Distributions in Lattice QCD

abstract:
  We investigate the connection of lattice calculations of moments of isovector
parton distributions to the physical regime through extrapolations in the quark
mass. We consider the one pion loop renormalisation of the nucleon matrix
elements of the corresponding operators and thereby develop formulae with which
to extrapolate the moments of the unpolarised, helicity and transversity
distributions. These formulae are consistent with chiral perturbation theory in
the chiral limit and incorporate the correct heavy quark limits. In the
polarised cases, the inclusion of intermediate states involving the $\Delta$
isobar is found to be very important. The results of our extrapolations are in
general agreement with the phenomenological values of these moments where they
are known, and for the first time we perform an extrapolation of the low
moments of the isovector transversity distribution which is consistent with
chiral symmetry.