title:
Testing universality and the fractional power prescription for the
  staggered fermion determinant

abstract:
  In [Phys.Rev.Lett.92:162002 (2004), hep-lat/0312025] expressions for the
continuous Euclidean time limits of various lattice fermion determinants were
derived and compared in order to test universality expectations in Lattice QCD.
Here we review that work with emphasis on its relevance for assessing the
fractional power prescription for the determinant in dynamical staggered
fermion simulations. Some new supplementary material is presented; in
particular the status of the "universality anomaly" is clarified: it is shown
to be gauge field-independent and therefore physically inconsequential.


title: Excited hadrons from improved interpolating fields

abstract:
  The calculation of quark propagators for Ginsparg-Wilson-type Dirac operators
is costly and thus limited to a few different sources. We present a new
approach for determining spatially optimized operators for lattice spectroscopy
of excited hadrons. Jacobi smeared quark sources with different widths are
combined to construct hadron operators with different spatial wave functions.
We study the Roper state and excited rho and pion mesons.


title: Lattice Supersymmetry via Twisting

abstract:
  We describe how the usual supercharges of extended supersymmetry may be {\it
twisted} to produce a BRST-like supercharge $Q$. The usual supersymmetry
algebra is then replaced by a twisted algebra and the action of the twisted
theory is shown to be generically $Q$-exact. In flat space the twisting
procedure can be regarded as a change of variables carrying no physical
significance. However, the twisted theories can often be transferred to the
lattice while preserving the twisted supersymmetry. As an example we construct
a lattice version of the two-dimensional supersymmetric sigma model.


title:
Bulk first-order phase transition in three-flavor lattice QCD with
  $O(a)$-improved Wilson fermion action at zero temperature

abstract:
  Three-flavor QCD simulation with the $O(a)$-improved Wilson fermion action is
made employing an exact fermion algorithm developed for odd number of quark
flavors. For the plaquette gauge action, an unexpected first-order phase
transition is found in the strong coupling regime ($\beta\lesssim$ 5.0) at
relatively heavy quark masses ($m_{\mathrm{PS}}/m_{\mathrm{V}}\sim$
0.74--0.87). Strong metastability persists on a large lattice of size
$12^3\times 32$, which indicates that the transition has a bulk nature. The
phase gap becomes smaller toward weaker couplings and vanishes at $\beta\simeq
5.0$, which corresponds to a lattice spacing $a\simeq$ 0.1 fm. The phase
transition is not found if the improved gauge actions are employed. Our results
imply that realistic simulations of QCD with three flavors of dynamical
Wilson-type fermions at lattice spacings in the range $a=$ 0.1--0.2 fm require
use of improved gauge actions. Possible origins of the phase transition is
discussed.


title: Positivity and topology in lattice gauge theory

abstract:
  The admissibility condition usually used to define the topological charge in
lattice gauge theory is incompatible with a positive transfer matrix.


title: Staggered Chiral Perturbation Theory at Next-to-Leading Order

abstract:
  We study taste and Euclidean rotational symmetry violation for staggered
fermions at nonzero lattice spacing using staggered chiral perturbation theory.
We extend the staggered chiral Lagrangian to O(a^2 p^2), O(a^4) and O(a^2 m),
the orders necessary for a full next-to-leading order calculation of
pseudo-Goldstone boson masses and decay constants including analytic terms. We
then calculate a number of SO(4) taste-breaking quantities, which involve only
a small subset of these NLO operators. We predict relationships between SO(4)
taste-breaking splittings in masses, pseudoscalar decay constants, and
dispersion relations. We also find predictions for a few quantities that are
not SO(4) breaking. All these results hold also for theories in which the
fourth-root of the fermionic determinant is taken to reduce the number of quark
tastes; testing them will therefore provide evidence for or against the
validity of this trick.


title: RG Decimations and Confinement

abstract:
  We outline the steps in a derivation of the statement that the SU(2) gauge
theory is in a confining phase for all values of the coupling, $0 < \beta
<\infty$, defined at lattice spacing a. The approach employed is to obtain both
upper and lower bounds for the partition function and the `twisted' partition
function in terms of approximate decimation transformations. The behavior of
the exact quantities is thus constrained by that of the easily computable
bounding decimations.


title: $Re(A_0)$, $Re(A_2)$ and RG evolution for $N_f=3$

abstract:
  We present results of $Re (A_0)$ and $Re (A_2)$ calculated using HYP
staggered fermions on the lattice of $16^3 \times 64$ at $\beta=6.0$. These
results are obtained using leading order chiral perturbation in quenched QCD.
Buras's original RG evolution matrix develops a removable singularity for
$N_f=3$. This subtlety is resolved by finding a finite solution to RG equation
and the results are presented.


title:
Theta vacuum effects on the pseudoscalar condensates and the eta^prime
  meson in 2-dimensional lattice QED

abstract:
  We study the chiral condensates and the eta^prime meson correlators of the
massive Schwinger model in non-zero theta vacuum. Our data suggest that the
pseudoscalar operator does condense in a fixed topological sector and gives
long range correlations of the eta^prime meson. We find that this is well
understood from the clustering decomposition and statistical picture. Our
result also indicates that even in theta=0 case, the long range correlation of
eta^prime meson receives non-zero contributions from all the topological
sectors and that their cancellation is non-trivial and requires accurate
measurement of the reweighting factors as well as the expectation values. It is
then clear that the fluctuation of the disconnected diagram originates from the
pseudoscalar condensates.


title: Finite temperature 2-color QCD for real and imaginary chemical potential

abstract:
  In this work we study the finite temperature SU(2) gauge theory with
staggered fermions for real and imaginary chemical potential. We test the
method of analytical continuation of Monte Carlo results obtained for imaginary
chemical potential, by comparison with those obtained {\em directly} for real
chemical potential.


title:
Generation of confinement and other nonperturbative effects by infrared
  gluonic degrees of freedom

abstract:
  Recent progress in understanding the emergence of confinement and other
nonperturbative effects in the strong interaction vacuum is reviewed. Special
emphasis is placed on the role of different types of collective infrared
gluonic degrees of freedom in this respect. After a survey of complementary
approaches, models of the QCD vacuum based on center vortices, Abelian magnetic
monopoles and topological charge lumps such as instantons, merons and calorons
are examined. Both the physical mechanisms governing these models as well as
recent lattice studies of the respective degrees of freedom are reviewed.


title: Numerical test of Polyakov loop models in high temperature SU(2)

abstract:
  We study the compatibility of effective mean-field models of the Polyakov
loop for the deconfined phase of SU(N) pure gauge theories with lattice data
obtained for the case of SU(2), in the temperature range T_c - 4.8 T_c.


title:
One-loop renormalisation for the second moment of GPDs with Wilson
  fermions

abstract:
  We calculate the non-forward quark matrix elements for operators with two
covariant derivatives in one-loop lattice perturbation theory using Wilson
fermions. These matrix elements are needed in the renormalisation of the second
moment of generalised parton distributions measured in lattice QCD. For some
commonly used representations of the hypercubic group we determine the sets of
all mixing operators and find the matrices of mixing and renormalisation
factors.


title: Precision computation of B_K in quenched lattice QCD

abstract:
  We present the results of a precision computation of B_K with Wilson
fermions. Simulations are performed at different lattice spacings, enabling
continuum limit extrapolations. Two different twisted mass QCD (tmQCD)
regularisations are considered for the computation of bare matrix elements. In
both cases the relevant four-fermion operator renormalises multiplicatively. In
one regularisation it is possible to perform the computation directly at the
physical kaon mass value, thus avoiding extrapolations in the mass.
Nonperturbative renormalisation is carried out using available Schroedinger
Functional results.


title: Staggered Chiral Perturbation Theory with Heavy-Light Mesons

abstract:
  We merge heavy quark effective theory with staggered chiral perturbation
theory to calculate heavy-light (B, D) meson quantities. We present results at
NLO for the $B(D)$ meson decay constant in the partially quenched and full QCD
cases, and discuss the calculation of the form factors for $B(D) \to \pi(K)
\ell \nu$ decays.


title: The F model on dynamical quadrangulations

abstract:
  The dynamically triangulated random surface (DTRS) approach to Euclidean
quantum gravity in two dimensions is considered for the case of the elemental
building blocks being quadrangles instead of the usually used triangles. The
well-known algorithmic tools for treating dynamical triangulations in a Monte
Carlo simulation are adapted to the problem of these dynamical
quadrangulations. The thus defined ensemble of 4-valent graphs is appropriate
for coupling to it the 6- and 8-vertex models of statistical mechanics. Using a
series of extensive Monte Carlo simulations and accompanying finite-size
scaling analyses, we investigate the critical behaviour of the 6-vertex F model
coupled to the ensemble of dynamical quadrangulations and determine the matter
related as well as the graph related critical exponents of the model.


title: Dynamical overlap simulations using HMC

abstract:
  We apply the Hybrid Monte Carlo method to the simulation of overlap fermions.
We give the fermionic force for the molecular dynamics update. We present early
results on a small dynamical chiral ensemble.


title: Improving Inversions of the Overlap Operator

abstract:
  We present relaxation and preconditioning techniques which accelerate the
inversion of the overlap operator by a factor of four on small lattices, with
larger gains as the lattice size increases. These improvements can be used in
both propagator calculations and dynamical simulations.


title: Correlation functions at small quark masses with overlap fermions

abstract:
  We report on recent work on the determination of low-energy constants
describing Delta{S}=1 weak transitions, in order to investigate the origins of
the Delta{I}=1/2 rule. We focus on numerical techniques designed to enhance the
statistical signal in three-point correlation functions computed with overlap
fermions near the chiral limit.


title:
Chiral condensate of lattice QCD with massless quarks from the
  probability distribution function method

abstract:
  We apply the probability distribution function method to the study of chiral
properties of QCD with quarks in the exact massless limit. A relation among the
chiral condensate, zeros of the Bessel function and eigenvalue of Dirac
operator is also given. The chiral condensate in this limit can be measured
with small number of eigenvalues of the massless Dirac operator and without any
ambiguous mass extrapolation. Results for SU(3) gauge theory with quenched
Kogut-Susskind quarks on the $10^4$ lattice are shown.


title:
Fluctuations in the vicinity of the phase transition line for two flavor
  QCD

abstract:
  We study the susceptibilities of quark number, isospin number and electric
charge in numerical simulations of lattice QCD at high temperature and density.
We discuss the equation of state for 2 flavor QCD at non-zero temperature and
density. Derivatives of $\ln Z$ with respect to quark chemical potential
$(\mu_q)$ are calculated up to sixth order. From this Taylor series, the
susceptibilities are estimated as functions of temperature and $\mu_q$.
Moreover, we comment on the hadron resonance gas model, which explains well our
simulation results below $T_c$.


title:
QCD Phase Diagram at small Baryon Densities from Imaginary mu: Status
  Report

abstract:
  We summarize our recent results for the (T,mu)-phase diagram of N_f=3 QCD.
Finding a strong variation of the critical endpoint mu_c with the quark mass m,
we point out that an endpoint within reach of experiment requires fine-tuned
quark masses. We further discuss the strategy and first data towards extending
our results to the physical N_f=2+1 theory.


title: The QCD Phase Diagram at Non-zero Baryon and Isospin Chemical Potentials

abstract:
  In heavy ion collision experiments as well as in neutron stars, both baryon
and isospin chemical potentials are different from zero. In particular, the
regime of small isospin chemical potential is phenomenologically important.
Using a random matrix model, we find that the phase diagram at non-zero
temperature and baryon chemical potential is greatly altered by an arbitrarily
small isospin chemical potential: There are two first order phase transitions
at low temperature, two critical endpoints, and two crossovers at high
temperature. As a consequence, in the region of the phase diagram explored by
RHIC experiments, there are two crossovers that separate the hadronic phase
from the quark-gluon plasma phase at high temperature.


title:
A Lattice Formulation of Super Yang-Mills Theories with Exact
  Supersymmetry

abstract:
  We construct SU($N$) super Yang-Mills theories with extended supersymmetry on
hypercubic lattices of various dimensions keeping one or two supercharges
exactly.
  It is based on topological field theory formulation for the super Yang-Mills
theories. Gauge fields are represented by compact unitary link variables, and
the exact supercharges on the lattice are nilpotent up to gauge
transformations. In particular, the lattice models are free from the vacuum
degeneracy problem, which was encountered in earlier approaches. Thus, we do
not need to introduce any supersymmetry breaking terms, and the exact
supersymmetry is preserved wholly in the process of taking the continuum limit.
  Among the models, we show that the desired continuum theories are obtained
without any fine tuning of parameters for the cases ${\cal N}=2, 4, 8$ in
two-dimensions. Also, the cases ${\cal N}=4, 8$ in three-dimensions are
investigated, and a problem arising in four-dimensional models is discussed.


title: Remarks on the discretization of physical momenta in lattice QCD

abstract:
  The calculation on the lattice of cross--sections, form--factors and decay
rates associated to phenomenologically relevant physical processes is
complicated by the spatial momenta quantization rule arising from the
introduction of limited box sizes in numerical simulations. A method to
overcome this problem, based on the adoption of two distinct boundary
conditions for two fermions species on a finite lattice, is here discussed and
numerical results supporting the physical significance of this procedure are
shown.


title: Non-compact QED(3) coupled to a four-fermi interaction

abstract:
  We present preliminary numerical results for the three dimensional
non-compact QED with a weak four-fermion term in the lattice action. Approaches
based on Schwinger-Dyson studies, arguments based on thermodynamic inequalities
and numerical simulations lead to estimates of the critical number of fermion
flavors (below which chiral symmetry is broken) ranging from $N_{fc}=1$ to
$N_{fc}=4$. The weak four-fermion coupling provides the framework for an
improved algorithm, which allows us to simulate the chiral limit of massless
fermions and expose delicate effects.


title: The Quenched Continuum Limit

abstract:
  We show that all current formalisms for quarks in lattice QCD are consistent
in the quenched continuum limit, as they should be. We improve on previous
extrapolations to this limit, and the understanding of lattice systematic
errors there, by using a constrained fit including both leading and sub-leading
dependence on a.


title:
B Leptonic Decays and B- bar B Mixing with 2+1 Flavors of Dynamical
  Quarks

abstract:
  Calculations of B leptonic decays and B- bar B mixing using NRQCD heavy and
Asqtad light valence quarks on the MILC dynamical configurations are described.
Smearing has been implemented to substantially reduce the statistical errors of
the matrix elements needed for the determination of f_B. The four-fermion
matrix elements needed for the determination of f_{B_s}^2B_{B_s} have been
calculated and a preliminary result is given.


title: Results for light pseudoscalars from three-flavor simulations

abstract:
  We compute pseudoscalar meson masses and decay constants in partially
quenched QCD with three dynamical flavors of improved staggered quarks. Fitting
the lattice data to staggered chiral perturbation theory forms and
extrapolating in quark mass and lattice spacing, we find: $f_\pi = 129.5 \pm
0.9 \pm 3.5$ MeV, $f_K = 156.6 \pm 1.0 \pm 3.6$ MeV, and $f_K/f_\pi =
1.210(4)(13)$. The value for $f_K/f_\pi$ implies $|V_{us}|=0.2219(26)$. We also
obtain $m_u/m_d = 0.43(0)(1)(8)$, or, with more input on electromagnetic
effects from the continuum, $m_u/m_d = 0.41(0)(1)(4)$. Using the one-loop
perturbative mass renormalization, we determine $m_u$ and $m_d$ in the MSbar
scheme.


title: QCD on the BlueGene/L Supercomputer

abstract:
  In June 2004 QCD was simulated for the first time at sustained speed
exceeding 1 TeraFlops in the BlueGene/L supercomputer at the IBM T.J. Watson
Research Lab. The implementation and performance of QCD in the BlueGene/L is
presented.


title:
Chiral extrapolations with small sea quark mass data in two-flavor
  lattice QCD

abstract:
  We present results on the light hadron spectrum and quark mass in two-flavor
QCD calculated with small sea quark masses down to $m_{PS}/m_{V}=0.35$. The
configurations are generated using the RG improved gauge and tadpole-improved
clover quark action at $\beta=1.8$, where $a^{-1} \simeq 1$ GeV. Chiral
extrapolations are made using not only polynomials and ChPT in the continuum
but also formulae of Wilson chiral perturbation theory (WChPT) including
$O(a^2)$ chiral breaking terms. We examine the viability of WChPT and its
influence on quark masses.


title: A finite temperature investigation of the Georgi-Glashow model in 3D

abstract:
  We study the SU(2) gauge theory with scalar matter in the adjoint
representation in 3D at finite temperature. We find evidence for a finite
temperature phase transition both in the symmetric and in the broken phase;
such transitions are consistent with the universality class of Ising 2D, in
agreement with recent analytical arguments.


title:
Density profiles of small Dirac operator eigenvalues for two color QCD
  at nonzero chemical potential compared to matrix models

abstract:
  We investigate the eigenvalue spectrum of the staggered Dirac matrix in two
color QCD at finite chemical potential. The profiles of complex eigenvalues
close to the origin are compared to a complex generalization of the chiral
Gaussian Symplectic Ensemble, confirming its predictions for weak and strong
non-Hermiticity. They differ from the QCD symmetry class with three colors by a
level repulsion from both the real and imaginary axis.


title: Calculating $\epsilon'/\epsilon$ using HYP staggered fermions

abstract:
  We present preliminary results for $\epsilon'/\epsilon$ calculated using HYP
staggered fermions in the quenched approximation. We compare different choices
of quenched penguin operators.


title: Testing improved staggered fermions with $m_s$ and $B_K$

abstract:
  We study the improvement of staggered fermions using hypercubically smeared
(HYP) links. We calculate the strange quark mass and the kaon B-parameter,
$B_K$, in quenched QCD on a $16^3 \times 64$ lattice at $\beta=6.0$. We find
$m_s(\bar{\rm MS},2 {\rm GeV})=101.2\pm1.3\pm4 $MeV and $B_K(\bar{\rm MS},2
{\rm GeV}) = 0.578 \pm 0.018\pm 0.042$, where the first error is from
statistics and fitting, and the second from using one-loop matching factors.
The scale ($1/a=1.95$GeV) is set by $M_\rho$, and $m_s$ is determined using the
kaon mass. Comparing to quenched results obtained using unimproved staggered
fermions and other discretizations, we argue that the size of discretization
errors in $B_K$ is substantially reduced by improvement.


title: Semileptonic Hyperon Decays on the Lattice: an Exploratory Study

abstract:
  We present preliminary results of an exploratory lattice study of the vector
form factor $f_1(q^2 = 0)$ relevant for the semileptonic hyperon decay
$\Sigma^{-} --> n l \nu$. This study is based on the same method used for the
extraction of $f^+(0)$ for the decay $K^0 --> \pi^{-} l \nu$. The main purpose
of this study is to test the method for hyperon form factors in order to
estimate the precision that can be reached and the importance of SU(3)-breaking
effects.


title: B_K from improved staggered quarks

abstract:
  We compare calculations of B_K with improved staggered quarks (HYP, Asqtad)
and demonstrate the improved scaling behaviour that this gives rise to over
previous calculations with unimproved staggered quarks. This enables us to
perform the calculation of B_K on the MILC dynamical configurations (n_f=2+1),
for which we give preliminary results.


title: Deconfinement and Chiral Restoration in Hot and Dense Matter

abstract:
  We propose a picture that the chiral phase transition at zero quark mass and
the deconfinement transition at infinite quark mass are continuously connected.
This gives a simple interpretation on the coincidence of the pseudo-critical
temperatures observed in lattice QCD. We discuss a possible dynamical mechanism
behind the simultaneous crossovers and show the results in a model study.


title: Topological susceptibility with three flavors of staggered quarks

abstract:
  As one test of the validity of the staggered-fermion fourth-root determinant
trick, we examine the suppression of the topological susceptibility of the QCD
vacuum in the limit of small quark mass. The suppression is sensitive to the
number of light sea quark flavors. Our study is done in the presence of 2+1
flavors of dynamical quarks in the improved staggered fermion formulation.
Variance-reduction techniques provide better control of statistical errors. New
results from staggered chiral perturbation theory account for taste-breaking
effects in the low-quark mass behavior of the susceptibility, thereby reducing
scaling violations from this source. Measurements over a range of quark masses
at two lattice spacings permit a rough continuum extrapolation to remove the
remaining lattice artifacts. The results are consistent with chiral
perturbation theory with the correct flavor counting.


title: SU(N) chiral gauge theories on the lattice: a quick overview

abstract:
  We describe how an SU(N) chiral gauge theory can be put on the lattice using
non-perturbative gauge fixing. In particular, we explain how the Gribov problem
is dealt with. Our construction is local, avoids doublers, and weak-coupling
perturbation theory applies at the critical point which defines the continuum
limit of our lattice chiral gauge theory.


title: Is there an Aoki phase in quenched QCD?

abstract:
  We argue that quenched QCD has non-trivial phase structure for negative quark
mass, including the possibility of a parity-flavor breaking Aoki phase. This
has implications for simulations with domain-wall or overlap fermions.


title:
The scaling equation of state of the three-dimensional O(N) universality
  class: N >= 4

abstract:
  We determine the critical equation of state of the three-dimensional O(N)
universality class, for N=4, 5, 6, 32, 64. The N=4 is relevant for the chiral
phase transition in QCD with two flavors, the N=5 model is relevant for the
SO(5) theory of high-T_c superconductivity, while the N=6 model is relevant for
the chiral phase transition in two-color QCD with two flavors. We first
consider the small-field expansion of the effective potential (Helmholtz free
energy). Then, we apply a systematic approximation scheme based on polynomial
parametric representations that are valid in the whole critical regime, satisfy
the correct analytic properties (Griffiths' analyticity), take into account the
Goldstone singularities at the coexistence curve, and match the small-field
expansion of the effective potential. From the approximate representations of
the equation of state, we obtain estimates of universal amplitude ratios. We
also compare our approximate solutions with those obtained in the large-N
expansion, up to order 1/N, finding good agreement for N \gtrsim 32.


title: QCDml: First Milestone for building an international Lattice Data Grid

abstract:
  We present an XML schema for marking up gauge configurations called QCDml. We
discuss the general principles and include a tutorial on how to use the schema.


title: Improving meson two-point functions by low-mode averaging

abstract:
  Some meson correlation functions have a large contribution from the low lying
eigenmodes of the Dirac operator. The contribution of these eigenmodes can be
averaged over all positions of the source. This can improve the signal in these
channels significantly. We test the method for meson two-point functions.


title:
One-loop determination of mass dependent $O(a)$ improvement coefficients
  for the heavy-light vector and axial-vector currents with relativistic heavy
  and domain-wall light quarks

abstract:
  We present the one-loop results of the mass dependent $O(a)$ improvement
coefficients for the heavy-light vector and axial-vector currents consisting of
the relativistic heavy and the domain-wall light quarks. The calculations are
performed with the plaquette, Iwasaki and DBW2 gauge actions. The heavy quark
mass and domain-wall height dependence is investigated. We point out that the
exact chiral symmetry held by the lattice light quark action leads to an exact
relation between the improvement coefficients for the vector and axial-vector
currents without regard to the lattice heavy quark action.


title: Signal at subleading order in lattice HQET

abstract:
  We discuss the correlators in lattice HQET that are needed to go beyond the
static theory. Based on our implementation in the Schr\"odinger functional we
focus on their signal-to-noise ratios and check that a reasonable statistical
precision can be reached in quantities like $f_{B_s}$ and $M_{B^\star}-M_B$.


title: First Simulation Results for the Photon in a Non-Commutative Space

abstract:
  We present preliminary simulation results for QED in a non-commutative 4d
space-time, which is discretized to a fuzzy lattice. Its numerical treatment
becomes feasible after its mapping onto a dimensionally reduced twisted
Eguchi-Kawai matrix model. In this formulation we investigate the Wilson loops
and in particular the Creutz ratios. This is an ongoing project which aims at
non-perturbative predictions for the photon, which can be confronted with
phenomenology in order to verify the possible existence of non-commutativity in
nature.


title: Exploring Lattice Methods for Cold Fermionic Atoms

abstract:
  There has been a surge of experimental effort recently in cooling trapped
fermionic atoms to quantum degeneracy. By varying an external magnetic field,
interactions between atoms can be made arbitrarily strong. When the S wave
scattering length becomes comparable to and larger than the interparticle
spacing, standard mean field analysis breaks down. In this case the system
exhibits a type of universality, and J-W. Chen and D. B. Kaplan recently showed
how this system can be studied from first principles using lattice field
theory. This poster presents the first results of exploratory simulations. The
existence of a continuum limit is checked and the pairing condensate is studied
as a function of the external source strength over a range of temperatures.
Preliminary results show simulations can locate the critical temperature.

categories: hep-lat cond-mat.soft cond-mat.stat-mech nucl-th


title:
Analyticity in theta and infinite volume limit of the topological
  susceptibility in SU(3) gauge theory

abstract:
  The large volume behaviour of the topological susceptibility in SU(3) gauge
theory is investigated on the lattice to establish an upper limit on the parity
violating terms.


title: Index Theorem and Random Matrix Theory for Improved Staggered Quarks

abstract:
  We study various improved staggered quark Dirac operators on quenched gluon
backgrounds in lattice QCD generated using a Symanzik-improved gluon action. We
find a clear separation of the spectrum of eigenvalues into would-be zero modes
and others. The number of would-be zero modes depends on the topological charge
as expected from the Index Theorem, and their chirality expectation value is
large. The remaining modes have low chirality and show clear signs of
clustering into quartets and approaching the random matrix theory predictions
for all topological charge sectors. We conclude that improvement of the
fermionic and gauge actions moves the staggered quarks closer to the continuum
limit where they respond correctly to QCD topology.


title: I=2 Pion Scattering Length from Two-Pion Wave Function

abstract:
  We present a report on a calculation of scattering length for I=2 $S$-wave
two-pion system from two-pion wave function. Calculations are made with an
RG-improved action for gluons and improved Wilson action for quarks at
$a^{-1}=1.207(12) {\rm GeV}$ on $16^3 \times 80$, $20^3 \times 80$ and $24^3
\times 80$ lattices. We investigate the validity of necessary condition for
application of L\"uscher's formula through the wave function. We find that the
condition is satisfied for lattice volumes $L\ge 3.92 {\rm fm}$ for the quark
mass range $m_\pi^2 = 0.273-0.736 {\rm GeV}^2$. We also find that the
scattering length can be extracted with a smaller statistical error from the
wave function than with a time correlation function used in previous studies.


title: Pion scattering on the lattice with chirally improved fermions

abstract:
  We report preliminary results for the I=2 pion scattering length a_0,
calculated with chirally improved fermions. After chiral extrapolation our
results are in good agreement with both, experimental and theoretical
predictions.


title: The pentaquark potential, mass and density-density correlator

abstract:
  We evaluate the static $qqqq\bar{q}$ potential in the quenched theory at
$\beta=5.8$ and $\beta=6.0$ on a lattice of size $16^3\times 32$. The mass and
density-density correlator for the $\Theta^+$ is investigated in the quenched
theory at $\beta=6.0$ on lattices of size $16^3\times 32$, $24^3\times 32$ and
$32^3 \times 64$.


title: Chiral perturbation theory for twisted mass QCD

abstract:
  Quantum Chromodynamics on a lattice with Wilson fermions and a chirally
twisted mass term for two degenerate quark flavours is considered in the
framework of chiral perturbation theory. The pion masses and decay constants
are calculated in next-to-leading order including terms linear in the lattice
spacing a. We treat both unquenched and partially quenched QCD. We also discuss
the phase structure of twisted mass lattice QCD.


title:
Lattice artefacts in SU(3) lattice gauge theory with a mixed fundamental
  and adjoint plaquette action

abstract:
  We investigated SU(3) lattice gauge theory with a fundamental and adjoint
plaquette term in the action. The purpose is to test whether the choice of a
negative adjoint coupling can reduce lattice artefacts and improve the scaling
b ehaviour. To this end, we have studied the finite temperature phase
transition, the static potential and the mass of the 0^{++} glueball. We found
that indeed the lattice artefacts in e.g. m_{0^{++}}/T_c can be reduced
considerably compared with the pure Wilson (fundamental) gauge action at the
same lattice spacing.


title: Exact supersymmetry on the lattice: the Wess-Zumino model

abstract:
  It is shown that the lattice Wess-Zumino model written in terms of
Ginsparg-Wilson fermions is invariant under a generalized supersymmetry
transformation which is determined by an iterative procedure in the coupling
constant. This transformation is non-linear in the scalar fields and depends on
the superpotential parameters. The implications of this lattice invariance are
discussed.


title:
Improving Algorithms to Compute All Elements of the Lattice Quark
  Propagator

abstract:
  We present a new exact algorithm for estimating all elements of the quark
propagator. The advantage of the method is that the exact all-to-all propagator
is reproduced in a large but finite number of inversions. The efficacy of the
algorithm is tested in Monte Carlo simulations of Wilson quarks in quenched
QCD. Applications that are difficult to probe with point propagators are
discussed.


title: Dynamical overlap fermions, results with HMC algorithm

abstract:
  We present results of a hybrid Monte-Carlo algorithm for dynamical, $n_f=2$,
four-dimensional QCD with overlap fermions. The fermionic force requires
careful treatment, when changing topological sectors. The pion mass dependence
of the topological susceptibility is studied on $6^4$ and $12\cdot 6^3$
lattices. The results are transformed into physical units.


title: APENet: LQCD clusters a la APE

abstract:
  Developed by the APE group, APENet is a new high speed, low latency,
3-dimensional interconnect architecture optimized for PC clusters running
LQCD-like numerical applications. The hardware implementation is based on a
single PCI-X 133MHz network interface card hosting six indipendent
bi-directional channels with a peak bandwidth of 676 MB/s each direction. We
discuss preliminary benchmark results showing exciting performances similar or
better than those found in high-end commercial network systems.


title: QCD at small baryon number

abstract:
  We consider the difficulties of finite density QCD from the canonical
formalism. We present results for small baryon numbers, where the sign problem
can be controlled, in particular by supplementing the mu=0 sampling with
imaginary mu ensembles. We initiate the thermodynamic study of few-nucleon
systems, starting with the measurement of the free energy of a few baryons in
the confined and deconfined phase. We present a simple model for the phase
transition, whose results are in good agreement with the literature, but extend
to lower temperatures.


title: Testing a Topology Conserving Gauge Action in QCD

abstract:
  We study lattice QCD with a gauge action, which suppresses small plaquette
values. Thus the MC history is confined to a single topological sector over a
significant time, while other observables are decorrelated. This enables the
cumulation of statistics with a specific topological charge, which is needed
for simulations of QCD in the $\epsilon$-regime. The same action may also be
useful for simulations with dynamical quarks. The update is performed with a
local HMC algorithm.


title: Study of the 2-d CP(N-1) models at \theta=0 and \pi

abstract:
  We present numerical results for 2-d CP(N-1) models at \theta=0 and \pi
obtained in the D-theory formulation. In this formulation we construct an
efficient cluster algorithm and we show numerical evidence for a first order
transition for CP(N-1\geq 2) models at \theta = \pi. By a finite size scaling
analysis, we also discuss the equivalence in the continuum limit of the
D-theory formulation of the 2-d CP(N-1) models and the usual lattice
definition.


title: Sea quark effects in B_K from N_f=2 clover-improved Wilson fermions

abstract:
  We report calculations of B_K using two flavours of dynamical clover-improved
Wilson lattice fermions and look for dependence on the dynamical quark mass at
fixed lattice spacing. We see some evidence for dynamical quark effects. In
particular B_K decreases as the sea quark masses are reduced towards the
up/down quark mass. Our meson masses are quite heavy and a firm prediction of
B_K is a task for future simulations.


title: Heavy meson chiral perturbation theory in finite volume

abstract:
  We present the first step towards the estimation of finite volume effects in
heavy-light meson systems using heavy meson chiral perturbation theory. We
demonstrate that these effects can be amplified in both light-quark and
heavy-quark mass extrapolations (interpolations) in lattice calculations. As an
explicit example, we perform a one-loop calculation for the neutral B meson
mixing system and show that finite volume effects, which can be comparable with
currently quoted errors, are not negligible in both quenched and partially
quenched QCD.


title:
The lattice QCD simulation of the quark-gluon mixed condensate g<\bar{q}
  \sigma G q> at finite temperature and the phase transition of QCD

abstract:
  The thermal effects on the quark-gluon mixed condensate g<\bar{q} \sigma G
q>, which is another chiral order parameter, are studied using the SU(3)c
lattice QCD with the Kogut-Susskind fermion at the quenched level. We perform
the accurate measurement of the mixed condensate as well as the quark
condensate for 0MeV<=T<=500MeV. We observe the sharp decrease of both the
condensates around T_c \simeq 280MeV, while the thermal effects below T_c are
found to be weak. We also find that the ratio m_0^2 = g<\bar{q} \sigma G
q>/<\bar{q}q> is almost independent of the temperature even in the very
vicinity of T_c, which indicates that the two condensates have nontrivial
similarity in the chiral behaviors. We also present the correlation between the
condensates and the Polyakov loop to understand the vacuum structure of QCD.


title: The two-grid algorithm confronts a shifted unitary orthogonal method

abstract:
  In this paper I describe a new optimal Krylov subspace solver for shifted
unitary matrices called the Shifted Unitary Orthogonal Method (SUOM). This
algorithm is used as a benchmark against any improvement like the two-grid
algorithm. I use the latter to show that the overlap operator can be inverted
by successive inversions of the truncated overlap operator. This strategy
results in large gains compared to SUOM.


title: Topological Charge Membranes in 2D and 4D Gauge Theory

abstract:
  Local topological charge structure in the 2D CP(N-1) sigma models is studied
using the overlap Dirac operator. Long-range coherence of topological charge
along locally 1D regions in 2D space-time is observed. We discuss the
connection between these results and the recent discovery of coherent 3D sheets
of topological charge in 4D QCD. In both cases, coherent regions of topological
charge form along surfaces of approximmate codimension 1.


title:
Baryonic sources using irreducible representations of the double-covered
  octahedral group

abstract:
  Irreducible representations (IRs) of the double-covered octahedral group are
used to construct lattice source and sink operators for three-quark baryons.
The goal is to achieve a good coupling to higher spin states as well as ground
states. Complete sets of local and nonlocal straight-link operators are
explicitly shown for isospin 1/2 and 3/2 baryons. The orthogonality relations
of the IR operators are confirmed in a quenched lattice simulation.


title: Pion form factor using domain wall valence and asqtad sea quarks

abstract:
  We compute the pion electromagnetic form factor in a hybrid calculation with
domain wall valence quarks and improved staggered (asqtad) sea quarks. This
method can easily be extended to rho-to-gamma-pi transition form factors.


title:
Analysis of $N^{\star}$ spectra using matrices of correlation functions
  based on irreducible baryon operators

abstract:
  We present results for ground and excited-state nucleon masses in quenched
lattice QCD using anisotropic lattices. Group theoretical constructions of
local and nonlocal straight-link irreducible operators are used to obtain
suitable sources and sinks. Matrices of correlation functions are diagonalized
to determine the eigenvectors. Both chi-square fitting and Bayesian inference
with an entropic prior are used to extract masses from the correlation
functions in a given channel. We observe clear separation of the excited state
masses from the ground state mass. States of spin >= 5/2 have been isolated by
use of G_2 operators.


title: Confinement from Instantons or Merons

abstract:
  In contrast to ensembles of singular gauge instantons, which are well known
to fail to produce confinement, it is shown that effective theories based on
ensembles of merons or regular gauge instantons do produce confinement.
Furthermore, when the scale is set by the string tension, the action density,
topological susceptibility, and glueball masses are similar to those arising in
lattice QCD.


title: Status of International Lattice Data Grid -- An Overview --

abstract: We report on the status of the International Lattice Data Grid.


title: Non-perturbative determination of heavy quark action coefficients

abstract:
  We propose to determine the coefficients in the Fermilab heavy quark action
by matching the finite-volume, off-shell, gauge-fixed propagator and vertex
functions with those determined in the exact, relativistic theory. The matching
relativistic amplitudes may be determined either from short-distance
perturbation theory or from finite-volume step-scaling recursion. Tree-level
matching and non-perturbative off-shell amplitudes are presented.


title:
Charmed meson spectra and decay constants with one-loop $O(a)$ improved
  relativistic heavy quark action

abstract:
  We calculate charmed meson spectra and decay constants in lattice QCD
employing one-loop $O(a)$ improved heavy quark action and axial-vector
currents. In quenched simulations at $a \sim 0.1$ fm with the plaquette gauge
action as well as a renormalization-group improved one, it is shown that the
deviation from the continuum dispersion relation and the violation of
space-time symmetry for the pseudoscalar meson decay constants are
substantially reduced, once the $O(a)$ improvement is applied. Preliminary
results with two flavors of dynamical quarks are also presented.


title: Excited S- and P-wave B mesons from the lattice

abstract:
  The energies of different angular momentum states of a heavy-light meson were
measured on a lattice in Michael and Peisa, Phys. Rev. D 58, 34506 (1998). We
have now repeated this study using several different lattices, quenched and
unquenched, that have different physical lattice sizes, clover coefficients and
quark-gluon couplings. The heavy quark is taken to be infinitely heavy, whereas
the light quark mass is approximately that of the strange quark. By
interpolating and extrapolating in the light quark mass we can thus compare the
lattice results with B and B_s meson experiments. Most interesting is the
lowest P-wave B_s state, since it is possible that it lies below the $BK$
threshold and hence is very narrow. Unfortunately, there are no experimental
results on P-wave B or B_s mesons available at present.
  In addition to the energy spectrum, we measured earlier also vector (charge)
and scalar (matter) radial distributions of the light quark in the S-wave
states of a heavy-light meson on a lattice (Phys. Rev. D 65, 014512 (2002) and
Eur. Phys. J. C 28, 79 (2003)). Now we are extending the study of radial
distributions to P-wave states.


title: The heavy quark's self energy from moving NRQCD on the lattice

abstract:
  We present a calculation of the heavy quark's self energy in moving NRQCD to
one-loop in perturbation theory. Results for the energy shift and external
momentum renormalisation are discussed and compared with non-perturbative
results. We show that the momentum renormalisation is small, which is the
result of a remnant of re-parameterisation invariance on the lattice.


title: The charm quark mass with dynamical fermions

abstract:
  We compute the charm quark mass in lattice QCD and compare different
formulations of the heavy quark, and quenched data to that with dynamical sea
quarks. We take the continuum limit of the quenched data by extrapolating from
three different lattice spacings, and compare to data with two flavours of
dynamical sea quarks with a mass around the strange at the coarsest lattice
spacing. Both the FNAL and ALPHA formalism are used. We find the different
heavy quark formulations have the same continuum limit in the quenched
approximation, and limited evidence that this approximation overestimates the
charm quark mass.


title: A precise determination of the Bc mass from dynamical lattice QCD

abstract:
  We perform a precise calculation of the mass of the B_c meson using
unquenched configurations from the MILC collaboration including 2+1 flavours of
improved staggered quarks. Lattice NRQCD and the Fermilab formalism are used to
describe the b and c quarks respectively. We find the mass of the B_c meson to
be 6.304(16) GeV


title: Non-perturbative tests of HQET in small-volume quenched QCD

abstract:
  We quantitatively investigate the quark mass dependence of current matrix
elements and energies, calculated over a wide range of quark masses in the
continuum limit of small-volume quenched lattice QCD. By a precise comparison
of these observables as functions of the heavy quark mass with the predictions
of HQET we are able to verify that their large quark mass behaviour is
described by the effective theory.


title: Twisted N=2 exact SUSY on the lattice for BF and Wess-Zumino

abstract:
  We formulate exact supersymmetric models on a lattice. We introduce
noncommutativity to ensure the Leibniz rule. With the help of superspace
formalism, we give supertransformations which keep the N=2 twisted SUSY algebra
exactly. The action is given as a product of (anti)chiral superfields on the
lattice. We present BF and Wess-Zumino models as explicit examples of our
formulation. Both models have exact N=2 twisted SUSY in 2 dimensional space at
a finite lattice spacing. In component fields, the action has supercharge exact
form.


title: Group-theoretical construction of extended baryon operators

abstract:
  The design and implementation of large sets of spatially extended baryon
operators for use in lattice simulations are described. The operators are
constructed to maximize overlaps with the low-lying states of interest, while
minimizing the number of sources needed in computing the required quark
propagators.


title: Eigenvalue correlations in QCD with a chemical potential

abstract:
  We discuss a new Random Matrix Model for QCD with a chemical potential that
is based on the symmetries of the Dirac operator and can be solved exactly for
all eigenvalue correlations for any number of flavors. In the microscopic limit
of small energy levels the results should be an accurate description of QCD.
This new model can also be scaled so that all physical observables remain at
their $\mu=0$ values until a first order chiral restoration transition is
reached. This gives a more realistic model for the QCD phase diagram than
previous RMM. We also mention how the model might aid in determining the phase
diagram of QCD from future numerical simulations.


title:
Phenomenology of static-light mesons from unquenched lattice QCD
  calculations

abstract:
  We present results for the static-light meson from unquenched lattice QCD.
The unquenched gauge configurations were generated using the non-perturbatively
improved clover action. At the fixed lattice spacing of 0.1 fm the lightest sea
quark mass used is a third of the strange quark mass. A comparison is made
between heavy-light chiral perturbation theory and the f_B^(static) decay
constant. The mass of the bottom quark is also reported: m_b(m_b) = 4.25(2)(11)
GeV, where the first error is statistical and the last error is the systematic
uncertainty.


title: Effects of large field cutoffs in scalar and gauge models

abstract:
  We discuss the notion of a large field cutoff for lattice gauge models with
compact groups. We propose and compare gauge invariant and gauge dependent (in
the Landau gauge) criteria to sort the configurations into ``large-field'' and
``small-field'' configurations. We show that the correlations between volume
average of field size indicators and the behavior of the tail of the
distribution are very different in the gauge and scalar cases. We show that the
effect of discarding the large field configurations on the plaquette average is
very different above, below and near beta=5.6 for a pure SU(3) LGT.


title: Three Flavor QCD at High Temperatures

abstract:
  We have continued our study of the phase diagram of high temperature QCD with
three flavors of improved staggered quarks. We are performing simulations with
three degenerate quarks with masses less than or equal to the strange quark
mass m_s and with degenerate up and down quarks with masses m_{u,d} less than
the strange quark mass. For the quark masses studied to date, we find a
crossover that strengthens as m_{u,d} decreases, rather than a bona fide phase
transition. We present new results for the crossover temperature extrapolated
to the physical value of m_{u,d}, and for quark number susceptibilities.


title: Exploring the phase structure of lattice QCD with twisted mass quarks

abstract:
  The phase structure of zero temperature twisted mass lattice QCD is
investigated. We find strong metastabilities in the plaquette observable when
the untwisted quark mass sweeps across zero.


title: Two-particle wave function in four dimensional Ising model

abstract:
  An exploratory study of two-particle wave function is carried out with a four
dimensional simple model. The wave functions not only for two-particle ground
and first excited states but also for an unstable state are calculated from
three- and four-point functions using the diagonalization method suggested by
L\"uscher and Wolff. The scattering phase shift is evaluated from these wave
functions.


title: Topological susceptibility for the SU(3) Yang--Mills theory

abstract:
  We present the results of a computation of the topological susceptibility in
the SU(3) Yang--Mills theory performed by employing the expression of the
topological charge density operator suggested by Neuberger's fermions. In the
continuum limit we find r_0^4 chi = 0.059(3), which corresponds to chi=(191 \pm
5 MeV)^4 if F_K is used to set the scale. Our result supports the
Witten--Veneziano explanation for the large mass of the eta'.


title: Static $\bar{Q}$-$Q$ Potential from $N_f=2$ Dynamical Domain-Wall QCD

abstract:
  We calculate the static quark and anti-quark potential both in quenched and
two-flavor dynamical quark lattice QCD using DBW2 gauge and domain-wall quark
actions. Lattice spacings from Sommer scale are determined. We find (i) mixing
of excited states is different in between quenched and dynamical, (ii) lattice
spacing $a_{r_0}\sim a_{m_{\rho}}$ in dynamical and (iii) coefficient of
Coulomb term being $\alpha_{N_f=0}<\alpha_{N_f=2}$ at $a^{-1}\sim$ 2 GeV.


title: Lattice Study of the O(3) Supersymmetric Sigma Model

abstract:
  We present preliminary numerical results from a lattice study of the
two-dimensional O(3) non-linear sigma model. In the continuum this model
possesses N=2 supersymmetry. The lattice formulation we use retains an exact
(twisted) supersymmetry except for a soft breaking associated with a Wilson
mass term needed to remove the doubles. Our numerical results show that the
partition function is independent of coupling as predicted by supersymmetry.


title: Effects of low-lying fermion modes in the epsilon regime

abstract:
  We investigate the effects of low-lying fermion modes on the QCD partition
function in the epsilon-regime. With the overlap Dirac operator we calculate
several tens of low-lying fermion eigenvalues on the quenched lattice. By
partially incorporating the fermion determinant through the truncated
determinant approximation, we calculate the partition function and other
related quantities for Nf = 1 and compare them with the theoretical predictions
obtained by Leutwyler and Smilga.


title: Penguin diagrams for improved staggered fermions

abstract:
  We calculate, at the one loop level, penguin diagrams for improved staggered
fermion operators constructed using various fat links. The main result is that
diagonal mixing coefficients with penguin operators are identical between the
unimproved operators and the improved operators using such fat links as Fat7,
Fat7+Lepage, $\bar{\rm Fat7}$, HYP (I) and HYP (II). In addition, it turns out
that the off-diagonal mixing vanishes for those constructed using fat links of
Fat7, $\bar{\rm Fat7}$ and HYP (II). This is a consequence of the the fact that
the improvement by various fat links changes only the mixing with higher
dimension operators and off-diagonal operators. The results of this paper,
combined with those for current-current diagrams, provide the complete matching
at the one loop level with all corrections of ${\cal O}(g^2)$ included.


title:
Detailed analysis of the gluonic excitation in the three-quark system in
  lattice QCD

abstract:
  We study the excited-state potential and the gluonic excitation in the static
three-quark (3Q) system using SU(3) lattice QCD with $16^3\times 32$ at
$\beta$=5.8 and 6.0 at the quenched level. For about 100 different patterns of
spatially-fixed 3Q systems, we accurately extract the excited-state potential
$V_{\rm 3Q}^{\rm e.s.}$ together with the ground-state potential $V_{\rm
3Q}^{\rm g.s.}$ by diagonalizing the QCD Hamiltonian in the presence of three
quarks. The gluonic excitation energy $\Delta E_{\rm 3Q} \equiv V_{\rm 3Q}^{\rm
e.s.}-V_{\rm 3Q}^{\rm g.s.}$ is found to be about 1 GeV at the typical hadronic
scale. This large gluonic-excitation energy is conjectured to give a physical
reason of the success of the quark model for low-lying hadrons even without
explicit gluonic modes. We investigate the functional form of $\Delta E_{\rm
3Q}$ in terms of the 3Q location. The lattice data of $\Delta E_{\rm 3Q}$ are
relatively well reproduced by the ``inverse Mercedes Ansatz'' with the
``modified Y-type flux-tube length'', which indicates that the
gluonic-excitation mode is realized as a complicated bulk excitation of the
whole 3Q system.


title: Schwarz-preconditioned HMC algorithm for two-flavour lattice QCD

abstract:
  The combination of a non-overlapping Schwarz preconditioner and the Hybrid
Monte Carlo (HMC) algorithm is shown to yield an efficient simulation algorithm
for two-flavour lattice QCD with Wilson quarks. Extensive tests are performed,
on lattices of size up to 32x24x24x24, with lattice spacings a~0.08 fm and at
bare current-quark masses as low as 21 MeV.


title: Comparing iterative methods for overlap and twisted mass fermions

abstract:
  We present a systematic comparison of various iterative methods to obtain the
fermion propagator with both overlap and twisted mass fermions at fixed pion
mass in the quenched approximation. Taking the best available algorithm in each
case we find that calculations with the overlap operator are by a factor of
20-40 more expensive than with the twisted mass operator at the parameter
values considered here. For the overlap operator we also compare the efficiency
of various methods for calculating the topological index.


title: A comparative study of overlap and staggered fermions in QCD

abstract:
  We perform a comparative study of the infrared properties of overlap and
staggered fermions in QCD. We observe that the infrared spectrum of the APE/HYP
improved staggered Dirac operator develops a four-fold near-degeneracy and is
in quantitative agreement with the infrared spectrum of the overlap operator.
The near-degeneracy allows us to identify the zero modes of the staggered
operator and we find that the number of zero modes is in line with the
topological index of the overlap operator.


title:
Comparison between overlap and twisted mass fermions towards the chiral
  limit

abstract:
  We compare overlap fermions, which are chirally invariant, and Wilson twisted
mass fermions in the approach to the chiral limit. Our quenched simulations
reveal that with both formulations of lattice fermions pion masses of O(250
MeV) can be reached in practical simulations. Our comparison is done at a fixed
lattice spacing a=0.123 fm. Several quantities are measured, such as hadron
masses and pseudoscalar decay constants.


title:
Light Hadron Spectrum, Renormalization Constants and Light Quark Masses
  with Two Dynamical Fermions

abstract:
  The results of a preliminary partially quenched (N_f=2) study of the light
hadron spectrum, renormalization constants and light quark masses are
presented. Numerical simulations are carried out with the LL-SSOR
preconditioned Hybrid Monte Carlo with two degenerate dynamical fermions, using
the plaquette gauge action and the Wilson quark action at beta = 5.8. Finite
volume effects have been investigated employing two lattice volumes: 16^3 x 48
and 24^3 x 48. Configurations have been generated at four values of the sea
quark mass corresponding to M_{PS}/M_V ~ 0.6 - 0.8.


title: Finite volume effects in chiral perturbation theory

abstract:
  There has recently been an intense activity in the study of finite volume
effects by means of chiral perturbation theory. In this contribution I review
recent work in this field both for the epsilon-- (Mpi L \lesssim 1) and the
p--regime (Mpi L \gg 1). For the latter I emphasize the importance of going
beyond leading order calculations in chiral perturbation theory and the
usefulness of asymptotic formulae a la L"uscher used in combination with CHPT.


title: Triviality and the Higgs mass lower bound

abstract:
  In the minimal Standard Model, it is commonly believed that the Higgs mass
cannot be too small, otherwise Top quark dynamics makes the Higgs potential
unstable. Although this Higgs mass lower bound is relevant for current
phenomenology, we show that the Higgs vacuum instability in fact does not exist
and only appears when treating incorrectly the cut-off in the renormalization
of a trivial theory. We also demonstrate how to calculate correctly the
regulator-dependent Higgs mass lower bound.


title:
Quenching effects in strong penguin contributions to
  $\epsilon'/\epsilon$

abstract:
  Quenching effects in strong penguin matrix elements are investigated. A
lattice determination of $\alpha_q^{NS}$, the constant that appears in the
quenched ChPT relevant for the lattice analysis of $K\to\pi\pi$ matrix
elements, shows that this constant is large. The original RBC analysis of $Q_6$
matrix elements is revisited in light of this result. Also, the numerical
effects of choosing the singlet Golterman-Pallante method of quenching $Q_6$ is
investigated.


title: Nucleon Decay Matrix Elements with N_f=0 and 2 Domain-Wall Quarks

abstract:
  The nucleon decay matrix elements of three-quark operators are calculated
with domain-wall fermions. Operators are renormalized non-perturbatively to
match the MS bar (NDR) scheme at NLO. Quenched simulation studies involve both
direct measurement of the matrix elements and the chiral Lagrangian parameters,
alpha and beta. We also report on the dynamical quark effects on these
parameters.


title: Rough Gauge Fields, Smearing and Domain Wall Fermions

abstract:
  At a fixed lattice spacing, as determined by say m_\rho, adding additional
fermion flavors to a dynamical simulation produces rougher gauge field
configurations at the lattice scale. For domain wall fermions, these rough
configurations lead to larger residual chiral symmetry breaking and larger
values for the residual masses, m_{res}. We discuss ongoing attempts to reduce
chiral symmetry breaking for N_f = 3 dynamical domain wall fermion simulations
by different smoothing choices for the gauge fields.


title: Semileptonic D->pi/K and B->pi/D decays in 2+1 flavor lattice QCD

abstract:
  We present results for form factors of semileptonic decays of $D$ and $B$
mesons in 2+1 flavor lattice QCD using the MILC gauge configurations. With an
improved staggered action for light quarks, we successfully reduce the
systematic error from the chiral extrapolation. The results for $D$ decays are
in agreement with experimental ones. The results for B decays are preliminary.
Combining our results with experimental branching ratios, we then obtain the
CKM matrix elements $|V_{cd}|$, $|V_{cs}|$, $|V_{cb}|$ and $|V_{ub}|$. We also
check CKM unitarity, for the first time, using only lattice QCD as the
theoretical input.


title:
A scaling study of the step scaling function of quenched QCD with
  improved gauge actions

abstract:
  We study the scaling behavior of the step scaling function for SU(3) gauge
theory, employing the Iwasaki gauge action and the Luescher-Weisz gauge action.
In particular, we test the choice of boundary counter terms and apply a
perturbative procedure for removal of lattice artifacts for the simulation
results in the extrapolation procedure. We confirm the universality of the step
scaling functions at both weak and strong coupling regions. We also measure the
low energy scale ratio with the Iwasaki action, and confirm its universality.


title: Mobius Fermions: Improved Domain Wall Chiral Fermions

abstract:
  A new class of domain wall fermions is defined that interpolates between
Shamir's and Bori\c{c}i's form without increasing the number of Dirac
applications per CG iteration. This class represents a full (real) M\"obius
transformation of the Wilson kernel. Simulations on quenched Wilson lattices
with $\beta = 6.0$ show that the number of lattice sites ($L_s$) in the fifth
dimension can be reduced by a factor of 2 or more at fixed value of chiral
symmetry violations measured by the residual mass ($m_{res}$).


title: Electromagnetic Hadronic Form-Factors

abstract:
  We present a calculation of the nucleon electromagnetic form-factors as well
as the pion and rho to pion transition form-factors in a hybrid calculation
with domain wall valence quarks and improved staggered (Asqtad) sea quarks.


title: Chiral Extension of Lattice Gauge Theory

abstract:
  Two approaches are presented to coupling explicit Goldstone modes to $N_f$
flavors of massless quarks preserving exact $SU(N_f) \times SU(N_f)$ chiral
symmetry on the lattice. The first approach is a generalization a chiral
extension to QCD (aka XQCD) proposed by Brower, Shen and Tan consistent with
the Ginsparg-Wilson relation. The second approach based on the Callan,Coleman,
Wess and Zumino coset construction has a real determinant atzero quark axial
coupling, $g_A = 0$.


title: Penta-Quark Anti-Decuplet in Anisotropic Lattice QCD

abstract:
  The penta-quark(5Q) Theta^+(1540) is studied in anisotropic lattice QCD with
renormalized anisotropy a_s/a_t=4 for a high-precision measurement. Both the
positive and the negative parity 5Q baryons are studied using a non-NK type
interpolating field with I=0 and J=1/2. After the chiral extrapolation, the
lowest positive parity state is found at m_{Theta}\simeq 2.25 GeV, which is too
heavy to be identified with Theta^+(1540). In the negative parity channel, the
lowest energy state is found at m_{Theta}\simeq 1.75 GeV. Although it is rather
close to the empirical value, it is considered to be an NK scattering state
rather than a localized resonance state.


title: The N to Delta electromagnetic transition form factors from Lattice QCD

abstract:
  The magnetic dipole, the electric quadrupole and the Coulomb quadrupole
amplitudes for the transition \gamma N\to \Delta are calculated in quenched
lattice QCD at \beta=6.0 with Wilson fermions. Using a new method combining an
optimal combination of interpolating fields for the $\Delta$ and an
overconstrained analysis, we obtain statistically accurate results for the
dipole form factor and for the ratios of the electric and Coulomb quadrupole
amplitudes to the magnetic dipole amplitude, R_{EM} and R_{SM}, up to momentum
transfer squared 1.5 GeV^2. We show for the first time using lattice QCD that
both R_{EM} and R_{SM} are non-zero and negative, in qualitative agreement with
experiment and indicating the presence of deformation in the N- Delta system.


title: Chiral perturbation theory at non-zero lattice spacing

abstract:
  A review of chiral perturbation theory for lattice QCD at non-zero lattice
spacing is given.


title:
Light hadron spectrum in 2+1 flavor full QCD by CP-PACS and JLQCD
  Collaborations

abstract:
  CP-PACS and JLQCD Collaborations are carrying out a joint project of the 2+1
flavor full QCD with the RG-improved gauge action and the non-perturbatively
${\cal O}(a)$-improved Wilson quark action. This simulation removes quenching
effects of all three light quarks, which is the last major uncertainty in
lattice QCD. In this report we present our results for the light meson spectrum
and quark masses on a $20^3\times 40$ lattice at the lattice spacing $a\simeq
0.10$ fm.


title: The gluon and ghost propagator and the influence of Gribov copies

abstract:
  The dependence of the Landau gauge gluon and ghost propagators on the choice
of Gribov copies is studied in pure SU(3) lattice gauge theory. Whereas the
influence on the gluon propagator is small, the ghost propagator becomes
clearly affected by the copies in the infrared region. We compare our data with
the infrared exponents predicted by the Dyson-Schwinger equation approach


title: Chiral dynamics in QCD at finite chemical potential

abstract:
  We present the renormalized Taylor expansion of the chiral condensate with
chemical potential. The relation with the Taylor coefficients of meson
susceptibilities and the quark mass dependence of the quark number
susceptibilities are obtained through chiral Ward identities and Maxwell
relations. The continuum limit is obtained in quenched and two flavour QCD. In
Nf=2 QCD, the quadratic response coefficients (QRCs) of the chiral condensate
to chemical potential indicate that pion fluctuations decrease at finite
chemical potential toward the critical end point. We discuss how these
observables can be used to test other features of the QCD phase diagram.


title:
Higher Loop Results for the Plaquette, Using the Clover and Overlap
  Actions

abstract:
  We calculate the perturbative value of the free energy in QCD on the lattice.
This quantity is directly related to the average plaquette.
  Our calculation is done to 3 loops using the clover action for fermions; the
results are presented for arbitrary values of the clover coefficient, and for a
wide range of fermion masses.
  In addition, we calculate the 2 loop result for the same quantity, using the
overlap action.


title: Charmonium Spectrum from Quenched QCD with Overlap Fermions

abstract:
  We present preliminary results using overlap fermions for the charmonium
spectrum, in particular for hyperfine splitting. Simulations are performed on
$16^3 \times 72$ lattices, with Wilson gauge action at $\beta=6.3345$.
Depending on how the scale is set, we obtain 104(5) MeV (using
$1\bar{P}-1\bar{S}$) or 88(4) MeV (using $r_0$=0.5 fm) for the hyperfine
splitting.


title: The Omega- and the strange quark mass

abstract:
  Omega- correlators have been calculated on the MILC collaboration's archive
of three flavor improved staggered quark lattices. The Omega- is stable under
strong interactions (140 MeV below threshold). It provides a valuable
consistency check on a combination of strange quark mass and lattice scale
determination from other quantities. Alternatively, the Omega- mass could be
used to fix the strange quark mass, which gives a check on computations of the
strange quark mass based on the kaon mass.


title:
Hadronic physics with domain-wall valence and improved staggered sea
  quarks

abstract:
  With the advent of chiral fermion formulations, the simulation of light
valence quarks has finally become realistic for numerical simulations of
lattice QCD. The simulation of light dynamical quarks, however, remains one of
the major challenges and is still an obstacle to realistic simulations. We
attempt to meet this challenge using a hybrid combination of Asqtad sea quarks
and domain-wall valence quarks. Initial results for the proton form factor and
the nucleon axial coupling are presented.


title: Electroweak penguins and SUSY K^0-\bar K^0 mixing with Neuberger quarks

abstract:
  We present results for Delta I=3/2 and Delta S=2 matrix elements relevant for
CP violation in K->Pi Pi decays and for the K_S-K_L mass difference in the
standard model and beyond. They were obtained with Neuberger fermions on
quenched gauge configurations generated with the Wilson plaquette action at
beta=6.0 on an 18^3x64 lattice.


title:
Light hadron spectra and wave functions in quenched QCD with overlap
  quarks on a large lattice

abstract:
  A simulation of quenched QCD with the overlap Dirac operator has been
completed using 100 Wilson gauge configurations at beta=6 on an 18^3x64
lattice. We present results for meson and baryon masses, meson final state
"wave functions'' and other observables.


title: Exact 2+1 flavour RHMC simulations

abstract:
  We consider the Rational Hybrid Monte Carlo algorithm for performing exact
2+1 flavour fermion simulations. The specific cases of ASQTAD and domain wall
fermions are considered. We find that in both cases the naive performance is
similar to conventional hybrid algorithms.


title: Accelerating Fermionic Molecular Dynamics

abstract:
  We consider how to accelerate fermionic molecular dynamics algorithms by
introducing n pseudofermion fields coupled with the nth root of the fermionic
kernel. This reduces the maximum pseudofermionic force, and thus allows a
larger molecular dynamics integration step size without hitting an instability
in the integrator.


title:
Finite temperature phase transition in the 4d compact U(1) lattice gauge
  theory

abstract:
  We study the phase diagram of the 4d compact U(1) gauge theory as a function
of the number of Euclidean time slices. We use the helicity modulus as order
parameter to probe the phase transitions. The order of the transition along the
phase boundaries is studied and the possibility of a continuum limit is
discussed. We present new, strong evidence that the T=0 bulk phase transition
is first-order.


title: Polyakov Loops, Z(N) Symmetry, and Sine-Law Scaling

abstract:
  We construct an effective action for Polyakov loops using the eigenvalues of
the Polyakov loops as the fundamental variables. We assume Z(N) symmetry in the
confined phase, a finite difference in energy densities between the confined
and deconfined phases as $T\to 0$, and a smooth connection to perturbation
theory for large $T$. The low-temperature phase consists of $N-1$ independent
fields fluctuating around an explicitly Z(N) symmetric background. In the
low-temperature phase, the effective action yields non-zero string tensions for
all representations with non-trivial $N$-ality. Mixing occurs naturally between
representations of the same $N$-ality. Sine-law scaling emerges as a special
case, associated with nearest-neighbor interactions between Polyakov loop
eigenvalues.


title: String breaking with dynamical Wilson fermions

abstract:
  We present results of our ongoing determination of string breaking in full
QCD with N_f=2 Wilson fermions. Our investigation of the fission of the static
quark-antiquark string into a static-light meson-antimeson system is based on
dynamical configurations of size 24^3 x 40 produced by the TxL collaboration.
Combining various optimization methods we determine the matrix elements of the
two-by-two system with so far unprecedented accuracy. The all-to-all light
quark propagators occurring in the transition element are computed from
eigenmodes of the Hermitian Wilson-Dirac matrix complemented by stochastic
estimates in the orthogonal subspace. We observe a clear signature for
level-splitting between ground state and excited potential. Thus, for the first
time, string breaking induced by sea quarks is observed in a simulation of
4-dimensional lattice-QCD.


title: Twisted mass Lattice QCD

abstract:
  I review the main theoretical properties and some recent analytical and
numerical investigations of the formulations of lattice QCD with chirally
twisted Wilson quarks (also known as twisted mass lattice QCD).


title: QCD Thermodynamics on lattice

abstract:
  I discuss recent developments in lattice QCD thermodynamics on the nature of
the transition at finite temperature and density, equation of state, screening
of static charges and meson spectral functions at high temperatures.


title:
Matching of the Heavy-Light Currents with NRQCD Heavy and Improved Naive
  Light Quarks

abstract:
  One-loop matching of heavy-light currents is carried out for a highly
improved lattice action, including the effects of mixings with dimension 4
O(1/M) and O(a) operators. We use the NRQCD action for heavy quarks, the Asqtad
improved naive action for light quarks, and the Symanzik improved glue action.
These results are being used in recent heavy meson decay constant and
semileptonic form factor calculations on the MILC dynamical configurations.


title: Gauge action improvement and smearing

abstract:
  The effect of repeatedly smearing SU(3) gauge configurations is investigated.
Six gauge actions (Wilson, Symanzik, Iwasaki, DBW2, Beinlich-Karsch-Laermann,
Langfeld; combined with a direct SU(3)-overrelaxation step) and three smearings
(APE, HYP, EXP) are compared. The impact on large Wilson loops is monitored,
confirming the signal-to-noise prediction by Lepage. The fat-link definition of
the ``naive'' topological charge proves most useful on improved action
ensembles.


title: Recent results on moments of parton distribution functions

abstract:
  We report on recent results for the pion and nucleon matrix element of the
twist-2 operator corresponding to the average momentum of non-singlet quark
densities. We discuss finite size effects for the nucleon matrix element and
present first preliminary results for the non-perturbative renormalisation from
full dynamical simulations.


title: Domain-Wall Fermions at Strong Coupling

abstract:
  The DWF formulation becomes increasingly problematic at gauge couplings for
which $a^{-1}<2$ GeV, where the roughness of the gauge field leads to increased
explicit chiral symmetry breaking ($\mres$). This problem becomes especially
severe for sufficiently strong coupling where the underlying 4-dimensional
Wilson theory is in the Aoki phase. We review our attempts to find a suitable
modification of the gauge and/or the fermion action which would allow the DWF
method to work reliably at stronger coupling.


title:
The fourth root of the Kogut-Susskind determinant via infinite component
  fields

abstract:
  An example of interpolation by means of local field theories between the case
of normal Kogut-Susskind fermions and the case of keeping just the fourth root
of the Kogut-Susskind determinant is given. For the fourth root trick to be a
valid approximation certain limits need to be smooth. The question about the
validity of the fourth root trick is not resolved, only cast into a local field
theoretical framework.


title: CP$^{N-1}$ model with the theta term and maximum entropy method

abstract:
  A $\theta$ term in lattice field theory causes the sign problem in Monte
Carlo simulations. This problem can be circumvented by Fourier-transforming the
topological charge distribution $P(Q)$. This strategy, however, has a
limitation, because errors of $P(Q)$ prevent one from calculating the partition
function
  ${\cal Z}(\theta)$ properly for large volumes. This is called flattening. As
an alternative approach to the Fourier method, we utilize the maximum entropy
method (MEM) to calculate ${\cal Z}(\theta)$. We apply the MEM to Monte Carlo
data of the CP$^3$ model. It is found that in the non-flattening case, the
result of the MEM agrees with that of the Fourier transform, while in the
flattening case, the MEM gives smooth
  ${\cal Z}(\theta)$.


title: MEM study of true flattening of free energy and the $\theta$ term

abstract:
  We study the sign problem in lattice field theory with a $\theta$ term, which
reveals as flattening phenomenon of the free energy density $f(\theta)$. We
report the result of the MEM analysis, where such mock data are used that
`true' flattening of $f(\theta)$ occurs. This is regarded as a simple model for
studying whether the MEM could correctly detect non trivial phase structure in
$\theta$ space. We discuss how the MEM distinguishes fictitious and true
flattening.


title: Charmonia at finite momenta in a deconfined plasma

abstract:
  Lattice studies of charmonium systems have indicated that in a deconfined
gluonic plasma ground state charmonia survive as bound states upto temperatures
\~ 2 Tc. After surveying the methodologies used in reaching these results, we
examine the behavior of these systems when the bound state is in motion with
respect to the heatbath frame. We find that the finite momenta charmonia show
medium modifications when the medium is deconfined; in particular, a
modification of the energy-momentum dispersion relation is indicated.


title: Measuring interface tensions in 4d SU(N) lattice gauge theories

abstract:
  We propose a new algorithm to compute the order-order interface tension in
SU(N) lattice gauge theories. The algorithm is trivially generalizable to a
variety of models, e.g., spin models. In the case N=3, via the perfect wetting
hypothesis, we can estimate the order-disorder interface tension. In the case
N=4, we study the ratio of dual k-tensions and find that it satisfies Casimir
scaling down to T=1.2 T_c.


title:
Two and three loops computations of renormalization constants for
  lattice QCD

abstract:
  Renormalization constants can be computed by means of Numerical Stochastic
Perturbation Theory to two/three loops in lattice perturbation theory, both in
the quenched approximation and in the full (unquenched) theory. As a case of
study we report on the computation of renormalization constants of the
propagator for Wilson fermions. We present our unquenched (N_f=2) computations
and compare the results with non perturbative determinations.


title: 3-d lattice SU(3) free energy to four loops

abstract:
  We report on the perturbative computation of the 3d lattice Yang-Mills free
energy to four loops by means of Numerical Stochastic Perturbation Theory. The
known first and second orders have been correctly reproduced; the third and
fourth order coefficients are new results and the known logarithmic IR
divergence in the fourth order has been correctly identified. Progress is being
made in switching to the gluon mass IR regularization and the related inclusion
of the Faddeev-Popov determinant.


title: The n_f=2 residual mass in lattice HQET to alpha^3 order

abstract:
  We compute the so called residual mass in Lattice Heavy Quark Effective
Theory to alpha^3 order in the n_f=2 (unquenched) case. The control of this
additive mass renormalization is crucial for the determination of the heavy
quark mass from lattice simulations. We discuss the impact on an unquenched
determination of the b-quark mass.


title: Large N QCD -- Continuum reduction and chiral condensate

abstract:
  Continuum reduction in large N QCD enables one to extract physical quantities
in the $N\to\infty$ limit of QCD by working in small physics volumes. The
computation of chiral condensate is an example of such a calculation.


title:
Finite temperature QCD with two flavors of dynamical quarks on 24^3*10
  lattice

abstract:
  We present results obtained in QCD with two flavors of non-perturbatively
improved Wilson fermions at finite temperature on $16^3 \times 8$ and $24^3
\times 10$ lattices. We determine the transition temperature in the range of
quark masses $0.6<m_\pi/m_\rho<0.8$ at lattice spacing a$\approx$0.1 fm and
extrapolate the transition temperature to the continuum and to the chiral
limits.


title: Non leptonic two-body decay amplitudes from finite volume calculations

abstract:
  We discuss the quantization of the energy levels of two-particle scattering
states in a finite volume in the case of Bloch-type boundary conditions. A
generalization of the Luescher quantization condition is obtained that can be
used in order to calculate the scattering phases, resulting for example by the
strong elastic interaction of two pions, at fixed physical momentum transfers
on a sequence of volumes of growing sizes. We also give a generalization of the
Lellouch-Luescher formula to be used to extract the physical decay rate for a
kaon decaying into two pions below the inelastic threshold from finite volume
calculations. The formula is valid up to corrections exponentially vanishing in
the volume. By using this formula the calculation can in principle be performed
on different finite volumes of growing sizes in order to keep under control the
corrections.


title: Technical notes on a 2-d lattice O(N) model problem

abstract:
  This paper provides a technical companion to M. Aguado and E. Seiler,
hep-lat/0406041, in which the fate of perturbation theory in the thermodynamic
limit is discussed for the O(N) model on a 2d lattice and different boundary
conditions. The techniques used to compute perturbative coefficients are
explained, and results for all boundary conditions considered reviewed in
detail.


title: A cluster algorithm for Lattice Gauge Theories

abstract:
  A new algorithm for simulating compact U(1) lattice gauge theory in three
dimensions is presented which is based on global changes in the configuration
space. We show that this algorithm provides an effective way to extract
partition functions at given external flux. As an application, we study
numerically the finite temperature deconfinement phase transition.


title: Finite Density QCD: a New Approach

abstract:
  We introduce a new approach to analyze the phase diagram of QCD at finite
chemical potential and temperature, test it in the Gross-Neveu model at finite
baryon density, and apply it to the study of the chemical potential-temperature
phase diagram of QCD with four degenerate flavors of Kogut-Susskind type.


title: New Ideas in Finite Density QCD

abstract:
  We introduce a new approach to analyze the phase diagram of QCD at finite
chemical potential and temperature, based on the definition of a generalized
QCD action. Several details of the method will be discussed, with particular
emphasis on the advantages respect to the imaginary chemical potential
approach.


title: Strong coupling analysis of diquark condensation

abstract:
  The phenomenon of diquark condensation at non-zero baryon density and zero
temperature is analyzed in the strong coupling limit of lattice QCD. The
results indicate that there is attraction in the quark-quark channel also at
strong coupling, and that the attraction is more effective at high baryon
density, but for infinite coupling it is not enough to produce diquark
condensation. It is argued that the absence of diquark condensation is not a
peculiarity of the strong coupling limit, but persists at sufficiently large
finite couplings.


title: Testing new strategies in finite density

abstract:
  A new approach for non zero chemical potential simulations is tested in the
Gross-Neveu model for infinite flavor number, where the critical line is
reconstructed in a large $\mu/T$ interval. A comparison with results from
standard imaginary chemical potential approach as well as first results for
$N_f=4$ QCD are presented.


title: Axial and tensor charge of the nucleon with dynamical fermions

abstract:
  We present preliminary results for the axial and tensor charge of the nucleon
obtained from simulations with N_f=2 clover fermions. A comparison with chiral
perturbation theory is attempted.


title:
Generalized parton distributions and structure functions from full
  lattice QCD

abstract:
  We present here the latest results from the QCDSF collaboration for (moments
of) structure functions and generalized form factors in full QCD with Nf=2
O(a)-improved Wilson fermions based on simulations closer to the chiral and
continuum limit.


title: Evidence for layered symmetry breaking in SU(2) lattice gauge theory

abstract:
  Simulations of four-dimensional SU(2) lattice gauge theory are performed with
partial axial gauge fixing trees spanning three of the four dimensions. The
remaining SU(2) gauge symmetry, global in three directions and local in one, is
found to break spontaneously at weak coupling, with the average
fourth-dimension-pointing link in each perpendicular hyperplane as order
parameter. The symmetry is restored at strong coupling. Symmetry breaking in
each hyperplane appears to be independent, and occurs regardless of boundary
conditions. The associated phase transition is likely coincident with the
Polyakov loop transition.


title: A lattice determination of g_A and <x> from overlap fermions

abstract:
  We present results for the nucleon's axial charge g_A and the first moment
<x> of the unpolarized parton distribution function from a simulation of
quenched overlap fermions.


title: ILDG Middleware Working Group Status Report

abstract: We report on the status of the ILDG Middleware Working Group.


title: Determination of Lambda in quenched and full QCD - an update

abstract:
  We present an update on our previous determination of the Lambda parameter in
QCD. The main emphasis is on results for two flavours of light dynamical
quarks, where we can now almost double the amount of data used, including
values at smaller lattice spacings. The calculations are performed using $O(a)$
improved Wilson fermions. Little change is found to previous numerical values.


title: Algorithms for Lattice QCD with Dynamical Fermions

abstract:
  We consider recent progress in algorithms for generating gauge field
configurations that include the dynamical effects of light fermions. We survey
what has been achieved in recent state-of-the-art computations, and examine the
trade-offs between performance and control of systematic errors. We briefly
review the use of polynomial and rational approximations in Hybrid Monte Carlo
algorithms, and some of the theory of on-shell chiral fermions on the lattice.
This provides a theoretical framework within which we compare algorithmic
alternatives for their implementation; and again we examine the trade-offs
between speed and error control.


title: The Dual Meissner Effect and Magnetic Displacement Currents

abstract:
  The dual Meissner effect is observed without monopoles in quenched $SU (2)$
QCD with Landau gauge-fixing. Magnetic displacement currents which are
time-dependent Abelian magnetic fields play a role of solenoidal currents
squeezing Abelian electric fields. Monopoles are not always necessary to the
dual Meissner effect. The squeezing of the electric flux means the dual London
equation and the massiveness of the Abelian electric fields as an asymptotic
field. The mass generation of the Abelian electric fields is related to a gluon
condensate $<A^a_{\mu}A^a_{\mu}>\neq 0$ of mass dimension 2.


title: Progress on a canonical finite density algorithm

abstract:
  We test the finite density algorithm in the canonical ensemble which combines
the HMC update with the accept/reject step according to the ratio of the
fermion number projected determinant to the unprojected one as a way of
avoiding the determinant fluctuation problem. We report our preliminary results
on the Polyakov loop in different baryon number sectors which exhibit
deconfinement transitions on small lattices. The largest density we obtain
around $T_c$ is an order of magnitude larger than that of nuclear matter. From
the conserved vector current, we calculate the quark number and verify that the
mixing of different baryon sectors is small.


title: Thermal Phase Transition in the NJL Model of QCD

abstract:
  We present results from numerical studies of the NJL model with two massless
quarks at nonzero temperature. We show that the model undergoes a second order
chiral phase transition which belongs to the 3d O(4) spin model universality
class.


title: A new lattice gauge action without scaling artifacts

abstract:
  I describe a new way of constructing a gauge action that eliminates scaling
artifacts, by writing the continuum formalism in terms of "gauge links"
(Schwinger line integrals) and using the optimal SLAC representation of the
lattice derivative. Computational performance can be maintained by implementing
the action as a "stochastic" operator, as has been recently implemented in the
MILC code for the optimal D-slash operator and the antialiasing filter.


title:
A perturbative determination of the parameters of an anisotropic quark
  action

abstract:
  The parameters of a 3+1 anisotropic quark action with Symanzik-improved glue
are determined at 1-loop in perturbation theory.


title: The pion form factor on the lattice at zero and finite temperature

abstract:
  We calculate the electromagnetic form factor of the pion in quenched lattice
QCD. The non-perturbatively improved Sheikoleslami-Wohlert lattice action is
used together with the consistently O(a) improved current. We calculate the
pion form factor for masses down to m_pi = 360 MeV, extract the charge radius,
and extrapolate toward the physical pion mass. In the second part, we discuss
results for the pion form factor and charge radius at 0.93 T_c and compare with
zero temperature results.


title: External Fields and Color Confinement

abstract:
  U(1), SU(2), and SU(3) lattice gauge theories in presence of external fields
are investigated both in (3+1) and (2+1) dimensions. The free energy of gauge
systems has been measured. While the phase transition in compact U(1) is not
influenced by the strength of an external constant magnetic field, the
deconfinement temperature for SU(2) and SU(3) gauge systems in a constant
abelian chromomagnetic field decreases when the strength of the applied field
increases. The dependence of the deconfinement temperature on the strength of
an external constant chromomagnetic field seems to be a peculiar feature of non
abelian gauge theories.


title: Status of Lattice Flavor Physics

abstract:
  This talk reviews recent lattice QCD calculations relevant for quark flavor
physics. Since lattice results must be accurate and precise to play a
definitive role in phenomenology, the focus is on unquenched results of
quantities which can be calculated most reliably.


title:
Perturbative Renormalisation of the Second Moment of Generalised Parton
  Distributions

abstract:
  We calculate the non-forward quark matrix elements of operators with two
covariant derivatives needed for the renormalisation of the second moment of
generalised parton distributions in one-loop lattice perturbation theory using
Wilson fermions. For some representations of the hypercubic group commonly used
in simulations we determine the sets of all possible mixing operators. For
those representations the one-loop mixing matrices of renormalisation factors
are found. Due to non-vanishing contributions of operators with external
ordinary derivatives the number of contributing operators increases compared to
forward matrix elements.


title: Numerical Stochastic Perturbation Theory for full QCD

abstract:
  We give a full account of the Numerical Stochastic Perturbation Theory method
for Lattice Gauge Theories. Particular relevance is given to the inclusion of
dynamical fermions, which turns out to be surprisingly cheap in this context.
We analyse the underlying stochastic process and discuss the convergence
properties. We perform some benchmark calculations and - as a byproduct - we
present original results for Wilson loops and the 3-loop critical mass for
Wilson fermions.


title: Flavour singlet physics in lattice QCD with background fields

abstract:
  We show that hadronic matrix elements can be extracted from lattice
simulations with background fields that arise from operator exponentiation.
Importantly, flavour-singlet matrix elements can be evaluated without requiring
the computation of disconnected diagrams, thus facilitating a calculation of
the quark contribution to the spin of the proton and the singlet axial
coupling, $g_A^0$. In the two nucleon sector, a background field approach will
allow calculation of the magnetic and quadrupole moments of the deuteron and an
investigation of the EMC effect directly from lattice QCD. Matrix elements
between states of differing momenta are also analysed in the presence of
background fields.


title: Predictions and recent results in susy on the lattice

abstract:
  In this brief review, I summarize the current theoretical knowledge in
supersymmetry on the lattice, with special emphasis on recent results in the
framework of N=1 supersymmetric Yang Mills theory, Wess-Zumino model and
Yang-Mills theory with extended supersymmetries.


title: Static-light matrix elements on a dynamical anisotropic lattice

abstract:
  The static-light matrix element needed to determine $f_B$ is studied on an
anisotropic lattice with $N_f=2$. The improvement in precision due to stout
links and all-to-all propagators is investigated.


title:
Heavy-light decay constants using clover valence quarks and three
  flavors of dynamical improved staggered quarks

abstract:
  Starting in 2001, the MILC Collaboration began a large scale calculation of
heavy-light meson decay constants using clover valence quarks on ensembles of
three flavor configurations. For the coarse configurations, with a=0.12 fm,
eight combinations of dynamical light and strange quarks have been analyzed.
For the fine configurations, with a=0.09 fm, three combinations of quark masses
are studied. Since we last reported on this calculation, statistics have been
increased on the fine ensembles, and, more importantly, a preliminary value for
the perturbative renormalization of the axial-vector current has become
available. Thus, results for f_B, f_{B_s}, f_D and f_{D_s} can, in principle,
be calculated in MeV, in addition to decay-constant ratios that were calculated
previously.


title: Formulation of chiral gauge theories

abstract:
  We present a formulation of chiral gauge theories, which admits more general
spectra of Dirac operators and reveals considerably more possibilities for the
structure of the chiral projections. Our two forms of correlation functions
both also apply in the presence of zero modes and for any value of the index.
The decomposition of the total set of pairs of bases into equivalence classes
is carefully analyzed. Transformation properties are derived.


title: Pentaquarks: Status and Perspectives for Lattice Calculations

abstract:
  The present status of pentaquark spectroscopy in lattice QCD is reviewed.
This talk also includes a brief introduction of pentaquark baryons.


title: Properties of hadron screening masses at small baryonic density

abstract:
  The properties of hadron screening masses around the deconfinement phase
transition at finite baryonic density can be studied by evaluating the Taylor
coefficients with respect to the iso-scalar and iso-vector chemical potentials.
We simulate 2-flavour lattice QCD with staggered fermions on a 12*12*24*6
lattice with ma = 0.05 and 0.10 and report investigations of nucleon,
pseudo-scalar and vector mesons. We present new, strong evidence that in the
confining phase, the screening masses at vanishing chemical potential have
significant temperature dependence, but the effect of the iso-scalar chemical
potential is very small. Above the critical temperature, the second derivative
terms of mesons rapidly increase as contrasted to the case of baryon. We also
study the responses of the screening masses to an iso-vector chemical potential
and discuss some of the issues related to the properties of hadron masses at
finite density.


title: Universality in the Gross-Neveu model

abstract:
  We consider universal finite size effects in the large-N limit of the
continuum Gross-Neveu model as well as in its discretized versions with Wilson
and with staggered fermions. After extrapolation to zero lattice spacing the
lattice results are compared to the continuum values.


title:
Model A Dynamics and the Deconfining Phase Transition for Pure Lattice
  Gauge Theory

abstract:
  We consider model A dynamics for a heating quench from the disordered
(confined) into the ordered (deconfined) phase of SU(3) lattice gauge theory.
For $4 N_{\sigma}^3$ lattices the exponential growth factors of low-lying
structure function modes are calculated. The linear theory of spinodal
decompositions is compared with the data from an effective model and the Debye
screening mass is estimated from the critical mode. Further, the quench leads
to competing vacuum domains, which make the equilibration of the QCD vacuum
after the heating non-trivial. We investigate the influence of such domains on
the gluonic energy density.


title: A Possible Aoki Phase for Staggered Fermions

abstract:
  The phase diagram for staggered fermions is discussed in the context of the
staggered chiral Lagrangian, extending previous work on the subject. When the
discretization errors are significant, there may be an Aoki-like phase for
staggered fermions, where the remnant SO(4) taste symmetry is broken down to
SO(3). We solve explicitly for the mass spectrum in the 3-flavor degenerate
mass case and discuss qualitatively the 2+1-flavor case. From numerical results
we find that current simulations are outside the staggered Aoki phase. As for
near-future simulations with more improved versions of the staggered action, it
seems unlikely that these will be in the Aoki phase for any realistic value of
the quark mass, although the evidence is not conclusive.


title: The Static Penta-quark Potential in Lattice QCD

abstract:
  We perform the first study for the static penta-quark (5Q) potential in
lattice QCD with $\beta$=6.0 and $16^3 \times 32$ at the quenched level.
Accurate results of the 5Q potential are extracted from the 5Q Wilson loop
using the smearing method, which enhances the ground-state component. The
tetra-quark potential for the $\rm QQ$-$\rm {\bar Q}{\bar Q}$ system is also
studied in lattice QCD. The multi-quark potentials are found to be well
described as a sum of the one-gluon-exchange Coulomb term and the multi-Y
linear confinement term based on the flux-tube picture.