title: QCD string from D0 branes

abstract:
  We report the results of a set of high precision simulations performed in the
3d gauge Ising model. We evaluated the interquark potential and the first few
energy levels and compared them with the predictions obtained with the
effective Nambu-Goto string and with the free bosonic string. The data are
precise enough to unambiguously distinguish between the free string predictions
and those obtained using the N-G effective string. At large distances we find a
remarkable agreement between Monte Carlo data and N-G predictions for the first
excited energy level, while the free string picture is definitely excluded. As
the interquark distance is decreased (and/or the finite temperature becomes
higher) the Monte Carlo results show larger and larger deviations both from the
N-G and from the free string predictions. In order to better understand this
behaviour we re-derived the effective Nambu-Goto theory result for the Polyakov
loop correlator using a covariant quantization. We chose as boundary conditions
those of an open string attached to two D0-branes at spatial distance $R$, in a
target space with compact euclidean time. Obviously our treatment is fully
consistent only in $d=26$. The extension to generic $d$ requires taking into
account the Liouville mode of Polyakov's formulation. The analogy with the
standard light cone calculation suggests that the contribution due to the
Liouville field can be neglected for large $R$. At shorter scales, the
Liouville mode cannot be neglected and its contribution to the interquark
potential might be the source of the discrepancies with respect to the
effective N-G results that we observe in our Monte Carlo simulations.


title: Nuclear models on a lattice

abstract:
  We present the first results of a quantum field approach to nuclear models
obtained by lattice techniques. Renormalization effects for fermion mass and
coupling constant in case of scalar and pseudoscalar interaction lagrangian
densities are discussed.


title:
Three Phases in the 3D Abelian Higgs Model with Nonlocal Gauge
  Interactions

abstract:
  We study the phase structure of the 3D nonlocal compact U(1) lattice gauge
theory coupled with a Higgs field by means of Monte-Carlo simulations. The
nonlocal interactions among gauge variables are along the temporal direction
and mimic the effect of local coupling to massless particles. We found that in
contrast to the 3D local abelian Higgs model which has only one phase, the
present model exhibits the confinement, Higgs, and Coulomb phases separated by
three second-order transition lines emanating from a triple point. This result
is quite important for studies on electron fractionalization phenomena in
strongly-correlated electron systems. Implications to them are discussed.


title: Baryons in 2+1 flavour domain wall QCD

abstract:
  We present results for some of the light baryon masses and their excited
states in 2+1 flavour domain wall QCD. We considered several lattice spacings,
with the DBW2 and Iwasaki gauge actions and different sea quark masses on a
volume of $16^3\times32$ and a fifth dimension of size 8. All data were
generated on the QCDOC machines. Despite large residual massses and a limited
number of sea quark mass values with which to perform chiral extrapolations,
our results are in reasonable agreement with experiment and scale within
errors. Finite size effects on most ensembles appear to be small.


title: Bulk Thermodynamics of SU(N) Lattice Gauge Theories at Large-N

abstract:
  We present a study of bulk thermodynamical quantities in the deconfined phase
of pure lattice SU(N) gauge theories. We find that the deficit in pressure and
entropy with respect to their free-gas values, for N=4,8, is remarkably close
to that of SU(3). Th is suggests that understanding the strongly interacting
nature of the deconfined phase, which is crucial for RHIC physics, can be done
at large N. There, different analytical approaches simplify or become soluble,
and one can check their predictions and point to their important ingredients.


title: Parton Distribution Functions with Twisted Mass Fermions

abstract:
  We present a first Wilson twisted mass fermion calculation of the matrix
element between pion states of the twist-2 operator, which is related to the
the lowest moment < x > of the valence quark parton distribution function in a
pion. Using Wilson twisted mass fermions in the quenched approximation we
demonstrate that < x > can be computed at small pseudoscalar meson masses down
to values of order 250 MeV. We investigate the scaling behaviour of this
physically important quantity by applying two definitions of the critical mass
and observe a scaling compatible with the expected O(a^2) behaviour in both
cases. A combined continuum extrapolation allows to obtain reliable results for
< x > at very small pseudoscalar meson masses, which previously could not be
explored by lattice QCD simulations.


title: Improved bilinears in lattice QCD with non-degenerate quarks

abstract:
  We describe the extension of the improvement program for bilinear operators
composed of Wilson fermions to non-degenerate dynamical quarks. We consider
two, three and four flavors, and both flavor non-singlet and singlet operators.
We find that there are many more improvement coefficients than with degenerate
quarks, but that, for three or four flavors, nearly all can be determined by
enforcing vector and axial Ward identities. The situation is worse for two
flavors, where many more coefficients remain undetermined.


title:
Estimate of the charmed 0-- hybrid meson spectrum from quenched lattice
  QCD

abstract:
  We compute from quenched lattice QCD the ground state masses of the charmed
hybrid mesons cbar c g, with exotic quantum numbers JPC=1-+, 0+- and 0--. The
0-- hybrid meson spectrum has never been provided by lattice simulations due to
the difficulties to extract high gluonic excitations from noise. We employ
improved gauge and fermion actions on the anisotropic lattice, which reduce
greatly the lattice artifacts, and lead to very good signals. The data are
extrapolated to the continuum limit, with finite size effects under well
control. For 1-+ and 0+- hybrid mesons, the ground state masses are 4.405(38)
GeV and 4.714(52) GeV. We predict for the first time from lattice QCD, the
ground state mass of 0-- to be 5.883(146) GeV.


title: Exploring Topology Conserving Gauge Actions for Lattice QCD

abstract:
  We explore gauge actions for lattice QCD, which are constructed such that the
occurrence of small plaquette values is strongly suppressed. By choosing strong
bare gauge couplings we arrive at values for the physical lattice spacings of
O(0.1 fm). Such gauge actions tend to confine the Monte Carlo history to a
single topological sector. This topological stability facilitates the
collection of a large set of configurations in a specific sector, which is
profitable for numerical studies in the epsilon-regime. The suppression of
small plaquette values is also expected to be favourable for simulations with
dynamical quarks. We use a local Hybrid Monte Carlo algorithm to simulate such
actions, and we present numerical results for the static potential, the
physical scale, the topological stability and the kernel condition number of
the overlap Dirac operator. In addition we discuss the question of reflection
positivity for a class of such gauge actions.


title: Order, Disorder and Confinement

abstract:
  Studying the order of the chiral transition for $N_f=2$ is of fundamental
importance to understand the mechanism of color confinement. We present results
of a numerical investigation on the order of the transition by use of a novel
strategy in finite size scaling analysis. The specific heat and a number of
susceptibilities are compared with the possible critical behaviours. A second
order transition in the O(4) and O(2) universality classes are excluded.
Substantial evidence emerges for a first order transition. Results are in
agreement with those found by studying the scaling properties of a disorder
parameter related to the dual superconductivity mechanism of color confinement.


title:
Study of color superconductivity with Ginzburg-Landau effective action
  on the lattice

abstract:
  We study thermal phase transitions of color superconductivity by the lattice
simulations of the Ginzburg-Landau (GL) effective theory. The theory is
equivalent to the SU_ f(3) cross SU_c(3) Higgs model coupled to SU_c(3) color
gauge fields. From the eigenvalues of a 3-by-3 gauge-invariant diquark
composite, a clear distinction between the 2-flavor color superconductivity
(2SC) and the color flavor locking (CFL) phase is made in a gauge invariant
manner. The thermal transitions between the normal phase and the
superconducting phases are found to be first-order due to thermal gluons. The
phase structure in the coupling-constant space is numerically explored and
three patterns of phase transition, i.e., normal to 2SC, normal to CFL and
normal to CFL via 2SC, are found in the chiral limit. These results agree
qualitatively with the weak-coupling analysis of the GL theory.


title: Effective Lattice Actions for Finite-Temperature Yang-Mills Theory

abstract:
  We determine effective lattice actions for the Polyakov loop using inverse
Monte Carlo techniques.


title:
Chiral Extrapolation of Lattice Data for Heavy Meson Hyperfine
  Splittings

abstract:
  We investigate the chiral extrapolation of the lattice data for the
light-heavy meson hyperfine splittings D^*-D and B^*-B to the physical region
for the light quark mass. The chiral loop corrections providing non-analytic
behavior in m_\pi are consistent with chiral perturbation theory for heavy
mesons. Since chiral loop corrections tend to decrease the already too low
splittings obtained from linear extrapolation, we investigate two models to
guide the form of the analytic background behavior: the constituent quark
potential model, and the covariant model of QCD based on the ladder-rainbow
truncation of the Dyson-Schwinger equations. The extrapolated hyperfine
splittings remain clearly below the experimental values even allowing for the
model dependence in the description of the analytic background.


title: Universality and Quark Masses of the Staggered Fermion Action

abstract:
  Staggered fermions with 4 tastes are expected to describe 4-flavor QCD in the
continuum limit, therefore at finite lattice spacing the staggered determinant
should be equivalent to an SU(4) flavor-symmetric system up to lattice
artifacts. This equivalence is the starting point of the 4th root trick used to
reduce the number of fermion flavors and provides the only consistent
description of 2 or 1 flavor systems. In this paper we argue that the quark
mass of the underlying flavor symmetric theory differs from the staggered mass
by an additive term due to the taste breaking of the staggered action. The
relation is the same for 2 and 1 flavor fermions. This additive mass shift
implies that at finite lattice spacing staggered simulations correspond to
heavier quark masses than indicated by the staggered Goldstone pion and that
staggered fermions cannot reach the chiral limit at finite lattice spacing.


title:
PQChPT with Staggered Sea and Valence Ginsparg-Wilson Quarks: Vector
  Meson Masses

abstract:
  We consider partially quenched, mixed chiral perturbation theory with
staggered sea and Ginsparg-Wilson valence quarks in order to extract a
chiral-continuum extrapolation expression for the vector meson mass up to order
O(a^2), at one-loop level. Based on general principles, we accomplish the task
without explicitly constructing a sophisticated, heavy vector meson chiral
Lagrangian.


title: Lattice QCD and String Theory

abstract:
  Bosonic string formation in gauge theories is reviewed with particular
attention to the confining flux in lattice QCD and its string theory
description. Recent results on the Casimir energy of the ground state and the
string excitation spectrum are analyzed in the Dirichlet string limit of large
separation between static sources. The closed string-soliton (torelon) with
electric flux winding around a compact dimension and the three-string with a
Y-junction created by three static sources are also reviewed. It is shown that
string spectra from lattice simulations are consistent with universal
predictions of the leading operators from the derivative expansion of a
Poincare invariant effective string Lagrangian with reparameterization
symmetry. Important characterisitics of the confining flux, like stiffness and
the related massive breather modes, are coded in operators with higher
derivatives and their determination remains a difficult challenge for lattice
gauge theory.


title: Correlations of center flux in SU(2) Yang-Mills theory

abstract:
  By using the method of center projection the center vortex part of the gauge
field is isolated and its propagator is evaluated in the center Landau gauge,
which minimizes the open 3-dimensional Dirac volumes of non-trivial center
links bounded by the closed 2-dimensional center vortex surfaces. The center
field propagator is found to dominate the gluon propagator (in Landau gauge) in
the low momentum regime and to give rise to an OPE correction to the latter of
$\sqrt{\sigma} /p^3 $.The screening mass of the center vortex field vanishes
above the critical temperature of the deconfinement phase transition, which
naturally explains the second order nature of this transition consistently with
the vortex picture. Finally, the ghost propagator of maximal center gauge is
found to be infrared finite and thus shows no signal of confinement.


title: Gauge invariance of the dual Meissner effect in QCD

abstract:
  The dual Meissner effect is described and numerically observed in a
gauge-invariant way in lattice Monte-Carlo simulations of pure SU(2) QCD.
  A gauge-invariant Abelian-like field strength is defined in terms of a
unit-vector in color space which is constructed by a non-Abelian field strength
itself. A gauge-invariant monopole-like quantity is defined by a violation of
the Bianchi identity with respect to the Abelian-like field strength. The
squeezing of the non-Abelian electric field $\sqrt{\sum_a(E^a_i)^2}$ between a
pair of static quark and anti-quark occurs due to the solenoidal current coming
from the gauge-invariant monopole-like quantity. An equation similar to the
dual London equation is confirmed approximately in the long-range region.


title: Gauge invariant 'monopoles' and color confinement mechanism

abstract:
  The dual Meissner effect is described and numerically observed in a
gauge-invariant way in lattice Monte-Carlo simulations of pure SU(2) QCD. A
gauge-invariant monopole-like quantity on the lattice is defined by a
gauge-invariant Abelian-like field strength. The Abelian-like field strength is
expressed in terms of a unit-vector in color space which is constructed by a
non-Abelian field strength itself. It is just equal to the absolute value of
the corresponding non-Abelian field strength except for the sign. In this note
we show the theoretical background and most numerical results will be published
in a separate report \cite{Suzuki:2005lat052} in this conference.


title: Gauge invariance of the Abelian dual Meissner effect in pure SU(2) QCD

abstract:
  The dual Meissner effect is described and numerically observed in a
gauge-invariant way in lattice Monte-Carlo simulations in pure SU(2) QCD. The
squeezing of the non-Abelian electric field between a pair of static quark and
anti-quark occurs due to the solenoidal current coming from the gauge-invariant
monopole-like quantity. Preliminary results are obtained with respect to the
vacuum type of the confinement phase. The SU(2) QCD vacuum seems near the
border between the type 1 and the type 2 dual superconductors. The theoretical
background of this idea is published in another report
\cite{Suzuki:2005lat051}. Here we show numerical results in this note.


title: Mesons at high temperature in Nf=2 QCD

abstract:
  We report first results for spectral functions of charmonium in 2-flavour
QCD. The spectral functions are determined from vector and pseudoscalar
correlators on a dynamical, anisotropic lattice. J/psi and eta_c are found to
survive well into the deconfined phase before melting away at T<~2T_c. Current
systematic uncertainties prevent us from drawing any definite conclusions at
this stage.


title:
QCD at High Temperature : Results from Lattice Simulations with an
  Imaginary mu

abstract:
  We summarize our results on the phase diagram of QCD with emphasis on the
high temperature regime. For $T \ge 1.5 T_c$ the results are compatible with a
free field behavior, while for $T \simeq 1.1 T_c$ this is not the case, clearly
exposing the strongly interacting nature of QCD in this region


title: Laplacian modes as a filter

abstract:
  We compute low-lying eigenmodes of the gauge covariant Laplace operator on
the lattice at finite temperature. For classical configurations we show how the
lowest mode localizes the monopole constituents inside calorons and that it
hops upon changing the boundary conditions. The latter effect we observe for
thermalized backgrounds, too, analogously to what is known for fermion zero
modes.
  We propose a new filter for equilibrium configurations which provides link
variables as a truncated sum involving the Laplacian modes. This method not
only reproduces classical structures, but also preserves the confining
potential, even when only a few modes are used.


title: Moebius Fermions

abstract:
  We introduce a new domain wall operator that represents a full (real) Moebius
transformation of a given non-chiral Dirac kernel. Shamir's and Borici's domain
wall fermions are special cases of this new class. By tuning the parameters of
the Moebius operator and by introducing a new Red/Black preconditioning, we are
able to reduce the computational effort substantially.


title: Nonperturbative investigation of the diquark potential

abstract:
  We perform an investigation of the static quark-quark-potential both in the
confined and the deconfined phase. We discuss conceptual and technical problems
and present first results of an exploratory numerical investigation.


title:
Grand Canonical Potential for a Static Quark-Antiquark Pair at finite
  chemical potential

abstract:
  The grand canonical potential for a static quark-antiquark pair at
non-vanishing chemical potential was determined at several temperatures. The
dynamical staggered simulations were carried out with 2+1 physical quarks along
the Lines of Constant Physiscs (LCP).


title: The Schrodinger functional with chirally rotated boundary conditions

abstract:
  Using orbifold techniques I construct the Schrodinger functional (SF) for a
doublet of Wilson quarks with chirally rotated boundary conditions. This allows
to perform checks of universality: for instance, the renormalized SF coupling
constant, defined with either boundary conditions, must have a unique continuum
limit. Similarly, SF correlation functions in twisted mass QCD and standard QCD
can be defined such that they share a common continuum limit. An additional
benefit of the new set-up consists in the observation that all the bulk O(a)
counterterms to the action and composite operators become irrelevant in the
chiral limit. This implies that (ratios of) SF renormalization constants can be
automatically O(a) improved, up to the effect of unavoidable boundary
counterterms. As a first application we calculate the running coupling for Nf=2
flavours in the SF-scheme to one-loop order of perturbation theory.
Universality of the continuum limit is confirmed and the irrelevance of the
Sheikholeslami-Wohlert term in the action is demonstrated explicitly


title: Lattice QCD at maximal twist

abstract:
  In this review we discuss the general features of maximally twisted lattice
QCD. In particular, we illustrate how automatic O(a) improvement can be
achieved and how it is possible to set up a lattice regularization scheme where
the problem of wrong chirality mixing (be it finite or infinite) affecting the
computation of the matrix elements of the CP-conserving effective weak
Hamiltonian is neatly avoided, while having at the same time a positive
determinant even for non-degenerate quark pairs. The question of reducing the
large cutoff effects that appear when the quark mass tends to zero as a
consequence of parity and iso-spin breaking in the action is also addressed. It
is shown that such dangerous lattice artifacts are strongly suppressed if the
clover term is added to the action or, alternatively, the critical mass is
chosen so as to enforce the restoration of parity.


title: Nf=2 Lattice QCD and Chiral Perturbation Theory

abstract:
  By employing a twisted mass term, we compare recent results from lattice
calculations of Nf=2 dynamical Wilson fermions with Wilson Chiral Perturbation
Theory (WChPT). The final goal is to determine some combinations of
Gasser-Leutwyler Low Energy Constants (LECs). A wide set of data with different
lattice spacings (a ~ 0.2-0.12 fm), different gauge actions (Wilson plaquette,
DBW2) and different quark masses (down to the lowest pion mass allowed by
lattice artifacts and including negative quark masses) provide a strong check
of the applicability of WChPT in this regime and the scaling behaviours in the
continuum limit.


title: An insight on the Proof of Orientifold Planar Equivalence on the Lattice

abstract:
  In a recent paper, Armoni, Shifman and Veneziano (ASV) gave a formal
non-perturbative proof of planar equivalence between the bosonic sectors of
SU(N) super Yang-Mills theory and of a gauge theory with a massless quark in
the antisymmetric two-indexes representation. In the case of three colors, the
latter theory is nothing but one-flavor QCD. Numerical simulations are
necessary to test the validity of that proof and to estimate the size of 1/N
corrections. As a first step towards numerical simulations, I will give a
lattice version of the ASV proof of orientifold planar equivalence in the
strong-coupling and large-mass phase.


title: Towards measuring the eta' mass with N_f=2+1 staggered fermions

abstract:
  Because the propagators of flavor-singlet states incorporate disconnected
diagrams, they are uniquely sensitive to any differences in the actions
governing sea and valence fermions on the lattice. As such, they present an
important test of the validity of the ``fourth-root trick'' in the staggered
fermion formulation. The pseudoscalar's relationship to topological charge also
makes it of theoretical interest. We present preliminary results from our
measurements of flavor-singlet pseudoscalar mesons on 2+1 flavor Asqtad
lattices, and discuss some strategies for improving the signal-to-error ratio
of disconnected singlet correlators.


title:
The functional form of open Wilson lines in gauge theories coupled to
  matter

abstract:
  The open Wilson lines are gauge-invariant operators made with a gauge
transporter along an open path saturated at the end-points with matter fields.
Here it is shown that numerical experiments on 3D Z2 Higgs model provide useful
guidance in addressing the problem of the functional form of their vacuum
expectation values. It turns out they satisfy, as long as their size does not
exceed the string breaking scale, a remarkable factorization, related to
finite-size scaling of the Fredenhagen-Marcu order parameter. This leads to
conjecture a decay area law, like ordinary Wilson loops, with the difference
that the boundary conditions of the confining string world-sheet are fixed
along the path of the gauge transporter whereas are free on the straight line
joining the two end-points. A consistency condition fixes uniquely the
contribution of the free boundary, which turns out to be proportional to the
string-breaking scale. Universal shape effects produced by quantum string
fluctuations are also studied.


title:
A lattice calculation of the pion form factor with Ginsparg-Wilson-type
  fermions

abstract:
  Results for Monte Carlo calculations of the electromagnetic vector and scalar
form factors of the pion in a quenched simulation are presented. We work with
two different lattice volumes up to a spatial size of 2.4 fm at a lattice
spacing of 0.148 fm. The pion form factors in the space-like region are
determined for pion masses down to 340 MeV.


title:
Perturbative Renormalisation for Low Moments of Generalised Parton
  Distributions with Clover Fermions

abstract:
  We present the non-forward quark matrix elements of operators with one and
two covariant derivatives needed for the renormalisation of the first and
second moments of generalised parton distributions in one-loop lattice
perturbation theory using clover fermions. For some representations of the
hypercubic group commonly used in simulations we define the sets of possible
mixing operators and compute the one-loop mixing matrices of renormalisation
factors. Tadpole improvement is applied to the results and some numerical
examples are presented.


title:
Running couplings in equivariantly gauge-fixed SU(N) Yang--Mills
  theories

abstract:
  In equivariantly gauge-fixed SU(N) Yang--Mills theories, the gauge symmetry
is only partially fixed, leaving a subgroup $H\subset SU(N)$ unfixed. Such
theories avoid Neuberger's nogo theorem if the subgroup $H$ contains at least
the Cartan subgroup $U(1)^{N-1}$, and they are thus non-perturbatively well
defined if regulated on a finite lattice. We calculate the one-loop beta
function for the coupling $\tilde{g}^2=\xi g^2$, where $g$ is the gauge
coupling and $\xi$ is the gauge parameter, for a class of subgroups including
the cases that $H=U(1)^{N-1}$ or $H=SU(M)\times SU(N-M)\times U(1)$. The
coupling $\tilde{g}$ represents the strength of the interaction of the gauge
degrees of freedom associated with the coset $SU(N)/H$. We find that
$\tilde{g}$, like $g$, is asymptotically free. We solve the
renormalization-group equations for the running of the couplings $g$ and
$\tilde{g}$, and find that dimensional transmutation takes place also for the
coupling $\tilde{g}$, generating a scale $\tilde{\Lambda}$ which can be larger
than or equal to the scale $\Lambda$ associated with the gauge coupling $g$,
but not smaller. We speculate on the possible implications of these results.


title:
Infrared Gluon Propagator from lattice QCD: results from large
  asymmetric lattices

abstract:
  The infrared limit of the lattice Landau gauge gluon propagator is studied.
We show that the lattice data is compatible with the pure power law $(q^2)^{2
\kappa}$ solution of the Dyson-Schwinger equations. Using various lattice
volumes, the infinite volume limit for the exponent $\kappa$ is measured.
Although, the results allow $\kappa = 0.498 - 0.525$, the lattice data favours
$\kappa \sim 0.52$, which would imply a vanishing zero momentum gluon
propagator.


title: Improving the dynamical overlap algorithm

abstract:
  We present algorithmic improvements to the overlap Hybrid Monte Carlo
algorithm, including preconditioning techniques and improvements to the
correction step, used when one of the eigenvalues of the Kernel operator
changes sign, which is now O(\Delta t^2) exact.


title: Unqueched Kogut-Susskind quark propagator in Lattice Landau Gauge QCD

abstract:
  Quark propagators of the unquenched Kogut-Susskind(KS) fermion obtained from
the gauge configurations of the MILC collaboration are measured after Landau
gauge fixing and using the Staple+Naik action. Presence of the $\bar q q$
condensates and $A^2$ condensates in the dynamical mass $M(q)$ and the quark
wave function renormalization $Z_\psi(q^2)$ are investigated. We obtain the
correlation of the renormalization factor of the running coupling taken at
$\mu\sim 6$GeV and that of the quark wave function renormalization
$Z_\psi(q^2)$ of the Staple+Naik action. The mass function $\displaystyle M(q)$
is finite at $q=0$ and its chiral limit is $\sim 0.38$GeV. We compared the
results corrected by the scale of the vertex renormalization and the tadpole
renormalization with the corresponding values obtained by the Asqtad action
without renormalization and observed good agreement.Implication of infrared
finite $Z_2(q)=1/Z_\psi(q^2)$ to the Kugo-Ojima confinement criterion is
discussed.


title: Physics prospects of UV-filtered overlap quarks

abstract:
  Some key features of the overlap operator with a UV-filtered Wilson kernel
are discussed. The first part concerns spectral properties of the underlying
shifted hermitean Wilson operator and the relation to the observed speedup of
the overlap construction. Next, the localization of the filtered overlap and
its axial-vector renormalization constant are discussed. Finally, results of an
exploratory scaling study for $m_{ud}, m_s$ and $f_\pi, f_K$ are presented.


title: Current status of Dynamical Overlap project

abstract:
  We discuss the adaptation of the Hybrid Monte Carlo algorithm to overlap
fermions. We derive a method which can be used to account for the delta
function in the fermionic force caused by the differential of the sign
function. We discuss the algoritmic difficulties that have been overcome, and
mention those that still need to be solved.


title:
Matrix elements and baryon spectroscopy from unquenched lattice QCD with
  improved staggered quarks

abstract:
  We look for the effect of open decay channels on the masses of baryons in
unquenched lattice QCD. We apply variational smearing using fuzzed basis states
to a staggered nucleon operator. The signal for the s_bar s current in the
nucleon is studied. The lattice calculations are done using improved staggered
fermions.


title:
Scaling Properties of the Probability Distribution of Lattice Gribov
  Copies

abstract:
  We study the problem of the Landau gauge fixing in the case of the SU(2)
lattice gauge theory. We show that the probability to find a lattice Gribov
copy increases considerably when the physical size of the lattice exceeds some
critical value $\approx2.75/\sqrt{\sigma}$, almost independent of the lattice
spacing. The impact of the choice of the copy on Green functions is presented.
We confirm that the ghost propagator depends on the choice of the copy, this
dependence decreasing for increasing volumes above the critical one. The gluon
propagator as well as the gluonic three-point functions are insensitive to
choice of the copy (within present statistical errors). Finally we show that
gauge copies which have the same value of the minimisation functional ($\int
d^4x (A^a_\mu)^2$) are equivalent, up to a global gauge transformation, and
yield the same Green functions.


title:
SU(2) Gluodynamics and HP1 sigma-model embedding: Scaling, Topology and
  Confinement

abstract:
  We investigate recently proposed HP1 sigma-model embedding method aimed to
study the topology of SU(2) gauge fields. The HP1 based topological charge is
shown to be fairly compatible with various known definitions. We study the
corresponding topological susceptibility and estimate its value in the
continuum limit. The geometrical clarity of HP1 approach allows to investigate
non-perturbative aspects of SU(2) gauge theory on qualitatively new level. In
particular, we obtain numerically precise estimation of gluon condensate and
its leading quadratic correction. Furthermore, we present clear evidences that
the string tension is to be associated with global (percolating) regions of
sign-coherent topological charge. As a byproduct of our analysis we estimate
the continuum value of quenched chiral condensate and the dimensionality of
regions, which localize the lowest eigenmodes of overlap Dirac operator.


title: Overlap Hypercube Fermions in QCD

abstract:
  We present simulation results obtained with overlap hypercube fermions in QCD
near the chiral limit. We relate our results to chiral perturbation theory in
both, the epsilon-regime and in the p-regime. In particular we measured the
pion decay constant by different methods, as well as the chiral condensate,
light meson masses, the PCAC quark mass and the renormalisation constant Z_A.


title: Fun with Dirac eigenvalues

abstract:
  It is popular to discuss low energy physics in lattice gauge theory in terms
of the small eigenvalues of the lattice Dirac operator. I play with some
ensuing pitfalls in the interpretation of these eigenvalue spectra.


title:
Landau gauge ghost and gluon propagators and the Faddeev-Popov operator
  spectrum

abstract:
  In this talk we report on a recent lattice investigation of the Landau gauge
gluon and ghost propagators in pure SU(3) lattice gauge theory with a special
emphasis on the Gribov copy problem. In the (infrared) region of momenta $q^2
\le 0.3 \mathrm{GeV}^2$ we find the corresponding MOM scheme running coupling
$\alpha_s(q^2)$ to rise in $q$. We also report on a first SU(3) computation of
the ghost-gluon vertex function showing that it deviates only weakly from being
constant. In addition we study the spectrum of low-lying eigenvalues and
eigenfunctions of the Faddeev-Popov operator as well as the spectral
representation of the ghost propagator.


title: Variational method for lattice spectroscopy with ghosts

abstract:
  We discuss the variational method used in lattice spectroscopy calculations.
In particular we address the role of ghost contributions which appear in
quenched or partially quenched simulations and have a non-standard euclidean
time dependence. We show that the ghosts can be separated from the physical
states. Our result is illustrated with numerical data for the scalar meson.


title: High accuracy simulations of d=4 SU(3) qcd-string

abstract:
  We present here the results of our high accuracy simulations of $q\bar q$
potential in $d=4$ SU(3) Yang-Mills theory. We measure this quantity by
measuring the {\it Polyakov Loop Correlators} using the {\it exponential
variance reduction technique(multilevel)} of Luscher and Weisz. We further use
numerical integration of the one-link integrals of SU(3) theory by adopting
techniques proposed by de Forcrand and Roiesnell achieving significant speed-up
in the process. Measurements were done at $\beta = 5.7$ on $24^3x32$ as well as
$32^4$ lattices for separations between the Polyakov loops in the range $r =
2-9$ in lattice units. We analyse the results in terms of the force between
$q\bar q$ pair as well as in terms of a {\em scaled second derivative} of the
potential. We show that the data is accurate enough to distinguish between
different string models and that it seems to favour the expression for ground
state energy of a Nambu-Goto string. We conclude by discussing future plans.


title:
Landau gauge ghost and gluon propagators in SU(2) lattice gauge theory:
  Gribov ambiguity revisited

abstract:
  We reinvestigate the problem of Gribov ambiguities within the Landau (or
Lorentz) gauge for the ghost and gluon propagators in pure SU(2) lattice gauge
theory. We make use of the full symmetry group of the action taking into
account {\it large}, i.e. non-periodic $\mathbb{Z}(2)$ gauge transformations
leaving lattice plaquettes invariant. Enlarging in this way the gauge orbits
for any given gauge field configuration the Landau gauge can be fixed at higher
local extrema of the gauge functional in comparison with standard
(overrelaxation) techniques. This has a clearly visible effect not only for the
ghost propagator at small momenta but also for the gluon propagator, in
contrast to the common belief.


title: Chiral transition and deconfinement in QCD

abstract:
  The study of QCD with two light dynamical fermions is of fundamental
importance to understand the mechanism of color confinement. We present results
of a numerical investigation on the order of the chiral phase transition with
$N_f = 2$ by use of a novel strategy in finite size scaling analysis. We
compare the critical behaviour of the specific heat, of the chiral
susceptibility and of the equation of state with the possible critical
behaviours. A second order transition in the O(4) and O(2) universality classes
are excluded by our data and substantial evidence emerges for a first order
transition. Like in most of previous works we have used the standard staggered
action with $L_t = 4$: possible scaling violations and the need for further
studies are discussed.


title:
The critical region of strong-coupling lattice QCD in different large-N
  limits

abstract:
  We study the critical behavior at nonzero temperature phase transitions of an
effective Hamiltonian derived from lattice QCD in the strong-coupling
expansion. Following studies of related quantum spin systems that have a
similar Hamiltonian, we show that for large $N_c$ and fixed $g^2N_c$, mean
field scaling is not expected, and that the critical region has a finite width
at $N_c=\infty$. A different behavior rises for $N_f\to \infty$ and fixed $N_c$
and $g^2/N_f$, which we study in two spatial dimensions and for $N_c=1$. We
find that the width of the critical region is suppressed by $1/N_f^p$ with
$p=1/2$, and argue that a generalization to $N_c>1$ and to three dimensions
will change this only in detail (e.g. the value of $p>0$), but not in
principle. We conclude by stating under what conditions this suppression is
expected, and remark on possible realizations of this phenomenon in lattice
gauge theories in the continuum.


title: Probing the Aoki phase with N_f=2 Wilson fermions at finite temperature

abstract:
  In this letter we report on a numerical investigation of the Aoki phase in
the case of finite temperature which continues our former study at zero
temperature. We have performed simulations with Wilson fermions at $\beta=4.6$
using lattices with temporal extension $N_{\tau}=4$. In contrast to the zero
temperature case, the existence of an Aoki phase can be confirmed for a small
range in $\kappa$ at $\beta=4.6$, however, shifted slightly to lower $\kappa$.
Despite fine-tuning $\kappa$ we could not separate the thermal transition line
from the Aoki phase.


title: Large-N QCD at strong transverse lattice gauge coupling

abstract:
  We had previously obtained an integral equation for mesons in transverse
lattice QCD, in the limit of large number of colours and strong transverse
lattice gauge coupling [1]. This equation is a generalisation of the 't Hooft
equation [2], by inclusion of the spin degrees of freedom. We analyse this
equation to extract spectral properties and light-front wavefunctions of
mesons. We also extend the method to study baryon properties in the same limit.


title: What the lattice can tell us about nucleon structure

abstract:
  This review focuses on the current status of lattice calculations of three
observables which are both phenomenologically and experimentally relevant and
have been scrutinized recently. These three observables are the nucleon
electromagnetic form factors, the momentum fraction, <x>, and the nucleon axial
coupling, gA.


title: The pion and proton mass in finite volume

abstract:
  We calculate the finite volume effects for the pion and nucleon mass. For the
pion mass we present the results of a full two-loop calculation in chiral
perturbation theory. The outcome shows that the resummed version of the Luscher
formula we presented in an earlier work does indeed give an excellent
approximation to the two-loop result. In view of this result we apply the same
resummed formula to the nucleon mass. In the nucleon sector the extension of
the chiral expansion to higher quark masses appears to be more problematic and
it is therefore more difficult to make reliable predictions for the size of the
finite volume effects. We present some preliminary numerical estimates.


title: New features of the maximal abelian projection

abstract:
  After fixing the Maximal Abelian gauge in SU(2) lattice gauge theory we
decompose the nonabelian gauge field into the so called monopole field and the
modified nonabelian field with monopoles removed. We then calculate respective
static potentials and find that the potential due to the modified nonabelian
field is nonconfining while, as is well known, the monopole field potential is
linear. Furthermore, we show that the sum of these potentials approximates the
nonabelian static potential with 5% or higher precision at all distances
considered. We conclude that at large distances the monopole field potential
describes the classical energy of the hadronic string while the modified
nonabelian field potential describes the string fluctuations. Similar
decomposition was observed to work for the adjoint static potential. A check
was also made of the center projection in the direct center gauge. Two static
potentials, determined by projected $Z_2$ and by modified nonabelian field
without $Z_2$ component were calculated. It was found that their sum is a
substantially worse approximation of the SU(2) static potential than that found
in the monopole case. It is further demonstrated that similar decomposition can
be made for the flux tube action/energy density.


title:
Calculation of the neutron electric dipole moment with two dynamical
  flavors of domain wall fermions

abstract:
  We present a study of the neutron electric dipole moment ($\vec d_N$) within
the framework of lattice QCD with two flavors of dynamical lig ht quarks. The
dipole moment is sensitive to the topological structure of the gaug e fields,
and accuracy can only be achieved by using dynamical, or sea quark, calc
ulations. However, the topological charge evolves slowly in these calculations,
le ading to a relatively large uncertainty in $\vec d_N$. It is shown, using
quenched configurations, that a better sampling of the charge d istribution
reduces this problem, but because the CP even part of the fermion determinant
is absent, both the topological charge dis tribution and $\vec d_N$ are
pathological in the chiral limit. We discuss the statistical and systematic
uncertainties arising from the topological charge distr ibution and unphysical
size of the quark mass in our calculations and prospects fo r eliminating them.
  Our calculations employ the RBC collaboration two flavor domain wall fermion
and DBW2 gauge action lattices with inverse lattice spacing $a^{-1}\approx$ 1.7
GeV, physical volume $V\approx (2$ fm)$^3$, and light quark mass roughly equal
to the strange quark mass ($m_{sea}=0.03 $ and 0.04). We determine a value of
the electric dipole moment that is zero withi n (statistical) errors, $|\vec
d_N| = -0.04(20)$ e-$\theta$-fm at the smaller sea quark mass. Satisfactory
results for the magnetic and electric form factors of the proton and neutron
are also obtained and presented.


title:
Probing the topological structure of the QCD vacuum with overlap
  fermions

abstract:
  Overlap fermions implement exact chiral symmetry on the lattice and are thus
an appropriate tool for investigating the chiral and topological structure of
the QCD vacuum. We study various chiral and topological aspects on
Luescher-Weisz-type quenched gauge field configurations using overlap fermions
as a probe. Particular emphasis is placed upon the analysis of the spectral
density and the localisation properties of the eigenmodes as well as on the
local structure of topological charge fluctuations.


title: Mass of a quantum 't Hooft-Polyakov monopole

abstract:
  The quantum mechanical mass of 't Hooft-Polyakov monopoles in the
four-dimensional Georgi-Glashow is calculated non-perturbatively using lattice
Monte Carlo simulations. This is done by imposing twisted boundary conditions
that ensure there is one unit of magnetic charge on the lattice, and measuring
the free energy difference between this ensemble and the vacuum. In the
weak-coupling limit, the results can be used to determine the quantum
correction to the classical mass, once renormalisation of couplings is taken
properly into account. The methods can also be used to study the masses at
strong coupling, i.e., near the critical point, where there are hints of a
possible electric-magnetic duality.


title:
B -> D* l nu and B -> D l nu form factors in staggered chiral
  perturbation theory

abstract:
  We calculate the B -> D and B -> D* form factors at zero recoil in Staggered
Chiral Perturbation Theory. We consider heavy-light mesons in which only the
light (u, d, or s) quark is staggered; current lattice simulations generally
use a highly improved action such as the Fermilab or NRQCD action for the heavy
(b or c) quark. We work to lowest nontrivial order in the heavy quark expansion
and to one-loop in the chiral expansion. We present results for a partially
quenched theory with three sea quarks in which there are no mass degeneracies
(the "1+1+1" theory) and for a partially quenched theory in which the u and d
sea quark masses are equal (the "2+1" theory). We also present results for full
(2+1) QCD, along with a numerical estimate of the size of staggered
discretization errors. Finally, we calculate the finite volume corrections to
the form factors and estimate their numerical size in current lattice
simulations.


title: Using the Mass Storage System at ZIB within I3HP

abstract:
  In the framework of I3HP there are two Transnational Access Activities
related to Computational Hadron Physics. One of these activities is access to
the mass storage system at Konrad-Zuse-Zentrum fuer Informationstechnik Berlin
(ZIB). European lattice physics collaborations can apply for mass storage
capacity in order to store and share their configurations or other data (see
http://www.zib.de/i3hp/). In this paper formal and technical aspects of usage
as well as the conformance to the International Lattice DataGrid (ILDG) are
explained.


title: Light meson masses and decay constants in 2+1 flavour domain wall QCD

abstract:
  We present results for light meson masses and psedoscalar meson decay
constants in 2+1 flavour domain wall QCD with the DBW2 and Iwasaki gauge
actions, using lattices with linear sizes in the range 1.6 to 2.2fm and $u$ and
$d$ quark masses as low as one quarter of the strange quark mass. All data were
generated on the QCDOC machines at the University of Edinburgh and Brookhaven
National Laboratory. Despite large residual masses and a limited number of sea
quark mass values with which to perform chiral extrapolations, our results
agree with experiment and scale within errors.


title:
The Z(2) gauge model revisited: as a possible testbed for the
  confinement and chiral symmetry phase transition of SU(2) lattice gauge
  theory

abstract:
  Adopting the cooling technique to smooth the discontinuous Z(2) lattice gauge
field, we found that on SU(2) gauge configurations obtained by this smoothing
there exists clear discontinuity of the topological property at almost the same
point as the confinement-deconfinement phase transition of the original Z(2)
gauge theory. This observation suggests the possibility that Z(2) gauge model
might be a testbed for analyzing the relation between the confinement and the
chiral phase transition in which the topological objects are believed to play
crucial roles.


title: Nucleon structure from generalized parton distributions in lattice QCD

abstract:
  This talk presents results from the QCDSF-UKQCD collaboration for moments of
leading twist generalized parton distributions in two-flavor lattice QCD based
on O(a) improved Wilson Fermions. We study helicity independent and helicity
flip GPDs with a focus on densities of quarks in the transverse plane.


title:
Perturbative Wilson loops from unquenched Monte Carlo simulations at
  weak couplings

abstract:
  Perturbative expansions of several small Wilson loops are computed through
next-to-next-to-leading order in unquenched lattice QCD, from Monte Carlo
simulations at weak couplings. This approach provides a much simpler
alternative to conventional diagrammatic perturbation theory, and is applied
here for the first time to full QCD. Two different sets of lattice actions are
considered: one set uses the unimproved plaquette gluon action together with
the unimproved staggered-quark action; the other set uses the one-loop-improved
Symanzik gauge-field action together with the so-called ``asqtad''
improved-staggered quark action. Simulations are also done with different
numbers of dynamical fermions. An extensive study of the systematic
uncertainties is presented, which demonstrates that the small third-order
perturbative component of the observables can be reliably extracted from
simulation data. We also investigate the use of the rational hybrid Monte Carlo
algorithm for unquenched simulations with unimproved-staggered fermions. Our
results are in excellent agreement with diagrammatic perturbation theory, and
provide an important cross-check of the perturbation theory input to a recent
determination of the strong coupling $\alpha_{\bar{\rm MS}}(M_Z)$ by the HPQCD
collaboration.


title:
The John von Neumann Institute for Computing (NIC): A survey of its
  supercomputer facilities and its Europe-wide computational science activities

abstract:
  The John von Neumann Institute for Computing (NIC) at the Research Centre
Juelich, Germany, is one of the leading supercomputing centres in Europe.
Founded as a national centre in the mid-eighties it now provides more and more
resources to European scientists. This happens within EU-funded projects (I3HP,
DEISA) or Europe-wide scientific collaborations. Beyond these activities NIC
started an initiative towards the new EU member states in summer 2004.
Outstanding research groups are offered to exploit the supercomputers at NIC to
accelerate their investigations on leading-edge technology.
  The article gives an overview of the organisational structure of NIC, its
current supercomputer systems, and its user support. Transnational Access (TA)
within I3HP is described as well as access by the initiative for new EU member
states. The volume of these offers and the procedure of how to apply for
supercomputer resources is introduced in detail.


title: QCD with two dynamical flavors of chirally improved quarks

abstract:
  Considering Ginsparg-Wilson type fermions dynamically in lattice QCD
simulations is a challenging task. The hope is to be able to approach smaller
pion masses and to eventually reach physical situations. The price to pay is
substantially higher computational costs. Here we discuss first results of a
dynamical implementation of the so-called Chirally Improved Fermions, a Dirac
operator that obeys the Ginsparg-Wilson condition approximately. The simulation
is for two species of mass-degenerate quarks on 12^3x24 lattices with spatial
size up to 1.55 fm. Implementation of the Hybrid Monte-Carlo algorithm and an
analysis of the results are presented.


title:
Center vortex model for the infrared sector of SU(4) Yang-Mills theory:
  String tensions and deconfinement transition

abstract:
  A random vortex world-surface model for the infrared sector of SU(4)
Yang-Mills theory is constructed, focusing on the confinement properties and
the behavior at the deconfinement phase transition. Although the corresponding
data from lattice Yang-Mills theory can be reproduced, the model requires a
more complex action and considerably more tuning than the SU(2) and SU(3) cases
studied previously. Its predictive capabilities are accordingly reduced. This
behavior has a definite physical origin, which is elucidated in detail in the
present work. As the number of colors is raised in Yang-Mills theory, the
corresponding infrared effective vortex description cannot indefinitely
continue to rely on dynamics determined purely by vortex world-surface
characteristics; additional color structures present on the vortices begin to
play a role. As evidenced by the modeling effort reported here, definite
signatures of this behavior appear in the case of four colors.


title: Partially Quenched Chiral Perturbation Theory to NNLO

abstract:
  This paper summarizes the recent calculations of the masses and decay
constants of the pseudoscalar mesons at the two-loop level, or NNLO, in
Partially Quenched Chiral Perturbation Theory (PQxPT). Possible applications
include chiral extrapolations of Lattice QCD, as well as the determination of
the low-energy constants (LEC:s) of QCD.


title:
Numerical simulations with two flavours of twisted-mass Wilson quarks
  and DBW2 gauge action

abstract:
  Discretisation errors in two-flavour lattice QCD with Wilson-quarks and DBW2
gauge action are investigated by comparing numerical simulation data at two
values of the bare gauge coupling. Both non-zero and zero twisted mass values
are considered. The results, including also data from simulations using the
Wilson plaquette gauge action, are compared to next-to-leading order chiral
perturbation theory formulas.


title: String breaking

abstract:
  We numerically investigate the transition of the static quark-antiquark
string into a static-light meson-antimeson system. Improving noise reduction
techniques, we are able to resolve the signature of string breaking dynamics
for Nf=2 lattice QCD at zero temperature. We discuss the lattice techniques
used and present results on energy levels and mixing angle of the static
two-state system. We visualize the action density distribution in the region of
string breaking as a function of the static colour source-antisource
separation. The results can be related to properties of quarkonium systems.


title: Random membrane model for lattice gluodynamics

abstract:
  odel for studying coupling dependence on lattice spacing a in gluodynamics is
suggested. The model predicts $g-> g_{0}>0 with a->0. Free energy density in
the model does not depend on temperature.


title:
Lattice study of semileptonic form factors with twisted boundary
  conditions

abstract:
  We apply twisted boundary conditions to lattice QCD simulations of
three-point correlation functions in order to access spatial components of
hadronic momenta different from the integer multiples of 2 pi / L. We calculate
the vector and scalar form factors relevant to the K -> pi semileptonic decay
and consider all the possible ways of twisting one of the quark lines in the
three-point functions. We show that the momentum shift produced by the twisted
boundary conditions does not introduce any additional noise and easily allows
to determine within a few percent statistical accuracy the form factors at
quite small values of the four-momentum transfer, which are not accessible when
periodic boundary conditions are considered. The use of twisted boundary
conditions turns out to be crucial for a precise determination of the form
factor at zero-momentum transfer, when a precise lattice point sufficiently
close to zero-momentum transfer is not accessible with periodic boundary
conditions.


title: Stability of lattice QCD simulations and the thermodynamic limit

abstract:
  We study the spectral gap of the Wilson--Dirac operator in two-flavour
lattice QCD as a function of the lattice spacing $a$, the space-time volume $V$
and the current-quark mass $m$. It turns out that the median of the probability
distribution of the gap scales proportionally to $m$ and that its width is
practically equal to $a/\sqrt{V}$. In particular, numerical simulations are
safe from accidental zero modes in the large-volume regime of QCD.


title: Properties of phase transitions of higher order

abstract:
  There is only limited experimental evidence for the existence in nature of
phase transitions of Ehrenfest order greater than two. However, there is no
physical reason for their non-existence, and such transitions certainly exist
in a number of theoretical models in statistical physics and lattice field
theory. Here, higher-order transitions are analysed through the medium of
partition function zeros. Results concerning the distributions of zeros are
derived as are scaling relations between some of the critical exponents.


title:
Phase diagram at finite temperature and quark density in the strong
  coupling limit of lattice QCD for color SU(3)

abstract:
  We study the phase diagram of quark matter at finite temperature (T) and
finite chemical potential (mu) in the strong coupling limit of lattice QCD for
color SU(3). We derive an analytical expression of the effective free energy as
a function of T and mu, including baryon effects. The finite temperature
effects are evaluated by integrating over the temporal link variable exactly in
the Polyakov gauge with anti-periodic boundary condition for fermions. The
obtained phase diagram shows the first order phase transition at low
temperatures and the second order phase transition at high temperatures
separated by the tri-critical point in the chiral limit. Baryon has effects to
reduce the effective free energy and to extend the hadron phase to a larger mu
direction at low temperatures.


title:
The behavior of the sextic coupling for the scalar field at the
  intermediate and strong coupling regime

abstract:
  We study the behavior of the renormalized sextic coupling at the intermediate
and strong coupling regime for the $\phi^4 $ theory defined in $d=2$-dimension.
We found a good agreement with the results obtained by the field-theoretical
renormalization-group in the Ising limit. In this work we use the lattice
regularization method.


title:
Chiral phase transition and Anderson localization in the Instanton
  Liquid Model for QCD

abstract:
  We study the spectrum and eigenmodes of the QCD Dirac operator in a gauge
background given by an Instanton Liquid Model (ILM) at temperatures around the
chiral phase transition. Generically we find the Dirac eigenvectors become more
localized as the temperature is increased. At the chiral phase transition, both
the low lying eigenmodes and the spectrum of the QCD Dirac operator undergo a
transition to localization similar to the one observed in a disordered
conductor. This suggests that Anderson localization is the fundamental
mechanism driving the chiral phase transition. We also find an additional
temperature dependent mobility edge (separating delocalized from localized
eigenstates) in the bulk of the spectrum which moves toward lower eigenvalues
as the temperature is increased. In both regions, the origin and the bulk, the
transition to localization exhibits features of a 3D Anderson transition
including multifractal eigenstates and spectral properties that are well
described by critical statistics. Similar results are obtained in both the
quenched and the unquenched case though the critical temperature in the
unquenched case is lower. Finally we argue that our findings are not in
principle restricted to the ILM approximation and may also be found in lattice
simulations.


title: Quark mass dependence of nucleon mass and axial-vector coupling constant

abstract:
  We present an updated analysis of the quark mass dependence of the nucleon
mass and nucleon axial-vector coupling g_A, comparing different formulations of
SU(2) Baryon Chiral Effective Field Theory, with and without explicit delta
(1232) degrees of freedom. We discuss the outcome of the corresponding
interpolations between lattice QCD data and the physical values for these two
nucleon observables. It turns out that in order to obtain successful
interpolating functions at one-loop order, the inclusion of explicit delta
(1232) degrees of freedom is not decisive for the nucleon mass but crucial for
g_A. A chiral extrapolation of recent lattice results by the LHP collaborations
is also shown.


title: Quark masses from quenched overlap fermions

abstract:
  We compute light and strange quark masses for quenched overlap fermions at
two values of the gauge coupling. The renormalisation is done
non-perturbatively. We test the predictions of quenched chiral perturbation
theory for the quark mass dependence of the hadron spectrum and see evidence
for the existence of chiral logs.


title: Exact Ward-Takahashi identity for the lattice N=1 Wess-Zumino model

abstract:
  The lattice Wess-Zumino model written in terms of the Ginsparg-Wilson
relation is invariant under a generalized supersymmetry transformation which is
determined by an iterative procedure in the coupling constant. By studying the
associated Ward-Takahashi identity up to order $g^2$ we show that this lattice
supersymmetry automatically leads to restoration of continuum supersymmetry
without fine tuning. In particular, the scalar and fermion renormalization wave
functions coincide.


title: Y(4260) on the lattice

abstract:
  We investigate the mass spectra of closed-charm mesons with $ J^{PC} = 1^{--}
$, for hybrid charmonium, molecules, and diquark-antidiquark operators, in
quenched lattice QCD with exact chiral symmetry. For two lattice volumes $ 24^3
\times 48 $ and $ 20^3 \times 40 $, each of 100 gauge configurations generated
with single-plaquette action at $ \beta = 6.1 $, we compute point-to-point
quark propagators and measure the time-correlation functions of these exotic
meson operators. For the molecular operator $
\{(\qbar\gamma_5\gamma_i\c)(\cbar\gamma_5\q)-
  (\cbar\gamma_5\gamma_i\q)(\qbar\gamma_5\c) \} $, it detects a resonance with
mass around $ 4238 \pm 31 $ MeV, which is naturally identified with $ Y(4260)
$. Further, for any molecular and diquark-antidiquark operator, it detects
heavier exotic charmed mesons, with quark content $ (\c\s\cbar\sbar) $ around $
4450 \pm 100 $ MeV, and $ (\c\c\cbar\cbar) $ around $ 6400 \pm 50 $ MeV.


title:
Hedgehogs in Wilson loops and phase transition in SU(2) Yang-Mills
  theory

abstract:
  We suggest that the gauge-invariant hedgehoglike structures in the Wilson
loops are physically interesting degrees of freedom in the Yang--Mills theory.
The trajectories of these ``hedgehog loops'' are closed curves corresponding to
center-valued (untraced) Wilson loops and are characterized by the center
charge and winding number. We show numerically in the SU(2) Yang--Mills theory
that the density of hedgehog structures in the thermal Wilson--Polyakov line is
very sensitive to the finite-temperature phase transition. The (additively
normalized) hedgehog line density behaves like an order parameter: the density
is almost independent of the temperature in the confinement phase and changes
substantially as the system enters the deconfinement phase. In particular, our
results suggest that the (static) hedgehog lines may be relevant degrees of
freedom around the deconfinement transition and thus affect evolution of the
quark-gluon plasma in high-energy heavy-ion collisions.


title:
Quark antiquark energies and the screening mass in a Quark-Gluon plasma
  at low and high temperatures

abstract:
  We discuss quark antiquark energies and the screening mass in hot QCD using
the non-perturbative lattice approach. For this purpose we analyze properties
of quark antiquark energies and entropies at infinitely large separation of the
quark antiquark pair at low and high temperatures. In the limit of high
temperatures these energies and entropies can be related perturbatively to the
temperature dependence of the Debye mass and the coupling. On the one hand our
analysis thus suggests that the quark antiquark energies at (infinite) large
distances are rather related to the Debye screening mass and the coupling than
to the temperature dependence of heavy-light meson masses. On the other hand we
find no or only little differences in all mass scales introduced by us when
changing from quenched to 2-flavor QCD at temperatures which are only
moderately above the phase transition.


title: The Density of States Method at Finite Chemical Potential

abstract:
  We study the density of states method to explore the phase diagram of the
chiral transition on the temperature and quark chemical potential plane. Four
quark flavors are used in the analysis. Though the method is quite expensive
small lattices show an indication for a triple-point connecting three different
phases on the phase diagram.


title: Independent Operators at Different Dimension

abstract:
  To apply lattice QCD in the calculation of glueball spectrum it is needed
firstly to know associated operators acting on vacuum. We show how to find all
the independent representations and operators, of group $SO(3)^{PC}$ at
different dimension, since the work is not trivial. Then, we decompose these
representation into irreducible representation of $O^{PC}$ group, which are
listed in the note. At last we argue that $f_J(2220)$ and $g_T$ states can not
be tensor glueball simultaneously.


title: A Quasi-staggered Scheme on Lattice

abstract:
  Utilizing a picture of string and string spinors, we show a simpler version
of staggered action. The advantage of this action is that in this action there
always exist pair of quarks with different masses.


title: Electromagnetic vertex function of the pion at T > 0

abstract:
  The matrix element of the electromagnetic current between pion states is
calculated in quenched lattice QCD at a temperature of $T = 0.93 T_c$. The
nonperturbatively improved Sheikholeslami-Wohlert action is used together with
the corresponding ${\cal O}(a)$ improved vector current. The electromagnetic
vertex function is extracted for pion masses down to $360 {\rm MeV}$ and
momentum transfers $Q^2 \le 2.7 {\rm GeV}^2$.


title:
On topological properties of vacuum defects in lattice Yang-Mills
  theories

abstract:
  We study correlations between low-lying modes of the overlap Dirac operator
and vacuum defects, center vortices and three-dimensional volumes, in lattice
SU(2) gluodynamics. The low-lying modes are apparently sensitive to topological
properties of the underlying gluon field configurations while the vacuum
defects are crucial for the confinement. We find distinct positive correlation
in both cases. In case of vortices the correlation is stronger.


title:
The behavior of the sextic coupling for the the three-dimensional
  $\phi^4 $ theory

abstract:
  In this work we use the lattice regularization method to study the behavior
of the six point renormalized coupling constant defined at zero momentum for
the three-dimensional $\phi^4 $ theory in the intermediate and strong coupling
domain. The result is in good agreement with the corresponding study in the
Ising limit.


title:
Peculiar Properties of SU(2) Gauge Field Thermodynamics on a Finite
  Lattice. Calculation of Beta-function

abstract:
  The new method of nonperturbative calculation of the beta-function in the
lattice gauge theory is proposed. The method is based on the finite size
scaling hypothesis.


title:
Perturbative renormalization in parton distribution functions using
  improved actions

abstract:
  We calculate the 1-loop renormalization of a set of extended fermionic
bilinears which form a basis corresponding to moments of the parton
distribution functions.
  We use the overlap action for fermions and Luescher-Weisz (LW) action for
gluons.
  Our results are presented as a function of the overlap parameter rho and the
parameters entering the LW action.


title: The isentropic equation of state of 2-flavor QCD

abstract:
  Using Taylor expansions of the pressure obtained previously in studies of
2-flavor QCD at non-zero chemical potential we calculate expansion coefficients
for the energy and entropy densities up to ${\cal O}(\mu_q^6)$ in the quark
chemical potential. We use these series in $\mu_q/T$ to determine lines of
constant entropy per baryon number ($S/N_B$) that characterize the expansion of
dense matter created in heavy ion collisions. In the high temperature regime
these lines are found to be well approximated by lines of constant $\mu_q/T$.
In the low temperature phase, however, the quark chemical potential is found to
increase with decreasing temperature. This is in accordance with resonance gas
model calculations. Along the lines of constant $S/N_B$ we calculate the energy
density and pressure. Within the accuracy of our present analysis we find that
the ratio $p/\epsilon$ for $T>T_0$ as well as the softest point of the equation
of state, $(p/\epsilon)_{min}\simeq 0.075$, show no significant dependence on
$S/N_B$.


title: Embedded monopoles in quark eigenmodes in SU(2) Yang-Mills Theory

abstract:
  We study the embedded QCD monopoles (``quark monopoles'') using low-lying
eigenmodes of the overlap Dirac operator in zero- and finite-temperature SU(2)
Yang-Mills theory on the lattice. These monopoles correspond to the
gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles
were suggested to be agents of the chiral symmetry restoration since their
cores should suppress the chiral condensate. We study numerically the scalar,
axial and chirally invariant definitions of the embedded monopoles and show
that the monopole densities are in fact globally anti-correlated with the
density of the Dirac eigenmodes. We observe, that the embedded monopoles
corresponding to low-lying Dirac eigenvalues are dense in the chirally
invariant (high temperature) phase and dilute in the chirally broken (low
temperature) phase. We find that the scaling of the scalar and axial monopole
densities towards the continuum limit is similar to the scaling of the
string-like objects while the chirally invariant monopoles scale as membranes.
The excess of gluon energy at monopole positions reveals that the embedded QCD
monopole possesses a gluonic core, which is, however, empty at the very center
of the monopole.


title: Color confinement in Coulomb gauge QCD

abstract:
  We study the long-range behavior of the heavy quark potential in Coulomb
gauge using a quenched SU(3) lattice gauge simulation with partial-length
Polyakov line correlators. We show that the Coulomb heavy quark potential
associated with the instantaneous part of gluon propagators in Coulomb gauge,
presents a linearly rising behavior at large distances, and the resulting
Coulomb string tension is greater than the Wilson loop string tension, which
can be explained by Zwanziger's inequality. The linearly rising behavior of the
Coulomb heavy quark potential persists even in the deconfinement phase. The
heavy quark potential in Lorentz gauge shows completely different behavior than
that in Coulomb gauge. Our SU(3) result, i.e., the Coulomb heavy quark
potential is confining, qualitatively agrees with that of the SU(2) analysis
carried out by Greensite, Olejnik and Zwanziger.


title: QCD color interactions between two quarks

abstract:
  We study the QCD color interactions between static two heavy quarks at zero
temperature in a quenched SU(3) lattice gauge simulation: in addition to the
standard singlet $q\bar{q}$ potentials, we calculate octet $q\bar{q}$
potentials, symmetric and antisymmetric $qq$ potentials. It is shown that the
antisymmetric $qq$ channel behaves as a linearly rising potential at large
quark separations. We further find that the $q\bar{q}$ octet and $qq$ symmetric
channels have the complex dependence on the distance; at short distances they
are repulsive forces, while at large distances, they show linearly rising
feature. Ratio of string tensions between $q\bar{q}$ singlet and $qq$
antisymmetric potentials is described in terms of the Casimir factor.


title: Gluonic excitation of non-exotic hybrid charmonium from lattice QCD

abstract:
  The ground and first excited states of the hybrid charmonium ${\bar c} c g$,
with non-exotic quantum numbers $J^{PC}=0^{-+}$, $1^{--}$ and $1^{++}$ are
investigated using quenched lattice QCD. They are completely ignored in the
literature, only because their ground states are degenerate with $\eta_c$,
$J/\psi$, and $\chi_{c1}$, and are difficult to be distinguished from these
conventional charmonium mesons in experiment. However, we observe strong
gluonic radial excitations in the first excited states; We predict that their
masses are 4.352(225)GeV, 4.379(149)GeV and 7.315(257)GeV, completely different
from the first excited states of the corresponding conventional charmonium.
Their relevance to the recent discovery of the Y(4260) state and future
experimental search for other states are also discussed.


title: Dirac Eigenmodes in an Environment of Dynamical Fermions

abstract:
  We discuss some properties of zero and near-zero modes of the Dirac operator,
as observed in a recent simulation of 2-flavor QCD. The quarks have been
implemented with the so-called Chirally Improved Dirac operator, which obeys
the Ginsparg-Wilson relation to a good approximation. We present geometrical
and statistical properties of these eigenmodes and eigenvalues.


title: On the Interplay of Fermions and Monopoles in Compact QED_3

abstract:
  The infra-red properties of three-dimensional abelian lattice gauge theory
are known to be governed by a neutral plasma of magnetic monopole excitations.
We address the fate of these monopoles in the presence of light dynamical
fermions, using a lattice formulation of compact QED_3 with N_f=4 fermion
flavors supplemented by a four-fermi contact term permitting numerical Monte
Carlo simulations in the chiral limit. Our data hint at a restoration of chiral
symmetry above a critical value of the (inverse) coupling beta. By performing
simulations in a sector of non-vanishing magnetic charge, we are able to study
the response of the theory to an external magnetic test charge. Our results
suggest that the monopole plasma persists even once chiral symmetry is
restored, and hence survives the continuum limit.


title: Spontaneous breaking of residual gauge symmetries on the lattice

abstract:
  Lattice gauge theories are considered with a partial axial gauge fixing along
one direction only. This leaves a residual gauge symmetry that is still local
in three directions but now global in one. It is found that this $N^{d-1}$ fold
symmetry (on an $N^d$ lattice) breaks spontaneously at weak coupling with the
gauge field elements on links averaged over 1-d chains along the gauge-fixing
direction as order parameters. This phase transition is observed with
Monte-Carlo simulations for both 3-d Z2 and 4-d SU(2) pure gauge theories and
appears to be coincident with the deconfinement transition. This work calls
into question the equivalence of different gauges in certain circumstances.


title: Anisotropic lattice QCD studies of penta-quarks and tetra-quarks

abstract:
  Anisotropic lattice QCD studies of penta-quarks(5Q) with J^P=1/2^\pm and
3/2^{\pm} are presented at the quenched level together with tetra-quarks(4Q).
The standard gauge action at \beta=5.75 and O(a) improved quark (clover) action
with \kappa=0.1410(0.010)0.1440 are employed on the anisotropic lattice with
the renormalized anisotropy a_s/a_t = 4. The ``hybrid boundary condition(HBC)''
is adopted to discriminate a compact resonance state from scattering states.
Only massive 5Q states are found for J^P=1/2^+ and 3/2^{\pm}, which cannot be
identified as \Theta^+(1540). A low-lying 5Q state is found for J^P=1/2^- at
m_{5Q}\simeq 1.75 GeV, which however turns out to be an NK scattering state
through the HBC analysis. A preliminary result for 4Q states is presented
suggesting an existence of a compact 4Q resonance at m_{4Q} \simeq 1.1 GeV in
the idealized SU(4)_f chiral limit.


title:
Estimating the Unquenched Strange Quark Mass from the Lattice Axial Ward
  Identity

abstract:
  We present a determination of the strange quark mass for two flavours (nf=2)
of light dynamical quarks using the axial Ward identity. The calculations are
performed on the lattice using O(a) improved Wilson fermions and include a
fully non-perturbative determination of the renormalisation constant. In the
continuum limit we find in the MSbar scheme at 2GeV, ms = 111(6)(4)(6)MeV using
the force scale r0 = 0.467fm, where the first error is statistical, the second
and third are systematic due to the fit and scale uncertainties respectively.
Results are also presented for the light quark mass and the chiral condensate.
The corresponding results are also given for r0=0.5fm.


title: Multi-Quarks and Two-Baryon Interaction in Lattice QCD

abstract:
  We study multi-quark (3Q,4Q,5Q) systems in lattice QCD. We perform the
detailed studies of multi-quark potentials in lattice QCD to clarify the
inter-quark interaction in multi-quark systems. We find that all the
multi-quark potentials are well described by the OGE Coulomb plus multi-Y-type
linear potential, i.e., the multi-Y Ansatz. For multi-quark systems, we observe
lattice QCD evidences of ``flip-flop'', i.e., flux-tube recombination. These
lattice QCD studies give an important bridge between elementary particle
physics and nuclear physics.


title: Nuclear force in Lattice QCD

abstract:
  We perform the quenched lattice QCD analysis on the nuclear force
(baryon-baryon interactions). We employ $20^3\times 24$ lattice at $\beta=5.7$
($a\simeq 0.19$ fm) with the standard gauge action and the Wilson quark action
with the hopping parameters $\kappa=0.1600, 0.1625, 0.1650$, and generate about
200 gauge configurations. We measure the temporal correlators of the two-baryon
system which consists of heavy-light-light quarks. We extract the inter-baryon
force as a function of the relative distance $r$. We also evaluate the
contribution to the nuclear force from each ``Feynman diagram'' such as the
quark-exchange diagram individually, and single out the roles of Pauli-blocking
effects or quark exchanges in the inter-baryon interactions.


title: Non-Perturbative Approach to the Landau Gauge Gluodynamics

abstract:
  We discuss a non-perturbative lattice calculation of the ghost and gluon
propagators in the pure Yang-Mills theory in Landau gauge. The ultraviolet
behaviour is checked up to NNNLO yielding the value
$\Lambda^{n_f=0}_{\ms}=269(5)^{+12}_{-9}\text{MeV}$, and we show that lattice
Green functions satisfy the complete Schwinger-Dyson equation for the ghost
propagator for all considered momenta. The study of the above propagators at
small momenta showed that the infrared divergence of the ghost propagator is
enhanced, whereas the gluon propagator seem to remain finite and non-zero. The
result for the ghost propagator is consistent with the analysis of the
Slavnov-Taylor identity, whereas, according to this analysis, the gluon
propagator should diverge in the infrared, a result at odds with other
approaches.


title: Meson-Meson and Meson-Baryon Interactions in Lattice QCD

abstract:
  We study the meson-meson and meson-baryon interactions in lattice QCD. The
simulation is performed on 20^3 * 24 lattice at \beta=5.7 using Wilson gauge
action and Wilson fermion at the quenched level. By adopting one static quark
for each hadron as "heavy-light meson" and "heavy-light-light baryon", we
define the distance $r$ of two hadrons and extract the inter-hadron potential
from the energy difference of the two-particle state and its asymptotic state.
We find that both of the meson-meson and meson-baryon potentials are
nontrivially weak for the whole range of 0.2 fm <= r <= 0.8 fm. The effect of
including/excluding the quark-exchange diagrams is found to be marginal.


title:
Free Energy and Plaquette expectation value for gluons on the lattice,
  in three dimensions

abstract:
  We calculate the perturbative value of the Free Energy in Lattice QCD in
three dimensions, up to three loops. Our calculation is performed using the
Wilson formulation for gluons in SU(N) gauge theories.
  The Free Energy is directly related to the average plaquette. To carry out
the calculation, we compute the coefficients involved in the perturbative
expansion of the Free Energy up to three loops, using an automated set of
procedures developed by us in Mathematica. The dependence on N is shown
explicitly in our results.
  For purposes of comparison, we also present the individual contributions from
every diagram. These have been obtained by means of two independent
calculations, in order to cross check our results.


title: Effects of dynamical sea-quarks on quark and gluon propagators

abstract:
  We present an unquenched calculation of the quark propagator in Landau gauge
with 2+1 flavors of dynamical quarks. We study the scaling behavior of the
quark propagator in full QCD on two lattices with different lattice spacings
and similar physical volume. We use configurations generated with an improved
staggered (``Asqtad'') action by the MILC collaboration.


title: Where is the confining string in random percolation

abstract:
  The percolating phase of whatever random percolation process resembles the
confining vacuum of a gauge theory in most respects, with a string tension
having a well-behaved continuum limit, a non trivial glueball spectrum and a
deconfinement transition at a well determined temperature T_c. Simple numerical
experiments reveal an underlying, strongly fluctuating, confining string, with
an internal vortex structure formed by a core trapping inside a Coulomb-like
phase composed by the vacuum at the percolation threshold. The width of the
core almost coincides with 1/T_c and it turns out to be separated form the
confining vacuum by a domain wall of definite thickness.


title: Simulating the scalar field on the fuzzy sphere

abstract:
  The properties of the phi^4 scalar field theory on a fuzzy sphere are studied
numerically. The fuzzy sphere is a discretization of the sphere through
matrices in which the symmetries of the space are preserved. This model
presents three different phases: uniform and disordered phases, as in the usual
commutative scalar field theory, and a non-uniform ordered phase related to
UV-IR mixing like non-commutative effects. We have determined the coexistence
lines between phases, their triple point and their scaling.


title: Lattice QCD at High Temperature and the QGP

abstract:
  We review recent progress in studies of bulk thermodynamics of strongly
interacting matter, present results on the QCD equation of state and discuss
the status of studies of the phase diagram at non-vanishing quark chemical
potential.


title: Lattice Flavourdynamics

abstract:
  I present a selection of recent lattice results in flavourdynamics, including
the status of the calculation of quark masses and a variety of weak matrix
elements relevant for the determination of CKM matrix elements. Recent
improvements in the momentum resolution of lattice computations and progress
towards precise computations of $K\to\pi\pi$ decay amplitudes are also
reviewed.


title:
Cooling, smearing and Dirac eigenmodes - A comparison of filtering
  methods in lattice gauge theory

abstract:
  Starting from thermalized quenched SU(2) configurations we apply cooling or
iterated smearing, respectively, to produce sequences of gauge configurations
with less and less fluctuations. We compute the low lying spectrum and
eigenmodes of the lattice Dirac operator and compare them for the two types of
smoothing. Many characteristic properties of the eigensystem remain invariant
for all configurations in our sequences. We also find that cooling and smearing
produce surprisingly similar results. Both observations could be indications
that the two filtering methods do not drastically alter the long range
structures in the gauge field.


title: Repairing Stevenson's step in the 4d Ising model

abstract:
  In a recent paper Stevenson claimed that analysis of the data on the wave
function renormalization constant near the critical point of the 4d Ising model
is not consistent with analytical expectations. Here we present data with
improved statistics and show that the results are indeed consistent with
conventional wisdom once one takes into account the uncertainty of lattice
artifacts in the analytical computations.


title: Sign problem and MEM

abstract:
  The sign problem is notorious in Monte
  Carlo simulations of lattice QCD with the finite density, lattice field
theory (LFT) with a $\theta$ term and quantum spin models. In this report, to
deal with the sign problem, we apply the maximum entropy method (MEM) to LFT
with the $\theta$ term and investigate to what extent the
  MEM is applicable to this issue. Based on this study, we also make a brief
comment about lattice QCD with the finite density in terms of the
  MEM.


title: Large-N_f chiral transition in the Yukawa model

abstract:
  We investigate the finite-temperature behavior of the Yukawa model in which
$N_{f}$ fermions are coupled with a scalar field $\phi$ in the limit $N_f \to
\infty$. Close to the chiral transition the model shows a crossover between
mean-field behavior (observed for $N_f = \infty$) and Ising behavior (observed
for any finite $N_f$). We show that this crossover is universal and related to
that observed in the weakly-coupled $\phi^4$ theory. It corresponds to the
renormalization-group flow from the unstable Gaussian fixed point to the stable
Ising fixed point. This equivalence allows us to use results obtained in field
theory and in medium-range spin models to compute Yukawa correlation functions
in the crossover regime.


title: Vector meson masses in 2+1 flavor Wilson Chiral Perturbation Theory

abstract:
  We calculate the vector meson masses in $N_{\rm f} = 2+1$ Wilson chiral
perturbation theory at next-to-leading order. Generalizing the framework of
heavy vector meson chiral perturbation theory, the quark mass and the lattice
cutoff dependence of the vector meson masses is derived. Our chiral order
counting assumes that the lattice cut-off artifacts are of the order of the
typical pion momenta, $p \sim a\Lambda_{\rm QCD}^{2}$. This counting scheme is
consistent with the one in the pseudo scalar meson sector where the O($a^2$)
terms are included in the leading order chiral Lagrangian.


title:
Perturbative renormalization in parton distribution functions using
  Overlap fermions and Symanzik improved gluons

abstract:
  We calculate the 1-loop renormalization of the fermion self-energy, all local
fermion bilinears, as well as a set of extended bilinears which form a basis
corresponding to moments of the parton distribution functions.
  We use the overlap action for fermions and Symanzik improved action for
gluons.
  Our results are presented as a function of the overlap parameter rho and the
parameters entering the Symanzik action.


title: B Meson Semileptonic Form Factors from Unquenched Lattice QCD

abstract:
  The semileptonic process, B --> \pi l \nu, is studied via full QCD Lattice
simulations. We use unquenched gauge configurations generated by the MILC
collaboration. These include the effect of vacuum polarization from three quark
flavors: the $s$ quark and two very light flavors ($u/d$) of variable mass
allowing extrapolations to the physical chiral limit. We employ Nonrelativistic
QCD to simulate the $b$ quark and a highly improved staggered quark action for
the light sea and valence quarks. We calculate the form factors $f_+(q^2)$ and
$f_0(q^2)$ in the chiral limit for the range 16 GeV$^2 \leq q^2 < q^2_{max}$
and obtain $\int^{q^2_{max}}_{16 GeV^2} [d\Gamma/dq^2] dq^2 / |v_{ub}|^2 =
1.46(35) ps^{-1}$. Combining this with a preliminary average by the Heavy
Flavor Averaging Group (HFAG'05) of recent branching fraction data for
exclusive B semileptonic decays from the BaBar, Belle and CLEO collaborations,
leads to $|V_{ub}| = 4.22(30)(51) \times 10^{-3}$. PLEASE NOTE APPENDIX B with
an ERRATUM, to appear in Physical Review D, to the published version of this
e-print (Phys.Rev.D 73, 074502 (2006)). Results for the form factor $f_+(q^2)$
in the chiral limit have changed significantly. The last two sentences in this
abstract should now read; "We calculate the form factor $f_+(q^2)$ and
$f_0(q^2)$ in the chiral limit for the range 16 Gev$^2 \leq q^2 < q^2_{max}$
and obtain $\int^{q^2_{max}}_{16 GeV^2} [d\Gamma/dq^2] dq^2 / |V_{ub}|^2 =
2.07(57)ps^{-1}$. Combining this with a preliminary average by the Heavy Flavor
Averagibg Group (HFAG'05) of recent branching fraction data for exclusive B
semileptonic decays from the BaBar, Belle and CLEO collaborations, leads to
$|V_{ub}| = 3.55(25)(50) \times 10^{-3}$."


title: The CKM matrix and CP violation (in the continuum approximation)

abstract:
  The first part of this talk reviews recent developments in flavor physics
that can be made without detailed understanding of hadronic physics, driven by
the data. The error of sin(2beta) has shrunk below 5%, and the measurements of
alpha and gamma have reached interesting precisions. For the first time, there
are significant constraints on the deviations from the standard model in B-Bbar
mixing and in b->s and b->d transitions. In the second part, I review some
theoretical developments for exclusive semileptonic and nonleptonic B decays
that have become possible using the soft-collinear effective theory. I
concentrate on topics where the recent progress has model independent
implications for interpreting the data.


title:
High precision Monte Carlo simulations of interfaces in the
  three-dimensional Ising model: a comparison with the Nambu-Goto effective
  string model

abstract:
  Motivated by the recent progress in the effective string description of the
interquark potential in lattice gauge theory, we study interfaces with periodic
boundary conditions in the three-dimensional Ising model. Our Monte Carlo
results for the associated free energy are compared with the next-to-leading
order (NLO) approximation of the Nambu-Goto string model. We find clear
evidence for the validity of the effective string model at the level of the NLO
truncation.


title:
Two-Dimensional Compact N=(2,2) Lattice Super Yang-Mills Theory with
  Exact Supersymmetry

abstract:
  We construct two-dimensional N=(2,2) lattice super Yang-Mills theory, where
the gauge and Higgs fields are all represented by U(N) compact variables, with
keeping one exact supercharge along the line of the papers [1,2,3].
Interestingly, requirements of the exact supersymmetry as well as of the
compact gauge and Higgs fields lead to the gauge group U(N) rather than SU(N).
As a result of the perturbative renormalization argument, the model is shown to
flow to the target continuum theory without any fine-tuning. Different from the
case of noncompact Higgs fields, the path integral along the flat directions is
well-defined in this model.


title: Strange Electric Form Factor of the Proton

abstract:
  By combining the constraints of charge symmetry with new chiral extrapolation
techniques and recent low-mass quenched lattice QCD simulations of the
individual quark contributions to the electric charge radii of the baryon
octet, we obtain an accurate determination of the strange electric charge
radius of the proton. While this analysis provides a value for G_E^s(Q^2=0.1
GeV^2) in agreement with the best current data, the theoretical error is
comparable with that expected from future HAPPEx results from JLab. Together
with the earlier determination of G_M^s, this result considerably constrains
the role of hidden flavor in the structure of the nucleon.


title: Excited hadrons on the lattice: Mesons

abstract:
  We present results for masses of excited mesons from quenched calculations
using chirally improved quarks at pion masses down to 350 MeV. The key features
of our analysis are the use of a matrix of correlators from various source and
sink operators and a basis which includes quark sources with different spatial
widths, thereby improving overlap with states exhibiting radial excitations.


title: Gauge-variant propagators and the running coupling from lattice QCD

abstract:
  On the occasion of the 70th birthday of Prof. Adriano Di Giacomo we report on
recent numerical computations of the Landau gauge gluon and ghost propagators
as well as of a non-symmetric MOM-scheme ghost-gluon vertex in quenched and
full lattice QCD. Special emphasis is paid to the Gribov copy problem and to
the unquenching effect. The corresponding running coupling \alpha_s(q^2) is
found and shown to decrease for q^2 \le 0.3 GeV^2 in the infrared limit. No
indication for a non-trivial infrared fixed point is seen in agreement with
findings from truncated systems of Dyson-Schwinger equations treated on a
four-dimensional torus.


title:
The $\theta$-term, CP$^{N-1}$ Model and the Inversion Approach in the
  Imaginary $\theta$ Method

abstract:
  The weak coupling region of CP$^{N-1}$ lattice field theory with the
$\theta$-term is investigated. Both the usual real theta method and the
imaginary theta method are studied. The latter was first proposed by Bhanot and
David. Azcoiti et al. proposed an inversion approach based on the imaginary
theta method. The role of the inversion approach is investigated in this paper.
A wide range of values of $h=-{\rm Im} \theta$ is studied, where $\theta $
denotes the magnitude of the topological term. Step-like behavior in the
$x$-$h$ relation (where $x=Q/V$, $Q$ is the topological charge, and $V$ is the
two dimensional volume) is found in the weak coupling region. The physical
meaning of the position of the step-like behavior is discussed. The inversion
approach is applied to weak coupling regions.


title:
Towards a determination of the spectrum of QCD using a space-time
  lattice

abstract:
  Progress by the Lattice Hadron Physics Collaboration in determining the
baryon and meson resonance spectrum of QCD using Monte Carlo methods with
space-time lattices is described. The extraction of excited-state energies
necessitates the evaluation of correlation matrices of sets of operators, and
the importance of extended three-quark operators to capture both the radial and
orbital structures of baryons is emphasized. The use of both quark-field
smearing and link-field smearing in the operators is essential for reducing the
couplings of the operators to the high-frequency modes and for reducing
statistical noise in the correlators. The extraction of nine energy levels in a
given symmetry channel is demonstrated, and identifying the continuum spin
quantum numbers of the levels is discussed.


title: Reducing the beta-shift in domain wall fermion simulations

abstract:
  The beta-shift induced from dynamical domain wall quarks leads to increased
roughness of the gauge field, thus reversing the effect of smoothing from the
gauge action improvement. By exploiting the relation of overlap and domain wall
fermions in greater detail,we propose an algorithm which reduces the beta-shift
to the level of dynamical overlap fermions.


title: Shifted unitary orthogonal methods for the overlap inversion

abstract:
  In this work we compare the convergence of the shifted unitary orthogonal
method (SUOM) and different Krylov subspace solvers for propagator computations
with overlap fermions. We show that the SUOM algorithm performs similarly to
the shifted unitary minimal residual method (SUMR) with the latter converging
slightly faster. When the geometric optimality is applied to SUOM we get e new
algorithm which is faster than SUMR.


title: QCD Thermodynamics with an almost realistic quark mass spectrum

abstract:
  We will report on the status of a new large scale calculation of
thermodynamic quantities in QCD with light up and down quarks corresponding to
an almost physical light quark mass value and a heavier strange quark mass.
These calculations are currently being performed on the QCDOC Teraflops
computers at BNL. We will present new lattice calculations of the transition
temperature and various susceptibilities reflecting properties of the chiral
transition. All these quantities are of immediate interest for heavy ion
phenomenology.


title: Finite volume corrections to pi-pi scattering

abstract:
  Lattice QCD studies of hadron-hadron interactions are performed by computing
the energy levels of the system in a finite box. The shifts in energy levels
proportional to inverse powers of the volume are related to scattering
parameters in a model independent way. In addition, there are non-universal
exponentially suppressed corrections that distort this relation. These terms
are proportional to exp(-m_pi L) and become relevant as the chiral limit is
approached. In this paper we report on a one-loop chiral perturbation theory
calculation of the leading exponential corrections in the case of I=2 pi-pi
scattering near threshold.


title: Baryon Operators and Baryon Spectroscopy

abstract:
  The issues involved in a determination of the baryon resonance spectrum in
lattice QCD are discussed. The variational method is introduced and the need to
construct a sufficient basis of interpolating operators is emphasised. The
construction of baryon operators using group-theory techniques is outlined. We
find that the use both of quark-field smearing and link-field smearing in the
operators is essential firstly to reduce the coupling of operators to
high-frequency modes and secondly to reduce the gauge-field fluctuations in
correlators. We conclude with a status report of our current investigation of
baryon spectroscopy.


title:
The spontaneous generation of magnetic fields at high temperature in
  SU(2)-gluodynamics on a lattice

abstract:
  The spontaneous generation of the chromomagnetic field at high temperature is
investigated in a lattice formulation of the SU(2)-gluodynamics. The procedure
of studying this phenomenon is developed. The Monte Carlo simulations of the
free energy on the lattices 2 \times 8^3, 2\times 16^3 and 4 \times 8^3 at
various temperatures are carried out. The creation of the field is indicated by
means of the \chi^2-analysis of the data set accumulating 5-10 millions MC
configurations. A comparison with the results of other approaches is done.


title: Strange quarks in quenched twisted mass lattice QCD

abstract:
  Two twisted doublets, one containing the up and down quarks and the other
containing the strange quark with an SU(2)-flavor partner, are used for studies
in the meson sector. The relevant chiral perturbation theory is presented, and
quenched QCD simulations (where the partner of the strange quark is not active)
are performed. Pseudoscalar meson masses and decay constants are computed; the
vector and scalar mesons are also discussed. A comparison is made to the case
of an untwisted strange quark, and some effects due to quenching,
discretization, and the definition of maximal twist are explored.


title: On the Continuum Limit of Topological Charge Density Distribution

abstract:
  The bulk distribution of the topological charge density, constructed via HP^1
sigma-model embedding method, is investigated. We argue that the specific
pattern of leading power corrections to gluon condensate hints on a particular
UV divergent structure of HP^1 sigma-model fields, which in turn implies the
linear divergence of the corresponding topological density in the continuum
limit. We show that under testable assumptions the topological charge is to be
distributed within three-dimensional sign-coherent domains and conversely, the
dimensionality of sign-coherent regions dictates the leading divergence of the
topological density. Confronting the proposed scenario with lattice data we
present evidence for indeed peculiar divergence of the embedded fields. Then
the UV behavior of the topological density is studied directly and is found to
agree with our proposition. Finally, we introduce parameter-free method to
investigate the dimensionality of relevant topological fluctuations and show
that indeed topological charge sign-coherent regions are likely to be
three-dimensional.