title:
Color Confinement in lattice Landau gauge with unquenched Wilson and KS
  fermions

abstract:
  The Kugo-Ojima confinement criterion is verified in the unquenched Landau
gauge QCD simulation. The valence quark propagator of the Kogut-Susskind
fermion with use of the fermion action including the Naik term and the staple
contribution is calculated on MILC Asqtad unquenched gauge configurations, and
it shows infrared suppression of the quark propagator.


title: The IR gluon propagator from lattice QCD

abstract:
  The gluon propagator is computed in large asymmetric lattices, accessing
momenta around 100 MeV and smaller. Our study tries to check the compatibility
of the recent solutions of the gluon-ghost Dyson-Schwinger equations with
lattice results. In particular the exponent $\kappa$, which characterizes the
solutions for the infrared, is measured. Results favours a vanishing zero
momentum gluon propagator. We also report on the compatibility of various
functional forms used to fit the Dyson-Schwinger solution for the full range of
momenta and the lattice gluon propagator.


title:
The running coupling in lattice Landau gauge with unquenched Wilson
  fermion and KS fermion

abstract:
  The running coupling of the Wilson fermon(JLQCD/CP-PACS) and that of
Kogut-Susskind(KS) fermion(MILC) are measured in the lattice Landau gauge QCD
in $\widetilde{MOM}$ scheme. The quark propagator of the KS fermion is also
measured and we find that it is infrared suppressed. The renormalization factor
of the running coupling and the tadpole renormalization define the scale of the
quark wave function. Effects of the $A_\mu^2$ condensates of a few GeV$^2$ are
observed in the running coupling and also in the quark propagator.


title:
Twisted mass fermions: neutral pion masses from disconnected
  contributions

abstract:
  Twisted mass fermions allow light quarks to be explored but with the
consequence that there are mass splittings, such as between the neutral and
charged pion. Using a direct calculation of the connected neutral pion
correlator and stochastic methods to evaluate the disconnected correlations, we
determine the neutral pion mass. We explore the dependence on lattice spacing
and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the
splitting which is linked, via chiral PT, to the nature of the phase transition
at small quark mass.


title: Finite volume effects in the gluon propagator

abstract:
  We report on a preliminary study of the volume dependence of the gluon
propagator. The propagator is computed using different lattice volumes, its
extrapolation to infinite volume is investigated with particular attention to
the its IR behaviour. Our data shows a mild but measurable dependence with the
volume. Unfortunately, we are not able yet to clarify its behaviour close to
zero momentum.


title: Fermion propagators in QED3 with velocity anisotropies

abstract:
  QED3 with fermi and gap anisotropies is considered to be a candidate
effective field theory of high temperature superconductors. Simulations of a
variant of the theory have demonstrated that there is evidence consistent with
a phase transition to a chirally restored phase as the velocity anisotropy
increases, and that the correlation lengths of pions in spatial directions
behave in a manner consistent with the anisotropy being a relevant parameter of
the theory. We present the first measurements of the fermion propagator in
Landau gauge for this theory and suggest that the structure of this theory is
more complex than previously thought.


title:
Large Wilson loops with overlap and clover fermions: Two-loop evaluation
  of the b-quark mass shift and the quark-antiquark potential

abstract:
  We compute, to two loops in pertubation theory, the fermionic contribution to
rectangular RxT Wilson loops, for different values of R and T.
  We use the overlap fermionic action. We also employ the clover action, for
comparison with existing results in the literature.
  In the limit R, T -> Infinity our results lead to the shift in the b-quark
mass. We also evaluate the perturbative static potential as T -> Infinity.


title:
Evolution of the Structure Factors in Pure SU(N) Lattice Gauge Theory
  and Effective Spin Models

abstract:
  We consider model A dynamics for a quench from the disordered into the
ordered phase of SU(3) lattice gauge theory and the analogue 3d 3-state Potts
model. For the gauge model this corresponds to a rapid heating from the
confined to the deconfined phase. The exponential growth factors of low-lying
structure function modes are numerically calculated. The linear theory of
spinodal decomposition is used to determine the critical modes. This allows for
the Debye screening mass estimation in an effective phenomenological model. The
quench leads to competing vacuum domains, which make the equilibration of the
QCD vacuum after the heating non-trivial. The influence of such domains on the
gluonic energy density is studied.


title:
Another weak first order deconfinement transition: three-dimensional
  SU(5) gauge theory

abstract:
  We examine the finite-temperature deconfinement phase transition of
(2+1)-dimensional SU(5) Yang-Mills theory via non-perturbative lattice
simulations. Unsurprisingly, we find that the transition is of first order,
however it appears to be weak. This fits naturally into the general picture of
"large" gauge groups having a first order deconfinement transition, even when
the center symmetry associated with the transition might suggest otherwise.


title:
Two Loop Partially Quenched and Finite Volume Chiral Perturbation Theory
  Results

abstract:
  This talk presents some results relevant for lattice QCD at higher order in
ChPT. First we discuss the finite volume corrections at two loops for the quark
condensate as well as a L\"uscherlike finite volume formula for it. The latter
allows for an alternative determination of meson sigma terms. The second set of
results presented here are the calculations at two loops in partially quenched
chiral perturbation theory of masses and decay constants of the charged mesons.
We present results for all relevant quark mass combinations for the cases with
two and three sea quarks.


title: Cutoff effects in the O(N) sigma model at large N

abstract:
  The computation of the step scaling function for the finite size mass-gap in
the O(N) sigma model at large N is reviewed. Practically exact nonperturbative
results become available for both finite and vanishing lattice spacing. We use
them as a testbed to investigate standard procedures of continuum extrapolation
in lattice field theory.


title:
Two-loop evaluation of large Wilson loops with overlap fermions: the
  b-quark mass shift, and the quark-antiquark potential


title: Gauge invariance in a Z_2 hamiltonian lattice gauge theory

abstract:
  We propose an efficient variational method for $Z_2$ lattice gauge theory
based on the matrix product ansatz. The method is applied to ladder and square
lattices. The Gauss law needs to be imposed on quantum states to guarantee
gauge invariance when one studies gauge theory in hamiltonian formalism. On the
ladder lattice, we identify gauge invariant low-lying states by evaluating
expectation values of the Gauss law operator after numerical diagonalization of
the gauge hamiltonian. On the square lattice, the second order phase transition
is well reproduced.


title: Lattice QCD - A guide for people who want results

abstract:
  Lattice QCD was invented thirty years ago but only in the last few years has
it finally fulfilled its promise as a precision tool for calculations in hadron
physics. This review will cover the fundamentals of discretising QCD onto a
space-time lattice and how to reduce the errors associated with the
discretisation. This 'improvement' is the key that has made the enormous
computational task of a lattice QCD calculation tractable and enabled us to
reach the recent milestone of precision calculations of simple 'gold-plated'
hadron masses. Accurate decay matrix elements, such as those for leptonic and
semileptonic decays of heavy mesons needed by the B factory experimental
programme, are now within sight. I will describe what goes into such
calculations and what the future prospects and limitations are.


title:
Casimir Scaling of domain wall tensions in the deconfined phase of D=3+1
  SU(N) gauge theories

abstract:
  We perform lattice calculations of the spatial 't Hooft k-string tensions in
the deconfined phase of SU(N) gauge theories for N=2,3,4,6. These equal (up to
a factor of T) the surface tensions of the domain walls between the
corresponding (Euclidean) deconfined phases. For T much larger than T_c our
results match on to the known perturbative result, which exhibits Casimir
Scaling, being proportional to k(N-k). At lower T the coupling becomes stronger
and, not surprisingly, our calculations show large deviations from the
perturbative T-dependence. Despite this we find that the behaviour proportional
to k(N-k) persists very accurately down to temperatures very close to T_c. Thus
the Casimir Scaling of the 't Hooft tension appears to be a `universal' feature
that is more general than its origin in the low order high-T perturbative
calculation. We observe the `wetting' of these k-walls at T around T_c and the
(almost inevitable) `perfect wetting' of the k=N/2 domain wall. Our
calculations show that as T tends to T_c the magnitude of the spatial `t Hooft
string tension decreases rapidly.


title: Nuclear Physics and Lattice QCD

abstract:
  Lattice QCD is progressing toward being able to impact our understanding of
nuclei and nuclear processes. I discuss areas of nuclear physics that are
becoming possible to explore with lattice QCD, the techniques that are
currently available and the status of numerical explorations.


title:
Pseudo scalar meson masses in Wilson Chiral Perturbation Theory for 2+1
  flavors

abstract:
  We consider 2+1 flavor Wilson Chiral Perturbation Theory including the
lattice spacing contributions of O($a^{2}$). We adopt a power counting
appropriate for the unquenched lattice simulations carried out by the
CP-PACS/JLQCD collaboration and compute the pseudo scalar meson masses to one
loop. These expression are required to perform the chiral extrapolation of the
CP-PACS/JLQCD lattice data.


title:
Scaling of Nonperturbative Renormalization of Composite Operators with
  Overlap Fermions

abstract:
  We compute non-perturbatively the renormalization constants of composite
operators for overlap fermions by using the regularization independent scheme.
The scaling behavior of the renormalization constants is investigated using the
data from three lattices with similar physical volumes and different lattice
spacings. The approach of the renormalization constants to the continuum limit
is explored.


title: Baryon spectroscopy with spatially improved quark sources

abstract:
  We study baryons on the lattice with a special focus on excited states. For
that purpose we construct several interpolators which differ in their Dirac
structure. These interpolators are built from Jacobi smeared quarks with
different widths in order to allow for operators with improved spatial
wavefunctions. We compute all cross correlations and use the variational method
to determine which combinations of operators have best overlap with ground and
excited states. Our approach yields promising results for the spin-1/2 baryons:
nucleon, sigma, xi and lambda. For the spin-3/2 baryons, delta and omega, we
obtain results which are consistent with results of other groups.


title:
Topologically non-trivial field configurations - interplay of vortices
  and Dirac eigenmodes

abstract:
  Gluon field configurations with non-trivial topology like instantons,
magnetic monopoles and center vortices play a crucial role in QCD and, in
particular, for the spontaneous breaking of chiral symmetry. Moreover, center
vortices are strongly correlated with confinement. We present evidence, that
there is a deep connection between the topology of gauge fields and center
vortices. We use the chirally improved lattice Dirac operator to compute
eigenvectors and eigenvalues of various lattice gauge field configurations.
Removing vortices from thermalized configurations also removes the topological
content of the gauge field. As a consistency check, we apply random changes to
the raw configurations.


title: The Equation of State for QCD with 2+1 Flavors of Quarks

abstract:
  We report results for the interaction measure, pressure and energy density
for nonzero temperature QCD with 2+1 flavors of improved staggered quarks. In
our simulations we use a Symanzik improved gauge action and the Asqtad $O(a^2)$
improved staggered quark action for lattices with temporal extent $N_t=4$ and
6. The heavy quark mass $m_s$ is fixed at approximately the physical strange
quark mass and the two degenerate light quarks have masses $m_{ud} =0.1m_s$ or
$0.2m_s$. The calculation of the thermodynamic observables employs the integral
method where energy density and pressure are obtained by integration over the
interaction measure.


title: Gribov horizon under the (lattice) microscope

abstract:
  The infinite color-Coulomb energy of color-charged states is related to
enhanced density of near-zero modes of the Faddeev-Popov operator in Coulomb
gauge. We confirm the enhancement in numerical simulations and show that it is
tied to the presence of percolating center vortex configurations.


title: The hadron spectrum from twisted mass QCD with a strange quark

abstract:
  Various suggestions exist for incorporating the strange quark into twisted
mass QCD. One option for quenched simulations is to employ two twisted
doublets, (u,d) and (c,s), with separate twist angles. Working in the isospin
limit, preliminary results for the quenched spectrum of strange hadrons are
presented, with both twist angles tuned to pi/2. Splittings within the mass
multiplets provide some insight into the symmetry breaking effects of twisted
mass lattice QCD.


title: D-branes and Topological Charge in QCD

abstract:
  The recently observed long-range coherent structure of topological charge
fluctuations in QCD is compared with theoretical expectations based on the
AdS/CFT brane construction of nonsupersymmetric gauge theory by Witten. Similar
observations of coherent topologicalcharge structure in 2D $CP^{N-1}$ sigma
models are interpreted in terms of Wilson lines representing world lines of
screened electric charges. The analogy between 2D U(1) and 4D Yang-Mills theory
leads to the interpretation of the observed coherent sheets of topological
charge in QCD as screened ``Wilson bags'' first suggested by Luscher. The
duality between the Wilson bag surface and a wrapped 6-brane in IIA string
theory is discussed. The complete screening of the force between bag surfaces
for integer values of the bag charge $\theta/2\pi$ corresponds to the
observation by Polchinski that the net force between d-branes from closed
string exchange vanishes for quantized values of Ramond-Ramond charge.


title: Lattice QFT with FermiQCD

abstract:
  FermiQCD is a C++ library for fast development of parallel Lattice Quantum
Field Theory computations. It has been developed following a top-down fully
Object Oriented design approach with focus on simplicity of use. FermiQCD
includes: a heatbath algorithm for Wilson and $O(a^2)$ improved SU(n) gauge
actions; inversion algorithms for Wilson, Clover, Kogut-Susskind, Asqtad, and
Domain Wall fermionic actions; example programs for various types of meson
propagators; and converters for the most common gauge file formats.


title: Low energy constants from the chirally improved Dirac operator D_CI

abstract:
  The leading order low energy parameters like the pion decay constant or the
quark condensate are well-known from "classical" low energy theorems and
experiments. It is a challenge, however, to find these parameters based
exclusively on an ab-initio QCD calculation. We discuss results of a quenched
lattice calculation of low energy constants using the chirally improved Dirac
operator. Several lattice sizes at different lattice spacings are studied,
using pseudoscalar and axial vector correlators. We find consistent results for
f_\pi = 96(2) MeV, f_K = 105(2) MeV, \Sigma = -(286(4) MeV)^3, the average
light quark mass m = 4.1(2.4) MeV and m_s = 101(8) MeV.


title:
Two-colour Lattice QCD with dynamical fermions at non-zero density
  versus Matrix Models

abstract:
  We provide first evidence that Matrix Models describe the low lying complex
Dirac eigenvalues in a theory with dynamical fermions at non-zero density.
Lattice data for gauge group SU(2) with staggered fermions are compared to
detailed analytical results from Matrix Models in the corresponding symmetry
class, the complex chiral Symplectic Ensemble. They confirm the predicted
dependence on chemical potential, quark mass and volume.


title: Chiral extrapolation of hyperon vector form factors

abstract:
  We present a new study of SU(3)-breaking corrections in hyperon vector form
factors relevant for the extraction of Vus. A lattice quenched simulation has
been performed, showing that it is possible to reach the required precision to
extract SU(3)-breaking corrections in the regime of simulated masses. In order
to perform the chiral extrapolation we calculated the chiral corrections to the
vector form factor in HBChPT. Besides the one-loop O(p^2) contribution, we
included also the subleading O(p^3) and O(1/M_B) corrections that, due to the
Ademollo-Gatto theorem, are free from the contamination of unknown low energy
constants. The results complete and correct previous calculations, and show
that subleading corrections cannot be neglected. We also studied decuplet
contributions within HBChPT and show that, in this case, the chiral expansion
breaks down, rising doubts on the consistency of the theory.


title: On meson spectral functions at high temperature and nonzero momentum

abstract:
  In the high-temperature phase of QCD meson spectral functions at nonzero
momentum are expected to have a nontrivial and interesting structure. In order
to provide a reference point for lattice studies employing e.g. the Maximal
Entropy Method, we discuss several characteristics of meson spectral functions
in the infinite-temperature limit. We report on ongoing work in quenched QCD
with staggered fermions.


title: Large-N_f behavior of the Yukawa model: analytic results

abstract:
  We investigate the Yukawa model in which $N_f$ fermions are coupled with a
scalar field $\phi$ through a Yukawa interaction. The phase diagram is rather
well understood. If the fermions are massless, there is a chiral transition at
$T_c$: for $T < T_c$ chiral symmetry is spontaneously broken. At $N_f=\infty$
the transition is mean-field like, while, for any finite $N_f$, standard
arguments predict Ising behavior. This apparent contradiction has been
explained by Kogut et al., who showed by scaling arguments and Monte Carlo
simulations that in the large-$N_f$ limit the width of the Ising critical
region scales as a power of $1/N_f$, so that only mean-field behavior is
observed for $N_f$ strictly equal to infinity. We will show how the results of
Kogut et al. can be recovered analytically in the framework of a generalized
$1/N_f$ expansion. The method we use is a simple generalization of the method
we have recently applied to a two-dimensional generalized Heisenberg model.


title: Lowest Order Hadronic Contribution to the Muon g-2

abstract:
  We present the most recent lattice results for the lowest-order hadronic
contribution to the muon anomalous magnetic moment using 2+1 flavor improved
staggered fermions. A precise fit to the low-q^2 region of the vacuum
polarization is necessary to accurately extract the muon g-2. To obtain this
fit, we use staggered chiral perturbation theory with the inclusion of the
vector particles as resonances, to evaluate the vacuum polarization. We discuss
the preliminary fit results and attendant systematic uncertainties, paying
particular attention to the relative contributions of the pions and vector
mesons.


title:
Magnetic polarizability of hadrons from lattice QCD in the background
  field method

abstract:
  We present a calculation of hadron magnetic polarizability using the
techniques of lattice QCD. This is carried out by introducing a uniform
external magnetic field on the lattice and measuring the quadratic part of a
hadron's mass shift. The calculation is performed on a $24^4$ lattice with
standard Wilson actions at beta=6.0 (spacing $a=0.1$ fm) and pion mass down to
about 500 MeV. Results are obtained for 30 particles covering the entire baryon
octet ($n$, $p$, $\Sigma^0$, $\Sigma^-$, $\Sigma^+$, $\Xi^-$, $\Xi^0$,
$\Lambda$) and decuplet ($\Delta^0$, $\Delta^-$, $\Delta^+$, $\Delta^{++}$,
$\Sigma^{*0}$, $\Sigma^{*-}$, $\Sigma^{*+}$, $\Xi^{*0}$, $\Xi^{*-}$,
$\Omega^-$), plus selected mesons ($\pi^0$, $\pi^+$, $\pi^-$, $K^0$, $K^+$,
${K}^-$, $\rho^0$, $\rho^+$, $\rho^-$, $K^{*0}$, $K^{*+}$, $K^{*-}$). The
results are compared with available values from experiments and other
theoretical calculations.


title: Coherent Topological Charge Structure in $CP^{N-1}$ Models and QCD

abstract:
  In an effort to clarify the significance of the recent observation of
long-range topological charge coherence in QCD gauge configurations, we study
the local topological charge distributions in two-dimensional $CP^{N-1}$ sigma
models, using the overlap Dirac operator to construct the lattice topological
charge. We find long-range sign coherence of topological charge along extended
one-dimensional structures in two-dimensional spacetime. We discuss the
connection between the long range topological structure found in $CP^{N-1}$ and
the observed sign coherence along three-dimensional sheets in four-dimensional
QCD gauge configurations. In both cases, coherent regions of topological charge
form along membrane-like surfaces of codimension one. We show that the Monte
Carlo results, for both two-dimensional and four-dimensional gauge theory,
support a view of topological charge fluctuations suggested by Luscher and
Witten. In this framework, the observed membranes are associated with
boundaries between ``k-vacua,'' characterized by an effective local value of
$\theta$ which jumps by $\pm 2\pi$ across the boundary.


title: Baryon magnetic moments in the background field method

abstract:
  We present a calculation of the magnetic moments for the baryon octet and
decuplet using the background-field method and standard Wilson gauge and
fermion actions in the quenched approximation of lattice QCD. Progressively
smaller static magnetic fields are introduced on a $24^4$ lattice at beta=6.0
and the pion mass is probed down to about 500 MeV. Magnetic moments are
extracted from the linear response of the masses to the background field.


title: QCD Phases in Lattice QCD

abstract: I review the recent status of lattice QCD calculations at non-zero density.


title:
Lattice construction of Cho-Faddeev-Niemi decomposition and gauge
  invariant monopole

abstract:
  We present the first implementation of the Cho--Faddeev--Niemi decomposition
of the SU(2) Yang-Mills field on a lattice. Our construction retains the color
symmetry (global SU(2) gauge invariance) even after a new type of Maximally
Abelian gauge, as explicitly demonstrated by numerical simulations. Moreover,
we propose a gauge-invariant definition of the magnetic monopole current using
this formulation and compare the new definition with the conventional one by
DeGrand and Toussaint to exhibit its validity.


title: Localized eigenmodes of the covariant lattice Laplacian

abstract:
  We study numerically the eigenmode spectrum of the covariant lattice
Laplacian, in the fundamental SU(2) color group representation. It is found
that eigenmodes at the lower and upper ends of the spectrum are localized, and
that the localization volume scales. In contrast, the eigenmodes of the lattice
Faddeev-Popov operator are all extended rather than localized (as required for
confinement) despite the similarity of the kinetic and Faddeev-Popov operators.


title: Gauge theories on a five-dimensional orbifold

abstract:
  We present a construction of non-Abelian gauge theories on the R^4 x S^1/Z_2
orbifold. We show that no divergent boundary mass term for the Higgs field,
identified with some of the fifth dimensional components of the gauge field, is
generated. The formulation of the theories on the lattice requires only
Dirichlet boundary conditions that specify the breaking of the gauge group. The
first simulations in order to resolve the issue whether these theories can be
used at low energy as weakly interacting effective theories have been
performed. In case of a positive answer, these theories could provide us with a
new framework for studying electroweak symmetry breaking.


title:
Perturbative renormalisation of quark bilinear operators for overlap
  fermions with and without stout links and improved gauge action

abstract:
  We calculate lattice renormalisation constants of local and one-link quark
operators for overlap fermions and improved gauge actions in one-loop
perturbation theory. For the local operators we stout smear the SU(3) links in
the fermionic action. Using the popular tadpole improved L\"uscher-Weisz
actions at $\beta=8.45$ and $\beta=8.0$ we present numerical values for the Z
factors in the $\bar{MS}$ scheme (partly as function of the stout smearing
strength). We compare various levels of mean field (tadpole) improvement which
have been applied to our results.


title:
Towards a non-perturbative computation of the RGI strange quark mass
  with two dynamical flavors

abstract:
  The non-perturbative running of the quark mass in the Schroedinger functional
scheme is computed over a large energy range (covering scales differing by two
orders of magnitude). This allows to relate lattice estimates of the running
quark mass to the renormalization group invariant mass. The result is used in a
preliminary computation of the strange quark mass in the theory with two
flavors of non-perturbatively improved Wilson quarks. A more detailed
discussion of the calculation can be found in [1].


title: Large N reduction on a twisted torus

abstract:
  We consider SU(N) lattice gauge theory at infinite N defined on a torus with
a CP invariant twist. Massless fermions are incorporated in an elegant way,
while keeping them quenched. We present some numerical results which suggest
that twisting can make numerical simulations of planar QCD more efficient.


title: Lattice calculation of SU(3) flavor breaking ratios in B - anti-B mixing

abstract:
  We present an unquenched lattice calculation for the SU(3) flavor breaking
ratios of the heavy-light decay constants and the $\Delta B = 2$ matrix
elements. The calculation was performed on $16^3 \times 32$ lattices with two
dynamical flavors of domain-wall quarks and inverse lattice spacing $1/a =
1.69(5)$ GeV. Heavy quarks were implemented using an improved lattice
formulation of the static approximation. In the infinite heavy-quark mass limit
we obtain $f_{B_s}/f_{B_d} = 1.29(4)(6)$, $B_{B_s}/B_{B_d} = 1.06(6)(4)$, $\xi
= 1.33(8)(8)$ where the first error is statistical and the second systematic.


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

abstract:
  Some past and ongoing explorations of the spectrum of QCD using Monte Carlo
simulations on a space-time lattice are described. Glueball masses in the
pure-gauge theory are reviewed, and the energies of gluonic excitations in the
presence of a static quark-antiquark pair are discussed. Current efforts to
compute the baryon spectrum using extended three-quark operators are also
presented, emphasizing the need to use irreducible representations of the cubic
point group to identify spin quantum numbers in the continuum limit.


title: Restoring chiral symmetry to O(a^2) for dynamical Wilson fermions

abstract:
  We present results for the non-perturbative determination of the improvement
and renormalization factors of the isovector axial current for lattice QCD with
two flavors of dynamical Wilson quarks. The improvement and normalization
conditions are formulated in terms of matrix elements of the PCAC relation in
the Schroedinger functional setup and results are given in the form of
interpolating formulae for bare gauge couplings beta=6/g_0^2>5.2.


title: The pion mass in finite volume to two loops

abstract:
  We evaluate the pion mass in finite volume to two loops within Chiral
Perturbation Theory. The results are compared with a recently proposed
extension of the asymptotic formula of Luscher. We find that contributions,
which were neglected in the latter, are numerically very small at the two-loop
level.


title: Low-lying spectrum for lattice Dirac operators with twisted mass

abstract:
  We analyze the low-lying spectrum and eigenmodes of lattice Dirac operators
with a twisted mass term. The twist term expels the eigenvalues from a strip in
the complex plane and all eigenmodes obtain a non-vanishing matrix element with
gamma-5. For a twisted Ginsparg-Wilson operator the spectrum is located on two
arcs in the complex plane. Modes due to non-trivial topological charge of the
underlying gauge field have their eigenvalues at the edges of these arcs and
obey a remnant index theorem. For configurations in the confined phase we find
that the twist mainly affects the zero modes, while the bulk of the spectrum is
essentially unchanged.


title: Speeding up the HMC algorithm: Some new results

abstract:
  We give some new performance results for the Hybrid Monte Carlo (HMC)
simulation of dynamical clover-improved Wilson fermions using an improved
pseudo-fermion action. The generalisation of even-odd preconditioning for the
standard Wilson fermion matrix to the clover-improved case is not unique. In
the literature the so called symmetric and asymmetric versions are discussed.
Most of the previous simulations of dynamical clover-improved Wilson fermions
were done with the asymmetric version. Only recently, the JLQCD collaboration
has pointed out that the symmetric version leads to a better performance of the
HMC algorithm. Here, we show that also in combination with an improved
pseudo-fermion action, the symmetric version of even-odd preconditioning leads
to a better performance. For our lightest quark mass, which corresponds to
$m_{PS}/m_{V} \approx 0.44$, we see a gain in performance by a factor of about
1.3.


title: Kosterlitz-Thouless transition on the worldsheet of the QCD string

abstract:
  We investigate the properties of the QCD string in the Euclidean SU(N) pure
gauge theory when the space-time dimensions transverse to it are periodic. We
propose a generalisation of the Luscher-Weisz effective string action for the
flux-tube energy levels at finite L_perp. As the size of one transverse
dimension is varied, we predict a Kosterlitz-Thouless transition of the
worldsheet field theory driven by vortices, after which the periodic component
of the worldsheet displacement vector develops a mass gap and the effective
central charge drops by one unit. The universal properties of the transition
are emphasized.


title: The deconfining phase transition for SU(N) theories in 2+1 dimensions

abstract:
  The critical temperatures for the 2+1 dimensional $SU(N_c)$ gauge theories
are calculated, for $N_c = 4,5,6$. The transition is shown to be first order
for $N_c \geq 5$. The critical temperature and latent heat are extrapolated to
$N_c = \infty$.


title:
Effects of partial quenching and staggered fermions on the scalar
  correlator

abstract:
  We determine the mass of the lightest quark-antiquark scalar meson with I=1
using the simulation with two dynamical Domain Wall Fermions. The conventional
exponential fit of the scalar correlator is justified in this case giving the
mass 1.58 +/- 0.34 GeV. In general the scalar correlator receives also the
bubble contribution, which is the intermediate state with two pseudoscalar
mesons. This contribution is sizable at light quark masses and has to be
incorporated in the fit of the scalar correlator in order to extract the scalar
meson mass. We provide predictions for the bubble contribution in Partially
Quenched ChPT, Staggered ChPT and ChPT for Mixed quark actions. We find that
the bubble contribution is significantly affected by the unphysical
approximations that are employed in simulations. It can render the negative
sign and unphysical effective mass 2*Mpi in the scalar correlator with I=1.


title: A strategy for the computation of m_b including 1/m terms

abstract:
  We consider HQET including the first order correction in 1/m. A strategy for
the computation of the b-quark mass is discussed. Only two quantities Phi_1/2
have to be considered in order to match QCD and HQET, since the spin-dependent
interaction is easily eliminated due to the spin symmetry of the static theory.
Quite simple formulae relate the renormalization group invariant b-quark mass
(M_b) to the B-meson mass. All entries in these formulae are non-perturbatively
defined and can be computed in the continuum limit of the lattice regularized
theory. For the numerically most critical part, we illustrate the cancellation
of power divergences by a numerical example. Numerical results for the 1/m
correction to M_b, are presented in a companion talk.


title:
Screening of sources in higher representations of SU(N) gauge theories
  at zero and finite temperature

abstract:
  Completion of the Svetitsky-Yaffe conjecture in some (2+1) dimensional SU(N)
gauge theories allows mapping Polyakov loops in higher representations of the
gauge group into suitable conformal operators of the corresponding 2D CFT. As a
consequence, the critical exponents of the correlators of these Polyakov loops
are determined. The functional form of these correlators suggests a general
Ansatz to describe the large-distance screening of higher-representation
sources at zero temperature in any space-time dimension. A generalised Wilson
loop in which along part of its trajectory a source is converted in a gauge
invariant way into higher representations with same N-ality could be used to
estimate the decay scale of the unstable strings


title: Excited meson spectroscopy with chirally improved fermions

abstract:
  We present excited meson masses from quenched calculations using chirally
improved (CI) quarks at pion masses down to 350 MeV. The salient 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: Laplacian modes for calorons and 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: An Abelian two-Higgs model and high temperature superconductivity

abstract:
  We study a three dimensional Abelian Higgs model containing singly- and
doubly-charged scalar fields coupled to a compact Abelian gauge field in the
London limit. The model attracts interest because of its relevance to high-Tc
superconductors with charge 1 holon and charge 2 spinon-pair fields. It
contains two types of vortices carrying magnetic flux and one type of
instanton-like monopoles. Using thermodynamic and topological observables we
present the phase diagram in the parameter space of the gauge and holon and
spinon-pair couplings. The Fermi liquid, the spin gap, the superconductor and
the strange metallic phases have been identified in a wide region of
parameters. The model may serve as a toy system modelling non-perturbative
properties of the Yang-Mills theory.


title:
Towards SU(2) invariant formulation of the monopole confinement
  mechanism

abstract:
  The type of the vacuum is studied numerically in the maximally Abelian (MA)
gauge and in the Landau (LA) gauge of SU(2) gluodynamics. The type of the
vacuum is determined by a ratio between the dual coherence and the dual
penetration lengths. The dual penetration length is determined from
correlations between Wilson loops and electric fields in both gauges. The dual
coherence length is found from correlations between Wilson loops and
dimension-2 operators both in the MA and the LA gauges. This determination of
the coherence length is supported by theoretical and numerical observation that
the dimension-2 gluon operators in the studied gauges have a strong correlation
with the monopole current determined in the MA gauge. We find numerically that
the dual penetration lengths and the dual coherence lengths in the LA and the
MA gauges are almost the same. Therefore we conclude, that in both gauges the
type of the vacuum in the confinement phase is near to the border between the
type 1 and the type 2 dual superconductors.


title: Studying the infrared region in Landau gauge QCD

abstract:
  We report on the progress we made in studying the infrared behavior of the
ghost and gluon dressing functions in Landau gauge. Related to this we also
investigate a running coupling given in terms of those functions and compare
our results to those coming from the Dyson-Schwinger approach. We present first
numerical results for the SU(3) ghost-ghost-gluon vertex renormalization
constant. In addition the spectrum of low-lying eigenvalues and eigenfunctions
of the Faddeev-Popov operator is determined. The saturation of the ghost
propagator in terms of those eigenvalues and eigenmodes is discussed at lower
momenta.


title:
Non-perturbatively Renormalized Light Quark Masses with Two Dynamical
  Fermions

abstract:
  We present the results of a partially quenched lattice QCD calculation of
light quark masses with $N_f=2$ degenerate dynamical flavors. Numerical
simulations are carried out using the plaquette gauge action and the Wilson
quark action at $\beta = 5.8$ ($a^{-1} \simeq 3.2\gev$). The spatial extension
of the $24^3 \times 48$ lattice is about 1.5 fm. Configurations have been
generated at four values of the sea quark masses, for which the ratio of
pseudoscalar over vector meson masses is in the range $M_P/M_V \simeq 0.60 \div
0.75$. An important feature of the present study is the use of non-perturbative
renormalization, performed with the $\ri$ method. The effects of dynamical sea
quarks in the determination of light quark masses have been investigated by
performing a quenched calculation on a similar lattice. Our results for the
average up-down and strange quark masses are $m_{ud}^{MS} (2\gev) = 4.3(4)
(^{+1.1}_{-0.4})\mev$ and $m_s^{MS}(2\gev)=101(8)(^{+25}_{-9}) \mev$. These
values are larger than those obtained by evaluating the quark mass
renormalization constants with one-loop (boosted) perturbation theory. Our
results for the light quark masses are compatible with those obtained in the
quenched simulation. No significant sea quark effects are seen, at the values
of sea quark masses used in the present study.


title: Phase transitions and non-analyticities in large N gauge theories

abstract:
  We investigate numerically various phase transitions and non-analyticities at
large N using both twisted Eguchi-Kawai space-time reduction and the standard
Wilson theory.


title: Partially Twisted Boundary Conditions in Lattice Simulations

abstract:
  We use chiral perturbation theory to investigate twisted and partially
twisted boundary conditions which allow access to momenta other than integer
multiples of 2pi/L on a lattice with spatial volume L^3. For K -> pi pi decays
we show that the breaking of isospin symmetry by the twisted boundary
conditions implies that the amplitudes cannot be determined in general. We find
numerical evidence for the result that the finite volume effects of the
boundary conditions are exponentially suppressed for quantities without final
state interactions (meson masses and meson-to-vacuum matrix elements) in a
simulation with partial twisting on a sea of N_f=2 non-perturbatively improved
Wilson quarks.


title: Magnetic field production after inflation

abstract:
  We study the electromagnetic field production during preheating after hybrid
inflation in a model with the field content of the Standard Model, coupled to a
singlet inflaton. We find that very soon after symmetry breaking our system
enters a regime of kinetic turbulence, characterized by a self-similar
behaviour of the energy spectra and a power-like dependence on time of the
inflaton and Higgs field variances.


title:
3-flavour lattice QCD at finite density and temperature: QCD at finite
  isospin density revisited

abstract:
  We simulate 3-flavour lattice QCD at finite temperature and isospin chemical
potential $\mu_I$. In particular we study the nature of the finite temperature
transition for quark masses close to the critical mass at which this transition
for zero chemical potentials changes from a first order transition to a
crossover. We find that the Binder cumulants, used to determine the position of
this transition, have very strong dt dependence. This leads us to an estimate
of the critical mass which is about 20% below previous estimates. In addition,
when this dt dependence is taken into account, we find that the Binder
cumulants show very little dependence on mu_I. From this we conclude that we do
not as yet see any evidence for the expected critical endpoint. We have argued
previously that the position and nature of the finite temperature transition
for small mu_I should be the same as that for small quark-number chemical
potential mu.


title: Is there a third-order phase transition in quenched QCD?

abstract:
  We discuss the connection between the contributions of large field
configurations and the large order behavior of perturbation theory. For
quenched QCD, the sensitivity of the average plaquette to a removal of large
field configurations has a narrow peak near beta=5.6. Various analysis of the
order 10 weak coupling series for the plaquette give robust indications for a
singularity in the third derivative of the free energy (second derivative of
the plaquette) with respect to beta, near beta = 5.7. We report results of
numerical calculations. The peak in the third derivative of the free energy
present on 4^4 lattices disappears if the size of the lattice is increased
isotropically up to a 10^4 lattice. On the other hand, on 4xL^3 lattices, it
persists when L increases. The location of the peak coincides with the onset of
a non-zero average for the Polyakov loop and seems related to the finite
temperature transition. We also discuss the discrepancy between the
perturbative series and the numerical values of the plaquette.


title: Lattice simulations of Born-Infeld non-linear QED

abstract:
  Born-Infeld non-linear electrodynamics was introduced to render the self
energy of a point particle finite. It has recently been revived as a field
theory for branes and strings. We quantize this theory on a Euclidean
space-time lattice, using Metropolis Monte-Carlo simulations to measure the
properties of the quantum field theory. Luscher-Weisz methods are used to
measure the electromagnetic fields from a static point charge. The D field from
a point charge appears to be identical to that for the normal Maxwell
Lagrangian. The E field is enhanced by quantum fluctuations, and shows short
distance screening as it does in the classical theory.


title: Maximal twist and the spectrum of quenched twisted mass lattice QCD

abstract:
  Results on the hadron masses for a degenerate doublet of up and down quarks
from quenched twisted mass lattice QCD at maximal twist are presented. Two
definitions of maximal twist are used and the hadron masses for these
definitions are compared. Mass splittings within the Delta(1232) multiplet due
to flavor breaking effects are discussed.


title: Scaling test of the P4-improved staggered fermion action

abstract:
  We present a scaling study of the QCD spectrum using a smeared P4 staggered
fermion formulation, in which three, five, and seven-link staples are added to
reduce the effects of flavor symmetry breaking. These studies are performed on
quenched lattices generated using the one-loop improved Symanzik gauge action,
with Beta=10/g^2=7.40,7.75,8.00. The corresponding lattice spacings are a = .31
fm, .21 fm, and .14 fm. Particularly, we study the O(a^2) flavor symmetry
violations in the pion spectrum as well as the scaling dependence of m_rho,
measured in physical units, on lattice spacing. These results are compared
against previous results for the Asqtad action.


title:
What we are learning about the Quark Structure of Hadrons from Lattice
  QCD?

abstract:
  Developments in lattice field theory and computer technology have led to
dramatic advances in the use of lattice QCD to explore the quark structure of
hadrons. This talk will describe selected examples, including structure
functions, electromagnetic form factors, the nucleon axial charge, the origin
of the nucleon spin, the transverse structure of the nucleon, and the nucleon
to Delta transition form factor.


title: Hadron Structure from Lattice QCD

abstract:
  The structure of neutrons, protons, and other strongly interacting particles
is now being calculated in full, unquenched lattice QCD with quark masses
entering the chiral regime. This talk describes selected examples, including
the nucleon axial charge, structure functions, electromagnetic form factors,
the origin of the nucleon spin, the transverse structure of the nucleon, and
the nucleon to Delta transition form factor.


title: The Quark Structure of Pentaquarks

abstract:
  Motivated by the possible observation of the $\Theta^+(1530)$, we study the
quark structure of pentaquark states in quenched lattice QCD. The complete set
of 19 local sources that have the proper symmetry for positive or negative
parity isoscalar pentaquarks is constructed, as well as a nonlocal source
composed of two displaced ``good'' diquarks. Quantitative structure information
is determined from diagonalizing the 19-dimensional correlation matrix and from
calculating the overlaps of sources with the lattice eigenstates. The volume
dependence of the overlap is studied to differentiate between scattering and
localized resonant states. The positive parity state has a small component of
two ``good'' diquarks, and its energy is too much higher than the negative
parity state to be a candidate for the $\Theta^+(1530)$.


title: Performance of machines for lattice QCD simulations

abstract:
  We review the architecture of massively parallel machines used for lattice
QCD simulations and present benchmarks for the performance of popular
algorithms on these platforms. We cover commercial supercomputers, PC clusters,
and custom-designed machines. We also speculate on future developments.


title: Spatial string tension revisited

abstract:
  The spatial string tension, a classic non-perturbative probe for the
convergence of the weak-coupling expansion at high temperatures, can be
determined in full QCD as well as in a dimensionally reduced effective theory.
Comparing both approaches, we find surprisingly good agreement almost down to
the critical temperature of the deconfinement phase transition.


title:
Vortex-Line Percolation in the Three-Dimensional Complex Ginzburg-Landau
  Model

abstract:
  We study the phase transition of the three-dimensional complex |psi|^4 theory
by considering the geometrically defined vortex-loop network as well as the
magnetic properties of the system in the vicinity of the critical point. Using
high-precision Monte Carlo techniques we examine an alternative formulation of
the geometrical excitations in relation to the global O(2)-symmetry breaking,
and check if both of them exhibit the same critical behavior leading to the
same critical exponents and therefore to a consistent description of the phase
transition. Different percolation observables are taken into account and
compared with each other. We find that different definitions of constructing
the vortex-loop network lead to different results in the thermodynamic limit,
and the percolation thresholds do not coincide with the thermodynamic phase
transition point.


title: $1^{-+}$ exotic meson at light quark masses

abstract:
  The mass of the $1^{-+}$ exotic meson, created with hybrid interpolating
fields, is explored at light quark masses approaching 25 MeV ($m_\pi / m_\rho
\simeq 1/3$). Access to such light quark masses is facilitated by the use of
the Fat-Link Irrelevant Clover (FLIC) fermion action. Additionally, we make use
of large ($20^3 \times 40$) lattices to obtain good control of statistical and
finite volume errors. Our results indicate that the $1^{-+}$ exotic exhibits
significant curvature close the chiral limit, indicating previous linear
extrapolations, far from the chiral regime, have overestimated the mass of the
$1^{-+}$. We find for the first time in lattice studies a $1^{-+}$ mass in
agreement with the $\pi_1 (1600)$ candidate. We also find a strangeness $\pm$1
$J^P = 1^-$ state with a mass close to 2 GeV.


title: Non-perturbative plaquette in 3d pure SU(3)

abstract:
  We present a determination of the elementary plaquette and, after the
subsequent ultraviolet subtractions, of the finite part of the gluon
condensate, in lattice regularization in three-dimensional pure SU(3) gauge
theory. Through a change of regularization scheme to MSbar and a matching back
to full four-dimensional QCD, this result determines the first non-perturbative
contribution in the weak-coupling expansion of hot QCD pressure.


title: B meson decays at high velocity from mNRQCD

abstract:
  The moving NRQCD (mNRQCD) formalism facilitates the simulation of heavy meson
decays at large recoil. We present preliminary results for a number of
quantities including the energy splittings and the $B$ meson decay constant
that demonstrate that the formalism is accurate over a range of momenta.


title: The Exotic Baryon Theta^+(1540) on the Lattice

abstract:
  We report on a study of the pentaquark Theta^+(1540), using a variety of
different interpolating fields. We use Chirally Improved fermions in
combination with Jacobi smeared quark sources to improve the signal and get
reliable results even for small quark masses. The results of our quenched
calculations, which have been done on a 12^3x24 lattice with a lattice spacing
of a=0.148 fm, do not provide any evidence for the existence of a Theta^+ with
positive parity. We do observe, however, a signal compatible with nucleon-kaon
scattering state. For the negative parity the results are inconclusive, due to
the potential mixture with nucleon-kaon and N*-kaon scattering states.


title: Heavy two- and three-quark free energies at finite $T$

abstract:
  We investigate the behaviour of heavy $QQ$- and $QQQ$-free energies in SU(3)
pure gauge theory at finite temperature. After stating some general properties
of the free energies, we discuss the $QQ$-antitriplet and -sextet channels as
well as free energies in different $QQQ$-channels. We perform a detailed finite
volume scaling analysis of $QQ$-free energies below and above $T_c$. Moreover,
we also discuss the relation of the $QQ$-antitriplet to the $Q\bar Q$-singlet
free energies. A comparison of the effective running coupling indicates that
the $r$-dependence of the free energies differs by a factor of two in agreement
with the different Casimir factors. We observe that the baryonic free energies
can be decomposed into a sum of two particle interactions.


title: UV-filtered overlap fermions

abstract:
  We discuss the kernel spectrum, locality properties and the axial-vector
renormalization constant of UV-filtered overlap fermions. We find that
UV-filtered overlap fermions have a better conditioned kernel, better locality
and an axial-vector renormalization constant closer to 1 than their unfiltered
counterparts, even if the shift parameter $\rho$ is simply set to 1.


title: Evaporation/Condensation of Ising Droplets

abstract:
  Recently Biskup et al. [Europhys. Lett. 60 (2002) 21] studied the behaviour
of d-dimensional finite-volume liquid-vapour systems at a fixed excess $\delta
N$ of particles above the ambient gas density. They identify a dimensionless
parameter $\Delta (\delta N)$ and a universal constant $\Delta_\mathrm{c}(d)$
and show that for $\Delta < \Delta_c$ a droplet of the dense phase occurs while
for $\Delta > \Delta_c$ the excess is absorbed in the background. The fraction
$\lambda_\Delta$ of excess particles forming the droplet is given explicitly.
Furthermore, they state, that the same is true for solid-gas systems.
  To verify these results, we have simulated the spin-1/2 Ising model on a
square lattice at constant magnetisation equivalent to a fixed particle excess
in the lattice-gas picture. We measured the largest minority droplet,
corresponding to the solid phase, at various system sizes ($L=40, ..., 640$).
Using analytic values for the spontaneous magnetisation $m_0$, the
susceptibility $\chi$ and interfacial free energy $\tau_\mathrm{W}$ for the
infinite system, we were able to determine $\lambda_\Delta$ in very good
agreement with the theoretical prediction.


title: Searching for diquarks in hadrons

abstract:
  Since the early days of QCD, it has been argued that inside hadrons quarks
organise into substructures. Among those, popular pictures of various phenomena
(including exotica and colour superconductivity) give a prominent role to
diquarks, i.e. to colour antitriplet combinations of two quarks. Using a
gauge-invariant setup, which combines the diquark with a static quark, we study
spatial correlations of the two light quarks inside the diquark. After
illustrating the setup, we discuss our first results for both the scalar
(``good'') and the spin one (``bad'') diquark channels. In a regime in which
$m_{\pi} \simeq 830$ MeV, our data show unambiguously that a scalar diquark
forms with a size of $\simeq$ 0.9 fm. For the vector diquark we are able to put
a lower bound of 4.1(7) fm on its size. We also investigate the mass splitting
between the good and the bad diquark; our findings are compatible with
phenomenologically inspired predictions for this quantity.


title: Center Vortex Model for SU(3) Yang-Mills Theory

abstract:
  The center vortex model for the infrared sector of SU(3) Yang-Mills theory is
reviewed. After discussing the physical foundations underlying the model, some
technical aspects of its realisation are discussed. The confining properties of
the model are presented in some detail and compared to known results from full
lattice Yang-Mills theory. Particular emphasis is put on the new phenomenon of
vortex branching, which is instrumental in establishing first order behaviour
of the SU(3) phase transition. Finally, the vortex free energy is verified to
furnish an order parameter for the deconfinement phase transition. It is shown
to exhibit a weak discontinuity at the critical temperature, in agreement with
predictions from lattice gauge theory.


title: Charmonium spectral functions in Nf=2 QCD

abstract:
  We report on a study of charmonium at high temperature in 2-flavour QCD. This
is the first such study with dynamical fermions. Using an improved anisotropic
lattice action, spectral functions are extracted from correlators in the vector
and pseudoscalar channels. No signs of medium-induced suppression of the ground
states are seen for temperatures up to 1.5T_c, while at T~2T_c there are clear
signs of modifications. The current systematic and statistical uncertainties in
our data, in particular the relatively coarse lattice and small volume, do not
allow us to draw a firm conclusion at this stage.


title:
RG decimation-based approach to confinement and computation on coarser
  lattices

abstract:
  A systematic procedure is presented for connecting short to long scales in
LGT. Approximate decimations are used which can provide both upper and lower
bounds on the partition function. Its exact value is then obtained by
interpolation between the bounds. By iterating the procedure representations of
the partition function as well as other physical quantities can be obtained on
progressively coarser lattices. For SU(2) IR flow into the confining strong
coupling regime results for any initial $\beta$.


title: Chiral limit of 2-color QCD at strong couplings

abstract:
  We study two-color lattice QCD with massless staggered fermions in the strong
coupling limit using a new and efficient cluster algorithm. We focus on the
phase diagram of the model as a function of temperature $T$ and baryon chemical
potential $\mu$ by working on $L_t \times L^d$ lattices in both $d=2,3$. In
$d=3$ we find that at $\mu=0$ the ground state of the system breaks the global
U(2) symmetry present in the model to U(1), while the finite temperature phase
transition (with $L_t=4$) which restores the symmetry is a weak first order
transition. In $d=2$ we find evidence for a novel phase transition similar to
the Berezinky-Kosterlitz-Thouless phenomena. On the other hand the quantum
(T=0) phase transition to a symmetric phase as a function of $\mu$ is second
order in both $d=2,3$ and belongs to the mean field universality class.


title:
Chiral phase transition as an Anderson transition 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. For two massless quark flavors we observe that at the
chiral phase transition, both the low lying eigenmodes and the spectrum of the
QCD Dirac operator resemble those of a disordered conductor at the Anderson
transition. In particular we present results showing that the eigenvectors are
multifractal and the spectral correlations are well described by critical
statistics. We also find an additional temperature dependent mobility edge
located in the bulk of the spectrum with properties quantitatively similar to
those of a 3D disordered conductor at the Anderson transition. This feature is
present in both quenched and unquenched simulations. Finally we argue that our
findings are not in principle restricted to the ILM approximation and may also
be found in lattice simulations.


title: QCD Level Density from Maximum Entropy Method

abstract:
  We propose a method to calculate the QCD level density directly from the
thermodynamic quantities obtained by lattice QCD simulations with the use of
the maximum entropy method (MEM). Understanding QCD thermodynamics from QCD
spectral properties has its own importance. Also it has a close connection to
phenomenological analyses of the lattice data as well as experimental data on
the basis of hadronic resonances. Our feasibility study shows that the MEM can
provide a useful tool to study QCD level density.


title: Electromagnetic mass difference on the lattice

abstract:
  We calculate electromagnetic mass difference of mesons using a method
proposed by Duncan {\it et al}. The RG-improved gauge action and the
non-compact Abelian gauge action are employed to generate configurations. Quark
propagators in the range of $m_{PS}/m_{V}=0.76-0.51$ are obtained with the
meanfield-improved clover quark action. Chiral and continuum extrapolations are
performed and the results are compared with experiments. Finite size effects
are also examined. Quark masses are extracted from the measured spectrum. Our
preliminary values for light quark masses are $m_{u}^{\bar{MS}}(\mu =2 {GeV}) =
3.03(19)$ MeV, $m_{d}^{\bar{MS}}(\mu = 2 {GeV}) = 4.44(28)$ MeV,
$m_{s}^{\bar{MS}}(\mu = 2 {GeV}) = 99.2(52)$ MeV.


title: Lattice QCD Evidence for Exotic Tetraquark Resonance

abstract:
  We study the manifestly exotic tetraquark D$_{\rm s0}^{++}(cu\bar s \bar d)$
and the scalar tetraquark $f_0(ud \bar u \bar d)$ in SU(3)$_c$ anisotropic
quenched lattice QCD with the $O(a)$-improved Wilson (clover) fermion with
various quark masses including the idealized SU(4)$_f$ case. For $f_0(ud\bar u
\bar d)$ etc., we only consider connected diagrams at the quenched level, i.e.,
the tetraquark $f_0(ud\bar u\bar d)$ is identical with D$_{\rm s0}^{++} (cu\bar
s \bar d)$ in the idealized SU(4)$_f$ case. First, for comparison, we study the
lowest $q\bar q$ scalar meson, and find that it has a large mass of about
1.37GeV after chiral extrapolation, which corresponds to $f_0(1370)$. Second,
we investigate the lowest 4Q state in the spatial periodic boundary condition,
and find that it is just a scattering state of two pseudoscalar mesons, as is
expected. Third, to extract spatially-localized 4Q resonances, we use the
Hybrid Boundary Condition (HBC) method, where anti-periodic and periodic
boundary conditions are imposed on quarks ($c$,$u$) and antiquarks ($\bar
s$,$\bar d$), respectively. By applying the HBC on a finite-volume lattice, the
threshold of the two-meson scattering state is raised up, while the mass of a
compact 4Q resonance is almost unchanged. In HBC, we find a nontrivial 4Q
resonance state about 100 MeV below the two-meson threshold in some quark-mass
region. Its chiral behavior largely differs from a two-meson scattering state.
The scalar tetraquark $f_0(ud\bar u\bar d)$ is found to have the mass of about
1.1GeV after chiral extrapolation, and seems to correspond to $f_0(980)$. Then,
the manifestly exotic tetraquark D$_{\rm s0}^{++}(cu\bar s \bar d)$ would exist
around 1GeV in the idealized SU(4)$_f$ chiral limit. Finally, MEM analysis is
applied to obtain the spectral function of the 4Q system.


title: Critical temperature in QCD with two flavors of dynamical quarks

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


title: Neutron electric dipole moment on the lattice

abstract:
  We carry out a feasibility study toward a lattice QCD calculation of the
neutron electric dipole moment (NEDM) in the presence of the $\theta$ term
using two different approaches. In the first method, we calculate the CP-odd
electromagnetic form factor $F_3$, which becomes the NEDM in the zero momentum
transfer limit. At the first order in $\theta$, we derive a formula connecting
the lattice three-point function to the CP-odd electromagnetic form factor. In
the second method we directly extract the NEDM from the energy difference
between spin-up and spin-down neutron states in the presence of a constant
electric field, without expanding a small but non-zero $\theta$. We test both
approaches numerically, employing the domain-wall quark action with the RG
improved gauge action in quenched QCD at $a^{-1}\simeq 2$ GeV on a $16^3\times
32\times 16$ lattice, and further applying the second method to the clover
quark action at a similar lattice spacing and nucleon mass. We obtain good
signals from both approaches. In particular the second method works well with
both fermion formulations.


title:
Electromagnetic properties of hadrons with two flavors of dynamical
  domain wall fermions

abstract:
  We present the determination of the light quark masses using electromagnetic
splittings of pions and kaons. The meson masses are calculated on $SU(3)\times
U(1)$ gauge configurations, where SU(3) gauge fields include sea quark effects
of two degenerate flavors and the U(1) gauge fields are incorporated in
non-compact form. Possible sources of systematic uncertainty are discussed.


title: Density-density correlators using all-to-all propagators

abstract:
  We present a study of gauge invariant density-density correlators.
Density-density correlators probe hadron wave functions and thus can be used to
study hadron deformation. Their zero momentum projection requires the
computation of all-to-all propagators, which are evaluated with the standard
stochastic technique, the dilution method and the stochastic sequential
technique. We compare the results to a previous analysis that did not employ
the zero momentum projection.


title:
Dynamical supersymmetry breaking and phase diagram of the lattice
  Wess-Zumino model

abstract:
  We study dynamical supersymmetry breaking and the transition point by
non-perturbative lattice techniques in a class of two-dimensional N=1
Wess-Zumino model. The method is based on the calculation of rigorous lower
bounds on the ground state energy density in the infinite-lattice limit. Such
bounds are useful in the discussion of supersymmetry phase transition. The
transition point is determined with this method and then compared with recent
results based on large-scale Green Function Monte Carlo simulations with good
agreement.


title:
A new method for computation of QCD thermodynamics: EOS, specific heat
  and speed of sound

abstract:
  We propose a new variant of the operator method for the computation of the
equation of state of QCD, which yields positive pressure for all temperatures
and all values of temporal lattice spacings. Using this new method, we
calculate the continuum limit of pressure, energy density, entropy density,
specific heat, and the speed of sound, in quenched QCD, for 0.9 \le T/T_c \le
3.


title: Heavy quark masses from Fermilab Fermions

abstract:
  Using automated perturbation theory techniques, we have computed the one-loop
mass of Fermilab fermions, with an improved gluon action. We will present the
results of these calculations, and the resulting predictions for the charm and
bottom quark masses in the MSbar scheme. We report mc(mc) = 1:22(9) GeV and
mb(mb) = 4:7(4) GeV. In addition we present results for the one-loop
coeffcients of the Fermilab action.


title: J/\Psi at high temperatures in anisotropic lattice QCD

abstract:
  J/\Psi and \eta_c above the QCD critical temperature T_c are studied in
anisotropic quenched lattice QCD, considering whether the c\bar c systems above
T_c are compact quasi-bound states or scattering states. We adopt the standard
Wilson gauge action and O(a)-improved Wilson quark action with renormalized
anisotropy a_s/a_t =4 at \beta=6.10 on 16^3\times (14-26) lattices, which
correspond to the spatial lattice volume V\equiv L^3\simeq(1.55{\rm fm})^3 and
temperatures T\simeq(1.11-2.07)T_c. To clarify whether compact charmonia
survive in the deconfinement phase, we investigate spatial boundary-condition
dependence of the energy of the c\bar c systems above T_c. In fact, for
low-lying c \bar c scattering states, there appears a significant energy
difference \Delta E \equiv E{\rm (APBC)}-E{\rm (PBC)} between periodic and
anti-periodic boundary conditions as \Delta
E\simeq2\sqrt{m_c^2+3\pi^2/L^2}-2m_c (m_c: charm quark mass) on the
finite-volume lattice. In contrast, for compact charmonia, there is no
significant energy difference between periodic and anti-periodic boundary
conditions. As a lattice QCD result, we find almost no spatial
boundary-condition dependence for the energy of the c\bar c system in J/\Psi
and \eta_c channels for T\simeq(1.11-2.07)T_c, which indicates that J/\Psi and
\eta_c would survive as compact c\bar c quasi-bound states below 2T_c.


title: Status of the APENet project

abstract:
  We present the current status of APENet, our custom 3-dimensional
interconnect architecture for PC clusters environment. We report some
micro-benchmarks on our recent large installation as well as new developments
on the software and hardware side. The low level device driver has been
reworked by following a custom hardware RDMA architecture, and MPICH-VMI, an
implementation of the MPI library, has been ported to APENet.


title: Dynamical twisted mass fermions

abstract:
  We summarize four contributions about dynamical twisted mass fermions. The
resulting report covers results for N_f=2 obtained from three different gauge
actions, namely the standard Wilson plaquette gauge action, the DBW2 and the
tree-level Symanzik improved gauge action. In addition, first results for
N_f=2+1+1 flavours of twisted mass fermions are discussed.


title: Monte-Carlo simulation of the chiral Gross-Neveu model

abstract:
  We investigate the two flavor chiral Gross-Neveu model in the Schroedinger
functional on the lattice. The procedure necessary to recover chiral symmetry
in the continuum limit of this model with Wilson fermions is discussed. We
introduce several useful observables and present a first demonstration of the
feasibility of Monte-Carlo simulations in this model.


title: Structure of the Pion from Full Lattice QCD

abstract:
  Moments of generalised parton distributions can be related to off-forward
matrix elements of local operators. We calculate a few of the leading twist
matrix elements for the pion on the lattice. The simulations are performed
using two flavours of dynamical fermions and a range of pion masses from 550 to
1090 MeV. Our lattice spacings and spatial volumes lie in the range 0.07-0.12
fm and (1.6-2.2 fm)^3, respectively. Key features of our investigation are the
use of O(a) improved Wilson fermions and non-perturbative renormalisation. We
present first results for the two lowest moments of the generalised parton
distributions of the pion and compare the pion electromagnetic form factor F_pi
to experimental data. Good agreement is found between lattice data and
experiment.


title:
The Gluon Propagator in Lattice Landau Gauge with twisted boundary
  conditions

abstract:
  We investigate the infrared behaviour of the gluon propagator in Landau gauge
on a lattice with twisted boundary conditions. Analytic calculations using
Dyson-Schwinger equations, exact renormalization group and stochastic
quantization show that the gluon propagator in Landau gauge approaches zero for
small momentum. On the other hand lattice calculations and calculations on a
four-torus seem to give rise to a non-zero limit. One possible reason for this
difference is the existence of zero-momentum fluctuation modes which
potentially give a massive contribution to the gluon propagator. Our
simulations show that with twisted boundary conditions these zero-momentum
modes are suppressed and the gluon propagator becomes smaller than in a
periodic ensemble.


title: $\Delta I = 3/2$ kaon weak matrix elements with non-zero total momentum

abstract:
  We present preliminary results for the $\Delta I = 3/2$ kaon decay matrix
elements using domain wall fermions and the DBW2 gauge action at one coarse
lattice spacing corresponding to $a^{-1} = 1.3$ GeV. We employ an extention of
the Lellouch and L\"uscher formula for non-zero total momentum to extract the
infinite volume, center-of-mass system decay amplitudes. We compare the result
of $\mathrm{Re}A_2$ with previous results calculated by several methods, and
experiment. We also show the I=2 $\pi\pi$ scattering phase shift.


title: Dirac-K\"{a}hler fermions and exact lattice supersymmetry

abstract:
  We discuss a new approach to putting supersymmetric theories on the lattice.
The basic idea is to start from a {\it twisted} formulation of the underlying
supersymmetric theory in which the fermions are represented as grassmann valued
antisymmetric tensor fields. The original supersymmetry algebra is replaced by
a twisted algebra which contains a scalar nilpotent supercharge $Q$.
Furthermore the action of the theory can then be written as the $Q$-variation
of some function. The case of ${\cal N}=2$ super Yang-Mills theory in two
dimensions is discussed in some detail. We then present our proposal for
discretizing this theory and derive the resultant lattice action. The latter is
local, free of spectrum doubling, gauge invariant and preserves the scalar
supercharge invariance exactly. Some preliminary numerical results are then
presented. The approach can be naturally generalized to yield a lattice action
for ${\cal N}=4$ super Yang-Mills in four dimensions.


title: Update on pi and K Physics

abstract:
  We present an update of the MILC studies of the physics of light
pseudoscalars using improved staggered fermions. New runs at lighter quark
mass, as well as increased statistics for older sets, are enabling us to
improve the results for decay constants in full QCD. In addition, we have
analyzed quenched runs at two different lattice spacings. This makes possible a
test of the applicability of staggered chiral perturbation theory in a
different context.


title:
Bottomonia correlators and spectral functions at zero and finite
  temperature

abstract:
  We present preliminary studies of bottomonia spectral functions at zero and
finite temperature using quenched anisotropic lattices. The heavy quark is
treated within Fermilab approach. We find no modification of the $\eta_b$ and
$\Upsilon$ states up to temperatures $2.3T_c$ while our study suggest
dissolution of $\chi_b$ state at $1.15T_c$.


title: The volume dependence of spectral weights and the pentaquark state

abstract:
  Before studying the pentaquark system we examine the spectral weights of the
two lowest scattering states in the two-pion system in the isospin I=2 channel
on lattices of size $16^3\times 32$, $24^3 \times 32$ and $32^3 \times 64$ at
$\beta=6.0$ in the quenched theory. We find that the spectral weights scale
with the volume for large time separations. Therefore very accurate data are
necessary in order that the spectral weights determined on different volumes
yield a ratio that is precise enough to distinguish a scattering state from a
single particle state. The pentaquark system is studied on the same lattices
and scaling of the spectral weights of the low lying state is investigated. The
accuracy of the results obtained for the scaling of spectral weights do not
allow us to exclude a pentaquark resonance.


title: A study of the N to Delta transition form factors in full QCD

abstract:
  The N to Delta transition form factors GM1, GE2 and GC2 are evaluated using
dynamical MILC configurations and valence domain wall fermions at three values
of quark mass corresponding to pion mass 606 MeV, 502 MeV and 364 MeV on
lattices of spatial size $20^3$ and $28^3$. The unquenched results are compared
to those obtained at similar pion mass in the quenched theory.


title: Fermionic observables in Numerical Stochastic Perturbation Theory

abstract:
  We present technical details of fermionic observables computations in NSPT.
In particular we discuss the construction of composite operators starting from
the inverse Dirac operator building block, the subtraction of UV divergences
and the treatment of irrelevant contributions in extracting the continuum
limit.


title: Light hadron spectrum and quark masses in 2+1 flavor QCD

abstract:
  CP-PACS and JLQCD collaborations are carrying out a joint project of the 2+1
flavor full QCD simulation. Gauge configurations are generated for the
non-perturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge
action using PHMC algorithm at three lattice spacings, $a\sim 0.076$, 0.010 and
0.122 fm, with a fixed physical volume $(2.0 fm)^3$. We present analysis for
the light meson spectrum and quark masses in the continuum limit, which are
determined using data obtained from the simulations at the two coarser
lattices. Our simulations reproduce experimental values of meson masses. The ud
and strange quark masses turn out to be $m_{ud}^{\bar{MS}}(\mu=2 GeV)=3.34(23)
MeV$ and $m_s^{\bar{MS}}(\mu=2 GeV)=86.7(5.9) MeV$. We also show preliminary
results at our finest lattice spacing for which simulations are still being
continued.


title: The canonical approach to Finite Density QCD

abstract:
  We present a canonical approach to study properties of QCD at finite baryon
density rho, and apply it to the determination of the phase diagram of
four-flavour QCD. For a pion mass of about 350 MeV, the first-order transition
between the hadronic and the plasma phase gives rise to a co-existence region
in the T-rho plane, which we study in detail. We obtain accurate results for
systems containing up to 30 baryons and quark chemical potentials mu up to 2T.
Our T-mu phase diagram agrees with the literature when mu/T < 1. At larger
chemical potential, we observe a ``bending down'' of the phase boundary. We
characterise the two phases with simple models: the hadron resonance gas in the
hadronic phase, the free massless quark gas in the plasma phase.


title: Perturbative renormalisation of the chiral Gross-Neveu model

abstract:
  We study the chiral Gross-Neveu model with Wilson fermions. In the framework
of the Schroedinger functional we show that in general not only the bare mass
has to be tuned to achieve chiral symmetry in the continuum, but also coupling
constants multiplying chirally non-invariant four fermion terms. The strategy
for fixing the parameters of the theory is explained in perturbation theory and
the results of a first order calculation are presented. The results are shown
to agree with the infinite flavour limit.


title: Anisotropic lattice QCD study of pentaquark baryons in spin 3/2 channel

abstract:
  We perform the comprehensive analysis of the pentaquark (5Q) in J^P=3/2^{\pm}
channel using anisotropic quenched lattice QCD. We employ the standard Wilson
gauge action at \beta=5.75 and the O(a) improved Wilson (clover) quark action
on a 12^3*96 lattice with the renormalized anisotropy as a_s/a_t = 4. A large
number of gauge configurations as Nconf=1000 is analyzed, which is found to be
essential to achieve a reliable measurement. We study three types of the
Rarita-Schwinger intepolationg fields with I=0: (a) the NK*-type, (b) the
(color-)twisted NK*-type, (c) a diquark-type. As a result, we find only massive
states as m(5Q)= 2.1-2.2 GeV in J^P=3/2^- channel, and m(5Q) = 2.4-2.6 GeV in
J^P=3/2^+ channel in the chiral limit. The analysis with the hybrid boundary
condition (HBC) is performed to distinguish whether these resonances are
compact 5Q resonances or two-particle scattering states. No low-lying compact
5Q resonance states are found below 2.1GeV.


title: The Scaling of QED in a Non-Commutative Space-Time

abstract:
  We present results of numerical simulations for pure U(1) gauge theory in a
non-commutative space. The theory is mapped onto a dimensionally reduced matrix
model, which renders its numerical treatment feasible. New data on large
lattices reveal the scaling of Wilson loops and their correlation functions in
the simultaneous limit to the continuum and to infinite volume, at fixed
non-commutativity. In this on-going project we are particularly interested in
the IR behaviour, the ``photo-ball'' spectrum and in the photon dispersion
relation.


title: A toy model of (grand) unified monopoles

abstract:
  We explore the old idea that, in a theory containing several gauge groups,
the topological defects of one gauge group coincide with those of another gauge
group. This simple 'unification' constraint has deep consequences, the best
known of which is a natural explanation of the fractional electric charge of
quarks. Here we explore the consequences of this idea for the phase diagram, in
a toy model U(1)x U(1).


title: Search for the S=+1 pentaquarks in quenched lattice QCD

abstract:
  We study spin $\frac12$ hadronic states in quenched lattice QCD to search for
a possible $S=+1$ pentaquark resonance. Our work is the first systematic
lattice QCD study which properly carries out the following analyses: {\it (1)
the careful extraction of the first two low energy states with very high
statistics and the variational method} and {\it (2) the study of volume
dependences of eigenenergies and spectral weights to distinguish resonance
states from scattering states}.
  Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times
24$ and $16^3\times 24$ lattices at $\beta$=5.7 with the standard plaquette
gauge action and the Wilson quark action. Our result indicates the existence of
a resonance state lying slightly above the NK threshold in
$(I,J^P)=(0,\frac12^-)$ channel in quenched QCD.


title:
Leibniz rule and exact supersymmetry on lattice: a case of
  supersymmetrical quantum mechanics

abstract:
  We propose a new formulation of lattice theory. It is given by a matrix form
and suitable for satisfying Leibniz rule on lattice. The theory may be
interpreted as a multi-flavor system. By realizing the difference operator as a
commutator, we may obtain exact supersymmetric theories on lattice explicitly.
Some problems such as locality and single flavor reduction are also commented.


title:
Heavy quark free energies and screening at finite temperature and
  density

abstract:
  We study the free energies of heavy quarks calculated from Polyakov loop
correlation functions in full 2-flavour QCD using the p4-improved staggered
fermion action. A small but finite Baryon number density is included via Taylor
expansion of the fermion determinant in the Baryo-chemical potential mu. For
temperatures above Tc we extract Debye screening masses from the large distance
behaviour of the free energies and compare their mu-dependence to perturbative
results.


title: The critical end point of quantum chromodynamics

abstract:
  We investigate the critical end point (CEP) of QCD with
  two flavours of light dynamical quarks at finite lattice cutoff
  a=1/4T using a Taylor expansion of the baryon number
  susceptibility. We find a strong volume dependence of the position
  of the critical end point. In the large volume limit we obtain\
  T^E/T_c approximately 0.95 and mu_B^E/T^E approximately 1.1, where T_c is
  the cross over temperature at zero chemical potential, and T^E
  and mu_B^E are the temperature and the baryon chemical potential
  at the critical end point. The small value of mu_B^E places it
  in the range of observability in energy scans at the RHIC.


title: Lattice QCD with light Wilson quarks

abstract:
  Wilson's formulation of lattice QCD is attractive for many reasons, but
perhaps mainly because of its simplicity and conceptual clarity. Numerical
simulations of the Wilson theory (and of its improved versions) tend to be
extremely demanding, however, to the extent that they rapidly become
impractical at small quark masses. Recent advances in simulation algorithms now
allow such simulations to be pushed to significantly smaller masses without
having to compromise in other ways. Contact with chiral perturbation theory can
thus be made and many physics questions can be addressed that previously
appeared to be inaccessible.


title: Searching for the critical endpoint in QCD with two quark flavors

abstract:
  I present a method which can be used to locate the expected critical endpoint
of the phase diagram of QCD with two light quark flavors. I illustrate the
ideas on a suitable Random Matrix Model and show preliminary results in QCD


title: A (P)HMC algorithm for N_f = 2 + 1 + 1 flavours of twisted mass fermions

abstract:
  We present a detailed design of a (P)HMC simulation algorithm for N_f = 2 + 1
+ 1 maximally twisted Wilson quark flavours. The algorithm retains even/odd and
mass-shift preconditionings combined with multiple Molecular Dynamics time
scales for both the light mass degenerate, u and d, quarks and the heavy mass
non-degenerate, s and c, quarks. Various non-standard aspects of the algorithm
are discussed, among which those connected to the use of a polynomial
approximation for the inverse (square root of the squared) Dirac matrix in the
s and c quark sector.


title: Four quark operators in maximally twisted Wilson LQCD

abstract:
  We discuss how the peculiar properties of maximally twisted Wilson fermions
can be exploited to set up a consistent LQCD computational scheme in which the
CP-conserving matrix elements of the $\Delta S =1,2$ effective weak Hamiltonian
can be evaluated without mixing with wrong-chirality and/or -parity operators.
The proposed lattice framework guarantees automatic O($a$) improvement and
positive determinant also for pairs of non-degenerate quarks.


title:
Zero density heavy quark SU(2) gauge theory and the Stefan-Boltzmann
  limit

abstract:
  SU(2) lattice gauge theory is investigated where the traces of the Wilson
lines at any lattice point and along each direction is constrained to zero.
Hence, each of the lattice configurations possesses a vanishing density of
heavy (anti-) quarks. The results are compared with those of pure SU(2) gauge
theory which can be interpreted as the grand canonical realization of the heavy
quark theory where only the ensemble average of the heavy quark density
vanishes.
  The static quark anti-quark potential of the constrained theory is obtained
from (spatially smeared) Wilson loops at zero temperature. We find that the
potential coincides with that of pure SU(2) gauge theory (without constraints).
Hence, the familiar "running" of the lattice spacing with beta is recovered.


title: Four-loop plaquette in 3d with a mass regulator

abstract:
  The QCD free energy can be studied by dimensional reduction to a
three-dimensional (3d) effective theory, whereby non-perturbative lattice
simulations become less demanding. To connect to the original QCD a
perturbative matching computation is required, which is conventionally carried
out in dimensional regularization. Therefore the 3d lattice results need to be
converted to this regularization scheme as well. The conversion must be carried
up to 4-loop order, where the free energy displays an infrared (IR)
singularity. We therefore need a regulator which can be implemented both on the
lattice and in the continuum computation. We introduce a mass regulator to
perform Numerical Stochastic Perturbation Theory computations. Covariant gauge
is fixed in the Faddeev-Popov scheme without introducing any ghost fields.


title: Wilson fermions quark bilinears to three loops

abstract:
  Quark currents renormalization constants can in principle be safely computed
in lattice perturbation theory. In practice, traditional lattice perturbative
computations are quite cumbersome, so that so far only the first loop results
were available. By making use of Numerical Stochastic Perturbation Theory we
reached three (and with less statistical precision even four) loops, both in
quenched and in unquenched theory. Convergence properties of the series can be
assessed and omparison with non perturbative results (where available) can be
made: high loops computations of renormalization constants can be a valuable
tool for lattice QCD.


title:
A determination of the strange quark mass for unquenched clover fermions
  using the AWI

abstract:
  Using the O(a) Symanzik improved action an estimate is given for the strange
quark mass for unquenched (nf=2) QCD. The determination is via the axial Ward
identity (AWI) and includes a non-perturbative evaluation of the
renormalisation constant. Numerical results have been obtained at several
lattice spacings, enabling the continuum limit to be taken. Results indicate a
value for the strange quark mass (in the MSbar-scheme at a scale of 2GeV) in
the range 100 - 130MeV.


title:
Scaling behavior of discretization errors in renormalization and
  improvement constants

abstract:
  Non-perturbative results for improvement and renormalization constants needed
for on-shell and off-shell O(a) improvement of bilinear operators composed of
Wilson fermions are presented. The calculations have been done in the quenched
approximation at beta=6.0, 6.2 and 6.4. To quantify residual discretization
errors we compare our data with results from other non-perturbative
calculations and with one-loop perturbation theory.


title: B_s meson excited states from the lattice

abstract:
  This is a follow-up to our earlier work [Phys. Rev. D 65, 014512 (2002); Eur.
Phys. J. C 28, 79 (2003); Phys. Rev. D 69, 094505 (2004)] for the energies and
the charge (vector) and matter (scalar) distributions for S-wave states in a
heavy-light meson, where the heavy quark is static and the light quark has a
mass about that of the strange quark. We study the radial distributions of
higher angular momentum states, namely P- and D-wave states. In nature the
closest equivalent of this heavy-light system is the B_s meson.
  The calculation is carried out with dynamical fermions on a 16^3 times 32
lattice with a lattice spacing of about 0.10 fm generated with the
non-perturbatively improved clover action. It is shown that several features of
the energies and radial distributions are in qualitative agreement with what
one expects from a simple one-body Dirac equation interpretation.


title:
Field Theory Simulations on a Fuzzy Sphere - an Alternative to the
  Lattice

abstract:
  We explore a new way to simulate quantum field theory, without introducing a
spatial lattice. As a pilot study we apply this method to the 3d \lambda \phi^4
model. The regularisation consists of a fuzzy sphere with radius R for the two
spatial directions, plus a discrete Euclidean time. The fuzzy sphere
approximates the algebra of functions of the sphere with a matrix algebra, and
the scalar field is represented by a Hermitian N x N matrix at each time site.
We evaluate the phase diagram, where we find a disordered phase and an ordered
regime, which splits into phases of uniform and non-uniform order. We discuss
the behaviour of the model in different limits of large N and R, which lead to
a commutative or to a non-commutative \lambda \phi^4 model in flat space.


title:
Renormalization-group blocking the fourth root of the staggered
  determinant

abstract:
  Lattice QCD simulations with staggered fermions rely on the ``fourth-root
trick.'' The validity of this trick has been proved for free staggered fermions
using renormalization-group block transformations. I review the elements of the
construction and discuss how it might be generalized to the interacting case.


title:
Localization properties of the topological charge density and the low
  lying eigenmodes of overlap fermions

abstract:
  Overlap fermions, which preserve exact chiral symmetry on the lattice,
provide a powerful tool for investigating the topological structure of the
vacuum. Applying this formulation to zero-temperature quenched SU(3)
configurations generated by means of the Luescher-Weisz action, we define the
topological charge density with and without UV filtering and study its
properties by looking at the density profile and the two-point correlation
function. We observe that the density possesses global sign coherent
structures, which get increasingly tangled as more and more modes are included.
This change of the structure is also detected by the increasing negative tail
of the two-point function. We also study the inverse participation ratio of the
eigenmodes and discuss their dimensionality.


title: B_s-\bar{B_s} mixing with a chiral light quark action

abstract:
  We study the $B^0_s-\bar{B^0_s}$ mixing amplitude in Standard Model by
computing the relevant hadronic matrix element in the static limit of lattice
HQET with the Neuberger light quark action. In the quenched approximation, and
after matching to the $\bar{\rm MS}$ scheme in QCD, we obtain $B^{\bar{\rm
MS}}_{B_s}(m_b)=0.940(16)(22)$.


title: Real-time dynamics of proton decay

abstract:
  Substituting Skyrmion for nucleon, one can potentially see -- in real time --
how the monopole is catalysing the proton (or neutron) decay, and even obtain a
plausible estimate for catalysis cross-section. Here we discuss the key aspects
of a practical implementation of such approach and demonstrate how one can
overcome the main technical problems: Gauss constraint violation and
reflections at the boundaries.


title:
The high density region of QCD in a large mass and chemical potential
  model

abstract:
  We study the high density region of QCD within an effective model obtained in
the frame of the hopping parameter expansion. The model still acknowledges the
sign problem peculiar to non-zero chemical potential, but it permits the
development of refined algorithms which ensure a good overlap of the Monte
Carlo ensemble with the true one. We review the main features of the model,
including the most explicit form of the resumed expansion, and present
calculations concerning the dependence of various observables on the chemical
potential and on the temperature, in particular of the charge density and the
diquark susceptibility, which may be used to characterize the various phases
expected at high baryonic density.


title: Cutoff effects in maximally twisted LQCD

abstract:
  The Symanzik analysis of correlators in lattice QCD with maximally twisted
Wilson fermions reveals that there exist cutoff artifacts which tend to become
large as the quark mass gets small. We show that these effects can be reduced
to a negligible level by either introducing the clover term in the action or,
as already suggested in the literature, by a suitable choice of the critical
mass. Recent simulation data support these conclusions.


title: Predictions from Lattice QCD

abstract:
  In the past year, we calculated with lattice QCD three quantities that were
unknown or poorly known. They are the $q^2$ dependence of the form factor in
semileptonic $D\to Kl\nu$ decay, the decay constant of the $D$ meson, and the
mass of the $B_c$ meson. In this talk, we summarize these calculations, with
emphasis on their (subsequent) confirmation by experiments.


title: Testing 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. Such actions
originate from the admissibility condition in order to conserve the topological
charge. The suppression of small plaquette values is expected to be
advantageous for numerical studies in the $\epsilon$-regime and also for
simulations with dynamical quarks. Performing simulations at a lattice spacing
of about 0.1 fm, we present numerical results for the static potential, the
physical scale $r_0$, the stability of the topological charge history, the
condition number of the kernel of the overlap operator and the acceptance rate
against the step size in the local HMC algorithm.


title:
Topological clusters in SU(2) gluodynamics at finite temperature and the
  evidence for KvB calorons

abstract:
  We report on our search for Kraan-van Baal calorons in finite temperature
SU(2) lattice ensembles. We also discuss recent progress made in developing a
caloron-anticaloron gas model decribing confinement and deconfinement in the
context of trivial and non-trivial holonomy.


title:
Pseudoscalar Mass and Decay Constant in Lattice QCD with Exact Chiral
  Symmetry

abstract:
  The masses and decay constants of pseudoscalar mesons $ D $, $ D_s $, and $ K
$ are determined in quenched lattice QCD with exact chiral symmetry. For 100
gauge configurations generated with single-plaquette action at $ \beta = 6.1 $
on the $ 20^3 \times 40 $ lattice, we compute point-to-point quark propagators
for 30 quark masses in the range $ 0.03 \le m_q a \le 0.80 $, and measure the
time-correlation functions of pseudoscalar and vector mesons. The inverse
lattice spacing $ a^{-1} $ is determined with the experimental input of $ f_\pi
$, while the strange quark bare mass ($ m_s a = 0.08 $), and the charm quark
bare mass ($ m_c a = 0.80 $) are fixed such that the masses of the
corresponding vector mesons are in good agreement with $ \phi(1020) $ and $
J/\psi(3097) $ respectively. Our results of pseudoscalar-meson decay constant
are: $ f_K = 152(6)(10) $ MeV, $ f_D = 235(8)(14)$ MeV, and $ f_{D_s} =
266(10)(18) $ MeV [hep-ph/0506266]. The latest experimental result of $ f_{D^+}
$ from CLEO [hep-ex/0508057] is in good agreement with our prediction.


title: A quenched study of m_b in HQET beyond the leading order

abstract:
  A non perturbative method to compute the mass of the b quark including the
1/m term in HQET has been presented in a companion talk. Following this
strategy, we find in the MS bar scheme m_b^{stat}(m_b) = 4.350(64) GeV for the
leading term, and m_b^{(1)}(m_b) = -0.049(29) GeV for the next to leading order
correction. This method involves several steps, including the simulation of the
relativistic theory in a small volume, and of the effective theory in a big
volume. Here we present some numerical details of our calculations.


title: Testing Fermion Actions: Scaling in the Schwinger Model

abstract:
  We test the scaling behaviour of Wilson, hypercube, maximally twisted mass
and overlap fermion actions in dynamical simulations of the 2-dimensional
massive Schwinger model. We also present possibilities to simulate overlap
fermions dynamically by replacing the exact overlap operator by an approximate
version. This approximation is used either as only the guidance Hamiltonian,
keeping the exact overlap operator as the accept/reject Hamiltonian or for
both, the guidance and accept/reject Hamiltonian in the Hybrid Monte Carlo
algorithm. In the latter case we test whether the approximation error can be
corrected for by computing the determinant ratio of the exact and the
approximate overlap operators stochastically.


title: Mass Spectra of Pentaquarks -- Overlap versus Wilson Fermions

abstract:
  We investigate the mass spectra of $\Theta^+(udud\bar s)$ in quenched lattice
QCD, with overlap and Wilson fermions respectively. Using three different
interpolating operators, we measure their correlation matrix, and extract the
mass spectra in even and odd parity channels, for 100 gauge configurations
generated with single plaquette action at $\beta=6.1$ on the $20^3 \times 40$
lattice. The lowest $ 1/2^- $ state agrees with the $ KN $ s-wave scattering
state, for both fermion schemes. On the other hand, for the lowest $ 1/2^+ $
state, it is different from any hadron scattering states for the overlap
fermion, while it seems to agree with $ KN^* $ s-wave for the Wilson fermion.


title:
The locality of the fourth root of staggered fermion determinant in the
  interacting case

abstract:
  The fourth root approximation in LQCD simulations with dynamical staggered
fermions requires justification. We test its validity numerically in the
interacting theory in a renormalization group framework.


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

abstract:
  We study various improved staggered quark Dirac operators on quenched gluon
backgrounds in lattice QCD. We find a clear separation of the spectrum of
eigenvalues into high chirality, would-be zero modes and others, in accordance
with the Index Theorem. We find the expected clustering of the non-zero modes
into quartets as we approach the continuum limit. The predictions of random
matrix theory for the epsilon regime are well reproduced. We conclude that
improved staggered quarks near the continuum limit respond correctly to QCD
topology.