title:
Calorons and monopoles from smeared SU(2) lattice fields at non-zero
  temperature

abstract:
  In equilibrium, at finite temperature below and above the deconfining phase
transition, we have generated lattice SU(2) gauge fields and have exposed them
to smearing in order to investigate the emerging clusters of topological
charge. Analysing in addition the monopole clusters according to the maximally
Abelian gauge, we have been able to characterize part of the topological
clusters to correspond either to non-static calorons or static dyons in the
context of Kraan-van Baal caloron solutions with non-trivial holonomy. We show
that the relative abundance of these calorons and dyons is changing with
temperature and offer an interpretation as dissociation of calorons into dyons
with increasing temperature. The profile of the Polyakov loop inside the
topological clusters and the (model-dependent) accumulated topological cluster
charges support this interpretation. Above the deconfining phase transition
light dyons (according to Kraan-van Baal caloron solutions with almost trivial
holonomy) become the most abundant topological objects. They are presumably
responsible for the magnetic confinement in the deconfined phase.


title:
Three-Flavor Partially Quenched Chiral Perturbation Theory at NNLO for
  Meson Masses and Decay Constants

abstract:
  We discuss Partially Quenched Chiral Perturbation Theory (PQ$\chi$PT) and
possible fitting strategies to Lattice QCD data at next-to-next-to-leading
order (NNLO) in the mesonic sector. We also present a complete calculation of
the masses of the charged pseudoscalar mesons, in the supersymmetric
formulation of PQ$\chi$PT. Explicit analytical results are given for up to
three nondegenerate sea quark flavors, along with the previously unpublished
expression for the pseudoscalar meson decay constant for three nondegenerate
sea quark flavors. The numerical analysis in this paper demonstrates that the
corrections at NNLO are sizable, as expected from earlier work.


title: Simulations of ${\cal N}=2$ super Yang-Mills theory in two dimensions

abstract:
  We present results from lattice simulations of ${\cal N}=2$ super Yang-Mills
theory in two dimensions. The lattice formulation we use was developed in
\cite{2dpaper} and retains both gauge invariance and an exact (twisted)
supersymmetry for any lattice spacing. Results for both U(2) and SU(2) gauge
groups are given. We focus on supersymmetric Ward identities, the phase of the
Pfaffian resulting from integration over the Grassmann fields and the nature of
the quantum moduli space.


title: QCD at Zero Baryon Density and the Polyakov Loop Paradox

abstract:
  We compare the grand canonical partition function at fixed chemical potential
mu with the canonical partition function at fixed baryon number B, formally and
by numerical simulations at mu=0 and B=0 with four flavours of staggered
quarks. We verify that the free energy densities are equal in the thermodynamic
limit, and show that they can be well described by the hadron resonance gas at
T < T_c and by the free fermion gas at T>T_c.
  Small differences between the two ensembles, for thermodynamic observables
characterising the deconfinement phase transition, vanish with increasing
lattice size. These differences are solely caused by contributions of non-zero
baryon density sectors, which are exponentially suppressed with increasing
volume. The Polyakov loop shows a different behaviour: for all temperatures and
volumes, its expectation value is exactly zero in the canonical formulation,
whereas it is always non-zero in the commonly used grand-canonical formulation.
We clarify this paradoxical difference, and show that the non-vanishing
Polyakov loop expectation value is due to contributions of non-zero triality
states, which are not physical, because they give zero contribution to the
partition function.


title: Short comment about the lattice gluon propagator at vanishing momentum

abstract:
  We argue that all evidences point towards a finite non-vanishing zero
momentum renormalised lattice gluon propagator in the infinite volume limit. We
argue that different simulations with different lattice setups end-up with
fairly compatible results for the gluon propagator at zero momentum, with
different positive slopes as a function of the inverse volume.


title:
Deconstruction and other approaches to supersymmetric lattice field
  theories

abstract:
  This report contains both a review of recent approaches to supersymmetric
lattice field theories and some new results on the deconstruction approach. The
essential reason for the complex phase problem of the fermion determinant is
shown to be derivative interactions that are not present in the continuum.
These irrelevant operators violate the self-conjugacy of the fermion action
that is present in the continuum. It is explained why this complex phase
problem does not disappear in the continuum limit. The fermion determinant
suppression of various branches of the classical moduli space is explored, and
found to be supportive of previous claims regarding the continuum limit.


title: Charmonium properties in deconfinement phase 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 spatially 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 =4.0 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. We
investigate the c\bar c system above T_c from the temporal correlators with
spatially-extended operators, where the overlap with the ground state is
enhanced. To clarify whether compact charmonia survive in the deconfinement
phase, we investigate spatial boundary-condition dependence of the energy of
c\bar c systems above T_c. In fact, for low-lying S-wave c \bar c scattering
states, it is expected that there appears a significant energy difference
\Delta E \equiv E{\rm (APBC)}-E{\rm (PBC)}\simeq2\sqrt{m_c^2+3\pi^2/L^2}-2m_c
(m_c: charm quark mass) between periodic and anti-periodic boundary conditions
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, almost no spatial boundary-condition
dependence is observed 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. This fact indicates that J/\Psi and
\eta_c would survive as spatially compact c\bar c (quasi-)bound states below
2T_c. We also investigate a $P$-wave channel at high temperature with maximally
entropy method (MEM) and find no low-lying peak structure corresponding to
\chi_{c1} at 1.62T_c.


title: Sign problem and MEM in lattice field theory with the $\theta$ term

abstract:
  Lattice field theory with the $\theta$ term suffers from the sign problem.
The sign problem appears as flattening of the free energy.
  As an alternative to the conventional method, the Fourier transform method
  (FTM), we apply the maximum entropy method (MEM) to Monte Carlo data obtained
using the CP$^3$ model with the $\theta$ term.
  For data without flattening, we obtain the most probable images of the
partition function ${\hat{\cal Z}}(\theta)$ with rather small errors. The
results are quantitatively close to the result obtained with the
  FTM. Motivated by this fact, we systematically investigate flattening in
terms of the MEM.
  Obtained images ${\hat{\cal Z}}(\theta)$ are consistent with the FTM for
small values of $\theta$, while the behavior of ${\hat{\cal Z}}(\theta)$
depends strongly on the default model for large values of $\theta$.
  This behavior of ${\hat{\cal Z}}(\theta)$ reflects the flattening phenomenon.


title: Nucleon-Nucleon Scattering From Fully-Dynamical Lattice QCD

abstract:
  We present results of the first fully-dynamical lattice QCD determination of
nucleon-nucleon scattering lengths in the 1S0 channel and 3S1-3D1 coupled
channels. The calculations are performed with domain-wall valence quarks on the
MILC staggered configurations with lattice spacing of b=0.125 fm in the
isospin-symmetric limit, and in the absence of electromagnetic interactions.


title: Confinement of color: open problems and perspectives

abstract:
  Some basic features of confinement are reviewed, in particular the symmetry
patterns of the dual dynamics. Open problems and possible directions of
progress are discussed.


title:
Infrared behavior of gluon and ghost propagators from asymmetric
  lattices

abstract:
  We present a numerical study of the lattice Landau gluon and ghost
propagators in three-dimensional pure SU(2) gauge theory. Data have been
obtained using asymmetric lattices (V = 20^2 X 40, 20^2 X 60, 8^2 X 64, 8^2 X
140, 12^2 X 140 and 16^2 X 140) for the lattice coupling beta = 3.4, in the
scaling region. We find that the gluon (respectively ghost) propagator is
suppressed (respec. enhanced) at small momenta in the limit of large lattice
volume V. By comparing these results with data obtained using symmetric
lattices (V = 60^3 and 140^3), we find that both propagators suffer from
systematic effects in the infrared region (p \lesssim 650 MeV). In particular,
the gluon (respec. ghost) propagator is less IR-suppressed (respec. enhanced)
than in the symmetric case. We discuss possible implications of the use of
asymmetric lattices.


title:
Mollifying Quantum Field Theory or Lattice QFT in Minkowski Spacetime
  and Symmetry Breaking

abstract:
  This work develops and applies the concept of mollification in order to
smooth out highly oscillatory exponentials. This idea, known for quite a while
in the mathematical community (mollifiers are a means to smooth distributions),
is new to numerical Quantum Field Theory. It is potentially very useful for
calculating phase transitions [highly oscillatory integrands in general], for
computations with imaginary chemical potentials and Lattice QFT in Minkowski
spacetime.


title: Renormalization of two-loop diagrams in scalar lattice field theory

abstract:
  We present a method to calculate to very high precision the coefficients of
the divergences occuring in two-loop diagrams for a massive scalar field on the
lattice. The approach is based on coordinate space techniques and extensive use
of the precisely known Green's function.


title: A fast minimal residual solver for overlap fermions

abstract:
  Computing quark propagators with overlap fermions requires the solution of a
shifted unitary linear system. Jagels and Reichel have shown that for such
systems it is possible to construct a minimal residual algorithm by short
recurrences. The J\"ulich-Wuppertal group have found this algorithm to be the
fastest among overlap solvers. In this paper we present a three-term recurrence
for the Arnoldi unitary process. Using the new recurrence we construct a
minimal residual solver which is the fastest among all Krylov subspace
algorithms considered so far for the overlap inversion.


title: Probing the QCD Vacuum Using External Fields

abstract:
  The QCD vacuum can be studied using external fields. We report here results
respectively obtained probing the lattice QCD vacuum by means of an abelian
monopole field and of an abelian chromomagnetic field


title: Finite volume effects for the pion mass at 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 and conclude that for Mpi*L>2, L>2fm the finite volume effects in the
meson sector are analytically well under control.


title: Efficient Cluster Algorithm for CP(N-1) Models

abstract:
  Despite several attempts, no efficient cluster algorithm has been constructed
for CP(N-1) models in the standard Wilson formulation of lattice field theory.
In fact, there is a no-go theorem that prevents the construction of an
efficient Wolff-type embedding algorithm. In this paper, we construct an
efficient cluster algorithm for ferromagnetic SU(N)-symmetric quantum spin
systems. Such systems provide a regularization for CP(N-1) models in the
framework of D-theory. We present detailed studies of the autocorrelations and
find a dynamical critical exponent that is consistent with z = 0.


title: Finite Volume Dependence of the Quark-Antiquark Vacuum Expectation Value

abstract:
  A general formula is derived for the finite volume dependence of vacuum
expectation values analogous to Luscher's formula for the masses. The result
involves no integrals over kinematic quantities and depends only on the matrix
element between pions at zero momentum transfer thus presenting a new way to
calculate the latter, i.e. pion sigma terms.
  The full order $p^6$ correction to the vacuum condensate $<\bar q q>$ is
evaluated and compared with the result from the Luscher formula. Due to the
size of the $p^6$ result no conclusion about the accuracy of the Luscher
formula can be drawn.


title: Preliminary Study of B_K on 2+1 flavor DWF lattices from QCDOC

abstract:
  I present some preliminary calculations of B_K on 2+1 flavor domain-wall
fermion lattices from the QCDOC, including a set of 16^3x32x8 lattices with
a^{-1} near 1.6 GeV. Although a final result awaits the production of a much
longer run, I will compare this preliminary value to previous results.


title: QCD, Symmetry Breaking and the Random Lattice

abstract:
  According to the Nielsen-Ninomiya No-Go theorem, the doubling of fermions on
the lattice cannot be suppressed in a chiral theory. Whereas Wilson and
staggered fermions suppress doublers with explicit breaking of chiral symmetry,
the random lattice does so by spontaneous chiral symmetry breaking even in the
free theory. I present results for meson masses, the chiral condensate and
fermionic eigenvalues from simulations of quenched QCD on random lattices in
four dimensions, focusing on chiral symmetry breaking.


title:
Behaviour of the topological susceptibility in two colour QCD across the
  finite density transition

abstract:
  The behaviour of the topological susceptibility \chi in QCD with two colours
and 8 flavours of quarks is studied at nonzero temperature on the lattice
across the finite density transition. It is shown that the signal of \chi drops
abruptly at a critical chemical potential \mu_c, much as it happens at the
finite temperature and zero density transition. The Polyakov loop and the
chiral condensate undergo their transitions at the same critical value \mu_c.
At a value \mu_s of the chemical potential, called saturation point, which in
our case satisfies \mu_s > \mu_c, Pauli blocking supervenes and consequently
the theory becomes quenched.


title:
Relation between bare lattice coupling and MSbar coupling at one loop
  with general lattice fermions

abstract:
  A compact general integral formula is derived from which the fermionic
contribution to the one-loop coefficient in the perturbative expansion of the
MSbar coupling in powers of the bare lattice coupling can be extracted. It is
seen to reproduce the known results for unimproved naive, staggered and Wilson
fermions, and has advantageous features which facilitate the evaluation in the
case of improved lattice fermion formulations. This is illustrated in the case
of Wilson clover fermions, and an expression in terms of known lattice
integrals is obtained in this case which gives the coefficient to much greater
numerical accuracy than in the previous literature.


title: Finite density QCD with a canonical approach

abstract:
  We present a canonical method where the properties of QCD are directly
obtained as a function of the baryon density rho, rather than the chemical
potential mu. We apply this method to the determination of the phase diagram of
four-flavor QCD. For a pion mass m_pi \sim 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, including the associated
interface tension. We obtain accurate results for systems containing up to 30
baryons and quark chemical potentials mu up to 2 T. Our T-mu phase diagram
agrees with the literature when mu/T \lesssim 1. At larger chemical potential,
we observe a ``bending down'' of the phase boundary. We compare the free energy
in the confined and deconfined phase with predictions from a hadron resonance
gas and from a free massless quark gas respectively.


title: Quenched penguins and the Delta I=1/2 rule

abstract:
  The transformation properties of strong penguin operators under the action of
the flavor group change when they are considered as operators in (partially)
quenched QCD instead of the unquenched theory. As a result, additional
operators and new low-energy constants appear in the effective theory
describing non-leptonic kaon decay matrix elements in the partially quenched
setting. These new low-energy constants do not have a counterpart in the
unquenched theory, and should thus be considered as an artifact of the quenched
approximation. Here we consider strong penguin operators consisting of products
of two left-handed flavor currents, and give a complete one-loop analysis in
the effective theory for K^0 to vacuum and K^+ to pi^+ matrix elements. We find
that the new low-energy constants already appear in these matrix elements at
leading order. This implies that (partially) quenched lattice computations of
for instance the Delta I=1/2 rule are affected by ambiguities intrinsic to the
use of the quenched approximation at leading order. The only exception is the
partially quenched case with three light sea quarks, consistent with general
expectations. Our results are also relevant when the charm quark is kept in the
theory.


title: Breakdown of staggered fermions at nonzero chemical potential

abstract:
  The staggered fermion determinant is complex when the quark chemical
potential mu is nonzero. Its fourth root, used in simulations with dynamical
fermions, will have phase ambiguities that become acute when Re mu is
sufficiently large. We show how to resolve these ambiguities, but our
prescription only works very close to the continuum limit. We argue that this
regime is far from current capabilities. Other procedures require being even
closer to the continuum limit, or fail altogether, because of unphysical
discontinuities in the measure. At zero temperature the breakdown is expected
when Re mu is greater than approximately half the pion mass. Estimates of the
location of the breakdown at nonzero temperature are less certain.


title:
Effects of the quark field on the ghost propagator of Lattice Landau
  Gauge QCD

abstract:
  Infrared features of the ghost propagator of color diagonal and color
antisymmetric ghost propagator of quenched SU(2) and quenched SU(3) are
compared with those of unquenched Kogut-Susskind fermion SU(3) lattice Landau
gauge.
  We compare 1) the fluctuation of the ghost propagator, 2) the ghost
condensate parameter $v$ of the local composite operator (LCO) approach and 3)
the Binder cumulant of color anti-symmetric ghost propagator between quenched
and unquenched configurations.


title: Determining the strange quark mass for 2-flavour QCD

abstract:
  Using the O(a) Symanzik improved action an estimate is given for the strange
quark mass for unquenched (n_f=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. Our results
indicate a value for the strange quark mass (in the MS-bar scheme at a scale of
2 GeV) in the range 100 - 130 MeV. A comparison is also made with other recent
lattice determinations of the strange quark mass using dynamical sea quarks.


title: Hadron masses: lattice QCD and chiral effective field theory

abstract:
  This work discusses reliability, possible obstacles and the future
perspective of chiral extrapolation of lattice results. In the first part,
chiral perturbation theory fits to lattice calculations of the nucleon mass are
thoroughly explored in terms of statistical uncertainty and convergence.
Lattice volume dependence is exploited as a source of additional fit
constraints. In discussing consistency with pion-nucleon scattering, the role
of the Delta(1232) excitation is clarified. In the second part of the work,
pion and kaon mass lattice data are analyzed using three-flavor chiral
perturbation theory. SU(3)-SU(2) matching conditions permit to examine
deviations from the Gell-Mann, Oakes, Renner relation. Introductory chapters
provide a quick start guide to manifestly covariant baryon chiral perturbation
theory, basic understanding of lattice QCD and a self-contained explanation of
the relevant statistical methods.


title: Extracting $F_\pi$ from small lattices: unquenched results

abstract:
  We calculate the response of the microscopic Dirac spectrum to an imaginary
isospin chemical potential for QCD with two dynamical flavors in the chiral
limit. This extends our previous calculation from the quenched to the
unquenched theory. The resulting spectral correlation function in the
$\epsilon$-regime provides here, too, a new and efficient way to measure
$F_\pi$ on the lattice. We test the method in a hybrid Monte Carlo simulation
of the theory with two staggered quarks.


title: Phase-diagram of two-color lattice QCD in the chiral limit

abstract:
  We study thermodynamics of strongly coupled lattice QCD with two colors of
massless staggered fermions as a function of the baryon chemical potential
$\mu$ in 3+1 dimensions using a new cluster algorithm. We find evidence that
the model undergoes a weak first order phase transition at $\mu=0$ which
becomes second order at a finite $\mu$. Symmetry considerations suggest that
the universality class of these phase transitions should be governed by an
$O(N)\times O(2)$ field theory with collinear order, with N=3 at $\mu=0$ and
N=2 at $\mu \neq 0$. The universality class of the second order phase
transition at $\mu\neq 0$ appears to be governed by the decoupled XY fixed
point present in the $O(2)\times O(2)$ field theory. Finally we show that the
quantum (T=0) phase transition as a function of $\mu$ is a second order mean
field transition.


title: Topology on the Lattice

abstract:
  We review the method developed in Pisa to determine the topological
susceptibility in lattice QCD and present a collection of new and old results
obtained by the method.


title: Nucleon mass: from lattice QCD to the chiral limit

abstract:
  Previous extrapolations of lattice QCD results for the nucleon mass to the
physically relevant region of small quark masses, using chiral effective field
theory, are extended and expanded in several directions. A detailed error
analysis is performed. An approach with explicit delta(1232) degrees of freedom
is compared to a calculation with only pion and nucleon degrees of freedom. The
role of the delta(1232) for the low-energy constants of the latter theory is
elucidated. The consistency with the chiral perturbation theory analysis of
pion-nucleon scattering data is examined. It is demonstrated that this
consistency can indeed be achieved if the delta(1232) dominance of the P-wave
pion-nucleon low-energy constant c3 is accounted for. Introduction of the
delta(1232) as an explicit propagating degree of freedom is not crucial in
order to describe the quark-mass dependence of the nucleon mass, in contrast to
the situation with spin observables of the nucleon. The dependence on finite
lattice volume is shown to yield valuable additional constraints. What emerges
is a consistent and stable extrapolation scheme for pion masses below 0.6 GeV.


title: Quarkonia in a deconfined gluonic plasma

abstract:
  We discuss lattice results on the properties of finite momentum charmonium
states in a gluonic plasma. We also present preliminary results for bottomonium
correlators and spectral functions in the plasma. Significant modifications of
chi_b states are seen at temperatures of 1.5 Tc.


title:
Noncommutativity Approach to Supersymmetry on the Lattice: SUSY Quantum
  Mechanics and an Inconsistency

abstract:
  It is argued that the noncommutativity approach to fully supersymmetric field
theories on the lattice suffers from an inconsistency. Supersymmetric quantum
mechanics is worked out in this formalism and the inconsistency is shown both
in general and explicitly for that system, as well as for the Abelian super BF
model.


title:
Unquenched complex Dirac spectra at nonzero chemical potential:
  two-colour QCD lattice data versus matrix model

abstract:
  We compare analytic predictions of non-Hermitian chiral random matrix theory
with the complex Dirac operator eigenvalue spectrum of two-colour lattice gauge
theory with dynamical fermions at nonzero chemical potential. The Dirac
eigenvalues come in complex conjugate pairs, making the action of this theory
real, and positive for our choice of two staggered flavours. This enables us to
use standard Monte-Carlo in testing the influence of chemical potential and
quark mass on complex eigenvalues close to the origin. We find an excellent
agreement between the analytic predictions and our data for two different
volumes over a range of chemical potentials below the chiral phase transition.
In particular we detect the effect of unquenching when going to very small
quark masses.


title: On Charmonia Survival Above Deconfinement

abstract:
  We study charmonium correlators and spectral functions at zero and finite
temperature using anisotropic lattices at several different lattice spacings.
We find evidence for survival of 1S charmonia states at leas till $1.5T_c$ and
dissolution of 1P states at $1.16T_c$.


title: Screening masses in thermal and dense medium

abstract:
  Screening masses of different hadronic states are studied in thermal and
dense medium on lattice. It has been found that screening masses increase with
the temperature. In deconfinement phase, chemical potential enhances the
screening masses. We use the normalization with respect to lowest Matsubara
frequency to characterize dissolving of hadronic bound states at high
temperatures. It has been found that different hadronic states have different
dissolving temperatures and their survivals are considerably improved at finite
chemical potentials.


title: Decay width of light quark hybrid meson from the lattice

abstract:
  Lattice QCD with $N_f=2$ flavours of sea quark is used to explore the
spectrum and decay of a $J^{PC}=1^{-+}$ spin-exotic hybrid meson.
  We test lattice determination of S-wave decay amplitudes at threshold using
$b_1 \to \pi \omega$ where agreement with data is found. We find a hybrid meson
state at 2.2(2) GeV with a partial width to $\pi b_1$ of 400(120) MeV and to
$\pi f_1$ of 90(60) MeV.


title: Lattice QCD with fixed topology

abstract:
  The overlap Dirac operator, which satisfies the Ginsparg-Wilson relation,
realizes exact chiral symmetry on the lattice without any unphysical doubler
modes. To perform the path integrals, one should, however, note that the
overlap fermion determinant has discontinuities where the topology is
ill-defined, its locality is doubtful, and the numerical cost is suddenly
enhanced.
  An interesting solution would be to concentrate on a fixed topological sector
in the full configuration space. In this thesis, we test a gauge action which
automatically satisfies Luescher's admissibility condition, as well as an
additional (large) negative mass Wilson fermion action in the quenched study
(with no light quark). Both of them would keep the topology along the HMC
simulations. The quark potential and the topology stability are investigated
with different lattice sizes and different couplings.
  The results of quenched QCD in the $\epsilon$-regime are also presented as an
example of the lattice studies with fixed topology. Remarkable quark mass and
topology dependences of meson correlators allow us to determine the fundamental
parameters of the effective theory, in which the exact chiral symmetry with the
Ginsparg Wilson relation plays a crucial role.


title: Aliasing modes in the lattice Schwinger model

abstract:
  We study the Schwinger model on a lattice consisting of zeros of the Hermite
polynomials that incorporates a lattice derivative and a discrete Fourier
transform with many properties. Such a lattice produces a Klein-Gordon equation
for the boson field and the exact value of the mass in the asymptotic limit if
the boundaries are not taken into account. On the contrary, if the lattice is
considered with boundaries new modes appear due to aliasing effects. In the
continuum limit, however, this lattice yields also a Klein-Gordon equation with
a reduced mass.


title: Properties of Color-Coulomb String Tension

abstract:
  We study the properties of the color-Coulomb string tension obtained from the
instantaneous part of gluon propagators in Coulomb gauge using quenched SU(3)
lattice simulation.
  In the confinement phase, the dependence of the color-Coulomb string tension
on the QCD coupling constant is smaller than that of the Wilson loop string
tension. On the other hand, in the deconfinement phase, the color-Coulomb
string tension does not vanish even for $T/T_c = 1 \sim 5$, the temperature
dependence of which is comparable with the magnetic scaling, dominating the
high temperature QCD. Thus, the color-Coulomb string tension is not an order
parameter of QGP phase transition.


title: Staggered Chiral Perturbation Theory and the Fourth-Root Trick

abstract:
  Staggered chiral perturbation theory (schpt) takes into account the
"fourth-root trick" for reducing unwanted (taste) degrees of freedom with
staggered quarks by multiplying the contribution of each sea quark loop by a
factor of 1/4. In the special case of four staggered fields (four flavors,
nF=4), I show here that certain assumptions about analyticity and phase
structure imply the validity of this procedure for representing the rooting
trick in the chiral sector. I start from the observation that, when the four
flavors are degenerate, the fourth root simply reduces nF=4 to nF=1. One can
then treat nondegenerate quark masses by expanding around the degenerate limit.
With additional assumptions on decoupling, the result can be extended to the
more interesting cases of nF=3, 2, or 1. A apparent paradox associated with the
one-flavor case is resolved. Coupled with some expected features of unrooted
staggered quarks in the continuum limit, in particular the restoration of taste
symmetry, schpt then implies that the fourth-root trick induces no problems
(for example, a violation of unitarity that persists in the continuum limit) in
the lowest energy sector of staggered lattice QCD. It also says that the theory
with staggered valence quarks and rooted staggered sea quarks behaves like a
simple, partially-quenched theory, not like a "mixed" theory in which sea and
valence quarks have different lattice actions. In most cases, the assumptions
made in this paper are not only sufficient but also necessary for the validity
of schpt, so that a variety of possible new routes for testing this validity
are opened.


title:
Perturbative renormalization factors for generic $\Delta s=2$ four-quark
  operators in domain-wall QCD with improved gauge action

abstract:
  We calculate one-loop renormalization factors of generic DeltaS=2 four-quark
operators for domain-wall QCD with the plaquette gauge action and the Iwasaki
gauge action. The renormalization factors are presented in the modified minimal
subtraction (MS-bar) scheme with the naive dimensional regularization. As an
important application we show how to construct the renormalization factors for
the operators contributing to K^0-K^0bar mixing in the supersymmetric models
with the use of our results.


title: Unexpected Spin-Off from Quantum Gravity

abstract:
  We propose a novel way of investigating the universal properties of spin
systems by coupling them to an ensemble of causal dynamically triangulated
lattices, instead of studying them on a fixed regular or random lattice.
Somewhat surprisingly, graph-counting methods to extract high- or
low-temperature series expansions can be adapted to this case. For the
two-dimensional Ising model, we present evidence that this ameliorates the
singularity structure of thermodynamic functions in the complex plane, and
improves the convergence of the power series.


title: QCD Critical Point and Complex Chemical Potential Singularities

abstract:
  The thermodynamic singularities of QCD in the plane of complex baryo-chemical
potential mu are studied. Predictions are made using scaling and universality
arguments in the vicinity of the massless quark limit. The results are
illustrated by a calculation of complex mu singularities in a random matrix
model at finite temperature. Implications for lattice QCD simulations aimed at
locating the QCD critical point are discussed.


title:
Static Quark Potential and the Renormalized Anisotropy on Tadpole
  Improved Anisotropic Lattices

abstract:
  Static quark potential is studied using a tadpole improved gauge lattice
action. The scale is set using the potential for a wide range of bare
parameters.
  The renormalized anisotropy of the lattice is also measured.


title: Glueball Wave Functions in U(1) Lattice Gauge Theory

abstract:
  Standard Monte Carlo simulations have been performed for 3-dimensional U(1)
lattice gauge model on improved lattices to measure the wavefunction and size
of the scalar and the tensor glueballs. Our results show the radii of ~ 0.60
and ~ 1.12 in the units of string tension, or ~0.28 and ~0.52 fm, for the
scalar and tensor glueballs, respectively. At finite temperature we see clear
evidence of the deconfined phase, and the transition appears to be similar to
that of the two-dimensional XY model as expected from universality arguments.
Preliminary results show no significant changes in the glueball wave functions
and the masses in the deconfined phase.


title:
Quantization and simulation of Born-Infeld non-linear electrodynamics on
  a lattice

abstract:
  Born-Infeld non-linear electrodynamics arises naturally as a field theory
description of the dynamics of strings and branes. Most analyses of this theory
have been limited to studying it as a classical field theory. We quantize this
theory on a Euclidean 4-dimensional space-time lattice and determine its
properties using Monte-Carlo simulations. The electromagnetic field around a
static point charge is measured using Luscher-Weisz methods to overcome the
sign problem associated with the introduction of this charge. The D field
appears identical to that of Maxwell QED. However, the E field is enhanced by
quantum fluctuations, while still showing the short distance screening observed
in the classical theory. In addition, whereas for the classical theory, the
screening increases without bound as the non-linearity increases, the quantum
theory approaches a limiting conformal field theory.


title: In-Medium Modifications of Hadron Properties

abstract:
  The in-medium modifications of hadron properties are briefly discussed. We
restrict the discussion to the lattice QCD calculations for the hadron masses,
screening masses, decay constants and wave functions. We review the progress
made so far and describe how to broaden its horizon.


title: Twisted mass lattice QCD with non-degenerate quark masses

abstract:
  Quantum Chromodynamics on a lattice with Wilson fermions and a chirally
twisted mass term is considered in the framework of chiral perturbation theory.
For two and three numbers of quark flavours, respectively, with non-degenerate
quark masses the pseudoscalar meson masses and decay constants are calculated
in next-to-leading order including lattice effects quadratic in the lattice
spacing a.


title: Flavor extrapolations and staggered fermions

abstract:
  A popular approximation in lattice gauge theory is an extrapolation in the
number of fermion species away from the four fold degeneracy natural with the
staggered fermions formulation. I show that at finite lattice spacing and for
an odd number of flavors this extrapolation misses terms which, on general
principles, must be present in the continuum theory. For a correct continuum
limit, this forces unphysical singularities in parameter regions where
continuum physics is smooth and all physical particles are massive. These
singularities are not expected with other lattice regulators. Finally, I argue
that unnatural constraints on certain correlation functions appear even when
all quarks are massive.


title:
Evidence for O(2) universality at the finite temperature transition for
  lattice QCD with 2 flavours of massless staggered quarks

abstract:
  We simulate lattice QCD with 2 flavours of massless quarks on lattices of
temporal extent N_t=8, to study the finite temperature transition from hadronic
matter to a quark-gluon plasma. A modified action which incorporates an
irrelevant chiral 4-fermion interaction is used, which allows simulations at
zero quark mass. We obtain excellent fits of the chiral condensates to the
magnetizations of a 3-dimensional O(2) spin model on lattices small enough to
model the finite size effects. This gives predictions for correlation lengths
and chiral susceptibilities from the corresponding spin-model quantities. These
are in good agreement with our measurements over the relevant range of
parameters. Binder cumulants are measured, but the errors are too large to draw
definite conclusions. From the properties of the O(2) spin model on the
relatively small lattices with which we fit our `data', we can see why earlier
attempts to fit staggered lattice data to leading-order infinite-volume scaling
functions, as well as finite size scaling studies, failed and led to erroneous
conclusions.


title: Monopole-Antimonopole Correlation Functions in 4D U(1) Gauge Theory

abstract:
  We study the two-point correlator of a modified Confined-Coulomb transition
order parameter in four dimensional compact U(1) lattice gauge theory with
Wilson action. Its long distance behavior in the confined phase turns out to be
governed by a single particle decay. The mass of this particle is computed and
found to be in agreement with previous calculations of the 0^{++} gaugeball
mass. Remarkably, our order parameter allows to extract a good signal to noise
ratio for masses with low statistics. The results we present provide a
numerical check of a theorem about the structure of the Hilbert space
describing the confined phase of four dimensional compact U(1) lattice gauge
theories.


title:
Unquenched determination of the kaon parameter B_K from improved
  staggered fermions

abstract:
  The use of improved staggered actions (HYP, Asqtad) has been proved to reduce
the scaling corrections that affected previous calculations of B_K with
unimproved (standard) staggered fermions in the quenched approximation. This
improved behaviour allows us to perform a reliable calculation of B_K including
quark vacuum polarization effects, using the MILC configurations with n_f=2+1
flavours of sea fermions. We perform such a calculation for a single lattice
spacing, a=0.125 fm, and with kaons made up of degenerate quarks with m_s/2.
The valence strange quark mass m_s is fixed to its physical value and we use
two different values of the light sea quark masses. After a chiral
extrapolation of the results to the physical value of the sea quark masses, we
find \hat B_K = 0.83+-0.18, where the error is dominated by the uncertainty in
the lattice to continuum matching at O(\alpha_s^2). The matching will need to
be improved to get the precision needed to make full use of the experimental
data on \epsilon_K to constrain the unitarity triangle.


title:
Vortices, Symmetry Breaking, and Temporary Confinement in SU(2)
  Gauge-Higgs Theory

abstract:
  We further investigate center vortex percolation and Coulomb gauge remnant
symmetry breaking in the SU(2) gauge-Higgs model. We show that string breaking
is visible in Polyakov line correlators on the center projected lattice, that
our usual numerical tests successfully relate P-vortices to center vortices,
and that vortex removal removes the linear potential, as in the pure gauge
theory. This data suggests that global center symmetry is not essential to the
vortex confinement mechanism. But we also find that the line of vortex
percolation-depercolation transitions, and the line of remnant symmetry
breaking transitions, do not coincide in the SU(2)-Higgs phase diagram. This
non-uniqueness of transition lines associated with non-local order parameters
favors a straightforward interpretation of the Fradkin-Shenker theorem, namely:
there is no unambiguous distinction, in the SU(2) gauge-Higgs models, between a
"confining" phase and a Higgs phase.


title:
Systematic effects of the quenched approximation on the strong penguin
  contribution to epsilon'/epsilon

abstract:
  We discuss the implementation and properties of the quenched approximation in
the calculation of the left-right, strong penguin contributions (i.e. Q_6) to
epsilon'/epsilon. The coefficient of the new chiral logarithm, discovered by
Golterman and Pallante, which appears at leading order in quenched chiral
perturbation theory is evaluated using both the method proposed by those
authors and by an improved approach which is free of power divergent
corrections. The result implies a large quenching artifact in the contribution
of Q_6 to epsilon'/epsilon. This failure of the quenched approximation affects
only the strong penguin operators and so does not affect the Q_8 contribution
to epsilon'/epsilon nor Re A_0, Re A_2 and thus the Delta I=1/2 rule at tree
level in chiral perturbation theory.


title: Electromagnetic and spin polarisabilities in lattice QCD

abstract:
  We discuss the extraction of the electromagnetic and spin polarisabilities of
nucleons from lattice QCD. We show that the external field method can be used
to measure all the electromagnetic and spin polarisabilities including those of
charged particles. We then turn to the extrapolations required to connect such
calculations to experiment in the context of finite volume chiral perturbation
theory. We derive results relevant for lattice simulations of QCD,
partially-quenched QCD and quenched QCD. Our results for the polarisabilities
show a strong dependence on the lattice volume and quark masses, typically
differing from the infinite volume limit by ~10% for current lattice volumes
and quark masses.


title: Comment on "Chiral anomalies and rooted staggered fermions"

abstract:
  In hep-lat/0701018, Creutz claims that the rooting trick used in simulations
of staggered fermions to reduce the number of tastes misses key physics
whenever the desired theory has an odd number of continuum flavors, and uses
this argument to call into question the rooting trick in general. Here we show
that his argument fails as the continuum limit is approached, and therefore
does not imply any problem for staggered simulations. We also show that the
cancellations necessary to restore unitarity in physical correlators in the
continuum limit are a straightforward consequence of the restoration of taste
symmetry.


title:
Axial coupling constant of the nucleon for two flavours of dynamical
  quarks in finite and infinite volume

abstract:
  We present data for the axial coupling constant g_A of the nucleon obtained
in lattice QCD with two degenerate flavours of dynamical non-perturbatively
improved Wilson quarks. The renormalisation is also performed
non-perturbatively. For the analysis we give a chiral extrapolation formula for
g_A based on the small scale expansion scheme of chiral effective field theory
for two degenerate quark flavours. Applying this formalism in a finite volume
we derive a formula that allows us to extrapolate our data simultaneously to
the infinite volume and to the chiral limit. Using the additional lattice data
in finite volume we are able to determine the axial coupling of the nucleon in
the chiral limit without imposing the known value at the physical point.


title: The Schr\"odinger functional in lattice QCD with exact chiral symmetry

abstract:
  Similarly to the interaction lagrangian, the possible boundary conditions in
quantum field theories on space-time manifolds with boundaries are strongly
constrained by the symmetry and scaling properties of the theory. Based on this
general insight, a lattice formulation of the QCD Schr\"odinger functional is
proposed for the case where the lattice Dirac operator in the bulk of the
lattice coincides with the Neuberger--Dirac operator. The construction
satisfies all basic requirements (locality, symmetries, hermiticity) and is
suitable for numerical simulations.


title: Sizes of Lightest Glueballs in SU(3) Lattice Gauge Theory

abstract:
  Standard Monte Carlo simulations have been performed on improved lattices to
measure the wave functions and sizes of the scalar and tensor glueballs at four
lattice spacings in the range $a= 0.05 - 0.145$ fm. Systematic errors from
discretization and finite volume are studied. Our results in the continuum
limit show that the size of the tensor state is approximately two times as
large as that of the scalar glueball.


title: Two-flavor QCD Thermodynamics using Anisotropic Lattices

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


title: Decay constants of P-wave heavy-light mesons from unquenched lattice QCD

abstract:
  We review some decays that require knowledge of the decay constants of
$0^{+}$ heavy-light mesons. We compute the decay constants of P-wave
heavy-light mesons from unquenched lattice QCD, with two degenerate flavours of
sea quarks, at a single lattice spacing. The lightest sea quark mass used in
the calculation is a third of the strange quark mass. For the charm-strange
meson we obtain the decay constant: $f_{D_{s 0^+}} = 340(110)$ MeV using our
normalisation conventions. We obtain the $f_{P_s}^{static}$ (static-strange
P-wave) decay constant as $302(39)$ MeV.


title: Schroedinger functional formalism with domain-wall fermion

abstract:
  Finite volume renormalization scheme is one of the most fascinating scheme
for non-perturbative renormalization on lattice.
  By using the step scaling function one can follow running of renormalized
quantities with reasonable cost.
  It has been established the Schroedinger functional is very convenient to
define a field theory in a finite volume for the renormalization scheme.
  The Schroedinger functional, which is characterized by a
  Dirichlet boundary condition in temporal direction, is well defined and works
well for the Yang-Mills theory and QCD with the Wilson fermion.
  However one easily runs into difficulties if one sets the same sort of the
Dirichlet boundary condition for the overlap Dirac operator or the domain-wall
fermion.
  In this paper we propose an orbifolding projection procedure to impose the
Schroedinger functional Dirichlet boundary condition on the domain-wall
fermion.


title: Overlap lattice fermion in a gravitational field

abstract:
  We construct a lattice Dirac operator of overlap type that describes the
propagation of a Dirac fermion in an external gravitational field. The local
Lorentz symmetry is manifestly realized as a lattice gauge symmetry, while it
is believed that the general coordinate invariance is restored only in the
continuum limit. Our doubler-free Dirac operator satisfies the conventional
Ginsparg-Wilson relation and possesses gamma_5 hermiticity with respect to the
inner product, which is suggested by the general coordinate invariance. The
lattice index theorem in the presence of a gravitational field holds, and the
classical continuum limit of the index density reproduces the Dirac genus.
Reduction to a single Majorana fermion is possible for 8k+2 and 8k+4
dimensions, but not for 8k dimensions, which is consistent with the existence
of the global gravitational/gauge anomalies in 8k dimensions. Other Lorentz
representations, such as the spinor-vector and the bi-spinor representations,
can also be treated. Matter fields with a definite chirality (with respect to
the lattice-modified chiral matrix) are briefly considered.


title: Deconfinement in dense 2-color QCD

abstract:
  We study SU(2) lattice gauge theory with two flavors of Wilson fermion at
non-zero chemical potential mu and low temperature on a 8^3x16 system. We
identify three regimes along the mu-axis. For mu<~m_pi/2 the system remains in
the vacuum phase, and all physical observables considered remain essentially
unchanged. The intermediate regime is characterised by a non-zero diquark
condensate and an associated increase in the baryon density, consistent with
what is expected for Bose-Einstein condensation of tightly bound diquarks. We
also observe screening of the static quark potential here. In the high-density
deconfined regime we find a non-zero Polyakov loop and a strong modification of
the gluon propagator, including significant screening in the magnetic sector in
the static limit, which must have a non-perturbative origin. The behaviour of
thermodynamic observables and the superfluid order parameter are consistent
with a Fermi surface disrupted by a BCS diquark condensate. The energy per
baryon as a function of mu exhibits a minimum in the deconfined regime,
implying that macroscopic objects such as stars formed in this theory are
largely composed of quark matter.


title: Lattice fermions with complex mass

abstract:
  We present evidence in the Schwinger model that rooted staggered fermions may
correctly describe the m<0 sector of a theory with an odd number of flavors. We
point out that in QCD-type theories with a complex-valued quark mass every
non-chiral action essentially "borrows" knowledge about the
theta-transformation properties from the overlap action.


title: Non-perturbative mass spectrum of an extra-dimensional orbifold

abstract:
  We analyse non-perturbatively a five-dimensional SU(2) gauge theory
compactified on the S^1/Z_2 orbifold. In particular, we present simulation
results for the mass spectrum of the theory, which contains a Higgs and a
photon. The Higgs mass is found to be free of divergences without fine-tuning.
The photon mass is non-zero, thus providing us with the first lattice evidence
for a Higgs mechanism derived from an extra dimension. Data from the static
potential are consistent with dimensional reduction at low energies.


title:
Analysis of systematic errors in the calculation of renormalization
  constants of the topological susceptibility on the lattice

abstract:
  A Ginsparg-Wilson based calibration of the topological charge is used to
calculate the renormalization constants which appear in the field-theoretical
determination of the topological susceptibility on the lattice. A systematic
comparison is made with calculations based on cooling. The two methods agree
within present statistical errors (3%-4%). We also discuss the independence of
the multiplicative renormalization constant Z from the background topological
charge used to determine it.


title: Pseudovector meson with strangeness and closed-charm

abstract:
  We investigate the mass spectrum of 1^{+} exotic mesons with quark content
(\c\s\cbar\qbar) or (\c\q\cbar\sbar), using molecular and diquark-antidiquark
operators, in quenched lattice QCD with exact chiral symmetry. For the
molecular operator
{(\qbar\gamma_i\c)(\cbar\gamma_5\s)-(\cbar\gamma_i\s)(\qbar\gamma_5\c)} and the
diquark-antidiquark operator {(\q^T C \gamma_i \c)(\sbar C \gamma_5 \cbar^T)-
(\q^T C \gamma_5 \c)(\sbar C \gamma_i^T \cbar^T)}, both detect a 1^{+}
resonance with mass around 4010 +- 50 MeV in the limit m_q -> m_{u,d}.


title: Properties of light scalar mesons from lattice QCD

abstract:
  Lattice QCD with $N_f=2$ flavours of sea quark is used to explore the
spectrum and decay of scalar mesons. We are able to determine the $b_1$ - $a_0$
mass difference and this leads to the conclusion that the lightest non-singlet
scalar meson ($a_0$) has a mass of 1.01(4) GeV. We determine from the lattice
the coupling strength to KK and $\pi \eta$. We compute the leptonic decay
constant of the lightest non-singlet scalar meson.
  We discuss the impact of these lattice results on the interpretation of the
$a_0(980)$ state. We also discuss $K^*_0$ states.


title: Validity of the Rooted Staggered Determinant in the continuum limit

abstract:
  We investigate the continuum limit of the rooted staggered determinant in the
2-dimensional Schwinger model. We match both the unrooted and rooted staggered
determinant with an overlap fermion determinant of two (one) flavors and a
local pure gauge effective action by fitting the coefficients of the effective
action and the mass of the overlap operator. The residue of this fit measures
the difference of the staggered and overlap fermion actions. We show that this
residue scales at least as O(a^2), implying that any difference, be it local or
non-local, between the staggered and overlap actions becomes irrelevant in the
continuum limit. This observation justifies the rooting procedure.


title: Gauge invariant discretization of Poincare quantum gravity

abstract:
  In this paper we suggest gauge invariant discretization of Poincare quantum
gravity. We generalize Regge calculus to the case of Riemann-Cartan space. The
basic element of the constructed discretization is piecewize linear
Riemann-Cartan space with flat pieces of hypercubic form. We consider the model
with squared curvature action and calculate the correspondent lattice action.
We construct local measure over the dynamical variables of the lattice model.


title:
Lattice formulation of (2,2) supersymmetric gauge theories with matter
  fields

abstract:
  We construct lattice actions for a variety of (2,2) supersymmetric gauge
theories in two dimensions with matter fields interacting via a superpotential.


title:
The Gell-Mann -- Okubo mass relation among baryons from fully-dynamical
  mixed-action lattice QCD

abstract:
  We explore the Gell-Mann--Okubo mass relation among the octet baryons using
fully-dynamical, mixed-action (domain-wall on rooted-staggered) lattice QCD
calculations at a lattice spacing of b ~ 0.125 fm and pion masses of m_pi ~ 290
MeV, 350 MeV, 490 MeV and 590 MeV. Deviations from the Gell-Mann--Okubo mass
relation are found to be small at each quark mass.


title:
A strategy for implementing non-perturbative renormalisation of
  heavy-light four-quark operators in the static approximation

abstract:
  We discuss the renormalisation properties of the complete set of $\Delta B =
2$ four-quark operators with the heavy quark treated in the static
approximation. We elucidate the role of heavy quark symmetry and other symmetry
transformations in constraining their mixing under renormalisation. By
employing the Schroedinger functional, a set of non-perturbative
renormalisation conditions can be defined in terms of suitable correlation
functions. As a first step in a fully non-perturbative determination of the
scale-dependent renormalisation factors, we evaluate these conditions in
lattice perturbation theory at one loop. Thereby we verify the expected mixing
patterns and determine the anomalous dimensions of the operators at NLO in the
Schroedinger functional scheme. Finally, by employing twisted-mass QCD it is
shown how finite subtractions arising from explicit chiral symmetry breaking
can be avoided completely.


title: Simulating an arbitrary number of flavors of dynamical overlap fermions

abstract:
  We present a set of related Hybrid Monte Carlo methods to simulate an
arbitrary number of dynamical overlap fermions. Each fermion is represented by
a chiral pseudo-fermion field. The new algorithm reduces critical slowing down
in the chiral limit and for sectors of nontrivial topology.


title:
Compact lattice formulation of Cho-Faddeev-Niemi decomposition: string
  tension from magnetic monopoles

abstract:
  In this paper we begin on a new lattice formulation of the non-linear change
of variables called the Cho--Faddeev--Niemi decomposition in SU(2) Yang-Mills
theory. This is a compact lattice formulation improving the non-compact lattice
formulation proposed in our previous paper. Based on this formulation, we
propose a new gauge-invariant definition of the magnetic monopole current which
guarantees the magnetic charge quantization and reproduces the conventional
magnetic-current density obtained in the Abelian projection based on the
DeGrand--Toussaint method. Finally, we demonstrate the magnetic monopole
dominance in the string tension in SU(2) Yang-Mills theory on a lattice. Our
formulation enables one to reproduce in the gauge-invariant way remarkable
results obtained so far only in the Maximally Abelian gauge.


title: Observations on staggered fermions at non-zero lattice spacing

abstract:
  We show that the use of the fourth-root trick in lattice QCD with staggered
fermions corresponds to a non-local theory at non-zero lattice spacing, but
argue that the non-local behavior is likely to go away in the continuum limit.
We give examples of this non-local behavior in the free theory, and for the
case of a fixed topologically non-trivial background gauge field. In both
special cases, the non-local behavior indeed disappears in the continuum limit.
Our results invalidate a recent claim that at non-zero lattice spacing an
additive mass renormalization is needed because of taste-symmetry breaking.


title:
Automatic O(a) improvement for twisted-mass QCD in the presence of
  spontaneous symmetry breaking

abstract:
  In this paper we present a proof for automatic O(a) improvement in twisted
mass lattice QCD at maximal twist, which uses only the symmetries of the
leading part in the Symanzik effective action. In the process of the proof we
clarify that the twist angle is dynamically determined by vacuum expectation
values in the Symanzik theory. For maximal twist according to this definition,
we show that scaling violations of all quantities which have non-zero values in
the continuum limit are even in a. In addition, using Wilson Chiral
Perturbation Theory (WChPT), we investigate this definition for maximal twist
and compare it to other definitions which were already employed in actual
simulations.


title: Excited hadrons on the lattice: Baryons

abstract:
  We present results for masses of excited baryons from a quenched calculation
with Chirally Improved quarks at pion masses down to 350 MeV. Our analysis of
the correlators is based on the variational method. In order to provide a large
basis set for spanning the physical states, we use interpolators with different
Dirac structures and Jacobi smeared quark sources of different width. Our
spectroscopy results for a wide range of ground state and excited baryons are
discussed.


title:
Overlap Dirac operator at nonzero chemical potential and random matrix
  theory

abstract:
  We show how to introduce a quark chemical potential in the overlap Dirac
operator. The resulting operator satisfies a Ginsparg-Wilson relation and has
exact zero modes. It is no longer gamma_5-hermitian, but its nonreal
eigenvalues still occur in pairs. We compute the spectral density of the
operator on the lattice and show that, for small eigenvalues, the data agree
with analytical predictions of nonhermitian chiral random matrix theory for
both trivial and nontrivial topology.


title: Dynamical QCD simulations on anisotropic lattices

abstract:
  The simulation of QCD on dynamical (Nf=2) anisotropic lattices is described.
A method for nonperturbative renormalisation of the parameters in the
anisotropic gauge and quark actions is presented. The precision with which this
tuning can be carried out is determined in dynamical simulations on 8^3x48 and
8^3x80 lattices.


title:
Precision Electromagnetic Structure of Octet Baryons in the Chiral
  Regime

abstract:
  The electromagnetic properties of the baryon octet are calculated in quenched
QCD on a 20^3 x 40 lattice with a lattice spacing of 0.128 fm using the
fat-link irrelevant clover (FLIC) fermion action. FLIC fermions enable
simulations to be performed efficiently at quark masses as low as 300 MeV. By
combining FLIC fermions with an improved-conserved vector current, we ensure
that discretisation errors occur only at O(a^2) while maintaining current
conservation. Magnetic moments and electric and magnetic radii are extracted
from the electric and magnetic form factors for each individual quark sector.
  From these, the corresponding baryon properties are constructed. Our results
are compared extensively with the predictions of quenched chiral perturbation
theory. We detect substantial curvature and environment sensitivity of the
quark contributions to electric charge radii and magnetic moments in the low
quark mass region. Furthermore, our quenched QCD simulation results are in
accord with the leading non-analytic behaviour of quenched chiral perturbation
theory, suggesting that the sum of higher-order terms makes only a small
contribution to chiral curvature.


title: Spin-3/2 baryons from an anisotropic lattice QCD action

abstract:
  The mass spectrum of baryons in the spin-3/2 sector is computed in quenched
lattice QCD using a tadpole-improved anisotropic action. Both isospin 1/2 and
3/2 (the traditional decuplet) are considered, as well as members that contain
strange quarks. States with positive and negative parities are isolated by
parity projection, while states with spin-3/2 and spin-1/2 are separated by
spin projection. The extent to which spin projection is needed is examined. The
issue of optimal interpolating field is also investigated. The results are
discussed in relation to previous calculations and experiment.


title: Glauber dynamics of phase transitions: SU(3) lattice gauge theory

abstract:
  Motivated by questions about the QCD deconfining phase transition, we studied
in two previous papers Model A (Glauber) dynamics of 2D and 3D Potts models,
focusing on structure factor evolution under heating (heating in the gauge
theory notation, i.e., cooling of the spin systems). In the present paper we
set for 3D Potts models (Ising and 3-state) the scale of the dynamical effects
by comparing to equilibrium results at first and second order phase transition
temperatures, obtained by re-weighting from a multicanonical ensemble. Our
finding is that the dynamics entirely overwhelms the critical and non-critical
equilibrium effects.
  In the second half of the paper we extend our results by investigating the
Glauber dynamics of pure SU(3) lattice gauge on $N_{\tau} N_{\sigma}^3$
lattices directly under heating quenches from the confined into the deconfined
regime. The exponential growth factors of the initial response are calculated,
which give Debye screening mass estimates. The quench leads to competing vacuum
domains of distinct $Z_3$ triality, which delay equilibration of pure gauge
theory forever, while their role in full QCD remains a subtle question. As in
spin systems we find for pure SU(3) gauge theory a dynamical growth of
structure factors, reaching maxima which scale approximately with the volume of
the system, before settling down to equilibrium. Their influence on various
observables is studied and different lattice sizes are simulated to illustrate
an approach to a finite volume continuum limit. Strong correlations are found
during the dynamical process, but not in the deconfined phase at equilibrium.


title:
Renormalisation of Composite Operators in Lattice Perturbation Theory
  with Clover Fermions: Non-forward Matrix Elements

abstract:
  We consider the renormalisation of lattice QCD operators with one and two
covariant derivatives related to the first and second moments of generalised
parton distributions and meson distribution amplitudes. Employing the clover
fermion action we calculate their non-forward quark matrix elements in one-loop
lattice perturbation theory. For some representations of the hypercubic group
commonly used in simulations we determine the sets of all possible mixing
operators and compute the matrices of renormalisation factors in one-loop
approximation. We describe how tadpole improvement is applied to the results.


title:
Chiral Lattice Gauge Theories from Warped Domain Walls and
  Ginsparg-Wilson Fermions

abstract:
  We propose a construction of a 2-dimensional lattice chiral gauge theory. The
construction may be viewed as a particular limit of an infinite warped
3-dimensional theory. We also present a "single-site'' construction using
Ginsparg-Wilson fermions which may avoid, in both 2 and 4 dimensions, the
problems of waveguide-Yukawa models.


title:
A deconstruction lattice description of the D1/D5 brane world-volume
  gauge theory

abstract:
  In this article, I generalize the deconstruction lattice formulation of
Endres and Kaplan [hep-lat/0604012] to two-dimensional super-QCD with eight
supercharges, denoted (4,4), and bifundamental matter. I specialize to a
particularly interesting (4,4) gauge theory, with gauge group U(N_c) \times
U(N_f), and U(N_f) weakly gauged. It describes the infrared limit of the D1/D5
brane system, which has been studied extensively as an example of the
AdS_3/CFT_2 correspondence. The construction here preserves two supercharges
exactly, and has a lattice structure quite similar to that which has previously
appeared in the deconstruction approach; i.e., site, link and diagonal fields
with both Bose and Fermi statistics. I remark on possible applications of the
lattice theory that would test the AdS_3/CFT_2 correspondence, particularly one
that would exploit the recent worldsheet instanton analysis of Chen and Tong
[hep-th/0604090].


title: Study of Possible Proton-Antiproton Hexaquark State in Lattice QCD

abstract:
  We have used standard techniques of lattice quantum chromodynamics to look
for evidence of the spin-zero six quark flavour singlet state ($J^{PC}=0^{-+}$)
observed by BES Collaboration, and to determine the splitting between the mass
of the possible proton-antiproton and the mass of two protons, its threshold.
Using the various interpolating fields we find indications that for
sufficiently light quarks proton-antiproton is slightly above the $2m_{p}$
threshold. The lattice resonance signal of binding observed near the physical
and continuum regimes do not support the existence of proton-antiproton state
as a spin-zero hexaquark state.


title: Exploring twisted mass Lattice QCD with the Clover term

abstract:
  It has been shown that in the twisted mass formulation of Lattice QCD at
maximal twist large cutoff effects are generated when the quark mass becomes of
O(a Lambda_QCD^2). In general, these effects can be suppressed in two ways:
either by choosing the critical quark mass in an "optimal way", or by adding
the Clover term to the twisted action. We investigate the second option by
performing a quenched lattice QCD simulation with twisted Clover fermions and
pion masses as low as 280 MeV. We show that the Clover term is indeed efficient
in reducing the large cutoff effects. In particular, the so-called bending
phenomenon observed in the determination of the pion decay constant is cured in
this way. In addition, by using maximally twisted Clover fermions, we provide a
non-perturbative determination of the vector current renormalization constant
Z_V as well as of the non-perturbatively renormalized light quark masses.
Finally, we calculate the connected contribution to the charged-neutral
pseudoscalar meson mass splitting, finding that the introduction of the Clover
term in the twisted action is also beneficial, in the quenched approximation,
in reducing cutoff effects related to the isospin symmetry breaking at finite
lattice spacing.


title:
Leptonic widths of heavy quarkonia: S-Wave QCD/NRQCD matching
  coefficients for the electromagnetic vector annihilation current at O(alpha_s
  v^2)

abstract:
  We construct the S-wave part of the electromagnetic vector annihilation
current to O(alpha_s v^2)$ on the lattice for heavy quarks whose dynamics are
described by the NRQCD action, where v is the non-relativistic quark velocity.
The lattice vector current for QQbar annihilation is expressed as a linear
combination of lattice operators with quantum numbers L=0, J^P=1^-, and the
coefficients are determined by matching this lattice current to the
corresponding continuum current in QCD to O(v^2) to one-loop. The annihilation
channel gives a complex amplitude and a proper choice for the contours of
integration is needed; a simple Wick rotation is not possible. In this way, and
with a careful choice of subtraction functions in the numerical integration,
the Coulomb-exchange and infrared singularities appearing in the amplitudes are
successfully treated. The matching coefficients are given as a function of the
heavy quark mass Ma in lattice units. An automated vertex generation program
written in Python is employed, allowing us to use a realistic NRQCD action and
an improved gluon lattice action. A change in the definition of either action
is easily accommodated in this procedure. The final result is applicable to the
electromagnetic decays of heavy quarkonia, notably the Upsilon meson.


title:
A Framework for Systematic Study of QCD Vacuum Structure I: Kolmogorov
  Entropy and the Principle of Chiral Ordering

abstract:
  In this series of articles we describe a systematic approach to studying QCD
vacuum structure using the methods of lattice gauge theory. Our framework
incorporates four major components. (i) The recently established existence of
space-time order at all scales (fundamental structure) observed directly in
typical configurations of regularized path-integral ensembles. (ii) The notion
of scale-dependent vacuum structure (effective structure) providing the means
for representing and quantifying the influence of fluctuations at various
scales on physical observables (phenomena). (iii) The unified description of
gauge and fermionic aspects of the theory which facilitates a high level of
space-time order in the path-integral ensembles. (iv) The strict ``Bottom-Up''
approach wherein the process of identifying the vacuum structure proceeds
inductively, using the information from valid lattice QCD ensembles as the only
input. In this work we first elaborate on the meaning of the notion of
space-time order in a given configuration which is conceptually at the heart of
the path-integral approach to vacuum structure. It is argued that the
algorithmic complexity of binary strings associated with coarse-grained
descriptions of the configuration provides a relevant quantitative measure. The
corresponding ensemble averages define the ranking of different lattice
theories at given cutoff by the degree of space-time order generated via their
dynamics. We then introduce the set of local transformations of a
configuration, chiral orderings, in which the transformed gauge connection
represents an effective matrix phase acquired by chiral fermion when hopping
over a given link. It is proposed that chiral orderings facilitate the
evolution in the set of actions which increases the degree of space-time order
while preserving the physical content of the theory, and should thus be used in
the search for the fundamental QCD vacuum structure. The relation to
renormalization group ideas is discussed, and the first step in general
formulation of effective lattice QCD realizing the notion of scale-dependent
vacuum structure is given.


title: First lattice study of low-energy charmonium-hadron interaction

abstract:
  We study the scattering lengths of charmonia (J/psi and eta_c) with light
hadrons (pi, rho and N) by the quenched lattice QCD simulations on 24x24x24x48,
32x32x32x48 and 48x48x48x48 lattices with the lattice spacing a = 0.068 fm. The
scattering length is extracted by using the Luscher's phase-shift formula
together with the measurement of the energy shift Delta E of two hadrons on the
lattice. We find that there exist attractive interactions in all channels,
J/psi(eta_c)-pi, J/psi(eta_c)-rho and J/psi(eta_c)-N: The s-wave J/psi-pi
(eta_c-pi) scattering length is determined as 0.0119+-0.0039 fm (0.0113+-0.0035
fm) and the corresponding elastic cross section at the threshold becomes
0.018+0.013-0.010 mb (0.016+0.011-0.008 mb). Also, the J/psi-N (eta_c-N)
spin-averaged scattering length is 0.71+-0.48 fm (0.70+-0.66 fm), which is at
least an order of magnitude larger than the charmonium-pion scattering length.
The volume dependence of the energy shifts is also investigated to check the
expected 1/L^3 behavior of Delta E at a large spatial size L.


title: The nucleon axial-vector coupling beyond one loop

abstract:
  We analyze the nucleon axial-vector coupling to two loops in chiral
perturbation theory. We show that chiral extrapolations based on this
representation require lattice data with pion masses below 300 MeV.


title:
Exploratory study of three-point Green's functions in Landau-gauge
  Yang-Mills theory

abstract:
  Green's functions are a central element in the attempt to understand
non-perturbative phenomena in Yang-Mills theory. Besides the propagators,
3-point Green's functions play a significant role, since they permit access to
the running coupling constant and are an important input in functional methods.
Here we present numerical results for the two non-vanishing 3-point Green's
functions in 3d pure SU(2) Yang-Mills theory in (minimal) Landau gauge, i.e.
the three-gluon vertex and the ghost-gluon vertex, considering various
kinematical regimes. In this exploratory investigation the lattice volumes are
limited to 20^3 and 30^3 at beta=4.2 and beta=6.0. We also present results for
the gluon and the ghost propagators, as well as for the eigenvalue spectrum of
the Faddeev-Popov operator. Finally, we compare two different numerical methods
for the evaluation of the inverse of the Faddeev-Popov matrix, the point-source
and the plane-wave-source methods.


title: Phase Structure of Z(3)-Polyakov-Loop Models

abstract:
  We study effective lattice actions describing the Polyakov loop dynamics
originating from finite-temperature Yang-Mills theory. Starting with a
strong-coupling expansion the effective action is obtained as a series of
Z(3)-invariant operators involving higher and higher powers of the Polyakov
loop, each with its own coupling. Truncating to a subclass with two couplings
we perform a detailed analysis of the statistical mechanics involved. To this
end we employ a modified mean field approximation and Monte Carlo simulations
based on a novel cluster algorithm. We find excellent agreement of both
approaches concerning the phase structure of the theories. The phase diagram
exhibits both first and second order transitions between symmetric,
ferromagnetic and anti-ferromagnetic phases with phase boundaries merging at
three tricritical points. The critical exponents nu and gamma at the continuous
transition between symmetric and anti-ferromagnetic phases are the same as for
the 3-state Potts model.


title: Overlap Hypercube Fermions in QCD Simulations Near the Chiral Limit

abstract:
  The overlap hypercube fermion is a variant of a chirally symmetric lattice
fermion, which is endowed with a higher level of locality than the standard
overlap fermion. We apply this formulation in quenched QCD simulations with
light quarks. In the p-regime we evaluate the masses of light pseudoscalar and
vector mesons, as well as the pion decay constant and the renormalisation
constant Z_A. In the epsilon-regime we present results for the leading Low
Energy Constants of the chiral Lagrangian, Sigma and F_pi. To this end, we
perform fits to predictions by chiral Random Matrix Theory and by different
versions of quenched Chiral Perturbation Theory, referring to distinct
correlation functions. These results, along with an evaluation of the
topological susceptibility, are also compared to the outcome based on the
standard overlap operator.


title:
Strong-Isospin Violation in the Neutron-Proton Mass Difference from
  Fully-Dynamical Lattice QCD and PQQCD

abstract:
  We determine the strong-isospin violating component of the neutron-proton
mass difference from fully-dynamical lattice QCD and partially-quenched QCD
calculations of the nucleon mass, constrained by partially-quenched chiral
perturbation theory at one-loop level. The lattice calculations were performed
with domain-wall valence quarks on MILC lattices with rooted staggered
sea-quarks at a lattice spacing of b=0.125 fm, lattice spatial size of L=2.5 fm
and pion masses ranging from m_pi ~ 290 MeV to ~ 350 MeV. At the physical value
of the pion mass, we predict M_n - M_p |(d-u) = 2.26 +- 0.57 +- 0.42 +- 0.10
MeV where the first error is statistical, the second error is due to the
uncertainty in the ratio of light-quark masses, eta=m_u/m_d, determined by
MILC, and the third error is an estimate of the systematic due to chiral
extrapolation.


title:
Dynamic Critical Behavior of Percolation Observables in the 2d Ising
  Model

abstract:
  We present preliminary results of our numerical study of the critical
dynamics of percolation observables for the two-dimensional Ising model. We
consider the (Monte-Carlo) short-time evolution of the system obtained with a
local heat-bath method and with the global Swendsen-Wang algorithm. In both
cases, we find qualitatively different dynamic behaviors for the magnetization
and Omega, the order parameter of the percolation transition. This may have
implications for the recent attempts to describe the dynamics of the QCD phase
transition using cluster observables.


title:
K^0-\bar K^0 mixing beyond the standard model and CP-violating
  electroweak penguins in quenched QCD with exact chiral symmetry

abstract:
  We present results for the \Delta S=2 matrix elements which are required to
study neutral kaon mixing in the standard model (SM) and beyond (BSM). We also
provide leading chiral order results for the matrix elements of the electroweak
penguin operators which give the dominant \Delta I=3/2 contribution to direct
CP violation in K->\pi\pi decays. Our calculations were performed with
Neuberger fermions on two sets of quenched Wilson gauge configurations at
inverse lattice spacings of approximately 2.2 GeV and 1.5 GeV. All
renormalizations were implemented non-perturbatively in the RI/MOM scheme,
where we accounted for sub-leading operator product expansion corrections and
discretization errors. We find ratios of non-SM to SM matrix elements which are
roughly twice as large as in the only other dedicated lattice study of these
amplitudes. On the other hand, our results for the electroweak penguin matrix
elements are in good agreement with two recent domain-wall fermion
calculations. As a by-product of our study, we determine the strange quark
mass. Our main results are summarized and discussed in Sec. VII. Within our
statistics, we find no evidence for scaling violations.


title: The nucleon electromagnetic form factors from Lattice QCD

abstract:
  We evaluate the isovector nucleon electromagnetic form factors in quenched
and full QCD on the lattice using Wilson fermions. In the quenched theory we
use a lattice of spatial size 3 fm at beta=6.0 enabling us to reach low
momentum transfers and a lowest pion mass of about 400 MeV. In the full theory
we use a lattice of spatial size 1.9 fm at beta=5.6 and lowest pion mass of
about 380 MeV enabling comparison with the results obtained in the quenched
theory. We compare our lattice results to the isovector part of the
experimentally measured form factors.


title: Linking confinement to spectral properties of the Dirac operator

abstract:
  We represent Polyakov loops and their correlators as spectral sums of
eigenvalues and eigenmodes of the lattice Dirac operator. The deconfinement
transition of pure gauge theory is characterized as a change in the response of
moments of eigenvalues to varying the boundary conditions of the Dirac
operator. We argue that the potential between static quarks is linked to
spatial correlations of Dirac eigenvectors.


title: Non-Perturbative U(1) Gauge Theory at Finite Temperature

abstract:
  For compact U(1) lattice gauge theory (LGT) we have performed a finite size
scaling analysis on $N_{\tau} N_s^3$ lattices for $N_{\tau}$ fixed by
extrapolating spatial volumes of size $N_s\le 18$ to $N_s\to\infty$. Within the
numerical accuracy of the thus obtained fits we find for $N_{\tau}=4$, 5 and~6
second order critical exponents, which exhibit no obvious $N_{\tau}$
dependence. The exponents are consistent with 3d Gaussian values, but not with
either first order transitions or the universality class of the 3d XY model. As
the 3d Gaussian fixed point is known to be unstable, the scenario of a yet
unidentified non-trivial fixed point close to the 3d Gaussian emerges as one of
the possible explanations.


title: Improved Perturbation Theory for Improved Lattice Actions

abstract:
  We study a systematic improvement of perturbation theory for gauge fields on
the lattice; the improvement entails resumming, to all orders in the coupling
constant, a dominant subclass of tadpole diagrams.
  This method, originally proposed for the Wilson gluon action, is extended
here to encompass all possible gluon actions made of closed Wilson loops; any
fermion action can be employed as well. The effect of resummation is to replace
various parameters in the action (coupling constant, Symanzik coefficients,
clover coefficient) by ``dressed'' values; the latter are solutions to certain
coupled integral equations, which are easy to solve numerically.
  Some positive features of this method are: a) It is gauge invariant, b) it
can be systematically applied to improve (to all orders) results obtained at
any given order in perturbation theory, c) it does indeed absorb in the dressed
parameters the bulk of tadpole contributions.
  Two different applications are presented: The additive renormalization of
fermion masses, and the multiplicative renormalization Z_V (Z_A) of the vector
(axial) current. In many cases where non-perturbative estimates of
renormalization functions are also available for comparison, the agreement with
improved perturbative results is significantly better as compared to results
from bare perturbation theory.


title:
Discretization errors in the spectrum of the Hermitian Wilson-Dirac
  operator

abstract:
  I study the leading effects of discretization errors on the low energy part
of the spectrum of the Hermitian Wilson-Dirac operator in infinite volume. The
method generalizes that used to study the spectrum of the Dirac operator in the
continuum, and uses partially quenched chiral perturbation theory for Wilson
fermions. The leading-order corrections are proportional to a^2 (a being the
lattice spacing). At this order I find that the method works only for one
choice of sign of one of the three low energy constants describing
discretization errors. If these constants have the relative magnitudes expected
from large N_c arguments, then the method works if the theory has an Aoki phase
for m of order a^2, but fails if there is a first-order transition. In the
former case, the dependence of the gap and the spectral density on m and a^2
are determined. In particular, the gap is found to vanish more quickly as
m_pi^2-> 0 than in the continuum. This reduces the region where simulations are
safe from fluctuations in the gap.


title: Power-counting theorem for staggered fermions

abstract:
  Lattice power-counting is extended to QCD with staggered fermions. As
preparation, the difficulties encountered by Reisz's original formulation of
the lattice power-counting theorem are illustrated. One of the assumptions that
is used in his proof does not hold for staggered fermions, as was pointed out
long ago by Luscher. Finally, I generalize the power-counting theorem, and the
methods of Reisz's proof, such that the difficulties posed by staggered
fermions are overcome.


title:
Exploring the HMC trajectory-length dependence of autocorrelation times
  in lattice QCD

abstract:
  We study autocorrelation times of physical observables in lattice QCD as a
function of the molecular dynamics trajectory length in the hybrid Monte-Carlo
algorithm. In an interval of trajectory lengths where energy and reversibility
violations can be kept under control, we find a variation of the integrated
autocorrelation times by a factor of about two in the quantities of interest.
Trajectories longer than conventionally used are found to be superior both in
the Nf=0 and Nf=2 examples considered here. We also provide evidence that they
lead to faster thermalization of systems with light quarks.


title: Exotic Meson Decay Widths using Lattice QCD

abstract:
  A decay width calculation for a hybrid exotic meson h, with JPC=1-+, is
presented for the channel h->pi+a1. This quenched lattice QCD simulation
employs Luescher's finite box method. Operators coupling to the h and pi+a1
states are used at various levels of smearing and fuzzing, and at four quark
masses. Eigenvalues of the corresponding correlation matrices yield energy
spectra that determine scattering phase shifts for a discrete set of relative
pi+a1 momenta. Although the phase shift data is sparse, fits to a Breit-Wigner
model are attempted, resulting in a decay width of about 60 MeV when averaged
over two lattice sizes.


title: Search for the Theta^+(1540) in lattice QCD

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 12^3 x 24 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: Quarkonia correlators and spectral functions from lattice QCD

abstract:
  I discuss recent progress in calculating quarkonia correlators and spectral
functions on the lattice in relation with the problem of quarkonia dissolution
at high temperatures and heavy quark transport in Quark Gluon Plasma.


title:
Peculiarities in the Spectrum of the Adjoint Scalar Kinetic Operator in
  Yang-Mills Theory

abstract:
  We study the spectrum of low-lying eigenmodes of the kinetic operator for
scalar particles, in the color adjoint representation of Yang-Mills theory. The
kinetic operator is the covariant Laplacian, plus a constant which serves to
renormalize mass. In the pure gauge theory, our data indicates that the
interval between the lowest eigenvalue and the mobility edge tends to infinity
in the continuum limit. On these grounds, it is suggested that the perturbative
expression for the scalar propagator may be misleading even at distance scales
that are small compared to the confinement scale. We also measure the density
of low-lying eigenmodes, and find a possible connection to multi-critical
matrix models of order m=1.


title: A gauge invariant cluster algorithm for the Ising spin glass

abstract:
  The frustrated Ising model in two dimensions is revisited. The frustration is
quantified in terms of the number of non-trivial plaquettes which is invariant
under the Nishimori gauge symmetry. The exact ground state energy is calculated
using Edmond's algorithm. A novel cluster algorithm is designed which treats
gauge equivalent spin glasses on equal footing and allows for efficient
simulations near criticality. As a first application, the specific heat near
criticality is investigated.


title:
$Z_6$ symmetry, electroweak transition, and magnetic monopoles at high
  temperature

abstract:
  We consider the lattice realization of the Standard Model with an additional
$Z_6$ symmetry. Numerical simulations were performed on the asymmetric lattice,
which corresponds to the finite temperature theory. Our choice of parameters
corresponds to large Higgs masses ($M_H > 90$ Gev). The phase diagram was
investigated and has been found to be different from that of the usual lattice
realization of the Standard Model. It has been found, that the
confinement-deconfinement phase transition lines for the SU(2) and SU(3) fields
coincide. The transition line between Higgs and symmetric deconfinement parts
of the phase diagram and the confinement-deconfinement transition line meet in
a triple point. The transition between Higgs and symmetric parts of the phase
diagram corresponds to the finite temperature electroweak transition/crossover.
We see for the first time evidence that Nambu monopoles are condensed at
$T>T_c$ while at $T<T_c$ their condensate vanishes.


title:
Numerical simulation of QCD with u, d, s and c quarks in the
  twisted-mass Wilson formulation

abstract:
  A first study of numerical Monte Carlo simulations with two quark doublets, a
mass-degenerate one and a mass-split one, interpreted as u, d, s and c quarks,
is carried out in the framework of the twisted mass Wilson lattice formulation.
Tuning the bare parameters of this theory is explored on 12^3x24 and 16^3x32
lattices at lattice spacings a=0.20fm and a=0.15fm, respectively.


title: Moments of pseudoscalar meson distribution amplitudes from the lattice

abstract:
  Based on lattice simulations with two flavours of dynamical, O(a)-improved
Wilson fermions we present results for the first two moments of the
distribution amplitudes of pseudoscalar mesons at several values of the valence
quark masses. By extrapolating our results to the physical masses of up/down
and strange quarks, we find the first two moments of the K^+ distribution
amplitude and the second moment of the pi^+ distribution amplitude. We use
nonperturbatively determined renormalisation coefficients to obtain results in
the MSbar scheme. At a scale of 4 GeV^2 we find a_2^pi=0.201(114) for the
second Gegenbauer moment of the pion's distribution amplitude, while for the
kaon, a_1^K=0.0453(9)(29) and a_2^K=0.175(18)(47).


title: Monte Carlo Simulation of a NC Gauge Theory on The Fuzzy Sphere

abstract:
  We find using Monte Carlo simulation the phase structure of noncommutative
U(1) gauge theory in two dimensions with the fuzzy sphere S^2_N as a
non-perturbative regulator. There are three phases of the model. i) A matrix
phase where the theory is essentially SU(N) Yang-Mills reduced to zero
dimension . ii) A weak coupling fuzzy sphere phase with constant specific heat
and iii) A strong coupling fuzzy sphere phase with non-constant specific heat.
The order parameter distinguishing the matrix phase from the sphere phase is
the radius of the fuzzy sphere. The three phases meet at a triple point. We
also give the theoretical one-loop and 1/N expansion predictions for the
transition lines which are in good agreement with the numerical data. A Monte
Carlo measurement of the triple point is also given.


title: Gap Domain Wall Fermions

abstract:
  I demonstrate that the chiral properties of Domain Wall Fermions (DWF) in the
large to intermediate lattice spacing regime of QCD, 1 to 2 GeV, are
significantly improved by adding to the action two standard Wilson fermions
with supercritical mass equal to the negative DWF five dimensional mass. Using
quenched DWF simulations I show that the eigenvalue spectrum of the transfer
matrix Hamiltonian develops a substantial gap and that the residual mass
decreases appreciatively. Furthermore, I confirm that topology changing remains
active and that the hadron spectrum of the added Wilson fermions is above the
lattice cutoff and therefore is irrelevant. I argue that this result should
also hold for dynamical DWF and furthermore that it should improve the chiral
properties of related fermion methods.


title:
Dilute Liquid of Instanton and Its Topological Charge Dominate the QCD
  Vacuum

abstract:
  APE smearing and overlap-Dirac operator are combined to filter QCD vacuum
configurations. The results obtained from overlap fermions and improved 5Li
cooling are compared, both of them exhibit structures of dilute liquid of
instanton. Finally the overlap fermions, improved 5Li cooling and APE smearing
are combined to calculate the topological charge and identify the structure of
QCD vacuum. The results suggest dilute liquid of instanton dominance of
topological charge fluctuations in quenched lattice QCD.


title: Gluon flux-tube distribution and linear confinement in baryons

abstract:
  We have observed the formation of gluon flux-tubes within baryons using
lattice QCD techniques. A high-statistics approach, based on translational and
rotational symmetries of the four-dimensional lattice, enables us to observe
correlations between vacuum action density and quark positions in a completely
gauge independent manner. This contrasts with earlier studies which used
gauge-dependent smoothing techniques. We used 200 O(a^2) improved quenched QCD
gauge-field configurations on a 16^3x32 lattice with a lattice spacing of 0.123
fm. In the presence of static quarks flux tubes representing the suppression of
gluon-field fluctuations are observed. We have analyzed 11 L-shapes and 8 T and
Y shapes of varying sizes in order to explore a variety of flux-tube
topologies, including the ground state. At large separations, Y-shape flux-tube
formation is observed. T-shaped paths are observed to relax towards a Y-shaped
topology, whereas L-shaped paths give rise to a large potential energy. We do
not find any evidence for the formation of a Delta-shaped flux-tube (empty
triangle) distribution. However, at small quark separations, we observe an
expulsion of gluon-field fluctuations in the shape of a filled triangle with
maximal expulsion at the centre of the triangle. Having identified the precise
geometry of the flux distribution, we are able to perform quantitative
comparison between the length of the flux-tube and the associated static quark
potential. For every source configuration considered we find a universal string
tension, and conclude that, for large quark separations, the ground state
potential is that which minimizes the length of the flux-tube. The flux tube
radius of the baryonic ground state potential is found to be 0.38 \pm 0.03 fm,
with vacuum fluctuations suppressed by 7.2 \pm 0.6 %.


title:
The eta mass and NNLO Three-Flavor Partially Quenched Chiral
  Perturbation Theory

abstract:
  We show how to resum neutral propagators to all orders in Partially Quenched
Chiral Perturbation Theory. We calculate the relevant quantities to
next-to-next-to-leading order (NNLO). Using these results we show how to extend
the proposal by Sharpe and Shoresh for determining the parameters relevant for
the eta mass from partially quenched lattice QCD calculations to NNLO.


title:
Robustness of baryon-strangeness correlation and related ratios of
  susceptibilities

abstract:
  Using quenched lattice QCD simulations we investigate the continuum limit of
baryon-strangeness correlation and other related conserved charge-flavour
correlations for temperatures T_c<T\le2T_c. By working with lattices having
large temporal extents (N_\tau=12, 10, 8, 4) we find that these quantities are
almost independent of the lattice spacing, i.e, robust. We also find that these
quantities have very mild dependence on the sea quark mass and acquire values
which are very close to their respective ideal gas limits. Our results also
confirm robustness of the Wroblewski parameter.


title: SU(3) gauge theory at finite temperature in 2 + 1 dimensions

abstract:
  In this article we will discuss numerical results on screening masses and
thermodynamic quantities in 2 + 1 dimensional SU(3) gauge theory. We will also
compare them to perturbation theory and the dimensionally reduced model.


title: QCD Thermodynamics with Almost Realistic Quark Masses

abstract:
  Ongoing calculations on the QCDOC supercomputer at Brookhaven National
Laboratory and the APEnext installation at the University of Bielefeld aim to
determine the critical temperature of the QCD phase transition as well as the
equation of state with almost realistic quark masses. We will discuss
preliminary results of the quark mass and cut-off dependence of order
parameters, susceptibilities, static quark potentials and the critical
temperature in (2+1)-flavor QCD. All these quantities are of immediate interest
for heavy ion phenomenology.


title: Lattice Regularization and Symmetries

abstract:
  Finding the relation between the symmetry transformations in the continuum
and on the lattice might be a nontrivial task as illustrated by the history of
chiral symmetry. Lattice actions induced by a renormalization group procedure
inherit all symmetries of the continuum theory. We give a general procedure
which gives the corresponding symmetry transformations on the lattice.