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Symmetries of spatial meson correlators in high temperature QCDFeb 08 2019Based on a complete set of $J = 0$ and $J=1$ spatial isovector correlation functions calculated with $N_F = 2$ domain wall fermions we identify an intermediate temperature regime of $T \sim 250 - 550$ MeV where chiral symmetry is restored but the correlators ... More

Excited State Spectroscopy in the Lattice Gross-Neveu ModelOct 09 2007We present preliminary results of an excited state spectroscopy calculation in the 2-d lattice Gross-Neveu model. We address the construction of suitable interpolators for the variational method and their overlap with excitations. We comment on the role ... More

Center clusters in the Yang-Mills vacuumNov 10 2010Jan 12 2011Properties of local Polyakov loops for SU(2) and SU(3) lattice gauge theory at finite temperature are analyzed. We show that spatial clusters can be identified where the local Polyakov loops have values close to the same center element. For a suitable ... More

Improving the Dirac Operator in Lattice QCDNov 22 2001Recently various new concepts for the construction of Dirac operators in lattice Quantum Chromodynamics (QCD) have been introduced. These operators satisfy the so-called Ginsparg-Wilson condition (GWC), thus obeying the Atiyah-Singer index theorem and ... More

Resonance Scattering Phase Shifts in a 2-d Lattice ModelJun 03 1992We study a simple 2-d model representing two fields with different mass and a 3-point coupling term. The phase shift in the resonating 2-particle channel is determined from the energy spectrum obtained in Monte Carlo simulations on finite lattices. Masses ... More

Pion form factor with chirally improved fermionsSep 12 2005We present results for Monte Carlo calculations of the electromagnetic vector and scalar form factors of the pion in a quenched simulation. We work at a lattice spacing of 0.15 fm and use two lattice volumes up to a spatial size of 2.4 fm. The pion form ... More

Lattice calculation of low energy constants with Ginsparg-Wilson type fermionsSep 01 2005Nov 08 2005We present a quenched lattice calculation of low energy constants using the chirally improved Dirac operator. Several lattice sizes at different lattice spacings are studied. We systematically compare various methods for computing these quantities, using ... More

The chiral limit of the two-flavor lattice Schwinger model with Wilson fermionsSep 03 1999Sep 24 1999We study the 2-flavor lattice Schwinger model with Wilson fermions in the chiral limit. The quark mass is determined using the PCAC definition. We numerically compute the masses of the iso-triplet (pi) and iso-singlet particles (eta) for different quark ... More

A lattice calculation of the pion form factor with Ginsparg-Wilson-type fermionsNov 18 2005Feb 03 2006Results for Monte Carlo calculations of the electromagnetic vector and scalar form factors of the pion in a quenched simulation are presented. We work with two different lattice volumes up to a spatial size of 2.4 fm at a lattice spacing of 0.148 fm. ... More

Low energy constants from the chirally improved Dirac operator D_CISep 19 2005Sep 30 2005The leading order low energy parameters like the pion decay constant or the quark condensate are well-known from "classical" low energy theorems and experiments. It is a challenge, however, to find these parameters based exclusively on an ab-initio QCD ... More

Approximate Ginsparg-Wilson fermions: A first testJul 27 2000Nov 30 2000We construct a 4-d lattice Dirac operator D using a systematical expansion in terms of simple operators on the lattice. The Ginsparg-Wilson equation turns into a system of coupled equations for the expansion coefficients of D. We solve these equations ... More

Properties of canonical fermion determinants with a fixed quark numberOct 19 2009Nov 17 2009Using a dimensional reduction formula for the lattice fermion determinant we study canonical determinants on quenched SU(3) gauge configurations. The canonical determinants decribe a fixed quark number and we analyze their properties below and above the ... More

Condensation phenomena in two-flavor scalar QED at finite chemical potentialJan 26 2015We study condensation in two-flavored, scalar QED with non-degenerate masses at finite chemical potential. The conventional formulation of the theory has a sign problem at finite density which can be solved using an exact reformulation of the theory in ... More

Solving the sign problem of two flavor scalar electrodynamics at finite chemical potentialNov 08 2013We explore two flavor scalar electrodynamics on the lattice, which has a complex phase problem at finite chemical potential. By rewriting the action in terms of dual variables this complex phase problem can be solved exactly. The dual variables are link- ... More

Developing and testing the density of states FFA method in the SU(3) spin modelJul 25 2016The Density of States Functional Fit Approach (DoS FFA) is a recently proposed modern density of states technique suitable for calculations in lattice field theories with a complex action problem. In this article we present an exploratory implementation ... More

Quantum Fluctuations versus Topology - a Study in U(1)_2 Lattice Gauge TheoryJun 12 1997Using the geometric definition of the topological charge we decompose the path integral of 2-dimensional U(1) lattice gauge theory into topological sectors. In a Monte Carlo simulation we compute the average value of the action as well as the distribution ... More

Remarks on the realization of the Atiyah-Singer index theorem in lattice gauge theorySep 11 1997We discuss the interplay between topologically non-trivial gauge field configurations and the spectrum of the Wilson-Dirac operator in lattice gauge theory. Our analysis is based on analytic arguments and numerical results from a lattice simulation of ... More

Topological Charge and the Spectrum of the Fermion Matrix in Lattice-QED_2Jul 15 1997Jul 28 1997We investigate the interplay between topological charge and the spectrum of the fermion matrix in lattice-QED_2 using analytic methods and Monte Carlo simulations with dynamical fermions. A new theorem on the spectral decomposition of the fermion matrix ... More

Scattering in a Simple 2-d Lattice ModelOct 21 1992L\"uscher has suggested a method to determine phase shifts from the finite volume dependence of the two-particle energy spectrum. We apply this to two models in d=2: (a) the Ising model, (b) a system of two Ising fields with different mass and coupled ... More

The Mixed Non-Abelian Coulomb Gas in Two DimensionsJun 26 1997The statistical mechanics of a mixed gas of adjoint and fundamental representation charges interacting via 1+1-dimensional U(N) gauge fields is investigated. In the limit of large N we show that there is a first order deconfining phase transition for ... More

Loops, Surfaces and Grassmann Representation in Two- and Three-Dimensional Ising ModelsJan 15 1998Starting from the known representation of the partition function of the 2- and 3-D Ising models as an integral over Grassmann variables, we perform a hopping expansion of the corresponding Pfaffian. We show that this expansion is an exact, algebraic representation ... More

Renormalization of bilinear quark operators for the chirally improved lattice Dirac operatorApr 05 2004Jun 13 2010We compute non-perturbative renormalization constants of fermionic bilinears for the chirally improved lattice fermions in the quenched approximation of QCD. We address finite size effects and the influence of Gribov copies. Our results are presented ... More

Deconfinement Transition for Quarks on a LineDec 03 1996Dec 05 1996We examine the statistical mechanics of a 1-dimensional gas of both adjoint and fundamental representation quarks which interact with each other through 1+1-dimensional U(N) gauge fields. Using large-N expansion we show that, when the density of fundamental ... More

Topology and Duality in Abelian Lattice TheoriesDec 18 1997Feb 26 1998We show how to obtain the dual of any lattice model with inhomogeneous local interactions based on an arbitrary Abelian group in any dimension and on lattices with arbitrary topology. It is shown that in general the dual theory contains disorder loops ... More

Lattice Regularization of the Chiral Schwinger ModelApr 03 1996We analyze the chiral Schwinger model on an infinite lattice using the continuum definition of the fermion determinant and a linear interpolation of the lattice gauge fields. For non-compact and Wilson formulation of the gauge field action it is proven ... More

Lattice Schwinger Model with interpolated Gauge FieldsNov 15 1995We analyze the Schwinger model on an infinite lattice using the continuum definition of the fermion determinant and a linear interpolation of the lattice gauge fields. The possible class of interpolations for the gauge fields, compatible with gauge invariance ... More

Coherent center domains in SU(3) gluodynamics and their percolation at T_cApr 13 2010May 05 2010For SU(3) lattice gauge theory we study properties of static quark sources represented by local Polyakov loops. We find that for temperatures both below and above T_c coherent domains exist where the phases of the local loops have similar values in the ... More

QED_2 and U(1)-ProblemMar 21 1995QED_2 with mass and N flavors of fermions is constructed using Euclidean path integrals. The fermion masses are treated perturbatively and the convergence of the mass perturbation series is proven for a finite space-time cutoff. The expectation functional ... More

A formula for the hopping expansion of 8-vertex models coupled to an external fieldNov 10 1998Aug 31 1999We study a generalized 8-vertex model where the vertices are coupled to a locally varying field. We rewrite the partition function as an integral over Grassmann variables. In this form it is possible to explicitly evaluate all terms of the hopping expansion. ... More

Discussing the U(1)-Problem of QED_2 without InstantonsFeb 06 1996We construct QED_2 with mass and flavor and an extra Thirring term. The vacuum expectation values are carefully decomposed into clustering states using the U(1)-axial symmetry of the considered operators and a limiting procedure. The properties of the ... More

On the U(1)-Problem of QED_2May 16 1995QED_2 with mass and flavor has in common many features with QCD, and thus is an interesting toy model relevant for four dimensional physics. The model is constructed using Euclidean path integrals and mass perturbation series. The vacuum functional is ... More

Linking confinement to spectral properties of the Dirac operatorMay 23 2006Jul 10 2006We 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 ... More

Hopping expansion as a tool for handling dual variables in lattice modelsSep 25 1998Oct 21 1998The hopping expansion of 8-vertex models in their Grassmann representation is studied. We use the functional similarity of the Ising model in this expansion with the hopping expansion of 2-D Wilson fermions to show that the lattice fermions are equivalent ... More

Center clusters and their percolation properties in lattice QCDOct 25 2010Properties of local Polyakov loops are studied in finite temperature lattice QCD and SU(3) lattice gauge theory. We evaluate local Polyakov loops, identify the closest center element for each loop and investigate cluster properties of these center phases. ... More

Coherent center domains from local Polyakov loopsJul 30 2010We analyze properties of local Polyakov loops using quenched as well as dynamical SU(3) gauge configurations for a wide range of temperatures. It is demonstrated that for both, the confined and the deconfined regime, the local Polyakov loop prefers phase ... More

Flux representation of an effective Polyakov loop model for QCD thermodynamicsApr 13 2011Apr 29 2011We discuss an effective Polyakov loop model for QCD thermodynamics with a chemical potential. Using high temperature expansion techniques the partition sum is mapped exactly onto the partition sum of a flux model. In the flux representation the complex ... More

Excited hadrons on the lattice - State of the art and future challengesNov 05 2007We review the techniques of lattice QCD calculations for excited hadrons with light quarks and outline the future challenges that are faced in calculations with fully dynamical fermions.

Testing the self-duality of topological lumps in SU(3) lattice gauge theoryFeb 01 2002Apr 22 2002We discuss a simple formula which connects the field-strength tensor to a spectral sum over certain quadratic forms of the eigenvectors of the lattice Dirac operator. We analyze these terms for the near zero-modes and find that they give rise to contributions ... More

Loop representation for 2-D Wilson lattice fermions in a scalar background fieldNov 10 1998We show that the fermion determinant for 2-D Wilson lattice fermions coupled to an external scalar field is equivalent to self avoiding loops interacting with the external field. In an application of the resulting formula we integrate the scalar field ... More

Calorons, instantons and constituent monopoles in SU(3) lattice gauge theoryOct 01 2002Jan 09 2003We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge configurations at non-zero temperature and compare periodic and anti-periodic temporal boundary conditions for the fermions. It is demonstrated that for the different boundary conditions ... More

Recent results from systematic parameterizations of Ginsparg-Wilson fermionsAug 26 2002Sep 27 2002The Fixed Point Dirac Operator and Chirally Improved Fermions both use large numbers of gauge paths and the full Dirac structure to approximate a solution of the Ginsparg-Wilson equation. After a brief review of the two approaches we present recent results ... More

The lattice Schwinger model as a discrete sum of filled Wilson loopsMar 11 1999Aug 31 1999Using techniques from hopping expansion we identically map the lattice Schwinger model with Wilson fermions to a model of oriented loops on the lattice. This is done by first computing the explicit form of the fermion determinant in the external field. ... More

Lattice Fermions Coupled to Interpolated Gauge Fields - Results in 2 DimensionsMar 16 1996We discuss a new approach for putting gauge theories on the lattice. The gauge fields are defined on the lattice only, but are interpolated to the interior of the lattice cells, where they couple to continuum fermions. The purpose of this approach is ... More

A new approach to Ginsparg-Wilson fermionsMar 07 2000We expand the most general lattice Dirac operator D in a basis of simple operators. The Ginsparg-Wilson equation turns into a system of coupled quadratic equations for the expansion coefficients. Our expansion of D allows for a natural cutoff and the ... More

New developments for dual methods in lattice field theory at non-zero densityJan 30 2014In recent years the complex action problem of lattice field theory at finite density was overcome for several system by mapping them to dual variables (flux lines and surfaces). We illustrate this mapping for the case of the U(1) gauge Higgs system and ... More

Excited meson spectroscopy with chirally improved fermionsSep 22 2005We present excited meson masses from quenched calculations using chirally improved (CI) quarks at pion masses down to 350 MeV. The salient features of our analysis are the use of a matrix of correlators from various source and sink operators and a basis ... More

Excited hadrons in n_f=2 QCDOct 15 2009The chirally improved (CI) fermion action allows us to obtain results for pion masses down to 320 MeV on (in lattice units) comparatively small lattices with physical extent of 2.4 fm. We use differently smeared quarks sources to build sets of several ... More

Meron-Cluster Solution of Fermion and Other Sign ProblemsSep 15 1999Numerical simulations of numerous quantum systems suffer from the notorious sign problem. Important examples include QCD and other field theories at non-zero chemical potential, at non-zero vacuum angle, or with an odd number of flavors, as well as the ... More

Canonical fermion determinants in lattice QCD - Numerical evaluation and propertiesJun 05 2009Jan 20 2011We analyze canonical fermion determinants, i.e., fermion determinants projected to a fixed quark number q. The canonical determinants are computed using a dimensional reduction formula and are studied for pure SU(3) gauge configurations in a wide range ... More

Excited nucleons with chirally improved fermionsJul 05 2003Apr 20 2004We study positive and negative parity nucleons on the lattice using the chirally improved lattice Dirac operator. Our analysis is based on a set of three operators chi_i with the nucleon quantum numbers but in different representations of the chiral group ... More

A lattice calculation of vector meson couplings to the vector and tensor currents using chirally improved fermionsJun 05 2003Jun 06 2003We present a quenched lattice calculation of $f_V^\perp/f_V$, the coupling of vector mesons to the tensor current normalized by the vector meson decay constant. The chirally improved lattice Dirac operator, which allows us to reach small quark masses, ... More

Excited hadrons from improved interpolating fieldsSep 03 2004The calculation of quark propagators for Ginsparg-Wilson-type Dirac operators is costly and thus limited to a few different sources. We present a new approach for determining spatially optimized operators for lattice spectroscopy of excited hadrons. Jacobi ... More

Comparing lattice Dirac operators in smooth instanton backgroundsAug 01 2001Nov 07 2001We compare the behavior of different lattice Dirac operators in gauge backgrounds which are lattice discretizations of a classical instanton. In particular we analyze the standard Wilson operator, a chirally improved Dirac operator and the overlap operators ... More

Baryon axial charges from Chirally Improved fermions - first resultsOct 21 2009We present first results from dynamical Chirally Improved (CI) fermion simulations for the axial charge $G_A$ of various hadrons. We work with 16^3x32 lattices of spatial extent 2.4 fm and use the variational method with a suitable basis of Jacobi-smeared ... More

Spectroscopy with dynamical Chirally Improved quarksSep 26 2008We present recent results of our dynamical simulations with Chirally Improved fermions and report on new developments in the determination of excited light-quark meson states using interpolators constructed by applying covariant derivatives on Jacobi-smeared ... More

Spatially improved operators for excited hadrons on the latticeMay 10 2004We present a new approach for determining spatially optimized operators that can be used for lattice spectroscopy of excited hadrons. Jacobi smeared quark sources with different widths are combined to construct hadron operators with different spatial ... More

Meson spectroscopy with derivative quark sourcesSep 27 2007We present results for masses of light mesons obtained with the variational method using an enhanced basis of interpolating field operators with different quark smearings. The interpolators are constructed from Jacobi-smeared quarks of a Gaussian type ... More

Excited hadrons on the lattice: MesonsJan 20 2006May 10 2006We present results for masses of excited mesons from quenched calculations using chirally improved quarks at pion masses down to 350 MeV. The key features of our analysis are the use of a matrix of correlators from various source and sink operators and ... More

Distribution of Canonical Determinants in QCDNov 15 2014The distribution of canonical determinants in QCD is determined by means of chiral perturbation theory. For a non-zero quark charge the canonical determinants take complex values. In the dilute pion gas approximation, we compute all moments of the magnitude ... More

Lattice QCD at finite temperature: Evidence for calorons from the eigenvectors of the Dirac operatorOct 22 2001We analyze the eigenvalues and eigenvectors of the staggered Dirac operator in quenched lattice QCD in the vicinity of the deconfinement phase transition using the L\"uscher-Weisz gauge action. The spectral and localization properties of the low-lying ... More

Excited hadrons on the lattice: BaryonsApr 23 2006We 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 ... More

Baryon spectroscopy with spatially improved quark sourcesSep 16 2005We study baryons on the lattice with a special focus on excited states. For that purpose we construct several interpolators which differ in their Dirac structure. These interpolators are built from Jacobi smeared quarks with different widths in order ... More

Chirally improved Dirac operators: Studying the sensitivity to topological excitations for zero and finite temperatureOct 05 2001We discuss the construction and properties of an approximate solution of the Ginsparg-Wilson equation, the so-called chirally improved lattice Dirac operator. In particular we study the behavior of its eigenmodes in smooth instanton backgrounds as well ... More

Hadron Spectroscopy with Dynamical Chirally Improved FermionsDec 09 2008We simulate two dynamical, mass degenerate light quarks on 16^3x32 lattices with a spatial extent of 2.4 fm using the Chirally Improved Dirac operator. The simulation method, the implementation of the action and signals of equilibration are discussed ... More

Derivative sources in lattice spectroscopy of excited light-quark mesonsFeb 14 2008May 14 2008We construct efficient interpolating fields for lattice spectroscopy of mesons by applying covariant derivatives on Jacobi smeared quark sources. These interpolators are tested in a quenched calculation of excited mesons based on the variational method. ... More

Dynamical Chirally Improved Quarks: First Results for Hadron MassesSep 28 2007We present first results for a study with two mass-degenerate dynamical Chirally Improved (CI) fermions on lattices of spatial extent 2.4 fm. The CI Dirac operator obeys the Ginsparg-Wilson condition in good approximation. The pion mass we use is still ... More

Variational method for lattice spectroscopy with ghostsNov 24 2005We discuss the variational method used in lattice spectroscopy calculations. In particular we address the role of ghost contributions which appear in quenched or partially quenched simulations and have a non-standard euclidean time dependence. We show ... More

Density of states method for the Z(3) spin modelMar 17 2015Jun 10 2015We apply the density of states approach to the Z(3) spin model with a chemical potential mu. For determining the density of states we use restricted Monte Carlo simulations on small intervals of the variable for the density. In each interval we probe ... More

Topological lumps and Dirac zero modes in SU(3) lattice gauge theory on the torusFeb 09 2004We compute eigenmodes of the lattice Dirac operator for quenched SU(3) gauge configurations on the 4-torus with topological charge 1. We find a strong dependence of the zero modes on the boundary conditions which we impose for the Dirac operator. The ... More

Dual simulation of finite density lattice QED at large massFeb 03 2015Feb 09 2015We discuss a mapping of lattice QED with two flavors and a chemical potential to dual variables, which are surfaces for the gauge fields and loops for the fermions. The gauge fields are completely dualized and the corresponding dual variables are integer ... More

Lattice study of the Silver Blaze phenomenon for a charged scalar phi-4 fieldJun 13 2012Dec 12 2012We analyze a complex scalar field with phi-4 interaction and a chemical potential mu on the lattice. An exact flux representation of the partition sum is used which avoids the complex action problem and based on a generalized worm algorithm we can run ... More

Dual representation for 1+1 dimensional fermions interacting with 3+1 dimensional U(1) gauge fieldsDec 21 2015Feb 02 2016We study a system of nanowires, i.e., the theory of 1+1 dimensional massless fermions interacting with 3+1 dimensional U(1) gauge fields. When allowing for non-zero chemical potentials, this system has a complex action problem in the conventional formulation. ... More

Clover improvement, spectrum and Atiyah-Singer index theorem for the Dirac operator on the latticeJun 28 1998Dec 16 1998We study the role of the O(a)-improving clover term for the spectrum of the lattice Dirac operator using cooled and thermalized SU(2) gauge field configurations. For cooled configurations we observe improvement of the spectral properties when adding the ... More

A test of Taylor- and modified Taylor-expansionNov 28 2013Apr 08 2014We compare Taylor expansion and a modified variant of Taylor expansion, which incorporates features of the fugacity series, for expansions in the chemical potential around a zero-density lattice field theory. As a first test we apply both series to the ... More

Dualization of non-abelian lattice gauge theory with Abelian Color Cycles (ACC)Nov 03 2016We discuss a new approach to strong coupling expansion and dual representations for non-abelian lattice gauge theories. The Wilson gauge action is decomposed into a sum over "abelian color cycles" (ACC), which are loops around plaquettes visiting different ... More

Functional Integral Approach to the N-Flavor Schwinger ModelDec 13 1993We study massless QED_2 with N flavors using path integrals. We identify the sector that is generated by the N^2 classically conserved vector currents. One of them (the U(1) current) creates a massive particle, while the others create massless ones. We ... More

Spectroscopy in finite density lattice field theory: An exploratory study in the relativistic Bose gasDec 16 2012Jan 31 2013We analyze 2-point functions in the relativistic Bose gas on the lattice, i.e., a charged scalar phi-4 field with chemical potential mu. Using a generalized worm algorithm we perform a Monte Carlo simulation in a dual representation in terms of fluxes ... More

Dual Methods for Lattice Field Theories at Finite DensityOct 31 2013We present a dual representation of the partition function of the charged scalar field in which the complex action problem at non-zero chemical potential is absent. In this dual representation Monte Carlo simulations are possible and we show some physical ... More

On the spectrum of the Wilson-Dirac lattice operator in topologically non-trivial background configurationsDec 12 1997Aug 12 1998We study characteristic features of the eigenvalues of the Wilson-Dirac operator in topologically non-trivial gauge field configurations by examining complete spectra of the fermion matrix. In particular we discuss the role of eigenvectors with real eigenvalues ... More

Energy density for chiral lattice fermions with chemical potentialApr 01 2007Jul 26 2007We study a recently proposed formulation of overlap fermions at finite density. In particular we compute the energy density as a function of the chemical potential and the temperature. It is shown that overlap fermions with chemical potential reproduce ... More

Remnant index theorem and low-lying eigenmodes for twisted mass fermionsMar 04 2005Jun 20 2005We analyze the low-lying spectrum and eigenmodes of lattice Dirac operators with a twisted mass term. The twist term expels the eigenvalues from a strip in the complex plane and all eigenmodes obtain a non-vanishing matrix element with gamma-5. For a ... More

Properties of canonical determinants and a test of fugacity expansion for finite density lattice QCD with Wilson fermionsApr 04 2012Jun 18 2012We analyze canonical determinants, i.e., grand canonical determinants projected to a fixed net quark number. The canonical determinants are the coefficients in a fugacity expansion of the grand canonical determinant and we evaluate them as the Fourier ... More

Winding expansion techniques for lattice QCD with chemical potentialSep 16 2008We analytically derive a decomposition of the lattice fermion determinant for Wilson's Dirac operator with chemical potential into winding sectors, i.e., factors with a fixed number of quarks. Dividing the lattice into four domains, the determinant is ... More

New overlap construction of Weyl fermionsFeb 18 2008Mar 28 2008In a recent article Hasenfratz and von Allmen have suggested a fixed point action for two flavors of Weyl fermions on the lattice with gauge group SU(2). The block-spin transformation they use maps the chiral and vector symmetries of the underlying vector ... More

Low-Lying Nucleons from Chirally Improved FermionsSep 10 2003We report on our preliminary results on the low-lying excited nucleon spectra which we obtain through a variational basis formed with three different interpolators.

Low-lying spectrum for lattice Dirac operators with twisted massSep 22 2005We analyze the low-lying spectrum and eigenmodes of lattice Dirac operators with a twisted mass term. The twist term expels the eigenvalues from a strip in the complex plane and all eigenmodes obtain a non-vanishing matrix element with gamma-5. For a ... More

New approximate solutions of the Ginsparg-Wilson equation - tests in 2-dFeb 01 2000Mar 23 2000A new method for finding approximate solutions of the Ginsparg-Wilson equation is tested in 2-d. The Dirac operator is first constructed and then used in a dynamical simulation of the 2-flavor Schwinger model. We find a very small mass of the pi-particle ... More

Analyzing the spectrum of general, non-hermitian Dirac operatorsSep 03 1998We discuss the computational problems when analyzing general, non-hermitian matrices and in particular the un-modified Wilson lattice Dirac operator. We report on our experiences with the Implicitly Restarted Arnoldi Method. The eigenstates of the Wilson-Dirac ... More

Approaches to the sign problem in lattice field theoryMar 31 2016Quantum field theories (QFTs) at finite densities of matter generically involve complex actions. Standard Monte-Carlo simulations based upon importance sampling, which have been producing quantitative first principle results in particle physics for almost ... More

Scalar QED$_2$ with a topological term - a lattice study in a dual representationOct 13 2014We present a dual representation for the partition function of 2-dimensional scalar quantum electrodynamics with a topological term ($\theta$-term). In the dual representation the complex action problem at non-zero $\theta$ is absent, which is an obstacle ... More

Dependence of Dirac eigenmodes on boundary conditions for SU(2) lattice gauge theoryOct 25 2004We analyze zero modes of the Dirac operator for SU(2) lattice gauge theory. We find that the zero modes are strongly localized in all 4 directions. The position of these lumps depends on the boundary conditions we use for the Dirac operator. We compare ... More

New findings for topological excitations in SU(3) lattice gauge theoryDec 17 2002Jan 30 2003We probe the SU(3) vacuum using eigenvectors of the Dirac operator with an arbitrary phase for the temporal boundary condition. We consider configurations with topological charge |Q| = 1 near the QCD phase transition and at low temperatures on a torus. ... More

Flux simulation of the SU(3) spin model at finite chemical potentialAug 06 2012Nov 29 2012We present a Monte Carlo simulation of an effective theory for local Polyakov loops at finite temperature and density. The sign problem is overcome by mapping the partition sum to a flux representation. We determine the phase diagram of the model as a ... More

Remarks on left-handed lattice fermionsOct 29 2007We study whether applying lattice projectors on a vector-like Ginsparg-Wilson Dirac operator is the only way to construct left-handed lattice fermions. Using RG transformations we derive an equation for the generating functional on the lattice, obtained ... More

Static quark-antiquark potential and Dirac eigenvector correlatorsMar 07 2008We represent the Polyakov loop correlator as a spectral sum of correlators of eigenvectors of the lattice Dirac operator. This spectral representation is studied numerically using quenched SU(3) configurations below and above the deconfinement temperature. ... More

Thermodynamical quantities for overlap fermions with chemical potentialAug 07 2007Recently a formulation of overlap fermions at finite density based on an analytic continuation of the sign function was proposed. We study this proposal by analyzing the energy and number densities for free fermions as a function of the chemical potential ... More

Abelian color cycles: a new approach to strong coupling expansion and dual representations for non-abelian lattice gauge theorySep 01 2016We propose a new approach to strong coupling series and dual representations for non-abelian lattice gauge theories using the SU(2) case as an example. The Wilson gauge action is written as a sum over "abelian color cycles" (ACC) which correspond to loops ... More

Gauge and matter fields as surfaces and loops - an exploratory lattice study of the Z(3) Gauge-Higgs modelAug 31 2012Oct 16 2012We discuss a representation of the Z(3) Gauge-Higgs lattice field theory at finite density in terms of dual variables, i.e., loops of flux and surfaces. In the dual representation the complex action problem of the conventional formulation is resolved ... More

Masses of excited baryons from chirally improved quenched lattice QCDJan 11 2005Jan 18 2005Whereas ground state spectroscopy for quenched QCD is well understood, it is still a challenge to obtain results for excited hadron states. In our study we present results from a new approach for determining spatially optimized operators for lattice spectroscopy ... More

Generalized quark number susceptibilities from fugacity expansion at finite chemical potential for $N_f$ = 2 Wilson fermionsNov 19 2014Apr 08 2015Generalized susceptibilities of the net quark number have been proposed to be good probes for the transitions in the QCD phase diagram and for the search of a possible critical end point. In this article we explore a new strategy for computing quark number ... More