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Low lying eigenmodes and meson propagator symmetriesMar 23 2018May 25 2018In situations where the low lying eigenmodes of the Dirac operator are suppressed one observed degeneracies of some meson masses. Based on these results a hidden symmetry was conjectured, which is not a symmetry of the Lagrangian but emerges in the quantization ... More

On the Spectrum of Lattice Dirac OperatorsJul 21 1999Jul 26 1999With the Schwinger model as example I discuss properties of lattice Dirac operators, with some emphasis on Monte Carlo results for topological charge, chiral fermions and eigenvalue spectra.

Hadron Structure and Spectrum from the LatticeDec 17 2015Lattice calculations for hadrons are now entering the domain of resonances and scattering, necessitating a better understanding of the observed discrete energy spectrum. This is a reviewing survey about recent lattice QCD results, with some emphasis on ... More

The Hadron Spectrum from Lattice QCDNov 20 2007Nov 29 2007Determining the hadron spectrum and hadron properties beyond the ground states is a challenge in lattice QCD. Most of these results have been in the quenched approximation but now we are entering the dynamical era. I review some of the ideas and methods ... More

Computer Stochastics in Scalar Quantum Field TheoryDec 01 1993This is a series of lectures on Monte Carlo results on the non-perturbative, lattice formulation approach to quantum field theory. Emphasis is put on 4D scalar quantum field theory. I discuss real space renormalization group, fixed point properties and ... More

Nucleon excited states on the latticeApr 15 2013Apr 18 2013We study the pion-nucleon system in s-wave in the framework of lattice QCD in order to gain new information on the nucleon excited states. We perform simulations for $n_f =2$ mass degenerate light quarks at a pion mass of 266 MeV. The results show that ... More

Lee-Yang zeroes in the one flavour massive lattice Schwinger modelAug 26 1994We study the partition function of the model formulated with Wilson fermions with only one species, both analytically and numerically. At strong coupling we construct the solution for lattice size up to $8\times 8$, a polynomial in the hopping parameter ... More

Compact U(1) Gauge Theory on Lattices with Trivial Homotopy GroupJul 13 1994We study the pure gauge model on a lattice manifold with trivial fundamental homotopy group, homotopically equivalent to an $S_4$. Monopole loops may fluctuate freely on that lattice without restrictions due to the boundary conditions. For the original ... More

Renormalization Group Analysis of Finite-Size Scaling in the $Φ^4_4$ ModelOct 07 1992Oct 08 1992A finite-size scaling theory for the $\phi^4_4$ model is derived using renormalization group methods. Particular attention is paid to the partition function zeroes, in terms of which all thermodynamic observables can be expressed. While the leading scaling ... More

Scattering in the pion-nucleon negative parity channel in lattice QCDDec 20 2012Feb 20 2013We study the coupled pion-nucleon system (negative parity, isospin 1/2) based on a lattice QCD simulation for nf=2 mass degenerate light quarks. Both, standard 3-quarks baryon operators as well as meson-baryon (4+1)-quark operators are included. This ... More

Rotational Symmetry and Regularization Dependence in the $Φ^4_4$-ModelSep 07 1992We study the one component $\Phi^4$ model for four different lattice actions in the Gaussian limit and for the Ising model in the broken phase. Emphasis is put on the euclidean invariance properties of the boson propagator. A measure of the violation ... More

Effects of the low lying Dirac modes on the spectrum of ground state mesonsOct 27 2011Oct 28 2011The lowest eigenmodes of the Dirac operator are related to the dynamical breaking of the chiral symmetry in Quantum Chromodynamics (QCD). In our work we construct quark propagators which exclude a varying number of the lowest Dirac eigenmodes and study ... More

Unbreaking chiral symmetryJul 26 2011Sep 30 2011In Quantum Chromodynamics (QCD) the eigenmodes of the Dirac operator with small absolute eigenvalues have a close relationship to the dynamical breaking of the chiral symmetry. In a simulation with two dynamical quarks, we study the behavior of meson ... More

Link smearing considered as MCRG transformationMar 28 2011May 02 2011Gauge link smearing is widely used in lattice QCD computations. The idea is to remove the local (UV) fluctuations of the gauge field configurations while keeping the longer-range (IR) properties intact. Important applications are in the definitions of ... More

On the Phase Structure of the Schwinger Model with Wilson FermionsNov 19 1993We study the phase structure of the massive one flavour lattice Schwinger model on the basis of the finite size scaling behaviour of the partition function zeroes. At $\beta = 0$ we observe and discuss a possible discrepancy with results obtained by a ... More

U(1) Gauge Theory with Villain Action on Spherical LatticesJul 19 1996We have studied the U(1) gauge field theory with Villain (periodic Gaussian) action on spherelike lattices. The effective size of the systems studied ranges from 6 to 16. We do not observe any 2-state signal in the distribution function of the plaquette ... More

Universality of the Ising Model on Sphere-like LatticesFeb 26 1996We study the 2D Ising model on three different types of lattices that are topologically equivalent to spheres. The geometrical shapes are reminiscent of the surface of a pillow, a 3D cube and a sphere, respectively. Systems of volumes ranging up to O($10^5$) ... 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

The eigenvalue spectrum for dynamical Chirally Improved fermionsSep 27 2007We study the eigenvalues of Dirac operators in QCD with two mass degenerate dynamical fermions. The gauge configurations have been obtained with HMC and the so-called Chirally Improved fermionic action. We compare eigenvalues obtained for the overlap ... More

Dirac zero-modes in compact U(1) gauge theoryNov 10 2004Mar 08 2005We study properties of the zero and near-zero eigenmodes of the overlap Dirac operator in compact U(1) gauge theory. In the confinement phase the exact zero-modes are localized as found by studying the values of the inverse participation ratio and other ... More

Pion Nucleon Scattering: Some Results from Lattice QCDSep 18 2013Including the meson-baryon (5 quark) intermediate states in a lattice simulation is challenging. However, it is important in order to obtain the correct energy eigenstates and to relate them to scattering phase shifts. Recent results for the negative ... More

Strong Coupling Lattice Schwinger Model on Large Spherelike LatticesJun 27 1995The lattice regularized Schwinger model for one fermion flavor and in the strong coupling limit is studied through its equivalent representation as a restricted 8-vertex model. The Monte Carlo simulation on lattices with torus-topology is handicapped ... More

Scaling and Density of Lee-Yang Zeroes in the Four Dimensional Ising ModelNov 20 1993The scaling behaviour of the edge of the Lee--Yang zeroes in the four dimensional Ising model is analyzed. This model is believed to belong to the same universality class as the $\phi^4_4$ model which plays a central role in relativistic quantum field ... More

The First Order Signal in Pure U(1) Gauge Theory May be FakeNov 22 1993We study the deconfinement phase transition of compact $U(1)$ pure lattice gauge theory with the Wilson action on {\em closed topology} lattices. In contrast to studies of compact QED on {\em hypercubic lattices with periodic boundary conditions}, we ... More

Lee-Yang Zeroes and Logarithmic Corrections in the $Φ^4_4$ TheoryOct 13 1992The leading mean-field critical behaviour of $\phi^4_4$-theory is modified by multiplicative logarithmic corrections. We analyse these corrections both analytically and numerically. In particular we present a finite-size scaling theory for the Lee-Yang ... More

Bound states for Overlap and Fixed Point Actions close to the chiral limitMay 16 2001We study the overlap and the fixed point Dirac operators for massive fermions in the two-flavor lattice Schwinger model. The masses of the triplet (pion) and singlet (eta) bound states are determined down to small fermion masses and the mass dependence ... 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

Lattice operators for scattering of particles with spinJul 22 2016We construct operators for simulating the scattering of two hadrons with spin on the lattice. Three methods are shown to give the consistent operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar, vector and nucleon. Explicit ... More

Prediction of positive parity $B_s$ mesons and search for the $X(5568)$Nov 08 2016We use a combination of quark-antiquark and $B^{(*)}K$ interpolating fields to predict the mass of two QCD bound states below the $B^*K$ threshold in the quantum channels $J^P=0^+$ and $1^+$. The mesons correspond to the b-quark cousins of the $D_{s0}^*(2317)$ ... More

X(3872) and Y(4140) using diquark-antidiquark operators with lattice QCDOct 30 2015We discuss a recent lattice study of charmonium-like mesons with $J^{PC}=1^{++}$ and three quark contents $\bar cc\bar du$, $\bar cc(\bar uu + \bar dd)$ and $\bar cc\bar ss$, where the latter two can mix with $\bar cc$. In this quantum channel, the long ... More

The lattice Schwinger model with the SW actionJul 06 1998We perform a model study on the 2-flavor lattice Schwinger model using standard Wilson and ${\cal O}(a)$ improved Sheikholeslami-Wohlert (SW) action. We find, that the phase diagram is altered, the critical line shifted closer towards its continuum value ... More

Dirac Eigenmodes in an Environment of Dynamical FermionsDec 30 2005Jan 07 2006We discuss some properties of zero and near-zero modes of the Dirac operator, as observed in a recent simulation of 2-flavor QCD. The quarks have been implemented with the so-called Chirally Improved Dirac operator, which obeys the Ginsparg-Wilson relation ... More

A fixed-point action for the lattice Schwinger modelSep 09 1997We determine non-perturbatively a fixed-point (FP) action for fermions in the two-dimensional U(1) gauge (Schwinger) model. Our parameterization for the fermionic action has terms within a $7\times 7$ square on the lattice, using compact link variables. ... 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

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

Chiral symmetry in the 2-flavour lattice Schwinger modelSep 11 1997We study the 2-flavour lattice Schwinger model: QED in D=2 with two fermion species of identical mass. In the simulation we are using Wilson fermions where chiral symmetry is explicitly broken. Since there is no known simple order parameter it is non-trivial ... More

Operators for scattering of particles with spinOct 04 2016Operators for simulating the scattering of two particles with spin are constructed. Three methods are shown to give the consistent lattice operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar meson, vector meson and nucleon. ... More

Implementing Hybrid Monte Carlo with stout-smeared chirally improved Dirac operatorsSep 01 2005We discuss our implementation of dynamical Ginsparg-Wilson type fermions using a stout-smeared chirally improved Dirac operator. Such operators have been studied extensively in quenched calculations within the Bern-Graz-Regensburg (BGR) collaboration. ... 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

X(3872) and Y(4140) using diquark-antidiquark operators with lattice QCDMar 11 2015Jul 23 2015We perform a lattice study of charmonium-like mesons with $J^{PC}=1^{++}$ and three quark contents $\bar cc \bar du$, $\bar cc(\bar uu+\bar dd)$ and $\bar cc \bar ss$, where the later two can mix with $\bar cc$. This simulation with $N_f=2$ and $m_\pi=266$ ... More

Experiences with dynamical chirally improved fermionsDec 08 2004Jun 28 2005We simulate Quantum Chromodynamics (QCD) in four Euclidean dimensions with two (degenerate mass) flavors of dynamical quarks. The Dirac operator we use is the so-called chirally improved Dirac operator. We discuss the algorithm used for the simulation ... More

Fixed point action for the massless lattice Schwinger modelJul 18 1997Dec 23 1998We determine non-perturbatively the fixed-point action for fermions in the two-dimensional U(1) gauge (Schwinger) model. This is done by iterating a block spin transformation in the background of non-compact gauge field configurations sampled according ... More

Four-dimensional pure compact U(1) gauge theory on a spherical latticeJun 22 1996We investigate the confinement-Coulomb phase transition in the four-dimensional (4D) pure compact U(1) gauge theory on spherical lattices. The action contains the Wilson coupling beta and the double charge coupling gamma. The lattice is obtained from ... More

Lattice operators for scattering of particles with spinJul 22 2016Jan 30 2017We construct operators for simulating the scattering of two hadrons with spin on the lattice. Three methods are shown to give the consistent operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar, vector and nucleon. Explicit ... 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

Comparing lattice Dirac operators with Random Matrix TheoryJul 19 1999We study the eigenvalue spectrum of different lattice Dirac operators (staggered, fixed point, overlap) and discuss their dependence on the topological sectors. Although the model is 2D (the Schwinger model with massless fermions) our observations indicate ... More

Wilson, fixed point and Neuberger's lattice Dirac operator for the Schwinger modelSep 03 1998Sep 08 1998We perform a comparison between different lattice regularizations of the Dirac operator for massless fermions in the framework of the single and two flavor Schwinger model. We consider a) the Wilson-Dirac operator at the critical value of the hopping ... 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

$B_sπ^+$ scattering and search for X(5568) with lattice QCDJul 11 2016We investigate $B_s\pi^+$ scattering in s-wave using lattice QCD in order to search for an exotic resonance X(5568) with flavor $\bar b s \bar d u$; such a state was recently reported by D0 but was not seen by LHCb. If X(5568) with $J^P=0^+$ exists, it ... More

$B_sπ^+$ scattering and search for X(5568) with lattice QCDJul 11 2016Oct 11 2016We investigate $B_s\pi^+$ scattering in s-wave using lattice QCD in order to search for an exotic resonance X(5568) with flavor $\bar b s \bar d u$; such a state was recently reported by D0 but was not seen by LHCb. If X(5568) with $J^P=0^+$ exists, it ... More

Scattering phase shift and resonance properties on the lattice: an introductionOct 20 2011We describe the method for extracting the elastic scattering phase shift from a lattice simulation at an introductory level, for non-lattice practitioners. We consider the scattering in a resonant channel, where the resulting phase shift delta(s) allows ... More

QCD with two dynamical flavors of chirally improved quarksDec 12 2005Feb 28 2006Considering Ginsparg-Wilson type fermions dynamically in lattice QCD simulations is a challenging task. The hope is to be able to approach smaller pion masses and to eventually reach physical situations. The price to pay is substantially higher computational ... More

Chiral properties of the fixed point action of the Schwinger modelApr 09 1998We study the spectrum properties for a recently constructed fixed point lattice Dirac operator. We also consider the problem of the extraction of the fermion condensate, both by direct computation, and through the Banks-Casher formula by analyzing the ... More

Non-Gaussian fixed point in four-dimensional pure compact U(1) gauge theory on the latticeJun 21 1996The line of phase transitions, separating the confinement and the Coulomb phases in the four-dimensional pure compact U(1) gauge theory with extended Wilson action, is reconsidered. We present new numerical evidence that a part of this line, including ... More

Evidence for a Critical Behavior in $4D$ Pure Compact QEDDec 09 1994We present evidence about a critical behavior of $4D$ compact QED (CQED) pure gauge theory. Regularizing the theory on lattices homotopic to a sphere, we present evidence for a critical, i.e. second order like behavior at the deconfinement phase transition ... More

The condensate for two dynamical chirally improved quarks in QCDNov 07 2006Apr 07 2007We compare the eigenvalue spectra of the Dirac operator from a simulation with two mass degenerate dynamical chirally improved fermions with Random Matrix Theory. Comparisons with distribution of k-th eigenvalues (k=1,2) in fixed topological sectors (nu=0,1) ... More

First results from dynamical chirally improved fermionsSep 01 2005We simulate Quantum Chromodynamics in four Euclidean dimensions with two (degenerate mass) flavors of dynamical quarks. The Dirac operator is the so-called chirally improved operator that has been studied so far in quenched calculations. We now present ... More

Effects of Topology in the Dirac Spectrum of Staggered FermionsSep 17 1999We compare the lower edge spectral fluctuations of the staggered lattice Dirac operator for the Schwinger model with the predictions of chiral Random Matrix Theory (chRMT). We verify their range of applicability, checking in particular the role of non-trivial ... More

SW action for the lattice Schwinger modelSep 11 1998We study some aspects of the ${\cal O}(a)$ improved Sheikholeslami-Wohlert (SW) action for the lattice Schwinger model. We find some improvement concerning the distribution of eigenvalues of the Dirac operator and of the masses but little or no improvement ... 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

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

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

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

Pion-nucleon scattering in the Roper channel from lattice QCDOct 05 2016We present a lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. The study is based on the PACS-CS ensemble of gauge configurations with $N_f=2+1$ Wilson-clover ... More

Mesons upon low-lying Dirac mode exclusionNov 06 2014We study the isoscalar and isovector $J=0,1$ mesons with the overlap operator within two flavour lattice QCD. After subtraction of the lowest-lying Dirac eigenmodes from the valence quark propagator all disconnected contributions vanish and all possible ... More

Effects of the low lying Dirac modes on excited hadrons in lattice QCDJul 31 2012Chiral symmetry breaking in Quantum Chromodynamics is associated with the low lying spectral modes of the Dirac operator according to the Banks-Casher relation. Here we study how removal of a variable number of low lying modes from the valence quark sector ... More

The chiral and angular momentum content of the $ρ$-mesons in lattice QCDOct 27 2010The variational method allows one to study the mixing of interpolators with different chiral transformation properties in the nonperturbatively determined physical state. It is then possible to define and calculate in a gauge-invariant manner the chiral ... More

Low-lying Lambda Baryons from the LatticeDec 10 2012Jan 14 2013In a lattice QCD calculation with two light dynamical Chirally Improved (CI) quarks we determine ground state and some excited state masses in all four Lambda baryon channels 1/2^\pm and 3/2^\pm. We perform an infinite volume extrapolation and confirm ... More

Study of the Zc+ channel in lattice QCDOct 31 2014Nov 24 2014Several charged charmonium-like hadrons called $Z_c$ have been recently discovered by different experiments. In contrast to conventional hadrons these contain at least two valence quarks and antiquarks ($\bar{c}c\bar{d}u$). We perform a lattice QCD simulation ... More

K pi scattering and the K* decay width from lattice QCDJul 02 2013Aug 12 2014K* mesons and in particular the K*(892) were frequently addressed in lattice simulations, but always while ignoring that the K*(892) decays strongly. We present an exploratory extraction of the masses and widths for the K* resonances by simulating K pi ... More

$Nπ$ scattering in the Roper channelNov 16 2017We present results from our recent lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. Using a variety of hadron operators, that include $qqq$-like, $N\pi$ ... More

Study of the $Z_c^+$ channel using lattice QCDMay 29 2014Jan 20 2015Recently experimentalists have discovered several charged charmonium-like hadrons $Z_c^+$ with unconventional quark content $\bar cc\bar d u$. We perform a search for $Z_c^+$ with mass below $4.2~$GeV in the channel $I^G(J^{PC})=1^+(1^{+-})$ using lattice ... More

QCD with Two Light Dynamical Chirally Improved Quarks: BaryonsJan 18 2013May 14 2013We present a study of baryon ground states and low lying excitations of non-strange and strange baryons. The results are based on seven gauge field ensembles with two dynamical light Chirally Improved (CI) quarks corresponding to pion masses between 255 ... More

Symmetries of mesons after unbreaking of chiral symmetry and their string interpretationFeb 08 2014Apr 26 2014Using the chirally invariant overlap Dirac operator we remove its lowest-lying quasizero modes from the valence quark propagators and study evolution of isovector mesons with J=1. At the truncation level about 50 MeV SU(2)_L \times SU(2)_R and U(1)_A ... More

Spectrum of the fixed point Dirac operator in the Schwinger modelSep 09 1998Recently, properties of the fixed point action for fermion theories have been pointed out indicating realization of chiral symmetry on the lattice. We check these properties by numerical analysis of the spectrum of a parametrized fixed point Dirac operator ... More

Isoscalar mesons upon unbreaking of chiral symmetryOct 31 2014Jan 20 2015In a dynamical lattice simulation with the overlap Dirac operator and $N_f=2$ mass degenerate quarks we study all possible $J=0$ and $J=1$ correlators upon exclusion of the low lying "quasi-zero" modes from the valence quark propagators. After subtraction ... More

Decay of rho and a1 mesons on the lattice using distillationNov 02 2011We extract the P-wave pi-pi phase shift for five values of pion relative momenta, which gives information on the rho resonance. The Breit-Wigner formula describes the pi-pi phase shift dependence nicely and we extract m(rho)=792(7)(8) MeV and the coupling ... More

Effective chiral restoration in the rho'-meson in lattice QCDJul 08 2010Oct 19 2010In simulations with dynamical quarks it has been established that the ground state rho in the infrared is a strong mixture of the two chiral representations (0,1)+(1,0) and (1/2,1/2)_b. Its angular momentum content is approximately the 3S1 partial wave ... 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

Chiral symmetry breaking and the spin content of hadronsNov 10 2011From the parton distributions in the infinite momentum frame one finds that only about 30% of the nucleon spin is carried by spins of the valence quarks, which gave rise to the term "spin crisis". Similar results hold for the lowest mesons, as it follows ... More

Eigenvalue spectrum of massless Dirac operators on the latticeDec 19 1998Apr 30 1999We present a detailed study of the interplay between chiral symmetry and spectral properties of the Dirac operator in lattice gauge theories. We consider, in the framework of the Schwinger model, the fixed point action and a fermion action recently proposed ... More

Predicting positive parity $B_{s}$ mesons from lattice QCDJan 07 2015Sep 04 2015We determine the spectrum of $B_s$ 1P states using lattice QCD. For the $B_{s1}(5830)$ and $B_{s2}^*(5840)$ mesons, the results are in good agreement with the experimental values. Two further mesons are expected in the quantum channels $J^P=0^+$ and $1^+$ ... More

Angular momentum content of the rho-meson in lattice QCDMay 06 2009Sep 14 2009The variational method allows one to study the mixing of interpolators with different chiral transformation properties in the non-perturbatively determined physical state. It is then possible to define and calculate in a gauge-invariant manner the chiral ... More

Coupled channel analysis of the rho meson decay in lattice QCDMay 27 2011Apr 18 2014We employ a variational basis with a number of $\bar{q}q$ and $\pi\pi$ lattice interpolating fields with quantum numbers of the $\rho$ resonance to extract the discrete energy spectrum in a finite volume. In the elastic region, this spectrum is related ... More

Excited light and strange hadrons from the lattice with two Chirally Improved quarksNov 26 2013Results for excited light and strange hadrons from the lattice with two flavors of Chirally Improved sea quarks are presented. We perform simulations at several values of the pion mass ranging from 250 to 600 MeV and extrapolate to the physical pion mass. ... More

QCD with Two Light Dynamical Chirally Improved QuarksMar 18 2013Results for the excited meson and baryon spectrum with two flavors of Chirally Improved sea quarks are presented. We simulate several ensembles with pion masses ranging from 250 to 600 MeV and extrapolate to the physical pion mass. Strange quarks are ... More

Non-Gaussian fixed point candidates in the 4D compact U(1) gauge theoriesJul 18 1996Some interesting nonperturbative properties of the strongly coupled 4D compact U(1) lattice gauge theories, both without and with matter fields, are pointed out. We demonstrate that the pure gauge theory has a non-Gaussian fixed point with $\nu = 0.365(8)$ ... More

Symmetries of hadrons after unbreaking the chiral symmetryMay 22 2012Jul 19 2012We study hadron correlators upon artificial restoration of the spontaneously broken chiral symmetry. In a dynamical lattice simulation we remove the lowest lying eigenmodes of the Dirac operator from the valence quark propagators and study evolution of ... More

Pion-nucleon scattering in the Roper channel from lattice QCDOct 05 2016Jan 31 2017We present a lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. The study is based on the PACS-CS ensemble of gauge configurations with $N_f=2+1$ Wilson-clover ... More

The zeros of the QCD partition functionAug 20 2001We establish a relationship between the zeros of the partition function in the complex mass plane and the spectral properties of the Dirac operator in QCD. This relation is derived within the context of chiral Random Matrix Theory and applies to QCD when ... More

Effects of Low vs. High Fermionic Modes on Hadron Mass GenerationOct 31 2013A nonvanishing spectral density of the low-lying eigenmodes of the Dirac operator naturally is a signal for dynamical chiral symmetry breaking (D$\chi$SB) via the Banks-Casher relation. The low-lying eigenmodes alone saturate the pseudoscalar channel ... More

Chiral symmetry breaking and the spin content of the rho and rho' mesonsJun 06 2011Using interpolators with different SU(2)_L \times SU(2)_R transformation properties we study the chiral symmetry and spin contents of the rho- and rho'-mesons in lattice simulations with dynamical quarks. A ratio of couplings of the $\qbar\gamma^i{\tau}q$ ... More

More effects of Dirac low-mode removalSep 01 2013In previous studies we have shown that hadrons, except for a pion, survive the removal of the lowest lying Dirac eigenmodes from the valence quark propagators. The low-modes are tied to the dynamical breaking of chiral symmetry and we found chiral symmetry ... More

The chiral and angular momentum content of the rho-mesonSep 16 2009It is possible to define and calculate in a gauge-invariant manner the chiral as well as the partial wave content of the quark-antiquark Fock component of a meson in the infrared, where mass is generated. Using the variational method and a set of interpolators ... More

Axial resonances a1(1260), b1(1235) and their decays from the latticeJan 09 2014May 05 2014The light axial-vector resonances $a_1(1260)$ and $b_1(1235)$ are explored in Nf=2 lattice QCD by simulating the corresponding scattering channels $\rho\pi$ and $\omega\pi$. Interpolating fields $\bar{q} q$ and $\rho\pi$ or $\omega\pi$ are used to extract ... More

K pi scattering in moving framesOct 18 2013We extend our study of the $K\pi$ system to moving frames and present an exploratory extraction of the masses and widths for the $K^*$ resonances by simulating $K\pi$ scattering in p-wave with $I=1/2$ on the lattice. Using $K\pi$ systems with non-vanishing ... More

K pi scattering for isospin 1/2 and 3/2 in lattice QCDJul 13 2012Sep 24 2012We simulate K pi scattering in s-wave and p-wave for both isospins I=1/2, 3/2 using quark-antiquark and meson-meson interpolating fields. We extract the elastic phase shifts delta at several values of the K-pi relative momenta. The resulting phases exhibit ... More

Vector and scalar charmonium resonances with lattice QCDMar 18 2015Sep 14 2015We perform an exploratory lattice QCD simulation of $D \bar D$ scattering, aimed at determining the masses as well as the decay widths of charmonium resonances above open charm threshold. Neglecting coupling to other channels, the resulting phase shift ... More

Charm-Production in e^+e^- Annihilation Around 4 GeVSep 30 2007Using the CLEO-c detector at the Cornell Electron Storage Ring, we have measured inclusive and exclusive cross sections for the production of $D^+$, $D^0$ and $D_s^+$ mesons in $e^{+}e^{-}$ annihilations at thirteen center-of-mass energies between 3.97 ... More