Wilson loops in very high order lattice perturbation theory (2009)
Nakamura, Y., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We calculate Wilson loops of various sizes up to loop order $n=20$ for lattice sizes of $L^4 (L=4, 6, 8, 12)$ using the technique of Numerical Stochastic Perturbation Theory in quenched QCD. This...
Results from 2+1 flavours of SLiNC fermions (2009)
Bietenholz, W., Bornyakov, V., Cundy, N., Göckeler, M., Horsley, R., Kennedy, A. D., ...
QCD results are presented for a 2+1 flavour fermion clover action (which we call the SLiNC action). A method of tuning the quark masses to their physical values is discussed. In this method the...
Bornyakov, V. G., Horsley, R., Morozov, S. M., Nakamura, Y., Polikarpov, M. I., Rakow, P. E. L., ...
The critical temperature and the nature of the QCD finite temperature phase transition are determined for Nf=2 dynamical flavors of nonperturbatively improved Wilson fermions. The calculations are...
A Non-Perturbative Operator Product Expansion (2009)
Bietenholz, W., Cundy, N., Goeckeler, M., Horsley, R., Perlt, H., Pleiter, D., ...
Nucleon structure functions can be observed in Deep Inelastic Scattering experiments, but it is an outstanding challenge to confront them with fully non-perturbative QCD results. For this purpose we...
Electroproduction of the N*(1535) resonance at large momentum transfer (2009)
Braun, V. M., Göckeler, M., Horsley, R., Kaltenbrunner, T., Lenz, A., Nakamura, Y., ...
We report on the first lattice calculation of light-cone distribution amplitudes of the N*(1535) resonance, which are used to calculate the transition form factors at large momentum transfers using...
Non-perturbative improvement of stout-smeared three flavour clover fermions (2009)
Cundy, N., Göckeler, M., Horsley, R., Kaltenbrunner, T., Kennedy, A. D., Nakamura, Y., ...
We discuss a 3-flavour lattice QCD action with clover improvement in which the fermion matrix has single level stout smearing for the hopping terms together with unsmeared links for the clover term....
Nucleon distribution amplitudes and proton decay matrix elements on the lattice (2008)
Braun, V. M., Göckeler, M., Horsley, R., Kaltenbrunner, T., Nakamura, Y., Pleiter, D., ...
Baryon distribution amplitudes (DAs) are crucial for the theory of hard exclusive reactions. We present a calculation of the first few moments of the leading-twist nucleon DA within lattice QCD. In...
Clover improvement for stout-smeared 2+1 flavour SLiNC fermions: non-perturbative results (2008)
Cundy, N., Göckeler, M., Horsley, R., Kaltenbrunner, T., Kennedy, A. D., Nakamura, Y., ...
We discuss an action in which the fermion matrix has single level stout smearing for the hopping terms together with unsmeared links for the clover term. With the (tree level) Symanzik improved gluon...
Extracting the rho resonance from lattice QCD simulations at small quark masses (2008)
Göckeler, M., Horsley, R., Nakamura, Y., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
Using established relations between the scattering matrix in infinite volume and the two-particle spectrum in a periodic box, we compute the mass and width of the rho meson from simulations of N_f=2...
Non-perturbative renormalization of three-quark operators (2008)
Göckeler, M., Horsley, R., Kaltenbrunner, T., Nakamura, Y., Pleiter, D., Rakow, P. E. L., ...
High luminosity accelerators have greatly increased the interest in semi-exclusive and exclusive reactions involving nucleons. The relevant theoretical information is contained in the nucleon...
Clover improvement for stout-smeared 2+1 flavour SLiNC fermions: perturbative results (2008)
Horsley, R., Rakow, P. E. L., Perlt, H., Schierholz, G., Schiller, A.
For the Stout Link Non-perturbative Clover (SLiNC) action we determine in one-loop lattice perturbation theory the critical hopping parameter $\kappa_c$ and the clover parameter $c_{SW}$ which is...
Nucleon structure in terms of OPE with non-perturbative Wilson coefficients (2008)
Bietenholz, W., Cundy, N., Gockeler, M., Horsley, R., Perlt, H., Pleiter, D., ...
Lattice calculations could boost our understanding of Deep Inelastic Scattering by evaluating moments of the Nucleon Structure Functions. To this end we study the product of electromagnetic currents...
The electric dipole moment of the nucleon from simulations at imaginary vacuum angle theta (2008)
Horsley, R., Izubuchi, T., Nakamura, Y., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We compute the electric dipole moment of proton and neutron from lattice QCD simulations with N_f=2 flavors of dynamical quarks at imaginary vacuum angle theta. The calculation proceeds via the CP...
Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
Using plaquette and Symanzik improved gauge action and stout link clover fermions we determine the improvement coefficient $c_{SW}$ in one-loop lattice perturbation theory from the off-shell...
The operator product expansion on the lattice (2007)
Bietenholz, W., Cundy, N., Göckeler, M., Horsley, R., Perlt, H., Pleiter, D., ...
We investigate the Operator Product Expansion (OPE) on the lattice by directly measuring the product (where J is the vector current) and comparing it with the expectation values of bilinear...
Probing the chiral limit with clover fermions II: The baryon sector (2007)
Göckeler, M., Hägler, Philipp, Horsley, R., Nakamura, Y., Ohtani, M., Pleiter, D., ...
Algorithmic progress in recent years made it possible to simulate QCD with Nf=2 flavours of O(a)-improved Wilson fermions at very light quark masses. We present the current results for baryon...
Distribution Amplitudes of Vector Mesons (2007)
Braun, V. M., Brömmel, D., Göckeler, M., Horsley, R., Nakamura, Y., Perlt, H., ...
Results are presented for the lowest moment of the distribution amplitude for the K-star vector meson. Both longitudinal and transverse moments are investigated. We use two flavours of O(a) improved...
Moments of nucleon distribution amplitudes from irreducible three-quark operators (2007)
Göckeler, M., Horsley, R., Kaltenbrunner, T., Nakamura, Y., Pleiter, D., Rakow, P. E. L., ...
Semi-exclusive and exclusive processes are becoming more and more important in high energy physics since they are excellently suited to study the internal hadronic structure. To analyze such...
Nucleon electromagnetic form factors with Wilson fermions (2007)
Gockeler, M., Hagler, Ph., Horsley, R., Nakamura, Y., Ohtani, M., Pleiter, D., ...
The nucleon electromagnetic form factors continue to be of major interest for experimentalists and phenomenologists alike. They provide important insights into the structure of nuclear matter. For a...
Moments of generalized parton distributions and quark angular momentum of the nucleon (2007)
Ohtani, QCDSF/UKQCD Collaboration: M., Brommel, D., Gockeler, M., Hagler, Ph., Horsley, R., Nakamura, Y., ...
The internal structure of hadrons is important for a variety of topics, including the hadron form factors, proton spin and spin asymmetry in polarized proton scattering. For a systematic study...
Perturbative determination of $c_{SW}$ with Symanzik improved gauge action and stout smearing (2007)
Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We determine the improvement factor $c_{SW}$ in one-loop lattice perturbation theory for the plaquette and Symanzik improved gauge actions. The fermionic action is ${\mathcal{O}(a)}$ clover improved...
The spin structure of the pion (2007)
Brömmel, D., Diehl, M., Göckeler, M., Hägler, Ph., Horsley, R., Nakamura, Y., ...
We present the first calculation of the transverse spin structure of the pion in lattice QCD. We find a characteristic asymmetry in the spatial distribution of transversely polarized quarks. This...
Transverse spin structure of the nucleon from lattice QCD simulations (2006)
Göckeler, M., Hägler, Ph., Horsley, R., Nakamura, Y., Pleiter, D., Rakow, P. E. L., ...
We present the first calculation in lattice QCD of the lowest two moments of transverse spin densities of quarks in the nucleon. They encode correlations between quark spin and orbital angular...
Nucleon Form Factors: Probing the Chiral Limit (2006)
Gockeler, M., Hageler, Ph., Horsley, R., Nakamura, Y., Pleiter, D., Rakow, P. E. L., ...
The electromagnetic form factors provide important hints for the internal structure of the nucleon and continue to be of major interest for experimentalists. For an intermediate range of momentum...
Simulating at Realistic Quark Masses: Light quark masses (2006)
Göckeler, M., Horsley, R., Nakamura, Y., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present new results for light quark masses. The calculations are performed using two flavours of $O(a)$ improved Wilson fermions. We have reached lattice spacings as small as $a \sim 0.07$fm and...
Operator product expansion on the lattice: analytic Wilson coefficients (2006)
Göckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We present first results for Wilson coefficients of operators up to first order in the covariant derivatives for the case of Wilson fermions. They are derived from the off-shell Compton scattering...
Simulating at Realistic Quark Masses: Pseudoscalar Decay Constants and Chiral Logarithms (2006)
Göckeler, M., Horsley, R., Nakamura, Y., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
Due to improvements in computer performance and algorithms, the rapidly increasing cost for unquenched Wilson-type fermions with lighter quarks has been ameliorated and new simulations are now...
Distribution Amplitudes of Pseudoscalar Mesons (2006)
Braun, V. M., Gockeler, M., Horsley, R., Perlt, H., Pleiter, D., Rakow, P. E. L., ...
We present results for the first two moments of the distribution amplitudes of pseudoscalar mesons. Using two flavors of non-perturbatively improved clover fermions and non-perturbative...
Göckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We consider the renormalisation of composite quark-antiquark operators with one and two lattice covariant derivatives related to the lowest moments of generalised parton distributions (GPDs) and...
Probing Nucleon Structure on the Lattice (2006)
Göckeler, M., Hägler, Ph., Horsley, R., Nakamura, Y., Pleiter, D., Rakow, P. E. L., ...
The QCDSF/UKQCD collaboration has an ongoing program to calculate nucleon matrix elements with two flavours of dynamical O(a) improved Wilson fermions. Here we present recent results on the...
The pion form factor from lattice QCD with two dynamical flavours (2006)
Brömmel, D., Diehl, M., Göckeler, M., Hägler, Ph., Horsley, R., Nakamura, Y., ...
We compute the electromagnetic form factor of the pion using non-perturbatively O(a) improved Wilson fermions. The calculations are done for a wide range of pion masses and lattice spacings. We check...
Galletly, D., Gürtler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., ...
We present results from a simulation of quenched overlap fermions with L\"uscher-Weisz gauge field action on lattices up to $24^3 48$ and for pion masses down to $\approx 250$ MeV. Among the...
Moments of pseudoscalar meson distribution amplitudes from the lattice (2006)
Braun, V. M., Göckeler, M., Horsley, R., Perlt, H., Pleiter, D., Rakow, P. E. L., ...
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...
Göckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schäfer, A., Schierholz, G., ...
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...
Khan, A. Ali, Göckeler, M., Hägler, Ph., Hemmert, T. R., Horsley, R., Pleiter, D., ...
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...
Determining the strange quark mass for 2-flavour QCD (2006)
Göckeler, M., Horsley, R., Irving, A. C., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
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...
Estimating the Unquenched Strange Quark Mass from the Lattice Axial Ward Identity (2006)
Göckeler, M., Horsley, R., Irving, A. C., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present a determination of the strange quark mass for two flavours (nf=2) of light dynamical quarks using the axial Ward identity. The calculations are performed on the lattice using O(a) improved...
Nucleon structure from generalized parton distributions in lattice QCD (2005)
Gockeler, M., Hagler, Ph., Horsley, R., Pleiter, D., Rakow, P. E. L., Schafer, A., ...
This talk presents results from the QCDSF-UKQCD collaboration for moments of leading twist generalized parton distributions in two-flavor lattice QCD based on O(a) improved Wilson Fermions. We study...
Gockeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schaefer, A., Schierholz, G., ...
We present the non-forward quark matrix elements of operators with one and two covariant derivatives needed for the renormalisation of the first and second moments of generalised parton distributions...
Soffer Bound and Transverse Spin Densities from Lattice QCD (2005)
Diehl, M., Gockeler, M., Hagler, Ph., Horsley, R., Pleiter, D., Rakow, P. E. L., ...
Generalized transversity distributions encode essential information on the internal structure of hadrons related to transversely polarized quarks. Lattice QCD allows us to compute the lowest moments...
Second moment of the pion's distribution amplitude (2005)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., Schierholz, G., ...
We present preliminary results from the QCDSF/UKQCD collaborations for the second moment of the pion's distribution amplitude with two flavours of dynamical fermions. We use nonperturbatively...
The axial charge of the nucleon on the lattice and in chiral perturbation theory (2005)
Khan, A. Ali, Göckeler, M., Hägler, P., Hemmert, T. R., Horsley, R., Irving, A. C., ...
We present recent Monte Carlo data for the axial charge of the nucleon obtained by the QCDSF-UKQCD collaboration for N_f=2 dynamical quarks. We compare them with formulae from chiral perturbation...
Nucleon Structure from Quenched Overlap Fermions (2005)
Galletly, D., Gürtler, M., Horsley, R., Koller, K., Linke, V., Rakow, P. E. L., ...
We compute the lowest moments of the nucleon's structure functions using quenched overlap fermions at two different lattice spacings. The renormalisation is done nonperturbatively in the...
Non-perturbative renormalisation for overlap fermions (2005)
Gürtler, M., Horsley, R., Rakow, P. E. L., Roberts, C. J., Schierholz, G., Streuer, T.
Using non-perturbative techniques we have found the renormalisation factor, Z, in the RI-MOM scheme for quark bilinear operators in quenched QCD. We worked with overlap fermions using the...
Stochastic Perturbation Theory and the Gluon Condensate (2005)
On the lattice searching for the gluon condensate is difficult because a large perturbative contribution to the expectation value of the action has to be subtracted before looking for a small...
Meson decay constants from Nf=2 clover fermions (2005)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G., Schroers, W., ...
We present recent results for meson decay constants calculated on configurations with two flavours of O(a)-improved Wilson fermions. Non-perturbative renormalisation is applied and quark mass...
A determination of the strange quark mass for unquenched clover fermions using the AWI (2005)
Göckeler, M., Horsley, R., Irving, A. C., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
Using the O(a) Symanzik improved action an estimate is given for the strange quark mass for unquenched (nf=2) QCD. The determination is via the axial Ward identity (AWI) and includes a...
Structure of the Pion from Full Lattice QCD (2005)
Brömmel, D., Diehl, M., Göckeler, M., Hägler, Ph., Horsley, R., Pleiter, D., ...
Moments of generalised parton distributions can be related to off-forward matrix elements of local operators. We calculate a few of the leading twist matrix elements for the pion on the lattice. The...
Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We calculate lattice renormalisation constants of local and one-link quark operators for overlap fermions and improved gauge actions in one-loop perturbation theory. For the local operators we stout...
Quark helicity flip generalized parton distributions from two-flavor lattice QCD (2005)
Gockeler, M., Hagler, Ph., Horsley, R., Pleiter, D., Rakow, P. E. L., Schafer, A., ...
We present an initiatory study of quark helicity flip generalized parton distributions (GPDs) in n_f=2 lattice QCD, based on clover-improved Wilson fermions for a large number of coupling constants...
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., Schierholz, G., ...
The reduced matrix elements a_2 and d_2 are computed in lattice QCD with N_f=2 flavors of light dynamical (sea) quarks. For proton and neutron targets we obtain as our best estimates d_2^(p)=0.004(5)...
Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We compute lattice renormalisation constants of one-link quark operators ({\it i.e.} operators with one covariant derivative) for overlap fermions and L\"uscher-Weisz gauge action in one-loop...
A Determination of the Lambda Parameter from Full Lattice QCD (2005)
Göckeler, M., Horsley, R., Irving, A. C., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present a determination of the QCD parameter Lambda in the quenched approximation (n_f=0) and for two flavours (n_f=2) of light dynamical quarks. The calculations are performed on the lattice...
Generalized parton distributions and transversity from full lattice QCD (2005)
Gockeler, M., Hagler, Ph., Horsley, R., Pleiter, D., Rakow, P. E. L., Schafer, A., ...
We present here the latest results from the QCDSF collaboration for moments of generalized parton distributions and transversity in two-flavour QCD, including a preliminary analysis of the pion mass...
Goeckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schaefer, A., Schierholz, G., ...
The reduced matrix elements a_2 and d_2 are computed in lattice QCD with N_f=2 flavors of light dynamical (sea) quarks. For proton and neutron targets we obtain as our best estimates d_2^(p)=0.004(5)...
Progress Towards finding Quark Masses and the QCD scale Lambda from the Lattice (2004)
We discuss recent work trying to extract the renormalised quark masses and Lambda, the QCD scale, from dynamical simulations in lattice gauge theory.
Generalized Parton Distributions in Full Lattice QCD (2004)
Göckeler, M., Hägler, Ph., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., ...
We present recent results on generalized parton distributions from dynamical lattice QCD calculations. Our set of twelve different combinations of couplings and quark masses allows for a preliminary...
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G.
Within the framework of quenched lattice QCD and using O(a) improved Wilson fermions and non-perturbative renormalisation, a high statistics computation of low moments of the unpolarised nucleon...
Perturbative Renormalisation of the Second Moment of Generalised Parton Distributions (2004)
Göckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schäfer, A., Schierholz, G., ...
We calculate the non-forward quark matrix elements of operators with two covariant derivatives needed for the renormalisation of the second moment of generalised parton distributions in one-loop...
A lattice determination of g_A and from overlap fermions (2004)
Gürtler, M., Horsley, R., Linke, V., Perlt, H., Rakow, P. E. L., Schierholz, G., ...
We present results for the nucleon's axial charge g_A and the first moment of the unpolarized parton distribution function from a simulation of quenched overlap fermions.
Determination of Lambda in quenched and full QCD - an update (2004)
Göckeler, M., Horsley, R., Irving, A. C., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present an update on our previous determination of the Lambda parameter in QCD. The main emphasis is on results for two flavours of light dynamical quarks, where we can now almost double the...
Axial and tensor charge of the nucleon with dynamical fermions (2004)
Khan, A. Ali, Göckeler, M., Hägler, P., Hemmert, T. R., Horsley, R., Irving, A. C., ...
We present preliminary results for the axial and tensor charge of the nucleon obtained from simulations with N_f=2 clover fermions. A comparison with chiral perturbation theory is attempted.
Generalized parton distributions and structure functions from full lattice QCD (2004)
Göckeler, M., Hägler, P., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., ...
We present here the latest results from the QCDSF collaboration for (moments of) structure functions and generalized form factors in full QCD with Nf=2 O(a)-improved Wilson fermions based on...
Determination of Light and Strange Quark Masses from Full Lattice QCD (2004)
Göckeler, M., Horsley, R., Irving, A. C., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We compute the light and strange quark masses m_l = (m_u+m_d)/2 and m_s, respectively, in full lattice QCD with N_f=2 flavors of light dynamical quarks. The renormalization constants, which convert...
One-loop renormalisation for the second moment of GPDs with Wilson fermions (2004)
Göckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schäfer, A., Schierholz, G., ...
We calculate the non-forward quark matrix elements for operators with two covariant derivatives in one-loop lattice perturbation theory using Wilson fermions. These matrix elements are needed in the...
One-loop renormalisation of quark bilinears for overlap fermions with improved gauge actions (2004)
Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., Schiller, A.
We compute lattice renormalisation constants of local bilinear quark operators for overlap fermions and improved gauge actions. Among the actions we consider are the Symanzik, L\"uscher-Weisz,...
The nucleon mass in N_f=2 lattice QCD: finite size effects from chiral perturbation theory (2003)
Khan, A. Ali, Bakeyev, T., Göckeler, M., Hemmert, T. R., Horsley, R., Irving, A. C., ...
In the framework of relativistic SU(2)_f baryon chiral perturbation theory we calculate the volume dependence of the nucleon mass up to and including O(p^4). Since the parameters in the resulting...
Vacuum Polarisation and Hadronic Contribution to muon g-2 from Lattice QCD (2003)
Göckeler, M., Horsley, R., Kürzinger, W., Pleiter, D., Rakow, P. E. L., Schierholz, G.
We compute the vacuum polarisation on the lattice in quenched QCD using non-perturbatively improved Wilson fermions. Above Q^2 of about 2 GeV^2 the results are very close to the predictions of...
Khan, A. Ali, Bakeyev, T., Göckeler, M., Hemmert, T. R., Horsley, R., Irving, A. C., ...
The finite size effects on nucleon masses are calculated in relativistic chiral perturbation theory. Results are compared with two-flavor lattice results.
Structure of the Nucleon (2003)
Göckeler, M., Hemmert, T. R., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., ...
Generalized parton distributions provide information on the longitudinal and transverse distribution of partons in the fast moving nucleon. Furthermore, they contain information on the spin structure...
Structure functions and form factors close to the chiral limit from lattice QCD (2003)
Bakeyev, T., Galletly, D., Göckeler, M., Gürtler, M., Horsley, R., Joó, B., ...
Results for nucleon matrix elements (arising from moments of structure functions) and form factors from a mixture of runs using Wilson, clover and overlap fermions (both quenched and unquenched) are...
Vacuum polarisation and the muon g-2 in lattice QCD (2003)
Göckeler, M., Horsley, R., Kürzinger, W., Pleiter, D., Rakow, P. E. L., Schierholz, G.
We measure the hadronic contribution to the vacuum polarisation tensor, and use it to estimate the hadronic contribution to (g-2)_mu, the muon anomalous magnetic moment.
Galletly, D., Gürtler, M., Horsley, R., Joo, B., Kennedy, A. D., Perlt, H., ...
We present first results from a simulation of quenched overlap fermions with improved gauge field action. Among the quantities we study are the spectral properties of the overlap operator, the chiral...
Chiral Perturbation Theory and Finite Size Effects on the Nucleon Mass in unquenched QCD (2003)
Khan, A. Ali, Bakeyev, T., Göckeler, M., Hemmert, T. R., Horsley, R., Irving, A. C., ...
We calculate finite size effects on nucleon masses in chiral perturbation theory. We confront the theoretical predictions with N_f=2 lattice results and discuss chiral extrapolation formulae.
Accelerating Hasenbusch's acceleration of Hybrid Monte Carlo (2003)
Khan, A. Ali, Bakeyev, T., Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., ...
Hasenbusch has proposed splitting the pseudo-fermionic action into two parts, in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a different splitting, also using...
Quenched spectroscopy with fixed-point and chirally improved fermions (2003)
Gattringer, BGR Collaboration: Christof, Gockeler, Meinulf, Hasenfratz, Peter, Hauswirth, Simon, Holland, Kieran, Jorg, Thomas, ...
We present results from quenched spectroscopy calculations with the parametrized fixed-point and the chirally improved Dirac operators. Both these operators are approximate solutions of the...
Bakeyev, T., Gockeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
By considering the local vector current between nucleon states and imposing charge conservation, we determine its renormalisation constant and quark mass improvement coefficient for Symanzik $O(a)$...
Generalized Parton Distributions from Lattice QCD (2003)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., Schierholz, G., ...
We perform a quenched lattice calculation of the first moment of twist-two generalized parton distribution functions of the proton, and assess the total quark (spin and orbital angular momentum)...
Nucleon electromagnetic form factors on the lattice and in chiral effective field theory (2003)
Göckeler, M., Hemmert, T. R., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., ...
We compute the electromagnetic form factors of the nucleon in quenched lattice QCD, using non-perturbatively improved Wilson fermions, and compare the results with phenomenology and chiral effective...
Calculation of Moments of Structure Functions (2002)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schäfer, A., Schierholz, G.
The progress on the lattice computation of low moments of both the unpolarised and polarised nucleon structure functions is reviewed with particular emphasis on continuum and chiral extrapolations...
Structure functions near the chiral limit (2002)
Goeckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G.
We compute hadron masses and the lowest moments of unpolarized and polarized nucleon structure functions down to pion masses of 300 MeV, in an effort to make unambiguous predictions at the physical...
Bakeyev, T., Gockeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schafer, A., ...
By considering the local vector current between nucleon states and imposing charge conservation we determine, for $O(a)$ improved Wilson fermions, its renormalisation constant and quark mass...
Quenched QCD with fixed-point and chirally improved fermion (2002)
Gattringer, Christof, Göckeler, Meinulf, Hasenfratz, Peter, Hauswirth, Simon, Holland, Kieran, Jörg, Thomas, ...
In this contribution we present results from quenched QCD simulations with the parameterized fixed-point (FP) and the chirally improved (CI) Dirac operator. Both these operators are approximate...
A lattice study of the spin structure of the Lambda hyperon (2002)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schaefer, S., Schäfer, A., ...
The internal spin structure of the Lambda is of special importance for the understanding of the spin structure of hadrons in general. The comparison between the nucleon and Lambda allows for a test...
Applied lattice gauge calculations: diquark content of the nucleon (2002)
Göckeler, M., Horsley, R., Klaus, B., Pleiter, D., Rakow, P. E. L., Schaefer, S., ...
As an example of an application of lattice QCD we describe a computation of four-quark operators in the nucleon. The results are interpreted in a diquark language.
Lattice Calculation of Baryon Masses using the Clover Fermion Action (2002)
Gockeler, QCDSF Collaboration: M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present a calculation of the lowest-lying baryon masses in the quenched approximation to QCD. The calculations are performed using a non-perturbatively improved clover fermion action, and a...
Chiral symmetry restoration and the Z3 sectors of QCD (2002)
Gattringer, Christof, Rakow, P. E. L., Schaefer, Andreas, Soeldner, Wolfgang
Quenched SU(3) lattice gauge theory shows three phase transitions, namely the chiral, the deconfinement and the Z3 phase transition. Knowing whether or not the chiral and the deconfinement phase...
Excited nucleon spectrum using a non-perturbatively improved clover fermion action (2001)
Gockeler, QCDSF Collaboration: M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We discuss the extraction of negative-parity baryon masses from lattice QCD calculations. The mass of the lowest-lying negative-parity $J = 1/2^{-}$ state is computed in quenched lattice QCD using an...
The strong coupling constant from lattice QCD with N_f=2 dynamical quarks (2001)
Booth, S., Göckeler, M., Horsley, R., Irving, A. C., Joo, B., Pickles, S., ...
We compute $\Lambda_{\bar{MS}}$ for two flavors of light dynamical quarks using non-perturbatively $O(a)$ improved Wilson fermions. We improve on a recent calculation by employing Pad\'e-improved...
Separating perturbative and non-perturbative contributions to the plaquette (2001)
Horsley, R., Rakow, P. E. L., Schierholz, G.
We try to separate the perturbative and non-perturbative contributions to the plaquette of pure SU(3) gauge theory. To do this we look at the large-n asymptotic behaviour of the perturbation series...
Gattringer, C., Göckeler, M., Rakow, P. E. L., Schäfer, A., Söldner, W., Wettig, T.
We 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...
The spin structure of the Lambda hyperon in quenched lattice QCD (2001)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schaefer, S., Schäfer, A., ...
It has been suggested to use the production of Lambda hyperons for investigating the nucleon spin structure. The viability of this idea depends crucially on the spin structure of the Lambda. Using...
Gattringer, Christof, Göckeler, Meinulf, Lang, C. B., Rakow, P. E. L., Schaefer, Stefan, Schäfer, Andreas
We 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...
Nucleon form factors and structure functions from Lattice QCD (2001)
Göckeler, M., Horsley, R., Pleiter, D., Rakow, P. E. L., Schierholz, G.
In this talk we highlight recent lattice calculations of the nucleon form factors and structure functions.
Comparing lattice Dirac operators in smooth instanton backgrounds (2001)
Gattringer, Christof, Göckeler, Meinulf, Lang, C. B., Rakow, P. E. L., Schäfer, Andreas
We 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...
Properties of near-zero modes and chiral symmetry breaking (2001)
Gattringer, Christof, Goeckeler, Meinulf, Rakow, P. E. L., Schaefer, Stefan, Schaefer, Andreas
We study localization and chirality properties of eigenvectors of the lattice Dirac operator. In particular we focus on the dependence of our observables on the size of the corresponding eigenvalue,...
Beyond the Thouless energy (2001)
Berbenni-Bitsch, M. E., Göckeler, M., Hehl, H., Meyer, S., Rakow, P.E.L., Schäfer, A., ...
Abstract: The distribution and the correlations of the small eigenvalues of the Dirac operator are described by random matrix theory (RMT) up to the Thouless energy E_= 1 / sqrt (V), where V is the...
Random Matrix Theory, Chiral Perturbation Theory, and Lattice Data (2001)
Berbenni-Bitsch, M. E., Göckeler, M., Hehl, H., Meyer, S., Rakow, P.E.L., Schäfer, A., ...
Abstract: Recently, the chiral logarithms predicted by quenched chiral perturbation theory have been extracted from lattice calculations of hadron masses. We argue that the deviations of lattice...
Random Matrix Theory and Chiral Logarithms (2001)
Berbenni-Bitsch, M. E., Göckeler, M., Hehl, H., Meyer, S., Rakow, P.E.L., Schäfer, A., ...
Abstract: Recently, the contributions of chiral logarithms predicted by quenched chiral perturbation theory have been extracted from lattice calculations of hadron masses. We argue that a detailed...
Negative-parity Baryon Masses using an O(a)-improved Fermion Action (2001)
Collaboration, LHPC, Collaboration, QCDSF, Gockeler, UKQCD Collaboration: M., Horsley, R., Maynard, C. M., Pleiter, D., ...
We present a calculation of the mass of the lowest-lying negative-parity J=1/2- state in quenched QCD. Results are obtained using a non-perturbatively O(a)-improved clover fermion action, and a...
A comprehensive picture of topological excitations in finite temperature lattice QCD (2001)
Gattringer, Christof, Göckeler, Meinulf, Rakow, P. E. L., Schaefer, Stefan, Schäfer, Andreas
We study spectra, localization properties and local chirality of eigenvectors of the lattice Dirac operator. We analyze ensembles of quenched SU(3) configurations on both sides of the QCD phase...
Göckeler, M., Hehl, H., Rakow, P. E. L., Schäfer, A., Wettig, T.
We calculate complete spectra of the Kogut-Susskind Dirac operator on the lattice in quenched SU(3) gauge theory for various values of coupling constant and lattice size. From these spectra we...
A lattice evaluation of four-quark operators in the nucleon (2001)
Göckeler, M., Horsley, R., Klaus, B., Pleiter, D., Rakow, P. E. L., Schaefer, S., ...
Nucleon matrix elements of various four-quark operators are evaluated in quenched lattice QCD using Wilson fermions. Some of these operators give rise to twist-four contributions to nucleon structure...
Calorons and localization of quark eigenvectors in lattice QCD (2001)
Göckeler, M., Rakow, P. E. L., Schäfer, A., Söldner, W., Wettig, T.
We analyze the localization properties for eigenvectors of the Dirac operator in quenched lattice QCD in the vicinity of the deconfinement phase transition. Studying the characteristic differences...
Determination of $\Lambda_{\overline{MS}}$ from quenched and $N_f = 2$ dynamical QCD (2001)
Booth, S., Göckeler, M., Horsley, R., Irving, A. C., Joo, B., Pickles, S., ...
The scale parameter $\Lambda_{\overline{MS}}$ is computed on the lattice in the quenched approximation and for $N_f = 2$ flavors of light dynamical quarks. The dynamical calculation is done with...
Calorons and Localization of Quark Eigenvectors in Lattice QCD (2001)
Göckeler, M., Rakow, P. E. L., Schäfer, A., Söldner, W., Wettig, T.
The Vacuum Polarization: Power Corrections beyond OPE ? (2000)
Gockeler, M., Horsley, R., Kurzinger, W., Linke, V., Pleiter, D., Rakow, P. E. L., ...
We compute the vacuum polarization on the lattice using non-perturbatively O(a) improved Wilson fermions. The result is compared with the operator product expansion (OPE).
A lattice calculation of the nucleon's spin-dependent structure function g_2 revisited (2000)
Gockeler, M., Horsley, R., Kurzinger, W., Oelrich, H., Pleiter, D., Rakow, P. E. L., ...
Our previous calculation of the spin-dependent structure function g_2 is revisited. The interest in this structure function is to a great extent motivated by the fact that it receives contributions...
Four-quark operators in hadrons (2000)
Capitani, S., Gockeler, M., Horsley, R., Klaus, B., Kurzinger, W., Petters, D., ...
We present calculations of matrix elements of 4-quark operators in the pion and in the nucleon extracted from quenched Monte Carlo simulations at beta = 6.0 using Wilson fermions. These operators are...
Dirac eigenvalues and eigenvectors at finite temperature (2000)
Göckeler, M., Hehl, H., Rakow, P. E. L., Schäfer, A., Söldner, W., Wettig, T.
We investigate the eigenvalues and eigenvectors of the staggered Dirac operator in the vicinity of the chiral phase transition of quenched SU(3) lattice gauge theory. We consider both the global...
Renormalisation and off-shell improvement in lattice perturbation theory (2000)
Capitani, S., Goeckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., ...
We discuss the improvement of flavour non-singlet point and one-link lattice quark operators, which describe the quark currents and the first moment of the DIS structure functions respectively....
Quenched QCD near the chiral limit (2000)
Gockeler, M., Horsley, R., Petters, D., Pleiter, D., Rakow, P. E. L., Schierholz, G.
A numerical study of quenched QCD for light quarks is presented using O(a) improved fermions. Particular attention is paid to the possible existence and determination of quenched chiral logarithms. A...
On-shell and off-shell improvement for Ginsparg-Wilson fermions (1999)
Capitani, S., Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G.
We discuss the improvement of bilinear fermionic operators for Ginsparg-Wilson fermions. We present explicit formulae for improved Green's functions, which apply both on-shell and off-shell.
Hadron masses and decay constants in quenched QCD (1999)
Goeckeler, M., Horsley, R., Petters, D., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present results for the mass spectrum and decay constants using non-perturbatively O(a) improved Wilson fermions. Three values of $\beta$ and 30 different quark masses are used to obtain the...
Beyond the Thouless energy (1999)
Berbenni-Bitsch, M. E., Göckeler, M., Hehl, H., Meyer, S., Rakow, P. E. L., Schäfer, A., ...
The distribution and the correlations of the small eigenvalues of the Dirac operator are described by random matrix theory (RMT) up to the Thouless energy $E_c\propto 1/\sqrt{V}$, where $V$ is the...
Operator improvement for Ginsparg-Wilson fermions (1999)
Capitani, S., Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G.
The improvement of fermionic operators for Ginsparg-Wilson fermions is investigated. We present explicit formulae for improved Green's functions, which apply both on-shell and off-shell.
Light quark masses from the lattice (1999)
Gockeler, M., Horsley, R., Klaus, B., Kurzinger, W., Oelrich, H., Petters, D., ...
A completely non-perturbative estimate is given for the u/d and strange quark masses in quenched QCD using O(a) improved fermions and, for comparison, Wilson fermions. For improved fermions we find...
Higher-Twist Contribution to Pion Structure Function: 4-Fermi Operators (1999)
Capitani, S., Göckeler, M., Horsley, R., Klaus, B., Linke, V., Rakow, P. E. L., ...
We present quenched lattice QCD results for the contribution of higher-twist operators to the lowest non-trivial moment of the pion structure function. To be specific, we consider the combination...
A Lattice Determination of Light Quark Masses (1999)
Gockeler, M., Horsley, R., Oelrich, H., Petters, D., Pleiter, D., Rakow, P. E. L., ...
A fully non-perturbative lattice determination of the up/down and strange quark masses is given for quenched QCD using both, $O(a)$ improved Wilson fermions and ordinary Wilson fermions. For the...
Random Matrix Theory, Chiral Perturbation Theory, and Lattice Data (1999)
Berbenni-Bitsch, M. E., Göckeler, M., Hehl, H., Meyer, S., Rakow, P. E. L., Schäfer, A., ...
Recently, the chiral logarithms predicted by quenched chiral perturbation theory have been extracted from lattice calculations of hadron masses. We argue that the deviations of lattice results from...
Towards a lattice calculation of $\Delta q$ and $\delta q$ (1999)
Capitani, S., Gockeler, M., Horsley, R., Perlt, H., Petters, D., Pleiter, D., ...
Within the framework of lattice QCD a high statistics computation of the nucleon axial and tensor charges is given. Particular attention is paid to the chiral and continuum extrapolations.
Random Matrix Theory and Chiral Logarithms (1999)
Berbenni-Bitsch, M. E., Göckeler, M., Hehl, H., Meyer, S., Rakow, P. E. L., Schäfer, A., ...
Recently, the contributions of chiral logarithms predicted by quenched chiral perturbation theory have been extracted from lattice calculations of hadron masses. We argue that a detailed comparison...
Small eigenvalues of the SU(3) Dirac operator on the lattice and in Random Matrix Theory (1998)
Göckeler, M., Hehl, H., Rakow, P. E. L., Schäfer, A., Wettig, T.
We have calculated complete spectra of the staggered Dirac operator on the lattice in quenched SU(3) gauge theory for \beta = 5.4 and various lattice sizes. The microscopic spectral density, the...
Mass spectrum and decay constants in the continuum limit (1998)
Goeckeler, M., Horsley, R., Linke, V., Pleiter, D., Rakow, P. E. L., Schierholz, G., ...
We present first results for light hadron masses, quark masses and decay constants in the continuum limit using O(a) improved fermions at three different values of the gauge coupling \beta.
Renormalization of four-fermion operators for higher twist calculations (1998)
Capitani, S., Göckeler, M., Horsley, R., Perlt, H., Rakow, P. E. L., Schierholz, G., ...
The evaluation of the higher twist contributions to Deep Inelastic Scattering amplitudes involves a non trivial choice of operator bases for the higher orders of the OPE expansion of the two hadronic...
Nucleon form factors and O(a) Improvement (1998)
Capitani, S., Gockeler, M., Horsley, R., Klaus, B., Oelrich, H., Perlt, H., ...
Nucleon form factors have been extensively studied both experimentally and theoretically for many years. We report here on new results of a high statistics quenched lattice QCD calculation of vector...
Composite operators in lattice QCD: nonperturbative renormalization (1998)
Gockeler, M., Horsley, R., Oelrich, H., Perlt, H., Petters, D., Rakow, P. E. L., ...
We investigate the nonperturbative renormalization of composite operators in lattice QCD restricting ourselves to operators that are bilinear in the quark fields. These include operators which are...
Nonperturbative Renormalisation of Composite Operators in Lattice QCD (1998)
Gockeler, M., Horsley, R., Oelrich, H., Perlt, H., Petters, D., Rakow, P. E. L., ...
We investigate the nonperturbative renormalisation of composite operators in lattice QCD restricting ourselves to operators that are bilinear in the quark fields. These include operators which are...
Lattice Renormalization of Quark Operators (1997)
Goeckeler, M., Horsley, R., Oelrich, H., Perlt, H., Rakow, P. E. L., Schierholz, G., ...
We have technically improved the non-perturbative renormalization method, proposed by Martinelli et al., by using quark momentum sources and sinks. Composite two-fermion operators up to three...
Non-perturbative improvement and renormalization of lattice operators (1997)
Capitani, S., Goeckeler, M., Horsley, R., Oelrich, H., Perlt, H., Pleiter, D., ...
The Alpha Collaboration has proposed an optimal value for c_SW in the Sheikholeslami-Wohlert action, chosen to remove O(a) effects. To measure hadronic matrix elements to the same accuracy we need a...
$O(a)$ Improvement of Nucleon Matrix Elements (1997)
Capitani, S., Goeckeler, M., Horsley, R., Oelrich, H., Perlt, H., Pleiter, D., ...
We report on preliminary results of a high statistics quenched lattice QCD calculation of nucleon matrix elements within the Symanzik improvement programme. Using the recently determined...
The Drell-Yan process and Deep Inelastic Scattering from the lattice (1996)
Goeckeler, M., Horsley, R., Oelrich, H., Perlt, H., Rakow, P. E. L., ...
We report on measurements of the h_1 structure function, relevant to calculating cross-sections for the Drell-Yan process. This is a quantity which can not be measured in Deep Inelastic Scattering,...
A Preliminary Lattice Study of the Glue in the Nucleon (1996)
Goeckeler, M., Horsley, R., Oelrich, H., Perlt, H., Rakow, P. E. L., ...
About half the mass of a hadron is given from gluonic contributions. In this talk we calculate the chromo-electric and chromo-magnetic components of the nucleon mass. These computations are...
Effective Yukawa Couplings in Noncompact Lattice QED (1995)
Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G.
We investigate effective Yukawa couplings of mesons to the elementary fermions in noncompact lattice QED. The couplings are extracted from suitable fermion-antifermion-meson three-point functions...
Probing the Continuum Limit in Non-Compact QED: New Results on Large Lattices (1994)
Goeckeler, M., Horsley, R., Linke, V., Rakow, P. E. L., Schierholz, G., Stueben, H.
We present new Monte Carlo results in non-compact lattice QED with staggered fermions down to m_0 = 0.005. This extends our previous investigations on the nature of the continuum limit of QED.
Spectroscopy and Renormalisation Group Flow of a Lattice Nambu-Jona-Lasinio Model (1994)
Khan, A. Ali, Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G., Stueben, H.
We investigate a lattice Nambu--Jona-Lasinio model both by the Monte Carlo method and Schwinger-Dyson equations. A comparison allows the discussion of finite size effects and the extrapolation to...
The Nambu-Jona-Lasinio model with staggered fermions (1994)
Khan, A. Ali, Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G., Stueben, H.
We investigate the neighbourhood of the chiral phase transition in a lattice Nambu--Jona-Lasinio model, using both Monte Carlo methods and lattice Schwinger-Dyson equations.
The present status of non-compact lattice QED (1993)
Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G., Stueben, H.
We give a 1993 update of non-compact lattice QED, in particular the chiral condensate, finite size effects and meson mass ratios. We compare descriptions of the phase transition. Our previous...
Three-point functions in noncompact lattice QED (1993)
Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G.
We calculate fermion-antifermion-"meson" three-point functions in noncompact lattice QED with dynamical staggered fermions and use them to extract effective Yukawa couplings. The results are...
Is the Chiral Phase Transition in Non-Compact Lattice QED Driven by Monopole Condensation? (1993)
Goeckeler, M., Horsley, R., Rakow, P. E. L., Schierholz, G.
We investigate the recent conjecture that the chiral phase transition in non-compact lattice QED is driven by monopole condensation. The comparison of analytic and numerical results shows that we...
Magnetic Monopoles in non-compact QED - is there a Phase Transition? (1992)
The existence of the monopole condensation transition reported by Kocic et al. in non-compact, quenched QED is tested. No phase transition is found. This shows that divergence of the `monopole...
The application of perturbative quantum chromodynamics to various processes. (1982)
Thesis (Ph. D.)--University of Cambridge, 1982.