Spin structure functions from lattice QCD

We report on new results of the spin dependent structure functions g_1 and h_1 of the nucleon. An attempt is made to convert the moments, which is what one computes on the lattice, to quark distribution functions. (orig.)Talk given by Schierholz, G., 2nd International Workshop deep-inelastic scattering of polarized targets: Theory meets experiment, Zeuthen (DE), September 1-5, 1997Available from TIB Hannover: RA 2999(97-217) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Lattice renormalization of quark operators

We have technically improved the non-perturbative renormalization method, proposed by Martinelli et al., by using quark momentum sources and sinks. 0 up to three derivatives have been measured for Wilson fermions and Sheikholeslami-Wohlert improved fermions in the quenched approximation. The calculations are performed in the Landau gauge on 16"332 lattices at #beta#=6.0 for 3 #kappa# values in each case. The improved sources greatly decrease the statistical noise. We extract and discuss here renormalization factors for local operators and moments of the structure functions for Wilson fermions. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(97-203) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The light hadron mass spectrum with non-perturbatively O(a) improved Wilson fermions

We compute the light hadron mass spectrum in quenched lattice QCD at #beta#=6.0 using the Sheikholeslami-Wohlert fermionic action. The calculation is done for several choices of the coefficient c_S_W, including c_S_W=0 and the recently proposed optimal value c_S_W=1.769. We find that the individual masses change by up to 30% under O(a) improvement. The spectrum calculation suggests c_S_W#approx#1.4 for the optimal value of the coefficient. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(96-173) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

New results for non-perturbative O(a) improvement in light hadrons

We have results from light hadron simulations in quenched QCD at #beta# 6.0 and 6.2 using non-perturbatively improved Sheikholeslami-Wohlert fermions in an effort to remove all O(a) effects. From looking at hadron masses and splittings and the RG-invariant quark masses (where we have one point at #beta# = 5.7) we suggest this is plausible even with the limited data set. The interpretation of the decay constants appears to be less clear. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(97-198) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Scaling of non-perturbative O(a) improved Wilson fermions: Hadron spectrum, quark masses and decay constants

We compute the hadron mass spectrum, the quark masses and the meson decay constants in quenched lattice QCD with non-perturbatively O(a) improved Wilson fermions. The calculations are done for two values of the coupling constant, #beta# = 6.0 and 6.2, and the results are compared with the predictions of ordinary Wilson fermions. We find that the improved action reduces lattice artifacts as expected. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

O(a) improvement of nucleon matrix elements

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 renormalisation constants from the alpha collaboration we present a fully non-pertubative calculation of the forward nucleon axial matrix element with O(a) lattice artifacts completely removed. Runs are made at #beta# = 6.0 and #beta# = 6.2, in an attempt to check scaling and O(a"2) effects. We shall also briefly describe results for left angle x right angle, the matrix element of a higher derivative operator. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Perturbative renormalization of improved lattice operators

We derive bases of improved operators for all bilinear quark currents up to spin two (including the operators measuring the first moment of DIS structure functions), and compute their one-loop renormalization constants for arbitrary coefficients of the improvement terms. We have thus control over O(a) corrections, and for a suitable choice of improvement coefficients we are only left with errors of O(a"2). (orig.)SIGLEAvailable from TIB Hannover: RA 2999(97-181) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Local bilinear operators on the lattice and their perturbative renormalisation including O(#alpha#) effects

Some basic concepts are discussed to derive renormalisation factors of local lattice operators relevant to deep inelastic structure functions and to other measurable quantities. These Z factors can be used to relate matrix elements measured by lattice techniques to their continuum counterparts. We discuss the O(a) improvement of point and one-link lattice quark operators. Suitable bases of improved operators are derived. Tadpole improvement is applied to get more reliable perturbative results. (orig.)Talk given by Schiller, A., 2nd SPIN Workshop, Zeuthen (DE), September 1-5, 1997Available from TIB Hannover: RA 2999(97-216) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Is there a Landau Pole problem in QED?

We investigate a lattice version of QED by numerical simulations. For the renormalized charge and mass we find results which are consistent with the renormalized charge vanishing in the continuum limit. A detailed study of the relation between bare and renormalized quantities reveals that the Landau pole lies in a region of parameter space which is made inaccessible by spontaneous chiral symmetry breaking. (orig.)10 refs.SIGLEAvailable from TIB Hannover: RA 2999(97-252) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Resolution of the Landau pole problem in QED

We present new numerical results for the renormalized mass and coupling in non-compact lattice QED with staggered fermions. Implications for the continuum limit and the role of the Landau pole are discussed. (orig.)4 refs.SIGLEAvailable from TIB Hannover: RA 2999(97-258) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman