Chiral Fermions on the Lattice

A recently proposed method for regularizing chiral gauge theories non-perturbatively is discussed in detail. The result is an effective action which can be computed from the lattice gauge field, and which is suited for numerical simulations.Comment: Talk given by G. Schierholz at Yukawa International Seminar on Non-Perturbative QCD: Structure of the QCD Vacuum (YKIS97), Kyoto, December 1997; typos correcte

Lattice chiral Schwinger model: selected results

We discuss a method for regularizing chiral gauge theories. The idea is to formulate the gauge fields on the lattice, while the fermion determinant is regularized and computed in the continuum. A simple effective action emerges which lends itself to numerical simulations. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(98-043) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

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

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

Theoretical uncertainties in the QCD evolution of structure functions and their impact on #alpha#_s(M"2_Z)

The differences are discussed between various next-to-leading order prescriptions for the QCD evolution of parton densities and structure functions. Their quantitative impact is understood to an accuracy of 0.02%. The uncertainties due to the freedom to choose the renormalization and factorization scales are studied. The quantitative consequences of the different uncertainties on the extraction of the strong coupling constant #alpha#, from scaling violations in deep-inelastic scattering are estimated for the kinematic regime accessible at HERA. (orig.)Available from TIB Hannover: RA 2999(96-172) / 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

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

Hadron masses in qQCD with Wilson fermions near the chiral limt

In quenched lattice QCD with standard Wilson fermions the quark propagator is computed very close to the chiral limit in the zero-temperature case. Starting from our experience with lattice QED we employ a modified statistical method in order to estimate reliably hadron masses. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(97-195) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman