Higher-twist contributions to the structure functions coming from 4-fermion operators

We evaluate the contribution of a class of higher-twist operators to the lowest moment of the structure functions, by computing appropriate matrix elements of six four-fermion operators in the quenched approximation. Their perturbative renormalization constants and mixing coefficients are calculated in the 't Hooft-Veltman scheme of dimensional regularization, using codes written in the algebraic manipulation computer language FORM. (orig.)11 refs.Available from TIB Hannover: RA 2999(99-116) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Determining g_A using non-perturbatively O(a) improved Wilson fermions

A completely non-perturbative estimate is given for g_A using both quenched and unquenched O(a) improved Wilson fermions. Particular attention is paid to the determination of the axial renormalisation constant, Z_A, using the Ward identity for the propagator. For the quenched case, we have results at three lattice spacings allowing a continuum extrapolation. (orig.)Available from TIB Hannover: RA 2999(00-153) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Polarized and unpolarized nucleon structure functions from lattice QCD

We report on a high statistics quenched lattice QCD calculation of the deep-inelastic structure functions F_1, F_2, g_1 and g_2 of the proton and neutron. The theoretical basis for the calculation is the operator product expansion. We consider the moments of the leading twist operators up to spin four. Using Wilson fermions the calculation is done for three values of K, and we perform the extrapolation to the chiral limit. The renormalization constants, which lead us from lattice to continuum operators, are calculated in perturbation theory to one loop order. (orig.)32 refs.Available from TIB Hannover: RA 2999(95-128) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The polarized structure function g_2: a lattice study revisited

A recent lattice calculation of the spin-dependent structure function g_2 is revisited. It has been recognized that the twist-three operator, which gives rise to d_2, mixes non-perturbatively with operators of lower dimensions under renormalization. This changes the results substantially. (orig.)8 refs.Available from TIB Hannover: RA 2999(99-129) / 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

Higher-twist contribution to pion structure function: 4-Fermi operators

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 F_2"#pi#""+ + F_2"#pi#""- - 2F_2"#pi#""0 which has I = 2 and receives contributions from 4-Fermi operators only. We introduce the basis of lattice operators. The renormalization of the operators is done perturbatively in the MS scheme using the 't Hooft-Veltman prescription for #gamma#_5, taking particular care of mixing effects. The contribution is found to be of O(f_#pi#"2/Q"2), relative to the leading contribution to the moment of F_2"#pi#""+. (orig.)14 refs.Available from TIB Hannover: RA 2999(99-098) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

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

Non-perturbative versus perturbative renormalization of lattice operators

Our objective is to compute the moments of the deep-inelastic structure functions of the nucleon on the lattice. A major source of uncertainty is the renormalization of the lattice operators that enter the calculation. In this talk we compare the renormalization constants of the most relevant twist-two bilinear quark operators which we have computed non-perturbatively and perturbatively to one loop order. Furthermore, we discuss the use of tadpole improved perturbation theory. (orig.)6 refs.SIGLEAvailable from TIB Hannover: RA 2999(95-179) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman