Untersuchungen zur inneren Struktur, insbesondere Spinstruktur der Nukleonen. 1. Teilprojekt: Berechnungen fuer laufende und zukuenftige Spinexperimente am DESY (HERMES) und CERN (COMPASS). 2. Teilprojekt: Polarisierte Proton-Proton Reaktionen. 3. Teilprojekt: Experimente fuer einen moeglichen zukuenftigen Elektron-Kern-Kollider (ENC) an der GSI Abschlussbericht

SIGLEAvailable from TIB Hannover: DtF QN1(92,29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Perturbative renormalisation of the second moment of generalised parton distributions

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 lattice perturbation theory using Wilson fermions. For some representations of the hypercubic group commonly used in simulations we determine the sets of all possible mixing operators. For those representations the one-loop mixing matrices of renormalisation factors are found. Due to non-vanishing contributions of operators with external ordinary derivatives the number of contributing operators increases compared to forward matrix elements. (orig.)SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

A lattice study of the spin structure of the #LAMBDA# hyperon

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 of the relevant flavour-symmetry breaking effects. Using nonperturbatively O(a) improved Wilson fermions in the quenched approximation we have calculated the first moments of the unpolarised, longitudinally polarised and transversity quark distribution functions in the #LAMBDA#. The results indicate that flavour symmetry breaking has little effect on the internal spin structure, in accordance with model based expectations. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(02-100) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Nucleon electromagnetic form factors on the lattice and in chiral effective field theory

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 field theory. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-032) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Accelerating the Hybrid Monte Carlo algorithm

An algorithm for separating the high- and low-frequency molecular dynamics modes in Hybrid Monte Carlo (HMC) simulations of gauge theories with dynamical fermions is presented. The separation is based on splitting the pseudo-fermion action into two parts, as was initially proposed by Hasenbusch. We propose to introduce different evolution time-scales for each part. We test our proposal in realistic simulations of two-flavor O(a) improved Wilson fermions. A speed-up of more than a factor of three compared to the standard HMC algorithm is observed in a typical run. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-040) / 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

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

Structure of the nucleon

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 of the nucleon. First results of a lattice study of generalized parton distributions are presented. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-193) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Accelerating Hasenbusch's acceleration of hybrid Monte Carlo

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 clover-improved Wilson fermions. An additional speed-up between 5 and 20% over the original proposal was achieved in production runs. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-142) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Composite operators in lattice QCD: nonperturbative renormalization

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 relevant to the calculation of moments of hadronic structure functions. The computations are based on Monte Carlo simulations using quenched Wilson fermions. (orig.)Available from TIB Hannover: RA 2999(98-116) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman