Diffractive meson production from virtual photons with odd charge-parity exchange

We calculate the cross section of diffractive charge-parity C=+1 neutral meson production in virtual photon proton collision at high energies. Due to the opposite C-parities of photon and meson M"+ (M"+=#eta#_c, #pi#"0, a_2) this process probes the t-channel C=-1 odderon exchange which is described here as noninteracting three-gluon exchange. Estimates for the cross section of inelastic diffractive process #gamma#"*p #-># #eta#_cX_p are presented. The total cross section of diffractive #eta#_c meson photoproduction is found to be 47 pb. The cross sections for the diffractive production of light mesons (#pi#"0, a_2) in #gamma#"*p collisions are of the same order if the photon virtuality Q"2 is m"2_c. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

On the evolution kernels of twist 2 light-ray operators for unpolarized and polarized deep inelastic scattering

The non-singlet and singlet evolution kernels of the twist-2 light-ray operators for unpolarized and polarized deep inelastic scattering are calculated in O(#alpha#_s) for the general case of virtualities q"2, q"'"2 #not =# 0. Special cases as the kernels for the general single-variable evolution equation and the Altarelli-Parisi and Brodsky-Lepage limits are derived from these results. (orig.)Available from TIB Hannover: RA 2999(97-074) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The virtual Compton amplitude in the generalized Bjorken region Twist-2 contributions

A systematic derivation is presented of the twist-2 anomalous dimensions of the general quark and gluon light-ray operators in the generalized Bjorken region in leading order both for unpolarized and polarized scattering. Various representations of the anomalous dimensions are derived in the non-local and local light cone expansion and their properties are discussed in detail. Evolution equations for these operators are derived using different representations. General two- and single-variable evolution equations are presented for the expectation values of these operators for non-forward scattering. The Compton amplitude is calculated in terms of these distribution amplitudes. In the limit of forward scattering a new derivation of the integral relations between the twist-2 contributions to the structure functions is given. Special limiting cases which are derived from the general relations are discussed, as the forward case, near-forward scattering, and vacuum-meson transition. Solutions of the two-variable evolution equations for non-forward scattering are presented. (orig.)44 refs.Available from TIB Hannover: RA 2999(99-020) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Twist-2 light-ray operators: anomalous dimensions and evolution equations

The non-singlet and singlet anomalous dimensions of the twist-2 light-ray operators for unpolarized and polarized deep inelastic scattering are calculated in O(#alpha#_s). We apply these results for the derivation of evolution equations for partition functions, structure functions, and wave functions which are defined as Fourier transforms of the matrix elements of the light-ray operators. Special cases are the Altarelli-Parisi and Brodsky-Lepage kernels. Finally we extend Radyushkin's solution from the non-singlet to the singlet case. (orig.)Available from TIB Hannover: RA 2999(97-209) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

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