Sigma models in (4,4) harmonic superspace

We define basics of (4,4) 2D harmonic superspace with two independent sets of SU(2) harmonic variables and apply it to construct new superfield actions of (4,4) supersymmetric two-dimensional sigma models with torsion and mutually commuting left and right complex structures, as well as of their massive deformations. We show that the generic off-shell sigma model action is the general action of constrained analytic superfields q"("1","1") representing twisted N=4 multiplets in (4,4) harmonic superspace. The massive term of q"("1","1") is shown to be unique; it generates a scalar potential the form of which is determined by the metric on the target bosonic manifold. We discuss in detail (4,4) supersymmetric group manifold SU(2) x U(1) WZNW sigma model and its Liouville deformation. A deep analogy of the relevant superconformally invariant analytic superfield action to that of the improved tensor N=2 4D multiplet is found. We define (4,4) duality transformation and find new off-shell dual representations of the previously constructed actions via unconstrained analytic (4,4) superfields. The main peculiarities of the (4,4) duality transformation are: (i) It preserves manifest (4,4) supersymmetry; (ii) dual actions reveal a gauge invariance needed for the onshell equivalence to the original description; (iii) in the actions dual to the massive ones 2D supersymmetry is modified off shell by SU(2) tensor central charges. The dual representation suggests some hints of how to describe (4,4) models with non-commuting complex structures in the harmonic superspace. (orig.)Available from TIB Hannover: RR 3949(94-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Double spin asymmetries in charmonium hadroproduction at HERA-#vector#N

We discuss the double spin asymmetries in charmonium hadroproduction with nonzero transverse momenta at fixed target energies, #sq root#(s) #approx =# 40 GeV, within the framework of the factorization approach. It is shown that the color octet contribution is dominant in the asymmetries. The size of the asymmetries and the projected statistical errors in a future option of HERA with longitudinally polarized protons scattering off a polarized target (HERA-#vector#N) should allow to distinguish between different parametrizations for the polarized gluon distribution in the proton. (orig.)Available from TIB Hannover: RA 2999(97-224) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Deep inelastic scattering with tagged photons at HERA

We calculate cross-sections for neutral current deep inelastic scattering at HERA with photon tagging. Both, the exact lowest-order cross-section and a leading logarithmic approximation of next-order corrections are calculated. The latter amounts to less than 20% in a large kinematical range. The integrations are performed numerically but without relying on Monte Carlo methods. (orig.)3 refs.Available from TIB Hannover: 2999(96-213) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Chiral fermion action with (8,0) worldsheet supersymmetry

We propose an action describing chiral fermions with an arbitrary gauge group and with manifest (8,0) worldsheet supersymmetry. The form of the action is inspired by and adapted for completing the twistor-like formulation of the D=10 heterotic superstring. (orig.)Available from TIB Hannover: RR 3949(1994,10) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Recent developments in radiative corrections at HERA

We describe several numerical results for radiative corrections for deep inelastic ep scattering at HERA which are calculated using the HECTOR package. We present radiative corrections for ten different choices of kinematical variables for unpolarized neutral and charged current deep inelastic scattering. Radiative corrections for neutral current scattering off polarized protons are calculated in leptonic variables and compared to those obtained by the POLRAD code for the kinematic regime of the HERMES experiment. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(96-198) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Model independent QED corrections to the process ep #-># eX

We give an exhaustive presentation of the semi-analytical approach to the model independent leptonic QED corrections to deep inelastic neutral current lepton-nucleon scattering. These corrections include photonic bremsstrahlung from and vertex corrections to the lepton current of the order #OMICRON#(#alpha#) with soft photon exponentiation. A common treatment of these radiative corrections in several variables - leptonic, hadronic, mixed, Jaquet-Blondel variables - has been developed and double differential cross-sections are calculated. In all sets of variables we use some structure functions, which depend on the hadronic variables and which do not have to be defined in the quark parton model. The remaining numerical integrations are twofold (for leptonic variables) or onefold (for all other variables). For the case of hadronic variables, all phase space integrals have been performed analytically. Numerical results are presented for a large kinematical range, covering fixed target as well as collider experiments at HERA or LEP x LHC, with a special emphasis on HERA physics. (orig.)Available from TIB Hannover: RA 2999(94-115) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Elastic proton-deuteron backward scattering: relativistic effects and polarization observables

The elastic proton-deuteron backward reaction is analyzed within a covariant approach based on the Bethe-Salpeter equation with 000. Lorentz boost and other relativistic effects in the cross section and spin correlation observables, like tensor analyzing power and polarization transfer etc., are investigated in explicit form. Results of numerical calculations for a complete set of polarization observables are presented. (orig.)Available from TIB Hannover: RR 1847(194) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

QED and electroweak corrections to deep inelastic scattering

We describe the state of the art in the field of radiative corrections for deep inelastic scattering. Different methods of calculation of radiative corrections are reviewed. Some new results for QED radiative corrections for polarized deep inelastic scattering at HERA are presented. A comparison of results obtained by the codes POLRAD and HECTOR is given for the kinematic regime of the HERMES experiment. Recent results on radiative corrections to deep inelastic scattering with tagged photons are briefly discussed. (orig.)33 refs.SIGLEAvailable from TIB Hannover: RA 2999(96-243) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

O(#alpha#) QED corrections to neutral current polarized deep-inelastic lepton-nucleon scattering

The O(#alpha#) leptonic QED corrections to neutral current polarized deep inelastic lepton-nucleon scattering are calculated in leptonic variables both for the case of longitudinal and transverse nucleon polarization. The results of the complete calculation are compared with the corresponding leading log expressions. Numerical results are presented for the corrections in the kinematic range of the HERMES experiment and possible future polarized proton beam experiments at HERA. (orig.)30 refs.Available from TIB Hannover: RA 2999(96-189) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Relativistic description of exclusive deuteron break-up reactions

The exclusive deuteron break-up reaction is analyzed within a covariant approach based on the Bethe-Salpeter equation with realistic meson-exchange interaction. Relativistic effects in the cross section, tensor analyzing power and polarization transfer are investigated in explicit form. Results of numerical calculations are presented for kinematical conditions in forthcoming p + D reactions at COSY. (orig.)20 refs.Available from TIB Hannover: RR 1847(96-161) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman