Status of Polarized and Unpolarized Deep Inelastic Scattering

The current status of deep inelastic scattering is briefly reviewed. We discuss future theoretical developments desired and measurements needed to further complete our understanding of the picture of nucleons at short distances.Comment: 9 pages, 2 figure

Precision of electro--weak couplings of scalar leptoquarks at TESLA

We investigate the potential to measure the electro-weak couplings of scalar leptoquarks $\Phi_s$ at TESLA for energies in the range of \sqrt{s} \simeq 1 \TeV using the pair production process $e^+e^- \to \Phi_s \bar{\Phi}_s$.Comment: 4 pages LATEX, 2 Refs. adde

A Kinematic Condition on Intrinsic Charm

We derive a kinematic condition on the resolution of intrinsic charm and discuss phenomenological consequences.Comment: 6 pages, 3 Figures, final version appearing in the Journa

Reduction of Multiple Harmonic Sums and Harmonic Polylogarithms

The alternating and non-alternating harmonic sums and other algebraic objects of the same equivalence class are connected by algebraic relations which are induced by the product of these quantities and which depend on their index calss rather than on their value. We show how to find a basis of the associated algebra. The length of the basis $l$ is found to be $\leq 1/d$, where $d$ is the depth of the sums considered and is given by the 2nd {\sc Witt} formula. It can be also determined counting the {\sc Lyndon} words of the respective index set. The relations derived can be used to simplify results of higher order calculations in QED and QCD.Comment: 4 pages, 1 style file, to appear in the Proceedings of ACAT03, Tsukuba, Japan Refereces update

Representation of the virtual Compton amplitude for polarized scattering in the generalized Bjorken region

The Compton amplitude is calculated in terms of expectation values of light-ray quark operators. As a technical tool we apply the nonlocal light-cone expansion. Thereby we express the expectation value of the vector light-ray operator with the help of the expectation value of the corresponding scalar operator of twist 2. This allows important simplifications. In the limit of forward scattering the integral relations between the twist-2 contributions of the structure functions are implied directly.Comment: 3 pages LATEX, 1 style file. Contribution to the Proceedings of the 7th International Workshop on Deep Inelastic Scattering and QCD, Zeuthen, April 1999, Nucl. Phys. B (Proc. Suppl.

Leptoquark Pair Production in \gamma\gamma Scattering: Threshold Resummation

The possibilities to pair-produce leptoquarks in photon-photon collisions are discussed. QCD threshold corrections lead to a strong enhancement of the production cross section. Suitably long-lived leptoquarks (\Gamma_\Phi \lsim 100 \MeV) may form Leptoquarkonium states.Comment: 7 pages LATEX, 2 eps figures. Contribution to the Proceedings of the \gamma \gamma Workshop, 200

Computer algebra tools for Feynman integrals and related multi-sums

In perturbative calculations, e.g., in the setting of Quantum Chromodynamics (QCD) one aims at the evaluation of Feynman integrals. Here one is often faced with the problem to simplify multiple nested integrals or sums to expressions in terms of indefinite nested integrals or sums. Furthermore, one seeks for solutions of coupled systems of linear differential equations, that can be represented in terms of indefinite nested sums (or integrals). In this article we elaborate the main tools and the corresponding packages, that we have developed and intensively used within the last 10 years in the course of our QCD-calculations

Universal Higher Order QED Corrections to Polarized Lepton Scattering

We calculate the universal radiative QED corrections to polarized lepton scattering for general scattering cross sections in analytic form. The flavor non--singlet and singlet radiation functions are calculated to $O((\alpha {\rm L})^5)$. The resummation of the non--singlet and singlet contributions to the QED--anomalous dimensions $\propto(\alpha \ln^2(x))^k$ is performed to all orders. Numerical results are presented for the individual radiation functions. Applications to polarized deeply inelastic lepton--nucleon scattering are given.Comment: 39 pages, latex, 1syle file, 11 figure

On the Structure of the Virtual Compton Amplitude in the Generalized Bjorken Region: Integral Relations

A systematic study is performed of the structure of the twist-2 contributions to the virtual Compton amplitude in deep-inelastic non-forward scattering for general spin states in the non-local light cone expansion. The gauge invariance is proven in this approach for the twist-2 contributions for non-forward scattering. Relations are derived between the contributing non-forward amplitudes.Comment: 23 pages LATEX, 1 style file, slightly extended versio

The Method of Arbitrarily Large Moments to Calculate Single Scale Processes in Quantum Field Theory

We device a new method to calculate a large number of Mellin moments of single scale quantities using the systems of differential and/or difference equations obtained by integration-by-parts identities between the corresponding Feynman integrals of loop corrections to physical quantities. These scalar quantities have a much simpler mathematical structure than the complete quantity. A sufficiently large set of moments may even allow the analytic reconstruction of the whole quantity considered, holding in case of first order factorizing systems. In any case, one may derive highly precise numerical representations in general using this method, which is otherwise completely analytic.Comment: 4 pages LATE