Higher order QED corrections to deep inelastic scattering

We calculate the leptonic ${\cal O}(\alpha^2 L)$ corrections for unpolarized deeply inelastic ep scattering using mixed variables.Comment: 5 pages LaTeX, 1 style file, presented at RADCOR 2002, Kloster Banz, Sept.8-13, 200

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

O(\alpha^2 L) Radiative Corrections to Deep Inelastic ep Scattering

The leptonic QED radiative corrections are calculated in the next-to-leading log approximation ${\cal O}[\alpha^2 \ln(Q^2/m_e^2)]$ for unpolarized deeply inelastic $ep$--scattering in the case of mixed variables. The corrections are determined using mass factorization in the OMS--scheme for the double--differential scattering cross sections.Comment: 10 pages LATEX, 1 style file

NNLO coefficient functions of Higgs and Drell--Yan cross sections in Mellin space

We calculate the Mellin moments of next-to-next-to-leading order coefficient functions of the Drell-Yan and Higgs production cross sections. The results can be expressed in term of finite harmonic sums which are maximally threefold up to weight four. Various algebraic relations among these finite sums reduce the complexity of the results suitable for fast numerical evaluations. It is shown that only five non--trivial functions occur besides Euler's $\psi$--function in the representation of these Wilson coefficients.Comment: 1 latex file, 1 style file, Contribution to the Proceedings of "Loops and Legs in Quantum Field Theory 2004", Zinnowitz, Usedom Island, Germany, April 200

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.

Mellin Representation for the Heavy Flavor Contributions to Deep Inelastic Structure Functions

We derive semi--analytic expressions for the analytic continuation of the Mellin transforms of the heavy flavor QCD coefficient functions for neutral current deep inelastic scattering in leading and next-to-leading order to complex values of the Mellin variable $N$. These representations are used in Mellin--space QCD evolution programs to provide fast evaluations of the heavy flavor contributions to the structure functions $F_2(x,Q^2), F_L(x,Q^2)$ and $g_1(x,Q^2)$.Comment: 13 pages Letex, 1 style file, 10 eps figure

Analytic Continuation of Mellin Transforms up to two-loop Order

The analytic continuation of the Mellin transforms to complex values of N for the basic functions $g_i(x)$ of the momentum fraction x emerging in the quantities of massless QED and QCD up to two-loop order, as the unpolarized and polarized splitting functions, coefficient functions, and hard scattering cross sections for space- and time-like momentum transfer are evaluated. These Mellin transforms provide the analytic continuations of all finite harmonic sums up to the level of the threefold sums of transcendentality four, where the basis-set ${g_i(x)}$ consists of products of {\sc Nielsen}-integrals up to transcendentality four. The computer code {\tt ANCONT} is provided.Comment: 31 pages LATEX, 1 style fil

Twist-4 Gluon Recombination Corrections for Deep Inelastic Structure Functions

We calculate twist--4 coefficient functions for the deep inelastic structure function $F_2(x,Q^2)$ associated to 4--gluon operator matrix elements for general values of the Bjorken variable $x$ and study the numerical effect on the slope $\partial F_2(x,Q^2)/\partial \log Q^2$. It is shown that these contributions diminish the strongly rising twist--2 terms towards small values of $x$.Comment: 10 pages LATEX, 2 style file, 3 eps-file

Mellin Moments of the Next-to-next-to Leading Order Coefficient Functions for the Drell-Yan Process and Hadronic Higgs-Boson Production

We calculate the Mellin moments of the next-to-next-to leading order coefficient functions for the Drell--Yan and Higgs production cross sections. The results can be expressed in terms of multiple finite harmonic sums of maximal weight w = 4. Using algebraic and structural relations between harmonic sums one finds that besides the single harmonic sums only five basic sums and their derivatives w.r.t. the summation index contribute. This representation reduces the large complexity being present in x-space calculations and is well suited for fast numerical implementations.Comment: 47 pages LATEX, version appearing in journa

On the Leptoquark Interpretation of the High Q2Q^2 Events at HERA

We investigate to which extent an interpretation of the recently observed excess of events in the high $Q^2$ range at HERA in terms of single leptoquark production is compatible with bounds from other experiments.Comment: 5 pages latex, to appear in the Proceedings of the International Conference on Deep Inelastic Scattering, Chicago, April 1997, AI