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

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

On the k⊥k_{\perp} dependent gluon density in hadrons and the photon

The $k_{\perp}$ dependent gluon distribution for protons, pions,and photons is calculated accounting for the resummation of small~$x$ effects due to the Lipatov equation. It is represented by a convolution of a gluon density in the collinear limit and a universal function ${\cal G}(x,k^2,\mu)$ for which an analytic expression is derived.Comment: 8 pages, uuencoded ps fil

QCD Evolution of Structure Functions at Small x

The status of the resummation of small x contributions to the unpolarized and polarized deep inelastic structure functions is reviewed.Comment: 15 pages LATEX including 6 eps-files; Lecture notes to appear in: 'New Trends in HERA Physics 1999', eds. G. Grindhammer, B. Kniehl, and G. Kramer (Springer, Berlin, 1999

On the k⊥k_{\perp} dependent gluon density of the proton

The $k_{\perp}$ dependent gluon distribution is calculated accounting for the resummation of small~$x$ effects due to the Lipatov equation. It is represented by a convolution of a gluon density in the collinear limit and a universal function ${\cal G}(x,k^2,\mu)$ for which an analytic expression is derived.Comment: 4 pages, uuencoded ps fil

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

On the Expectations for Leptoquarks in the Mass Range of O(200 GeV)

A summary is given on the experimental bounds for the couplings and masses of scalar and vector leptoquarks associated to the first fermion generation. We investigate to which extent an interpretation of the recently reported excess of events in the large $x$ and $Q^2$ range at HERA in terms of single leptoquark production is compatible with other experimental results.Comment: 11 pages latex, including 1 eps-figure, references updated, figure edite

Universal Higher Order Singlet QED Corrections to Unpolarized Lepton Scattering

We calculate the universal flavor-singlet radiative QED corrections to unpolarized lepton scattering applicable to general differential scattering cross sections, involving charged fermions or photons in initial or final states. The radiators are derived to $O((\alpha \ln(Q^2/m_f^2))^5)$ in analytic form. Numerical illustrations are given.Comment: 31 pages, 3 figures, 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