Data for D * ± (2010) meson electroproduction in the range 10 < Q 2 < 1350 GeV 2 has recently been presented by the ZEUS collaboration at HERA. We use these results together with their previously published data for 1 < Q 2 < 600 GeV 2 to test whether one can distinguish between different theoretical schemes for charm quark electroproduction. We find that up to the largest Q 2 measured, it is no...

The unitary isobar model MAID2007 has been developed to analyze the world data of pion photo-and electroproduction. The model contains both a common background and several resonance terms. The background is unitarized according to the K-matrix prescription, and the 13 four-star resonances with masses below 2 GeV are described by appropriately unitarized Breit-Wigner forms. The data have been an...

We discuss the possibility of measuring generalized parton distributions in exclusive electroproduction of mesons off the nucleon and estimate the uncertainty from perturbatively induced higher-twist corrections. We find that, while the magnitude of the cross section changes significantly taking into account twist-four contributions modeled via renormalons, the transverse spin asymmetry is weak...

We compare momentum sum rules from unpolarized electroproduction and the spin sum rule for g 1 in polarized electroproduction, and their Q 2 evolution in the framework of the operator product expansion. Second order effects in α s are included. We show that in comparing the evolution of the spin sum rule with the momentum sum rule one is not overly sensitive to using first or second order, even...

The electromagnetic radiative correction to the cross section of the vector meson electroproduction is calculated. Explicit covariant formulae for the observed cross section are obtained. The dependence of the radiative correction on the experimental resolution and on the inelasticity cut is discussed. FORTRAN code DIFFRAD based on both exact (ultrarelativistic) and approximate sets of the form...

We re-investigate Adler’s PCAC relation in the presence of an external electromagnetic field within the framework of QCD coupled to external fields. We discuss pion electroproduction within a tree-level approximation to chiral perturbation theory and explicitly verify a chiral Ward identity referred to as the Adler-Gilman relation. We critically examine soft-momentum techniques and point out ho...

Neutral pion photoand electroproduction at threshold is analyzed in the framework of dispersion relations. For this purpose, we evaluate the real threshold amplitudes in terms of Born contributions and dispersion integrals determined by the imaginary parts of the MAID and SAID multipoles. The results show considerable cancellations between Born terms and resonance contributions. Good agreement ...

Generalized nucleon polarizabilities for virtual photons can be defined in terms of electroproduction cross sections as function of the 4-momentum transfer Q 2. In particular, the sum of the generalized electric and magnetic polarizabilities Σ = α + β and the spin polarizability γ can be expressed by virtual photon absorption cross sections integrated over the excitation energy. These quantitie...