A model based on Reggeon field theory is used for the description of the photo- and electroproduction of vector mesons ($\rho^0, \omega, \phi, J /\psi$) on the proton. Its main feature is the dependence of the Pomeron intercept on the virtuality of the photon. The few parameters of the model were determined by fitting the total cross sections for real and virtual photons on the proton. This allows a parameter-free description of the energy dependence of vector meson production. Very good agreement with the existing high energy data is obtained.Comment: 6 pages and 3 figures included in a uuencoded fil

We consider the production of charm by real and virtual photons. Special attention is paid to diffractive charm production, which provides information on the gluonic content of the Pomeron. Our calculations are based on the gluon distributions of the CKMT-model, which is shown to lead to agreement with the data on open charm production in deep inelastic scattering. We compare predictions for diffractive charm production of different models for the distribution of gluons in the Pomeron. Experiments at HERA should be able to discriminate between them. Predictions for beauty production in diffractive and non-diffractive interactions of photons are also given.

Starting from the same input as the standard BFKL Pomeron, we directly calculate the ``hard'' Pomeron as a gluonic ladder by using Monte Carlo methods. We reproduce the characteristic features of the the BFKL Pomeron and are now also able to evaluate new observables. The applicability of the BFKL approach under realistic kinematical conditions can be tested and the influence of the running coupling constant examined.Comment: 9 pages and 4 figures included. To appear in Phys.Lett.

We discuss the BFKL equation with a running gauge coupling and identify in its solutions the contributions originating from different transverse momentum scales. We show that for a running coupling constant the distribution of the gluons making up the BFKL Pomeron shifts to smaller transverse momenta so that the dominant part of Pomeron can have a nonperturbative origin. It is demonstrated how this soft physics enters into the BFKL solution through the boundary condition. We consider two kinematical regimes leading to different behaviour of the rapidity and transverse momentum dependence of the gluon distribution. In the diffusion approximation to the BFKL kernel with running αs, we find a sequence of poles which replaces the cut for fixed αs. The second regime corresponds to the singular part of the kernel, which gives the dominant contribution in the limit of very large transverse momenta. Finally, a simple more general picture is obtained for the QCD Pomeron in hard processes: it is of soft, nonperturbative nature, but has hard ends of DGLAP-type.