Monte Carlo calculations for the hard Pomeron

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.

On the re-summation of enhanced Pomeron diagrams

Dominant contributions of enhanced Pomeron diagrams to elastic hadron-hadron scattering amplitude are re-summed to all orders. The formalism is applied to calculate total hadronic cross sections and elastic scattering slopes. An agreement with earlier results is obtained

The BFKL Pomeron with running coupling constant: how much of its hard nature survives?

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 $\alpha_s$, we find a sequence of poles which replaces the cut for fixed $\alpha_s$. 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.Comment: 23 pages REVTEX and 4 figures include