Can one improve the Froissart bound?

We explain why we hope that the Froissart bound can be improved, either qualitatively or, more likely, quantitatively, by making a better use of unitarity, in particular elastic unitarity. In other instances (Gribov's theorem) elastic unitarity played a crucial role. A preliminary requirement for this is to work with an appropriate average of the cross-section, to make the problem well defined. This is possible, without destroying the Lukaszuk--Martin bound.Comment: 4 pages, latex with AIP style, Talk given at "Diffraction 2008", Lalonde-les-Maures, France, September 2008. Missing square root restored p. 3. pi^2->pi corrected in eq. (1

Mechanisms of exclusive meson production at high energies

I discuss mechanisms of exclusive production of mesons at high energies. Some illustrative examples for the FNAL Tevatron and CERN LHC as well as for lower energies are shown.Comment: 5 pages, 6 figures based on a talk presented at Diffraction 2008, La Londe-les-Maures, France, September 200

The Color Dipole Picture and the Ratio of the Longitudinal to the Transverse Photoabsorption Cross Section

The transverse size of q q-bar fluctuations of a longitudinally polarized photon is reduced relative to the transerve size of q q-bar fluctuation of a transversely polarized photon. This implies a model-independent prediction of the ratio R(W2,Q2)=sigma_L/sigma_T=0.375, or, equivalently, F_L/F_2=0.27, for x=Q2/W2<<1 and Q2 sufficiently large, while R(W2,Q2)=0.50, if this effect is ignored. Experimental data from HERA confirm the transverse-size reduction.Comment: 6 pages, 2 figures, presented at Diffraction 200

Multipomeron Cuts and Hard Processes on Nuclei

With nuclear targets comes a new scale into the pQCD description of hard processes - the saturation scale. In the saturation regime, the familiar linear k_\perp-factorization breaks down and must be replaced by a nonlinear k_\perp-factorization, which accounts for absorptive and multiple scattering corrections to the hard process. Predictions for partial cross sections corresponding to a fixed number of cut Pomerons (the topological cross sections) can be obtained in a surprisingly straightforward manner. We discuss some applications to deep inelastic scattering.Comment: 4 pages, 2 figures, a talk given at Diffraction 2008: International Workshop On Diffraction In High Energy Physics; 9-14 Sep 2008, La Londe-les-Maures, Franc

ALICE diffractive physics in p-p and Pb-Pb collisions at the LHC

The ALICE detector is introduced and a double gap trigger is presented. The interest in studying double pomeron induced events both in proton-proton and in lead-lead reactions is discussed.Comment: 5 pages, 5 figures, to appear in proceedings conference Diffraction 2008, La Londe-les-Maures, France, sep 9-14, 200

The BSW Impact Picture 30 Years After

Thirty years ago Bourrely-Soffer-Wu (BSW) investigated an impact picture description of $p-p$ and $\bar p -p$ elastic scattering with success. For this anniversary, a short review of the main features of this picture will be presented with its evolution over the years. The future experiments at the LHC collider will provide decisive tests for the impact picture at high energy.Comment: 4 pages, 2 figures, Contribution to Diffraction 2008, International Workshop on Diffraction in High Energy Physics, La Londe-les-Maures, September 9-14 200