The black-disk limit in high-energy ep and pp scattering

We review a recently proposed framework for studying the approach to the unitarity limit in small-x processes in ep and pp scattering within the DGLAP approximation. Our formulation is based on the correspondence between the standard QCD factorization theorems for hard processes and the dipole picture of small-x scattering in the leading logarithmic approximation. It allows us to incorporate information about the transverse spatial distribution of gluons in the proton (GPD) from exclusive vector meson production at HERA. We show that the interaction of small-size color singlet configurations with the proton approaches the "black-disk limit" (BDL) due to the growth of the DGLAP gluon density at small x. This new dynamical regime is marginally visible in diffractive DIS at HERA, and will be fully reached in central pp collisions at LHC.Comment: 6 pages, 3 figures. Uses aipproc.cls. Contributed to proceedings of PANIC05, Santa Fe, NM, Oct. 24-28, 200

Two-pion light-cone distribution amplitudes from the instanton vacuum

We calculate the two-pion light-cone distribution amplitudes in the effective low-energy theory based on the instanton vacuum. These generalized distribution amplitudes describe the soft (non-perturbative) part of the process $\gamma^*\gamma \to \pi\pi$ in the region where the c.m. energy is much smaller than the photon virtuality. They can also be used in the analysis of exclusive processes such as $\gamma^* p \to p + 2\pi, 3\pi$ etc.Comment: 13 pages, LaTeX, 4 figures included using eps