High Energy Scattering from the AdS/CFTAdS/CFT Correspondence

We apply the AdS/CFT correspondence to derive expressions for the scattering amplitudes at high energy for gauge theories at strong coupling. A method is proposed based on the computation of correlators of Wilson loop operators by their stringy duals in AdS spaces using either the supergravity (weak field) or classical (minimal surface) approximations.Comment: 6 pages,1 figure,Invited talk at ``DIS 2000'', 25-30 April 2000, Liverpool, to appear in the Proceedings in a shortened versio

``Good-Walker'' + QCD dipoles = Hard Diffraction

The Good-Walker mechanism for diffraction is shown to provide a link between total and diffractive structure functions and to be relevant for QCD calculations at small x_{Bj}. For Deep-Inelastic scattering on a small-size target (cf. an onium) the r\^ ole of Good-Walker ``diffractive eigenstates'' is played by the QCD dipoles appearing in the $1/N_C$ limit of QCD. Hard diffraction is thus related to the QCD tripe-dipole vertex which has been recently identified (and calculated) as being a conformal invariant correlator and/or a closed-string amplitude. An extension to hard diffraction at HERA via $k_T-$factorisation of the proton vertices leads to interesting phenomenology.Comment: 6 pages latex + figure.eps; Invited talk at the DIS98 workshop, Brussels, April 199

Soft Physics and Intermittency: Open Question(s) in Krakow

This contribution contains a summary of the Krakow meeting on Soft Physics and Fluctuations. It emphasizes both the experimental and the theoretical investigations on correlations/fluctuations and intermittency in multi-particle processes and discusses of the present status of this concept. A clarification of the main open questions in this field of research is now within reach, thanks to the studies presented at the meeting. Summary Talk of the Krakow Workshop on Multiparticle Physics, May, 4-7, 1993. E-mail contact: [email protected]: 12p., Plain Tex file, Saclay-T93/11

Traveling waves in high energy QCD

Saturation is expected to occur when a high density of partons (mainly gluons)- or equivalently strong fields in Quantum Chromodynamics (QCD) - is realized in the weak coupling regime. A way to reach saturation is through the high-energy evolution of an extended target probed at a fixed hard scale. In this case, the transition to saturation is expected to occur from nonlinear perturbative QCD dynamics. We discuss this approach to saturation, which is mathematically characterized by the appearance of traveling wave patterns in a suitable kinematical representation. A short review on traveling waves in high energy QCD and a first evidence of this phenomenon in deep-inelastic proton scattering are presented.Comment: 10 pages, 5 figures, talk given at the XXXVth International Symposium on Multiparticle Dynamics (ISMD05), Kromeriz, Czech Republic, August 9-15 200

Testing resummed NLO-BFKL kernels

We propose a new method to test the (resummed) next-to-leading-order BFKL evolution kernels using the Mellin transformed j-moments of the proton structure function F_2.Comment: 12 pages,2 figures, To appear in the special issue of Acta Physica Polonica to celebrate the 65th Birthday of Professor Jan Kwiecinsk

Dynamical entropy of dense QCD states

We discuss dense states of QCD matter formed in high-energy hadronic and heavy-ion collisions from the point of view of statistical physics of non-equilibrium processes. For this sake, we first propose a formulation of the dynamical entropy of dense QCD states in the "saturation regime" leading to a color glass condensate (CGC). The statistical physics description amounts to describe the modification of the color correlation length with energy as a compression process for which non equilibrium thermodynamic properties are applicable. We derive an expression of the dynamical entropy in terms of the rapidity evolution of the unintegrated gluon distributions in the colliding nuclei, verifying suitable positivity and irreversibility properties. We extend this approach to the initial pre-equilibrium (glasma) state of an heavy-ion collision. It allows for a definition of the initial entropy before the evolution towards the hydrodynamic regime as a function of the glasma correlation length and an overlap parameter characterizing the low-momentum spectrum of the glasma state. This initial entropy, by extension to the N=4 SYM theory, is then matched as the key input parameter to the strong coupling evaluation of thermalization towards the hydrodynamic regime based on the AdS/CFT correspondence. It thus allows to cast a bridge between the weak and strong coupling phases of an heavy-ion reaction.Comment: Version mildly updated to match publication. Adding a discussion of the k_T factorization formula. Results and conclusions unchange

Unified approach to hard diffraction

Using a combination of S-Matrix and perturbative QCD properties in the small x_{Bj} regime, we propose a formulation of hard diffraction unifying the partonic (Ingelman-Schlein) Pomeron, Soft Colour Interaction and QCD dipole descriptions.Comment: 4 pages, 1 figure, to appear in Proceedings of 9th International Workshop on Deep Inelastic Scattering and QCD (DIS 2001), Bologna, Italy, 27 Apr-1 May 200