Small-x physics in perturbative QCD

We review the parton model and the Regge approach to the QCD description of the deep-inelastic ep scattering at the small Bjorken variable x and demonstrate their relation with the DGLAP and BFKL evolution equations. It is shown, that in the leading logarithmic approximation the gluon is reggeized and the pomeron is a compound state of two reggeized gluons. The conformal invariance of the BFKL pomeron in the impact parameter space is used to investigate the scattering amplitudes at high energies and fixed momentum transfers. The remarkable properties of the Schroedinger equation for compound states of an arbitrary number of reggeized gluons in the multi-colour QCD are reviewed. The gauge-invariant effective action describing the gluon-Reggeon interactions is constructed. The known next-to-leading corrections to the QCD pomeron are discussed. (orig.)Available from TIB Hannover: RA 2999(96-132) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

BFKL pomeron in the next-to-leading approximation

We find one-loop correction to the integral kernel of the BFKL equation for the total cross section of the high energy scattering in QCD and calculate the next-to-leading contribution to anomalous dimensions of twist-2 operators near j=1. (orig.)Available from TIB Hannover: RA 2999(98-033) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

DGLAP and BFKL evolution equations in the N=4 supersymmetric gauge theory

We discuss DGLAP and BFKL evolution equations in the N=4 supersymmetric gauge theory in the leading and next-to-leading approximations. Eigenvalues of the BFKL kernel in this model turn out to be analytic functions of the conformal spin. It allows us to find the residues of the anomalous dimensions of the twist-2 operators in the points j=1, 0, -1,... from the BFKL equation in an agreement with their direct calculation from the DGLAP equation. The holomorphic separability of the BFKL kernel and the integrability of the DGLAP dynamics in this model are also discussed. (orig.)Available from TIB Hannover: RA 2999(02-002) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

High energy asymptotics of multi-colour QCD and two-dimensional conformal field theories

In the multi-colour limit of perturbative QCD the holomorphic factorization of wave functions of compound states of n reggeized gluons in the impact parameter space is shown. The conformally invariant Hamiltonian for each holomorphic factor has a nontrivial integral of motion. The odderon in QCD is the simplest example of the composite system with these properties. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(93-055) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Gauge invariant effective action for high energy processes in QCD

The Born amplitudes for quasi-multi-Regge kinematics of produced gluons are constructed in accordance with the Feynman rules including apart from usual Yang-Mills vertices also an infinite number of induced vertices. The new vertices describe the interaction of physical gluons produced in direct channels with the reggeized gluons propagating in crossing channels. The nonlinear gauge invariant effective action reproducing these Feynman rules is constructed with the use of the Wilson countour integrals. After integrating over the physical degrees of freedom the reggeon action is derived. (orig.)Available from TIB Hannover: RA 2999(95-029) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

A new odderon solution in perturbative QCD

We present and discuss a new bound state solution of the three gluon system in perturbative QCD. It carries the quantum numbers of the odderon, has intercept at one and couples to the impact factor #gamma#"* #-># #eta#_c. (orig.)Available from TIB Hannover: RA 2999(99-195) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Next-to-loading corrections to the BFKL equation from the gluon and quark production

The gluon and quark production in the quasi-multi-Regge kinematics for the final particles is considered. The differential cross-section for different helicity states is calculated. The dimensional regularization is used to remove the infrared divergencies in the corresponding contributions to the BFKL equation. The other next-to-leading corrections are discussed. (orig.)16 refs.Available from TIB Hannover: RA 2999(96-020) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

How does the BFKL Pomeron couple to quarks?

We investigate the coupling of the BFKL Pomeron to quarks and to colorless states. Special emphasis is given to the effective quark-quark scattering amplitude of Mueller and Tang. (orig.)Available from TIB Hannover: RA 2999(94-244) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Symmetry properties of the effective action for high-energy scattering in QCD

We study the effective action describing high-energy scattering processes in the multi-Regge limit of QCD, which should provide the starting point for a new attempt to overcome the limitations of the leading logarithmic and the eikonal approximations. The action can be obtained via simple graphical rules or by integrating in the QCD functional integral over momentum modes of gluon and quark fields that do not appear explicitiley as scattering or exchanged particles in the considered processes. The supersymmetry is used to obtain the terms in the action involving quark fields from the pure gluonic ones. We observe a Weizsaecker - Williams type relation between terms describing scattering and production of particles. (orig.)Available from TIB Hannover: RA 2999(94-064) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Conformal invariance of the transition vertex 2 #-># 4 gluons

We show that the transition vertex: two reggeized gluons #-># four reggeized gluons is invariant under Moebius transformations. This provides an important step in defining a conformally invariant effective field theory for QCD in the Regge limit. (orig.)15 refs.Available from TIB Hannover: RA 2999(95-171) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman