R. Kirschner

Double logarithmic asymptotics and regge singularities of quark amplitudes with flavour exchange

Abstract We derive simple equations in terms of definite signature partial waves for the quark scattering and annihilation amplitudes in the double logarithmic approximation of QCD. We apply the method of isolating the softest virtual particle in the graphs which is based on gauge invariance and unitarity. Besides the particle Regge trajectories and corresponding cuts, there are further singularities in the angular momentum plane generated by perturbative double logarithmic contributions and which may be of phenomenological relevance. We also consider amplitudes with external currents and discuss how to include ultraviolet single logarithms and non-perturbative contributions.

Generalized {Lipatov-Altarelli-Parisi} Equations and Jet Calculus Rules

Abstract Within the leading logarithmic approximation of QCD using a method by Lipatov we derive generalized Lipatov-Altarelli-Parisi equations for the m -parton distributions from which the jet calculus rules proposed recently by Konishi, Ukawa and Veneziano can be obtained.

Yang–Baxter operators and scattering amplitudes in N=4 super-Yang–Mills theory

Abstract Yangian symmetry of amplitudes in N = 4 super-Yang–Mills theory is formulated in terms of eigenvalue relations for monodromy matrix operators. The Quantum Inverse Scattering Method provides the appropriate tools to treat the extended symmetry and to recover as its consequences many known features like cyclic and inversion symmetry, BCFW recursion, Inverse Soft Limit construction, Grassmannian integral representation, R-invariants and on-shell diagram approach.

Heavy-quark production as a sensitive test for an improved description of high-energy hadron collisions

QCD dynamics at small quark and gluon momentum fractions or large total energy, which plays a major role for HERA, the Tevatron, RHIC and LHC physics, is still poorly understood. For one of the simplest processes, namely bottom-antibottom production, next-to-leading-order perturbation theory fails. We show that the combination of two recently developed theoretical concepts, the k_perp-factorization and the next-to-leading-logarithmic-approximation BFKL vertex, gives perfect agreement with data. One can therefore hope that these concepts provide a valuable foundation for the description of other high energy processes.

Effective action for multi-Regge processes in QCD

Abstract We construct the effective Lagrangian describing QCD in the multi-Regge kinematics. It is obtained from the original QCD Lagrangian by eliminating modes of gluon and quark fields not appearing in this underlying kinematics.

Direct

The hadroproduction of direct

J/\psi

J/\ensuremath{\psi}

hadroproduction in

in the framework of the

k^-

{k}_{\ensuremath{\perp}}

perpendicular factorization and the color octet mechanism

-factorization approach is studied. The color-singlet contribution is essentially larger than in the collinear approach but is still an order of magnitude below the data. The deficit may be well described by the color octet contribution with the value of the matrix element