Instanton-induced production of QCD jets

We consider the instanton contributions for the production of a gluon jet with large transverse momentum in QCD. We find that Mueller's corrections corresponding to the rescattering of hard quanta are likely to remove contributions of large instantons, making this cross section well defined. This observation generalizes the previous discussion of instanton effects in the deep inelastic scattering and suggests that all hard processes in the QCD receive hard non-perturbative corrections from instantons of small size, of order $\rho\sim 1/(Q\alpha_s)$.Comment: LATEX, 7 pages, DESY 94-17

Instanton-induced production of jets with large transverse momentum in QCD

We consider the instanton-induced cross section for production of a gluon jet with large transverse momentum in QCD and point out that Mueller's corrections corresponding to the rescattering of hard quanta are likely to remove contributions of large instantons, making this cross section well defined. Some speculations about possible phenomenological signatures are presented.Comment: LATEX, requires espcrc2.sty file, appended at the end. (Invited talk presented by V. Braun at the conference ``QCD-94'', Montpellier, France, July 7 -13, 1994), MPI-PhT/94-5

A momentum Space Analysis of the Triple Pomeron Vertex in pQCD

We study properties of the momentum space Triple Pomeron Vertex in perturbative QCD. Particular attention is given to the collinear limit where transverse momenta on one side of the vertex are much larger than on the other side. We also comment on the kernels in nonlinear evolution equations.Comment: Minor misprints corrected. To be published in EPJ

The magnetic moments of 'Lambda_b' and 'Lambda_c' baryons in light cone QCD sum rules

Using the most general form of the interpolating currents of heavy baryons, the magnetic moments of heavy baryons "Lambda_Q (Q=b,c)" are calculated in framework of the light cone QCD sum rules. A comparison of our results on magnetic moments with the existing theoretical results calculated in various other frameworks are presented.Comment: 14 pp, 6 figures (postscript formatted), LaTex formatte

Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering

We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. A remarkable agreement is found between the calculated and the experimentally measured u-quark distribution up to light-cone distances $\Delta^- = \Delta^0 - \Delta^3$ of order $\sim 1$ fm in the proton rest frame. The calculation for valence d quarks gives much worse results; the reasons for this discrepancy are discussed.Comment: 24 pages plus 13 pages with figures, requires epsf.sty, revised version to appear in Phys.Rev.

Light-Ray Evolution Equations and Leading-Twist Parton Helicity-Dependent Nonforward Distributions

We discuss the calculation of the evolution kernels \Delta W_{\zeta}(X,Z) for the leading-twist nonforward parton distributions G_\zeta(X,t) sensitive to parton helicities. We present our results for the kernels governing evolution of the relevant light-ray operators and describe a simple method allowing to obtain from them the components of the nonforward kernels \Delta W_{\zeta}(X,Z).Comment: 8 pages; final version, to appear in Physics Letters

Non-linear QCD dynamics and exclusive production in epep collisions

The exclusive processes in electron-proton ($ep$) interactions are an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of proton which is strongly subject to parton saturation effects. In this paper we compute the cross sections for the exclusive vector meson production as well as the deeply virtual Compton scattering (DVCS) relying on the color dipole approach and considering the numerical solution of the Balitsky-Kovchegov equation including running coupling corrections. We show that the small-$x$ evolution given by this evolution equation is able to describe the DESY-HERA data and is relevant for the physics of the exclusive observables in future electron-proton colliders and in photoproduction processes to be measured in coherent interactions at the LHC.Comment: 6 pages, 4 figure

A solvable model for small-x physics in D > 4 dimensions

I present a simplified model for the gluon Green's function governing high-energy QCD dynamics, in arbitrary space-time dimensions. The BFKL integral equation (either with or without running coupling) reduces to a second order differential equation that can be solved in terms of Bessel and hypergeometric functions. Explicit expressions for the gluon density and its anomalous dimension are derived in MS and Q_0 factorization schemes. This analysis illustrates the qualitative features of the QCD gluon density in both factorization schemes. In addition, it clarifies the mathematical properties and validates the results of the ``gamma-representation'' method proposed by M.Ciafaloni and myself for extracting resummed next-to-leading-log x anomalous dimensions of phenomenological relevance in the two schemes.Comment: 30 pages, 9 figure

The (Sigma_Q-Lambda_Q) transition magnetic moments in light cone QCD sum rules

Using the general form of (Sigma_Q) and (Lambda_Q) (Q=b or c) currents, (Sigma_Q-Lambda_Q) transition magnetic moments are calculated in framework of the light cone QCD sum rules method. In this approach nonperturbative effects are described by the photon wave functions and only two-particle photon wave functions are taken into account. Our predictions on transition magnetic moments are (mu_{Sigma_c Lambda_c} = - (1.5 pm 0.4) mu_N) and (mu_{Sigma_b Lambda_b} = - (1.6 pm 0.4) mu_N). A comparison of our results with the ones existing in the literature is given.Comment: 15 pp, 6 figures (postscript formatted), LaTex formatte

Instanton contributions to the τ\tau decay widths

Contrary to some previous claims, we find a sizable instanton contribution to the finite energy sum rule used to extract the value of the strong coupling from the measured $\tau$ decay widths. It is of the same order of magnitude as standard nonperturbative corrections induced by vacuum quark and gluon condensates. Our result indicates that there might be no hierarchy of power corrections in finite energy sum rules at the scale of $\tau$ mass. Therefore, the standard nonperturbative corrections do not necessarily improve the accuracy of the theoretical predicition, but can rather be used to estimate an intrinsic accuracy of the pure perturbative calculation, which turns out to be rather high on this evidence, of order one percent.Comment: LATEX, 13 pages, 3 figures available upon request, MPI-Ph/93-6