SU(3) Flux Tubes in a Model of the stochastic Vacuum

We calculate the squared gluon field strengths of a heavy q-$\rm \bar{q}$-pair in the model of the stochastic vacuum. We observe that with increasing separation a chromoelectric flux tube is built. The properties of the emerging flux tube are investigated.Comment: 14, epsf, HD-THEP-94-3

Parton Saturation-An Overview

The idea of partons and the utility of using light-cone gauge in QCD are introduced. Saturation of quark and gluon distributions are discussed using simple models and in a more general context. The Golec-Biernat W\usthoff model and some simple phenomenology are described. A simple, but realistic, equation for unitary, the Kovchegov equation, is discussed, and an elementary derivation of the JIMWLK equation is given.Comment: Cargese Lectures, 34 pages, 19 figure

Two Photon Reactions at High Energies

Cross sections for the reactions gamma^(*) gamma^(*) --> hadrons and gamma^(*) gamma^(*) --> 2 vector mesons are calculated as functions of energy (sqrt(s) > 20 GeV) and photon virtualities. Good agreement with experiment is obtained for the total hadronic cross section and, after allowing for a valence-quark contribution from the hadronic part of the photon, with the photon structure function at small x. The cross section for vector meson production are shown to be experimentally accessible for moderate values of Q^2. This is sufficient to probe the nature of the hard pomeron which has recently been proposed.Comment: some changes in style, physics unchanged, final version to appear in Phys.Rev.D, LaTeX2e, graphicx package, 15 eps-figures, 15p

The Semiclassical Gluon Distribution at Next-to-Leading Order

The interaction of the partonic fluctuation of the virtual photon in deep inelastic scattering with soft color fields describing the hadron is treated in an eikonal approximation. It is known that, in this approach, the small-x limit of the leading-order gluon distribution xg(x,Q^2) is a constant characterizing the averaged local field strength in the target. Matching the next-to-leading order calculation in this semiclassical framework with the one-loop parton model result, we obtain the next-to-leading order contribution to xg(x,Q^2). It shows a ln(1/x) enhancement at small x and is sensitive to the large distance structure of the target. The final expression is a simple integral over non-Abelian eikonal factors measuring the target color field. We derive a quantitative relation between the short-distance cutoff of this integral and the scale of the gluon distribution function in the MS-bar scheme. Our calculation demonstrates that higher order contributions can be systematically included in the semiclassical approach.Comment: 19 pages LaTeX, 8 figures include

Decomposition of the QCD String into Dipoles and Unintegrated Gluon Distributions

We present the perturbative and non-perturbative QCD structure of the dipole-dipole scattering amplitude in momentum space. The perturbative contribution is described by two-gluon exchange and the non-perturbative contribution by the stochastic vacuum model which leads to confinement of the quark and antiquark in the dipole via a string of color fields. This QCD string gives important non-perturbative contributions to high-energy reactions. A new structure different from the perturbative dipole factors is found in the string-string scattering amplitude. The string can be represented as an integral over stringless dipoles with a given dipole number density. This decomposition of the QCD string into dipoles allows us to calculate the unintegrated gluon distribution of hadrons and photons from the dipole-hadron and dipole-photon cross section via kT-factorization.Comment: 43 pages, 14 figure

Elastic and quasi-elastic pppp and γ⋆p\gamma^\star p scattering in the Dipole Model

We have in earlier papers presented an extension of Mueller's dipole cascade model, which includes sub-leading effects from energy conservation and running coupling as well as colour suppressed saturation effects from pomeron loops via a ``dipole swing''. The model was applied to describe the total and diffractive cross sections in $pp$ and $\gamma^*p$ collisions, and also the elastic cross section in $pp$ scattering. In this paper we extend the model to describe the corresponding quasi-elastic cross sections in $\gamma^*p$, namely the exclusive production of vector mesons and deeply virtual compton scattering. Also for these reactions we find a good agrement with measured cross sections. In addition we obtain a reasonable description of the $t$-dependence of the elastic $pp$ and quasi-elastic $\gamma^\star p$ cross sections

A draft genome sequence of Nicotiana benthamiana to enhance molecular plant-microbe biology research

Nicotiana benthamiana is a widely used model plant species for the study of fundamental questions in molecular plant-microbe interactions and other areas of plant biology. This popularity derives from its well-characterized susceptibility to diverse pathogens and, especially, its amenability to virus-induced gene silencing and transient protein expression methods. Here, we report the generation of a 63-fold coverage draft genome sequence of N. benthamiana and its availability on the Sol Genomics Network for both BLAST searches and for downloading to local servers. The estimated genome size of N. benthamiana is 3 Gb (gigabases). The current assembly consists of approximately 141,000 scaffolds, spanning 2.6 Gb with 50% of the genome sequence contained within scaffolds >89 kilobases. Of the approximately 16,000 N. benthamiana unigenes available in GenBank, >90% are represented in the assembly. The usefulness of the sequence was demonstrated by the retrieval of N. benthamiana orthologs for 24 immunity-associated genes from other species including Ago2, Ago7, Bak1, Bik1, Crt1, Fls2, Pto, Prf, Rar1, and mitogen-activated protein kinases. The sequence will also be useful for comparative genomics in the Solanaceae family as shown here by the discovery of microsynteny between N. benthamiana and tomato in the region encompassing the Pto and Prf genes