Multiple Interactions in Low x DIS and High Energy pp Collisions

The LDC formalism for DIS can describe HERA structure functions, and also agrees well with CTEQ and MRST gluon distributions. It is also suitable for hadronic collisions, and provides a strong connection between ep and pp reactions. Some preliminary results are presented.Comment: Talk presented at XXXIII Int. Conf. on Multiparticle Dynamics, Krakow, Sept. 200

Transverse Energy and Minijets in High Energy Collisions

Minijet production and transverse energy are important not only to understand hadronic collisions, but also for the interpretation of nucleus collisions at RHIC and LHC, where it determines the ``initial conditions'' for the flow in a hadronic soup or a plasma. For high collision energies and small qT (minijets) we enter the BFKL region. This implies that we must take into account off-shell parton cross sections and non-integrated structure functions (kT-factorization). It is also essential to avoid double counting, as one emitted parton is a participant in two different subcollisions. The LDC model, developed in Lund to describe DIS, provides a very convenient formalism to handle these problems. The result is a dynamical suppression of minijets for small qT. The resulting transverse energy flow is similar to the result from a ''naive'' calculation based on integrated structure functions with a qT cut-off around 2 GeV.Comment: 6 pages, 7 figures, uses ws-p8-50x6-00.cls, contributed paper to the Proceedings of the XXXth International Symposium on Multiparticle Dynamics, Tihany, Hungary, October 200

Fluctuations and Fermi-Dirac Correlations in e+e- annihilation

In this talk I first present a short review of fluctuations in $e^+e^-$-annihilations. I then describe some new results on FD correlations. Experimental analyses of $pp$ and $\Lambda\Lambda$ correlations indicate a very small production radius. This result relies very strongly on comparisons with MC simulations. A study of the approximations and uncertainties is these simulations imply that it is premature to draw such a conclusion from the data.Comment: Talk presented at XXXVI Int. Symp. on Multiparticle Dynamics, Paraty, Brazil, 2 - 8 Sept. 200

Unintegrated Parton Densities and Applications

Different formalisms for unintegrated parton densities are discussed, and some results and applications are presented.Comment: Talk presented at the Ringberg Workshop, New Trends in HERA Physics, Schloss Ringberg, Germany, 28 Sept. - 3 Oct. 200

Baryon Production in the String Fragmentation Picture

An improved version of the ``pop-corn'' model for baryon production in quark and gluon jets is presented. With a reduced number of parameters the model reproduces well both production rates for different baryon species and baryon momentum distributions. Predictions are presented for a set of baryon-antibaryon correlations.Comment: 22 pages, 11 Postscript figure

Gravitational Scattering in the ADD-model at High and Low Energies

Gravitational scattering in the ADD-model is considered at both sub- and transplanckian energies using a common formalism. By keeping a physical cut-off in the KK tower associated with virtual KK exchange, such as the cut-off implied from a finite brane width, troublesome divergences are removed from the calculations in both energy ranges. The scattering behavior depends on three different energy scales: the fundamental Planck mass, the collision energy and the inverse brane width. The result for energies low compared to the effective cut-off (inverse brane width) is a contact-like interaction. At high energies the gravitational scattering associated with the extra dimensional version of Newton's law is recovered

Energy and Virtuality Scale Dependence in Quark and Gluon Jets

We discuss some important issues concerning multiplicities in quark and gluon jets in e+e- annihilation. In QCD the properties of a jet in general depend on two scales, the energy and virtuality of the jet. Frequently theoretical predictions apply to a situation where these scales coincide, while for experimental data they are often different. Thus an analysis to extract e.g. the asymptotic multiplicity ratio CF/CA between quark and gluon jets, needs a carefully specified jet definition, together with a calculation of nonleading corrections to the multiplicity evolution. We propose methods to systematically study the separate dependence upon the two scales in experimental data and compare the results with theory. We present jet finding algorithms which corresponds well to the theoretically considered jets. We also show that recoil effects add corrections to the modified leading log approximation which are quantitatively important, though formally suppressed at high energies.Comment: 31 pages, 15 figures. Submitted to JHEP. Replaced with extensively rewritten versio

Multiple Scattering, Underlying Event, and Minimum Bias

In this talk I first discuss the experimental evidence for multiple scattering and the properties of the underlying event. The extensive analyses by Rick Field of data from CDF cannot be reconciled with traditional wisdom concerning multiple collisions and the AGK cutting rules. Data seem to imply some kind of color recombination or unexpectedly strong effects from pomeron vertices. I then discuss theoretical ideas concerning the relation between multiple collisions and unitarity: the AGK rules, IP loops, dipole cascade models and diffraction.Comment: Talk presented at 12th Int. Conf. on Elastic and Diffractive Scattering, EDS07, DESY, Hamburg, 21-25 May 200

Exclusive final states in diffractive excitation

In this paper we describe a formalism for generating exclusive final states in diffractive excitation, based on the optical analogy where diffraction is fully determined by the absorption into inelastic channels. The formalism is based on the Good--Walker formalism for diffractive excitation, and it is assumed that the virtual parton cascades represent the diffractive eigenstates defined by a definite absorption amplitude. We emphasize that, although diffractive excitation is basically a quantum-mechanical phenomenon with strong interference effects, it is possible to calculate the different interfering components to the amplitude in an event generator, add them and thus calculate the reaction cross section for exclusive diffractive final states. The formalism is implemented in the DIPSY event generator, introducing no tunable parameters beyond what has been determined previously in studies of non-diffractive events. Some early results from DIS and proton-proton collisions are presented, and compared to experimental data