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We discuss what happens at the end of the QCD cascades. We show that, with just a few reasonable assumptions, the emission of soft gluons is constrained to produce an ordered field in the form of a helix. We describe how to modify the Lund fragmentation scheme in order to fragment such a field. Our modified fragmentation scheme yields results which are consistent with current experimental measurem
We investigate the construction of tree-level MHV gluon amplitudes in multiplet bases using BCFW recursion. The multiplet basis decomposition can either be obtained by decomposing results derived in (for example) the DDM basis or by formulating the recursion directly in the multiplet basis. We focus on the latter approach and show how to efficiently deal with the color structure appearing in the r
A semiclassical description of structure functions in DIS at small x is presented. It gives an intuitive picture of the transition from the Double Leading Log approximation at large Q(2), to the powerlike dependence on x in the BFKL region at limited Q(2). Formal derivations from perturbative QCD, e.g. in the BFKL or the CCFM formalisms, are technically complicated, and therefore such an intuitive
The CP conserving amplitudes for the decays K --> 3pi are calculated in chiral perturbation theory at the next-to-leading order. We present the expressions in a compact form with single parameter functions only. These expressions are then fitted to all available K --> 2pi and K --> 3pi data to obtain a fit of the parameters that occur. We compare with the work of Kambor, Missimer and Wyler. (C) 20
We compare different procedures for combining fixed-order tree-level matrix element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different implementations of the so-called CKKW scheme and one based on the so-called MLM scheme using different matrix element generators and different parton cascades. We find that although similar results are o
We show how a difference in the correlation length longitudinally and transversely, with respect to the jet axis in e+e− annihilation, arises naturally in a model for Bose-Einstein correlations based on the Lund string model. In genuine three-particle correlations the difference is even more apparent and they provide therefore a good probe for the longitudinal stretching of the string field. The c
At small x, the effects of finite transverse momenta of partons inside a hadron become increasingly important, especially in analyses of jets and heavy-quark production. These effects can be systematically accounted for in a formalism based on k(perpendicular to)-factorization and unintegrated distribution functions. We present results for the integrated and unintegrated distribution functions obt
The inclusive production of the gauge bosons W-+/- and Z(0) is studied within the color dipole formalism. Gluon saturation effects associated with nonlinear corrections to the QCD dynamics, which are expected to contribute at high energies, are naturally included in such formalism. We estimate the contribution of these effects at LHC energies and compare our results with the next-to-next-to-leadin
We extend earlier schemes for merging tree-level matrix elements with parton showers to include also merging with one-loop matrix elements. In this paper we make a first study on how to include one-loop corrections, not only for events with a given jet multiplicity, but simultaneously for several different jet multiplicities. Results are presented for the simplest non-trivial case of hadronic even
I give a very short introduction to chiral perturbation theory and an overview of the next-to-next-to-leading order three-flavour calculations done. I discuss those relevant for an improvement in the accuracy of the measurement of Vus in more detail. One major conclusion is that all needed p6 low energy constants can be obtained from experiment via the scalar form-factor in K
We extend the algorithm for matching fixed-order tree-level matrix element generators with the Dipole Cascade Model in Ariadne to apply to processes with incoming hadrons. We test the algoritm on for the process W+n jets at the Tevatron, and find that the results are fairly insensitive to the cutoff used to regularize the soft and collinear divergencies in the tree-level matrix elements. We also i
Theoretical arguments, supported by other indirect evidence, suggest that the wave function of high-x partons should be narrower than that of low-x ones. In this article, we present a modification to the variable impact parameter framework of PYTHIA 8 to model this effect. In particular, a Gaussian hadronic matter profile is introduced, with a width dependent on the x value of the constituent bein
A selection of the latest and most frequently used parton distribution functions (PDFs) is incorporated in Pythia8, including the Monte Carlo-adapted PDFs from the MSTW and CTEQ collaborations. This article examines the differences in PDFs as well as the effect they have on results of simulations and compare with data collected by the CDF experiment. Monte Carlo-adapted PDFs do a better job than l
Understanding the patterns of evolutionary sequence divergence is fundamental for comparative analyses like phylogenetics or genomics. The rate at which the different sites of protein sequences evolve is multifactorial and the causes of variation among them are highly convoluted. Inference methods have been developed to estimate site-specific evolution rates from sequence alignments. Moreover, sev
We have measured the lattice size dependence of the lightest glueball mass in SU(2) and SU(3) gauge theory at =2.2 and 2.3 [SU(2)] and =6.0 [SU(3)]. We observe an increase in the glueball mass when the lattice size shrinks below a critical value. The magnitude of this length scale, which we interpret as the physical size of the glueball, is roughly the same for SU(2) and SU(3) when expressed in un
The mcplots.cern.ch web site (mcplots) provides a simple online repository of plots made with high-energy-physics event generators, comparing them to a wide variety of experimental data. The repository is based on the hepdata online database of experimental results and on the rivet Monte Carlo analysis tool. The repository is continually updated and relies on computing power donated by volunteers,
In this article we describe simulations of the hadronic decay of Higgs bosons produced in association with vector bosons at linear and hadronic colliders. We use the Monte Carlo at next-to-leading-order (MC@NLO) matching prescription with the Herwig++ event generator to predict various spectra of the resulting b (b) over bar pairs and compare our results with leading order and matrix element corre
Theoretical and experimental results for the 2s(2) S-1(0)-2s2p P-3(1) intercombination line in beryllium-like ions are reviewed and revised, and some new data are presented. The uncertainty in the resulting transition rate is estimated, by using convergence of systematic calculations, accuracy of energy properties and theoretical tests, and is used to evaluate the accuracy of present and other cal
