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C. G. Papadopoulos

Publications and source records attributed to C. G. Papadopoulos.

At least 37 records · Page 2Linked to original sources
arXiv2008

Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions

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 and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.

hep-ph↗
arXiv2006

A standard format for Les Houches Event Files

A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.

hep-ph↗
arXiv2006

Recursive equations for arbitrary scattering processes

The usefulness of recursive equations to compute scattering matrix elements for arbitrary processes is discussed. Explicit results at tree and one-loop order, obtained by the HELAC/PHEGAS package that is based on the Dyson-Schwinger recursive equations approach, are briefly presented.

hep-ph↗
arXiv2006

HELAC - A Monte Carlo generator for multi-jet processes

The status of the multi-purpose event generator HELAC is briefly presented. The aim of this tool is the full simulation of events within the Standard Model at current and future high energy experiments, in particular the LHC. Some results related to the production of multi-jet final states at the LHC are also discussed.

hep-ph↗
arXiv2004

Challenges in calculations for multi-particle processes

The physics of high-energy collider experiments asks for delicate comparisons between theoretical predictions and experimental data. Signals and potential backgrounds for new physics have to be predicted at sufficient accuracy. The accuracy as well as the computational complexity of the calculations leading to the predictions depend on both the number of external particles in the process analyzed and the order of the quantum corrections, the number of loops, included in the calculation. We present some approaches to problems occurring in these calculations regarding the integration of phase-space and the inclusion of one-loop corrections.

hep-ph↗
arXiv2003

Cross sections for multi-particle final states at a linear collider

In this paper total cross sections for signals and backgrounds of top- and Higgs-production channels in electron-positron collisions at a future linear collider are presented. All channels considered are characterized by the emergence of six-particle final states. The calculation takes into account the full set of tree-level amplitudes in each process. Two multi-purpose parton level generators, HELAC/PHEGAS and AMEGIC++ are used, their results are found to be in perfect agreement.

hep-ph↗
arXiv2003

Towards an effective-action approach to fermion-loop corrections

We present a study of the effective action approach to incorporate higher-order effects in e^+e^- -> n fermions. In its minimal version, the effective action approach is found to exhibit problems with unitarity and high-energy behaviour. We identify the origin of these problems by investigating the zero-mode solutions of the Ward Identities. A numerical analysis of the importance of the zero-mode solutions is presented for four-fermion production processes.

hep-ph↗
arXiv2002

Recursive actions for scalar theories

We introduce a class of self-interacting scalar theories in which the various coupling contants obey a recursive relation. These imply a particularly simple form for the generating function of the Feynman amplitudes with vanishing external momenta, as well as for the effective potential. In addition we discuss an interesting duality inherent in these models. Specializing to the case of zero spacetime dimensions we find intriguing nullification properties for the amplitudes.

hep-ph↗
arXiv2001

Zero-dimensional field theory

A study of zero-dimensional theories, based on exact results, is presented. First, relying on a simple diagrammatic representation of the theory, equations involving the generating function of all connected Green's functions are constructed. Second, exact solutions of these equations are obtained for several theories. Finally, renormalization is carried out. Based on the anticipated knowledge of the exact solutionsthe full dependence on the renormalized coupling constant is studied.

hep-ph↗
arXiv2000

Four-Fermion Production in Electron-Positron Collisions

This report summarises the results of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the calculation of four-fermion processes in electron-positron collisions at LEP-2 centre-of-mass energies are presented, concentrating on predictions for four main reactions: W-pair production, visible photons in four-fermion events, single-W production and Z-pair production. Based on a comparison of results derived within different approaches, theoretical uncertainties on these predictions are established.

hep-ph↗
arXiv2000

Four-fermion production in electron-positron collisions with NEXTCALIBUR

We introduce a new, fully massive, Monte Carlo program to compute all four-fermion processes in electron-positron collisions, including Higgs production. We outline our strategy for the matrix element evaluation, the phase space generation and the implementation of the leading higher order effects, and show, where available, comparisons with existing results.

hep-ph↗
arXiv1999

Quantum field theory for discrepancies II: 1/N corrections using fermions

We calculate the 1/N corrections to the probability distributions of quadratic discrepancies for sets of N random points. This is achieved by the introduction of fermionic variables. We give the diagrammatic expansion up to and including the second order in 1/N. For some discrepancies, we give the explicit expansion to first order.

hep-ph↗
arXiv1998

Fractals at T=Tc due to instanton-like configurations

We investigate the geometry of the critical fluctuations for a general system undergoing a thermal second order phase transition. Adopting a generalized effective action for the local description of the fluctuations of the order parameter at the critical point ($T=T_c$) we show that instanton-like configurations, corresponding to the minima of the effective action functional, build up clusters with fractal geometry characterizing locally the critical fluctuations. The connection between the corresponding (local) fractal dimension and the critical exponents is derived. Possible extension of the local geometry of the system to a global picture is also discussed.

hep-ph↗
arXiv1998

WEXTER and ERAFITTER: two programs to fit M_W at LEP2 using the best measurable kinematical variables

In this paper, we present two programs to fit M_W at LEP2 using the best measurable kinematical variables. The theoretical probabilities of observing the final-state kinematical configurations are computed by integrating over the quantities that are not well measured. Therefore, an event-by-event kinematical reconstruction is avoided. M_W is then determined through a maximum likelihood fit.

hep-ph↗
arXiv1998

On the computation of multigluon amplitudes

A computational algorithm based on recursive equations is developed in order to estimate multigluon production processes at high energy hadron colliders. The partonic reactions gg->(n-2)g with n up to n=9 are studied and comparisons with known approximations are presented.

hep-ph↗