arXiv subjects

T. Hahn

Publications and source records attributed to T. Hahn.

81 records · Page 5Linked to original sources

arXiv2001

The Implementation of the Minimal Supersymmetric Standard Model in FeynArts and FormCalc

We describe the implementation of the MSSM in the diagram generator FeynArts and the calculational tool FormCalc. This extension allows to perform loop calculations of MSSM processes almost fully automatically. The actual implementation has two aspects: The MSSM Feynman rules are specified in a new model file for FeynArts. The computation of the parameters in the MSSM Lagrangian from the input parameters is realized as a Fortran subroutine in the framework of FormCalc. The model file does not depend on the latter, however, and can be used even if one does not want to continue the calculation with FormCalc. The Feynman rules have been entered in a very generic way to allow e.g. scenarios with complex parameters, and have been tested extensively by reproducing known results for several non-trivial scattering processes.

hep-ph↗

arXiv2001

Generating Feynman Diagrams and Amplitudes with FeynArts 3

This paper describes the Mathematica package FeynArts used for the generation and visualization of Feynman diagrams and amplitudes. The main features of version 3 are: generation of diagrams at three levels, user-definable model files, support for supersymmetric models, and publication-quality Feynman diagrams in PostScript or LaTeX.

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arXiv2000

Automatic Loop Calculations with FeynArts, FormCalc, and LoopTools

This article describes three Mathematica packages for the automatic calculation of one-loop Feynman diagrams: the diagrams are generated with FeynArts, algebraically simplified with FormCalc, and finally evaluated numerically using the LoopTools package. The calculations are performed analytically as far as possible, with results given in a form well suited for numerical evaluation. The latter is straightforward with the utility programs provided by FormCalc (e.g. for translation into Fortran code) and the implementations of the one-loop integrals in LoopTools. The programs are also equipped for calculations in supersymmetric models.

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arXiv1999

Top production above threshold: Electroweak and QCD corrections combined

Top quark production in electron-positron annihilation is one of the benchmark reactions at a future linear collider. Both electroweak and QCD corrections are large, amounting to 10% or even more in specific kinematic regions. In this note we present a method which allows to combine the dominant terms from both sources, thus improving considerably the result based on a simple addition of both corrections.

hep-ph↗

arXiv1999

Loop Calculations with FeynArts, FormCalc, and LoopTools

Three programs are presented for automatically generating and calculating Feynman diagrams: the diagrams are generated with FeynArts, algebraically simplified with FormCalc, and finally evaluated numerically using the LoopTools package. The calculations are performed analytically as far as possible, with results given in a form well suited for numerical evaluation. The latter is then straightforward using the implementations of the one-loop integrals in LoopTools.

hep-ph↗

arXiv1999

Generating and Calculating One-loop Feynman Diagrams with FeynArts, FormCalc, and LoopTools

A set of programs is presented for automatically generating and calculating Feynman diagrams. Diagrams are generated with FeynArts, then algebraically simplified using a combination of Mathematica and FORM implemented in the package FormCalc, and finally evaluated numerically using the LoopTools package. FormCalc works either in dimensional regularization or in constrained differential renormalization, the latter of which is equivalent at the one-loop level to regularization by dimensional reduction. FormCalc combines the speed of FORM with the powerful instruction set of Mathematica, and the latter greatly eases further processing of the results (e.g. selecting or modifying terms). The output is in a form well suited for numerical evaluation, which is then straightforward using the implementations of the one-loop integrals in LoopTools.

hep-ph↗

arXiv1998

Automatized One-Loop Calculations in 4 and D dimensions

Two program packages are presented for evaluating one-loop amplitudes. They can work either in dimensional regularization or in constrained differential renormalization. The latter method is found at the one-loop level to be equivalent to regularization by dimensional reduction.

hep-ph↗

arXiv1998

Radiative Corrections to W^+W^- \to W^+W^- in the Electroweak Standard Model

The cross-section for W^+W^- \to W^+W^- with arbitrarily polarized W bosons is calculated within the Electroweak Standard Model including the complete virtual and soft-photonic O(alpha) corrections. We show the numerical importance of the radiative corrections for the dominating polarized cross-sections and for the unpolarized cross-section. The numerical accuracy of the equivalence theorem is investigated in O(alpha) by comparing the cross-section for purely longitudinal W bosons obtained from the equivalence theorem and from the direct calculation. We point out that the instability of the W boson, which is inherent in the one-loop corrections, prevents a consistent calculation of radiative corrections to the scattering of on-real-mass-shell longitudinal W bosons beyond O(alpha).

hep-ph↗

arXiv1996

Radiative Corrections to ZZ->ZZ in the Electroweak Standard Model

The cross-section for ZZ->ZZ with arbitrarily polarized Z bosons is calculated within the electroweak Standard Model including the complete O(alpha) corrections. We show the numerical importance of the radiative corrections and elaborate its characteristic features. The treatment of the Higgs-boson resonance is discussed in different schemes including the S-matrix-motivated pole scheme and the background-field method. The numerical accuracy of the equivalence theorem is investigated by comparing the cross-sections for purely longitudinal Z bosons obtained from the equivalence theorem and from the complete calculation. In this context the full O(alpha) corrections are also confronted with the enhanced corrections of O(alpha M_H^2/s_w^2 M_W^2), which were frequently used in the literature.

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