Christian Schappacher

The Implementation of the minimal supersymmetric standard model in FeynArts and FormCalc

Abstract 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.

Top dipole form factors and loop-induced CP violation in supersymmetry

The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of the top quark are presented. Far from the Z peak, they are not sufficient to account for all the new physics effects. In the context of the calculation of the process e+ e− → tt- to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.

Heavy scalar top quark decays in the complex MSSM: A full one-loop analysis

The work of S. H. was supported in part by CICYT (Grant No. FPA 2007-66387), in part by CICYT (Grant No. FPA 2010-22163-C02-01), and by the Spanish MICINN’s Consolider-Ingenio 2010 Program under Grant MultiDark No. CSD2009-00064. This work was supported in part by the European Community’s Marie-Curie Research Training Network under Contract No. MRTN-CT-2006-035505 ‘‘Tools and Precision Calculations for Physics Discoveries at Colliders.’’

Neutralino decays in the complex MSSM at one loop: A comparison of on-shell renormalization schemes

We evaluate two-body decay modes of neutralinos in the minimal supersymmetric Standard Model with complex parameters. Assuming heavy scalar quarks, we take into account all two-body decay channels involving charginos, neutralinos, (scalar) leptons, Higgs bosons and Standard Model gauge bosons. The evaluation of the decay widths is based on a full one-loop calculation including hard and soft QED radiation. Of particular phenomenological interest are decays involving the lightest supersymmetric particle (LSP), i.e., the lightest neutralino, or a neutral or charged Higgs boson. For the chargino/ neutralino sector we employ two different renormalization schemes, which differ in the treatment of the complex phases. In the numerical analysis, we concentrate on the decay of the heaviest neutralino and show the results in the two different schemes. The higher-order corrections of the heaviest neutralino decay widths involving the LSP can easily reach a level of about 10–15%, while the corrections to the decays to Higgs bosons can be up to 20–30%, translating into corrections of similar size in the respective branching ratios. The difference between the two schemes, indicating the size of unknown two-loop corrections, is less than Oð0:1%Þ. These corrections are important for the correct interpretation of LSP and

Chargino decays in the complex MSSM: a full one-loop analysis

We evaluate two-body decay modes of charginos in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM). Assuming heavy scalar quarks we take into account all decay channels involving charginos, neutralinos, (scalar) leptons, Higgs bosons and Standard Model gauge bosons. The evaluation of the decay widths is based on a full one-loop calculation including hard and soft QED radiation. Special attention is paid to decays involving the Lightest Supersymmetric Particle (LSP), i.e. the lightest neutralino, or a neutral or charged Higgs boson. The higher-order corrections of the chargino decay widths involving the LSP can easily reach a level of about ±10%, while the corrections to the decays to Higgs bosons are slightly smaller, translating into corrections of similar size in the respective branching ratios. These corrections are important for the correct interpretation of LSP and Higgs production at the LHC and at a future linear e+e− collider. The results will be implemented into the Fortran code FeynHiggs.

Supersymmetry and precision data after LEP2

Abstract We study one loop supersymmetric corrections to precision observables. Adding LEP2 e e ¯ → f f ¯ cross sections to the data-set removes previous hints for SUSY and the resulting constraints are in some cases stronger than direct bounds on sparticle masses. We consider specific models: split SUSY, CMSSM, gauge mediation, anomaly and radion mediation. Beyond performing a complete one-loop analysis, we also develop a simple approximation, based on the S ˆ , T ˆ , W , Y ‘universal’ parameters. SUSY corrections give W , Y > 0 and mainly depend on the left-handed slepton and squark masses, on M 2 and on μ.

New Developments in FormCalc 8.4

We present new developments in FeynArts 3.9 and FormCalc 8.4, in particular the MSSMCT model file including the complete one-loop renormalization, vectorization/parallelization issues, and the interface to the Ninja library for tensor reduction.

Gluino decays in the complex MSSM: a full one-loop analysis

We evaluate all two-body decay modes of the gluino, in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM). This constitutes an important step in the cascade decays of SUSY particles at the LHC. The evaluation is based on a full one-loop calculation of all two-body decay channels, also including hard QED and QCD radiation. The dependence of the gluino decay to a scalar quark and a quark on the relevant cMSSM parameters is analyzed numerically. We find sizable contributions to the decay widths and branching ratios. They are, roughly of

Supersymmetric one-loop corrections to the process e+e− → f f

\mathcal{O}({\pm 5\%)}

Erratum to “Top dipole form factors and loop-induced CP violation in supersymmetry” [Nucl. Phys. B 551 (1999) 3]☆

, but can go up to ±10% or higher, where the pure SUSY QCD contributions alone can give an insufficient approximation to the full one-loop result. Therefore the full corrections are important for the correct interpretation of gluino decays at the LHC. The results will be implemented into the Fortran code FeynHiggs.