S. Hesselbach

A T-odd asymmetry in neutralino production and decay

We study CP-violating effects in neutralino production and subsequent decay within the Minimal Supersymmetric Standard Model with complex parameters M1 and ?. The observable we propose is a T-odd asymmetry based on a triple product in neutralino production e+e??0i02, i = 1,...,4?, with subsequent leptonic three-body decay 02?01?+??, ? = e,?, at an e+e? linear collider with (s)1/2 = 500?GeV and polarised beams. We provide compact analytical formulae for the cross section and the T-odd asymmetry taking into account the complete spin correlations between production and decay. We give numerical predictions for the cross section and the T-odd asymmetry. The asymmetry can go up to 10 %.

Top Squarks and Bottom Squarks in the MSSM with Complex Parameters

We present a phenomenological study of top squarks (˜1,2) and bottom squarks (˜b1,2) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters At,Ab,µ and M1. In particular we focus on the CP phase dependence of the branching ratios of ˜1,2 and ˜1,2 decays. We give the formulae of the two-body decay widths and present numerical results. We find that the effect of the phases on the ˜1,2 and ˜1,2 decays can be quite significant in a large region of the MSSM parameter space. This could have important implications for ˜1,2 and ˜1,2 searches and the MSSM parameter determination in future collider experiments. We have ˜

Impact of CP phases on stop and sbottom searches

Abstract We study the decays of top squarks ( t 1,2 ) and bottom squarks ( b 1,2 ) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A t , A b , μ and M 1 . We show that including the corresponding phases substantially affects the branching ratios of t 1,2 and b 1,2 decays in a large domain of the MSSM parameter space. We find that the branching ratios can easily change by a factor of 2 and more when varying the phases. This could have an important impact on the search for t 1,2 and b 1,2 and the determination of the MSSM parameters at future colliders.

Production of singlino dominated neutralinos in extended supersymmetric models

Abstract Neutralinos with a large singlino component may appear in extended supersymmetric models with additional singlet Higgs fields. Since singlinos do not couple to (s)fermions and gauge bosons, the cross sections for the production of singlino dominated neutralinos are generally small. Within the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and an E 6 inspired model we study neutralino production e + e − → χ 0 1 χ 0 2 ( χ 0 1,2 χ 0 3 ) with a singlino dominated χ 0 2 ( χ 0 3 ). It is shown that neutralinos with a singlino contribution up to 99% can be produced with a cross section larger than 1 fb and may therefore be detected at a high luminosity e + e − linear collider even if they are not the LSP.

Effects of CP phases on the phenomenology of SUSY particles

We review our recent studies on the effects of CP-violating supersymmetric (SUSY) parameters on the phenomenology of neutralinos, charginos and third generation squarks. The CP-even branching ratios of the squarks show a pronounced dependence on the phases of A_t, A_b, mu and M_1 in a large region of the supersymmetric parameter space, which can be used to get information on these phases. In addition we have studied CP-odd observables, like asymmetries based on triple product correlations. In neutralino and chargino production with subsequent three-body decays these asymmetries can be as large as 20%.

Physics possibilities at a linear collider

We review some recent studies about the parameter determination of top quarks,W bosons, Higgs bosons, supersymmetric particles and in the ADD model of extra dimensions at a linear collider.

Standard model and beyond

We first discuss the basic features of electroweak 1-loop corrections in the Standard Model. We also give a short and elementary review on Higgs boson searches, grand unification, supersymmetry and extra dimensions.