SUSY--QCD corrections to scalar quark decays into charginos and neutralinos

We calculate the supersymmetric QCD corrections in order $\alpha_s$ to the decays \squark_i \to q' \chargino_j (i,j = 1,2) and \squark_i \to q \neutralino_k (k = 1,...4) within the Minimal Supersymmetric Standard Model. In particular we consider the decays of squarks of the third generation, \stop_i and \sbottom_i (i = 1,2), where the left--right mixing must be taken into account. The corrections turn out to be of about 10\%, except for higgsino--like charginos or neutralinos, where they can go up to 40\%.Comment: 15 pages (including 5 figures). Tiny corrections in the text are made. An acknowledgement is added. Figures 2 - 5 are replaced by new ones (change in one curve in each figure). To be published in Phys. Lett.

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.Comment: 20 pages, LaTeX, 7 eps figures, uses ws-procs9x6.cls, lecture given by A. Bartl at the VII School on Non-Accelerator Astroparticle Physics, Trieste, Italy, July 26 - August 6, 200

Prediction of claims in export credit finance: a comparison of four machine learning techniques

This study evaluates four machine learning (ML) techniques (Decision Trees (DT), Random Forests (RF), Neural Networks (NN) and Probabilistic Neural Networks (PNN)) on their ability to accurately predict export credit insurance claims. Additionally, we compare the performance of the ML techniques against a simple benchmark (BM) heuristic. The analysis is based on the utilisation of a dataset provided by the Berne Union, which is the most comprehensive collection of export credit insurance data and has been used in only two scientific studies so far. All ML techniques performed relatively well in predicting whether or not claims would be incurred, and, with limitations, in predicting the order of magnitude of the claims. No satisfactory results were achieved predicting actual claim ratios. RF performed significantly better than DT, NN and PNN against all prediction tasks, and most reliably carried their validation performance forward to test performance

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%.Comment: 10 pages, LaTeX, 4 eps figures, uses ws-procs9x6.cls, invited plenary talk presented by A. Bartl at the "10th International Symposium on Particles, Strings and Cosmology (PASCOS'04/NathFest)", Northeastern University, Boston, MA, August 16-22, 200

Impact of CP phases on stop and sbottom searches

We study the decays of top squarks (stop_{1,2}) and bottom squarks (sbottom_{1,2}) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, mu and M_1. We show that including the corresponding phases substantially affects the branching ratios of stop_{1,2} and sbottom_{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 stop_{1,2} and sbottom_{1,2} and the determination of the MSSM parameters at future colliders.Comment: 17 pages, 5 figures, LaTeX2

CP asymmetries in scalar bottom quark decays

We propose CP asymmetries based on triple product correlations in the decays sbottom_m -> top chargino_j with subsequent decays of top and chargino_j. For the subsequent chargino_j decay into a leptonic final state l^- \nu neutralino_1 we consider the three possible decay chains chargino_j -> l^- sneutrino -> l^- \nu neutralino_1, chargino_j -> slepton_n \nu -> l^- \nu neutralino_1 and chargino_j -> W^- neutralino_1 -> l^- \nu neutralino_1. We consider two classes of CP asymmetries. In the first class it must be possible to distinguish between different leptonic chargino_j decay chains, whereas in the second class this is not necessary. We consider also the 2-body decay chargino_j -> W^- neutralino_1, and we assume that the momentum of the W boson can be measured. Our framework is the minimal supersymmetric standard model with complex parameters. The proposed CP asymmetries are non-vanishing due to non-zero phases for the parameters \mu and/or A_b. We present numerical results and estimate the observability of these CP asymmetries.Comment: 27 page

Impact of bosonic decays on the search for stau_2 and tau-sneutrino

We perform a detailed study of the decays of the heavier tau slepton (stau_2) and tau-sneutrino (snu_tau) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons, i.e. stau_2 -> stau_1 + (h^0, H^0, A^0 or Z^0), stau_2 -> snu_tau + (H^- or W^-), and snu_tau -> stau_1 + (H^+ or W^+), can be very important due to the sizable tau Yukawa coupling and large mixing parameters of stau. Compared to the decays into fermions, such as stau_2 -> tau + neutralino_i and stau_2 -> nu_tau + chargino_j^-, these bosonic decay modes can have significantly different decay distributions. This could have an important influence on the search for stau_2 and snu_tau and the determination of the MSSM parameters at future colliders.Comment: 12 pages, 3 figures, LaTeX2

SPYTHIA, A Supersymmetric Extension of PYTHIA 5.7

SPYTHIA is an event level Monte Carlo program which simulates particle production and decay at lepton and hadron colliders in the Minimal Supersymmetric Standard Model (MSSM). It is an extension of PYTHIA 5.7, with all of its previous capabilities. This paper is meant to supplement the PYTHIA/JETSET user manual, providing a description of the new particle spectrum, hard scattering processes, and decay modes. Several examples of using the program are provided.Comment: 12 pages, Latex2e, also available at http://www.hep.anl.gov/theory/mrenna