Precision Calculation for Supersymmetric Particle Decays

In the Minimal Supersymmetric Standard Model with conserved R-parity, the decays of the next-to-lightest neutralino into the lightest neutralino and two leptons are always involved in each supersymmetric particle decay chain. In this thesis we calculate one-loop corrections to the two-body decays of the next-to-lightest neutralino into a lepton and a slepton, which again decays into another lepton and the lightest neutralino. We also investigate a scenario where the next-to-lightest neutralino can undergo three-body decays. Not only the branching ratios of leptonic decay modes, but also the dilepton invariant mass distribution, are studied. Its endpoint is often used to reconstruct mass-differences of supersymmetric particles. At one-loop level the branching ratios of these leptonic decays are increased significantly and the shape of dilepton invariant mass distribution is altered by the hard photon emission.