Scattering Amplitudes in String Theory

Multi-parton superstring amplitudes are of considerable theoretical interest in the framework of a full-fledged superstring theory as well as describing phenomenological aspects like corrections to four-dimensional scattering processes. Neveu-Schwarz fermions and Ramond spin fields enter string scattering amplitudes through vertex operators of bosonic and fermionic string states and determine the Lorentz structure of the total amplitude. In this thesis we provide calculational tools to evaluate correlation functions of Ramond-Neveu-Schwarz fields for tree- and loop-scattering in four, six, eight and ten space-time dimensions. In certain cases we even derive results for arbitrary many external fields. To complement the discussion we calculate the tree-level amplitude of two gauge fields and four gauginos for string compactifications to four dimensions and give its field theory limit. This open string amplitude is of particular interest because it can be related to an open-closed amplitude involving gauge fields and bulk moduli.