Topics in sym theories: * Ads/CFT & Mesonic Spectra ** Superspace & Scattering Amplitudes

In this thesis two different topics in SYM theories are investigated. In the first part we use the AdS/CFT correspondence to study the problem of flavor symmetry for theories that are marginal deformations of the maximal SYM theory. In particular, we compute exactly the masses of the mesons of these theories. The results show that the mass spectrum is discrete, with a mass gap and a Zeeman-like splitting of the mass levels occurs. In the second part of the thesis, we develop a direct computational technique for scattering amplitudes in SYM theories. A combined use of background field method, superspace technologies and new pc programs makes a Feynman diagrammatic approach available. We apply this technique to compute the full two-loop MHV effective action of the maximal SYM theory. From there we move towards the extraction of the four point MHV scattering amplitude.