Özet:
In this thesis, existence of standing waves for the DaveyStewartson (DS) and generalized DaveyStewartson (GDS) systems are established using variational methods. Since both the DS system and the GDS system reduce to a non-linear Schr¨odinger (NLS) equation with the only difference in their non-local term, arguments used in this thesis apply to a larger class of equations which include the DS and GDS systems as special cases. Existence of standing waves for an NLS equation is investigated in two ways: by considering an unconstrained minimization problem and a constrained minimization problem. These two variational methods apply to the GDS system as well and here the sufficient conditions on the existence of standing wave solutions for the GDS system which are imposed by these methods and the minimizers obtained are investigated in comparison.
