Spectral Properties and Stability of Self-Similar Wave Maps

In this thesis the Cauchy problem and in particular the question of singularity formation for co-rotational wave maps from Minkowski space to the three-sphere is studied. Numerics indicate that self-similar solutions play a crucial role in dynamical time evolution. In particular, it is conjectured that a certain solution f defines a universal blow up pattern in the sense that the future development of a large set of generic blow up initial data approaches f. Thus, singularity formation is closely related to stability properties of self-similar solutions. In this work, the problem of linear stability is studied by functional analytic methods. In particular, a complete spectral analysis of the perturbation operators is given and well-posedness of the linearized Cauchy problem is proved by means of semigroup theory and, alternatively, the functional calculus for self-adjoint operators. These results lead to growth estimates which provide information on the stability of self-similar wave maps. The thesis is intended to be self-contained, i.e. all the mathematical requirements are carefully introduced, including proofs for many results which could be found elsewhere.