S-matrix network models for coherent waves in random media: Construction and renormalization

Networks of random quantum scatterers (S-matrices) form paradigmatic models for the propagation of coherent waves in random media. S-matrix network mo dels cover universal localization-delocalization properties and have some a dvantages over more traditional Hamiltonian models. In particular, a straig htforward implementation of real space renormalization techniques is possib le. Starting from a finite elementary cell of the S-matrix network, hierarc hical network models can be constructed by recursion. The localization-delo calization properties are contained in the flow of the forward scattering s trength ('conductance') under increasing system size. With the aid of 'smal l scale' numerics qualitative aspects of the localization-delocalization pr operties of S-matrix network models can be worked out.