Random band matrix approach to chaotic scattering: the average $S$-matrix and its pole distribution

Random band matrices relevant for open chaotic systems are introduced and studied. The scattering model based on such matrices may serve for the description of preequilibrium chaotic scattering. In the limit of a large number of open channels we calculate the average $S$-matrix and $S$-matrix’s pole distribution which are found to reduce to those of the full matrix (GOE) case under proper renormalization of the energy scale and strength of coupling to the continuum.