Parametric S-matrix fluctuations in quantum theory of chaotic scattering

We study the effects of an arbitrary external perturbation in the statistical properties of the S-matrix of quantum chaotic scattering systems in the limit of isolated resonances. We derive, using supersymmetry, an exact non-perturbative expression for the parameter dependent autocorrelator of two S-matrix elements. Universality is obtained by appropriate rescaling of the physical parameters. We propose this universal function as a new signature of quantum chaos in open systems.Comment: 4 pages, 1 figure appended, written in REVTeX, Preprint OUTP-94-13S (University of Oxford