  Exact analytical expressions for the cross-section correlation functions of
chaotic scattering sys- tems have hitherto been derived only under special
conditions. The objective of the present article is to provide expressions that
are applicable beyond these restrictions. The derivation is based on a
statistical model of Breit-Wigner type for chaotic scattering amplitudes which
has been shown to describe the exact analytical results for the scattering
(S)-matrix correlation functions accurately. Our results are given in the
energy and in the time representations and apply in the whole range from
isolated to overlapping resonances. The S-matrix contributions to the
cross-section correla- tions are obtained in terms of explicit irreducible and
reducible correlation functions. Consequently, the model can be used for a
detailed exploration of the key features of the cross-section correlations and
the underlying physical mechanisms. In the region of isolated resonances, the
cross-section correlations contain a dominant contribution from the
self-correlation term. For narrow states the self-correlations originate
predominantly from widely spaced states with exceptionally large partial width.
In the asymptotic region of well-overlapping resonances, the cross-section
autocorrelation functions are given in terms of the S-matrix autocorrelation
functions. For inelastic correlations, in particular, the Ericson fluctuations
rapidly dominate in that region. Agreement with known analytical and with
experimental results is excellent.
