Modeling complex nuclear spectra: Regularity versus chaos.

A statistical analysis of the spectrum of two particle two hole doorway states in a finite nucleus is performed. On the unperturbed mean-field level sizable attractive correlations are present in such a spectrum. Including particle-hole rescattering effects via the residual interaction introduces repulsive dynamical correlations which generate the fluctuation properties characteristic of the Gaussian Orthogonal Ensemble. This signals that the underlying dynamics becomes chaotic. This feature turns out to be independent of the detailed form of the residual interaction and hence reflects the generic nature of the fluctuations studied. PACS numbers: 05.45.+b, 21.60.Jz, 24.60.Dr, 24.60.Lz also at: Institut für Theoretische Kernphysik, Universität Bonn, D-5300 Bonn, Germany