Breit-Wigner width and inverse participation ratio in finite interacting Fermi systems

For many-body Fermi systems we determine the dependence of the Breit-Wigner width Gamma and inverse participation ratio xi on interaction strength U greater than or equal to U-c and energy excitation delta E greater than or equal to delta E-ch when a crossover from Poisson to Wigner-Dyson P(s) statistics takes place. At U greater than or equal to U, the eigenstates are composed of a large number of noninteracting states and even for U < U-c there is a regime where P(s)is close to the Poisson distribution but xi much greater than 1.