Wave function structure in two-body random matrix ensembles

We study the structure of eigenstates in two-body interaction random matrix ensembles and find significant deviations from random matrix theory expect ations. The deviations are most prominent in the tails of the spectral dens ity and indicate localization of the eigenstates in Fock space. Using ideas related to soar theory we derive an analytical formula that relates fluctu ations in wave function intensities to fluctuations of the two-body interac tion matrix elements. Numerical results for many-body fermion systems agree well with the theoretical predictions.