Fluctuations in transitional regions of finite Fermi systems

Transitional regions are investigated of models describing finite Fermi systems which give rise to phase transitions. The emphasis lies on the connection between the pattern of the exceptional points of the Hamiltonian and fluctuations induced by multiple level crossings. It is found that the Lipkin model produces no fluctuations in the transitional region. Fluctuations emerge when deviations from the Lipkin model are considered. (orig.)