2 INTERACTING QUASI-PARTICLES ABOVE THE FERMI SEA

We study numerically the interaction and disorder effects for two quas iparticles in two and three dimensions. The dependence of tile interac tion-induced Breit-Wigner width Gamma on the excitation energy above t he Fermi level (epsilon), the disorder strength, and the system size a re determined, A regime is found where Gamma is practically independen t of epsilon. The results allow us to estimate the two quasiparticle m obility edge.