An effective low-energy quasiparticle model with attractive interaction

We consider the "high-energy" single-particle states of a strongly interact ing electron liquid. These states should be taken into account whenever the re are strong incoherent effects produced by interactions. Considering the presence of these particles which are confined in a thin shell in momentum space around p = (p) over bar > p(F) as well as "low-energy" quasiparticles we derive an effective model by integrating out the "high-energy" fields. The resulting theory produces an effective interaction for the quasiparticl es which may be large and negative. This produces an instability which driv es the electron liquid towards superconductivity or another non-perturbativ e regime.