2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/57882We consider a general weak perturbation of a non-interacting quantum lattice system with a non-degenerate gapped ground state. We prove that the presence of isolated eigenvalues in the spectrum of the decoupled model leads to the existence of quasi-particles in the perturbed model. Also, a scattering theory for asymptotically free many-particle states is developed.17 pagesMathematical Physicstext