2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/90507The low-lying bound states of a microscopic quantum many-body system of $n$ particles and the related physical observables can be worked out in a truncated $n$--particle Hilbert space. We present here a non-perturbative analysis of this problem which relies on a renormalisation concept and work out the link with perturbative approaches.5 pages, no figures, LateX fileQuantum PhysicsNuclear TheoryAtomic and Molecular Clusterstext