A Renormalisation Approach to Effective Interactions in Hilbert Space
  The 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. 
J. Richert