2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/142188Earlier two of us (J.L. and L.P.) considered a matrix model for a two-level system interacting with a $n\times n$ reservoir and assuming that the interaction is modelled by a random matrix. We presented there a formula for the reduced density matrix in the limit $n\to \infty $ as well as several its properties and asymptotic forms in various regimes. In this paper we give the proofs of the assertions, and present also a new fact about the model.21 pagesMathematical Physics15A52 ; 15A57text