2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/29346We investigate the properties of the ground state of a system of interacting bosons on regular lattices with coordination number $k\geq 2$. The interaction is a pure, infinite, on-site repulsion. Our concern is to give an improved upper bound on the ground state energy per site. For a density $ρ$ a trivial upper bound is known to be $-kρ(1-ρ)$. We obtain a smaller variational bound within a reasonably large family of trial functions. The estimates make use of a large deviation principle for the energy of the Ising model on the same lattice.17 pages, 4 tablesStatistical Mechanicstext