2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/209702Using an imaginary-time path integral approach, we develop the perturbation theory suited to the boson Hubbard model, and apply it to calculate the effects of a dilute gas of spin-polarized fermions weakly interacting with the bosons. The full theory captures both the static and the dynamic effects of the fermions on the generic superfluid-insulator phase diagram. We find that, in a homogenous system described by a single-band boson Hubbard Hamiltonian, the intrinsic perturbative effect of the fermions is to generically suppress the insulating lobes and to enhance the superfluid phase.4 pages, 1 figure; final version as published in PRBStrongly Correlated ElectronsSuperconductivityQuantum Physicstext