2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/210248We propose an approximation scheme to describe the dynamics of the spin-boson model when the spectral density of the environment shows a peak at a characteristic frequency $Ω$ which can be very close (or even equal) to the spin Zeeman frequency $Δ$. Mapping the problem onto a two-state system (TSS) coupled to a harmonic oscillator (HO) with frequency $ω_0$ we show that the representation of displaced HO states provides an appropriate basis to truncate the Hilbert space of the TSS-HO system and therefore a better picture of the system dynamics. We derive an effective Hamiltonian for the TSS-HO system, and show it furnishes a very good approximation for the system dynamics even when its two subsystems are moderately coupled. Finally, assuming the regime of weak HO-bath coupling and low temperatures, we are able to analytically evaluate the dissipative TSS dynamics.12 pages, 2 figures; V2: Published versionQuantum PhysicsMesoscale and Nanoscale Physicstext