2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/175448We review the theoretical status of the lifetime ratios $τ_{B^+} / τ_{B_d}$ and $τ_{B_s} / τ_{B_d}$ and of the mixing quantities $ΔM_s$, $ΔΓ_s$ and $ϕ_s$. We show that the ratio $ΔΓ_s / ΔM_s$ can be determined with almost no non-perturbative uncertainties. Finally we explain how this precise determination of the standard model values can be used to find possible new physics contributions in $ΔM_s $, $ΔΓ_s$, $ΔΓ_s / ΔM_s$ and $a_{fs}^s$. Combining the latest experimental bounds on these quantities one already gets some hints for new physics contributions.16 pages, 3 figures, plenary talk at Heavy Quarks and Leptons 16.10. - 20.10.2006 Munich, Germany; to appear in the proceedingsHigh Energy Physics - Phenomenologytext