2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46756We show that there is a double counting in the standard model of $n\bar{n}$ mixing in the medium, resulting in full cancellation of leading terms. The direct calculation of $n\bar{n}$ transition, annihilation is performed. For lower limit on the free-space $n\bar{n}$ oscillation time we get $τ_{min} \sim 10^{31}y$.7 pages, LaTeXHigh Energy Physics - PhenomenologyNuclear Theorytext