2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40961In the framework of field approach with finite time interval the particle oscillations in a medium are considered. The absorption in a final states do not lead to dramatic suppression of ab-transitions. Also we touch on the problem of infrared singularities. The approach under study is infrared-free. It is shown that "correction" published recently [A.Gal, Phys. Rev. C61 (2000) 028201] is clearly wrong.10 LATEX pgs., 2 PS figures. Nonprincipal changes madeHigh Energy Physics - PhenomenologyNuclear Theorytext