2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/207825Contributions of flavour-changing neutral currents in the 3 3 1 model with right-handed neutrinos to mass difference of the neutral meson system $Δm_P (P = K, D, B)$ are calculated. Using the Fritzsch anzats on quark mixing, we show that the third family should be different from the first two. We obtain a lower bound on mass of the new heavy neutral gauge boson as 1.02 TeV.7 pages, no figures, to appear in J. Phys. G (1999), October issueHigh Energy Physics - Phenomenologytext