2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/126988Using the experimental values for the rates $R^{LEP} _{exp}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.016$, $R^{Giga-Z_1}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.012$ (most conservative) and $R^{Giga-Z_1}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.006$ (most optimistic) we derive constraints on the number of neutrinos light species $(N_ν)_{LRSM}$ with the invisible width method in the framework of a left-right symmetric model (LRSM) as a function of the LR mixing angle $ϕ$. Using the LEP result for $N_ν$ we may place a bound on this angle, $-1.6\times 10^{-3}\leqϕ\leq 1.1\times 10^{-3}$, which is stronger than those obtained in previous studies of the LRSM.8 pages, 3 figuresHigh Energy Physics - Phenomenologytext