The Number of Neutrinos and the Left-Right Symmetric Model

The meaning of $N_\nu$ in the Left-Right Symmetric Model (LRSM) is discussed. In its original definition $N_\nu$ is the number of neutrinos or generations of leptons, so, in the Standard Model its value is three. However the determination of $N_\nu$ in experiments and in astrophysical observations is subject to different theoretical interpretations. We present arguments that gives $N_\nu$ as a parameter of the LRSM. Using an experimental value for the rate $Gamma_{inv}/Gamma_{l\bar{l}}$ we calculate the bound $2.90\leq N_{\nu_LR}\leq 3.04$ (90 % C. L.), where $N_{\nu_LR}$ is a function of the left-right mixing angle $\phi$. This range is less restrictive than the one of the standard model.