Bounding the Number of Light Neutrinos Species in a Left-Right Symmetric Model

Abstract

Using the experimental values for the rates $R_{exp}^{LEP}={\Gamma }_{inv}/{\Gamma }_{l\bar{l}}=5.942\pm 0.016$, $R^{Giga-Z_1}={\Gamma }_{inv}/{\Gamma }_{l\bar{l}}=5.942\pm 0.012$ (most conservative) and $R^{Giga-Z_1}={\Gamma }_{inv}/{\Gamma }_{l\bar{l}}=5.942\pm 0.006$ (most optimistic) we derive constraints on the number of neutrinos light species $(N_{\nu }{)}_{LRSM}$ with the invisible width method in the framework of a left-right symmetric model (LRSM) as a function of the LR mixing angle $\varphi$. Using the LEP result for $N_{\nu }$ we may place a bound on this angle, $-1.6\times 10^{-3}\le \varphi \le 1.1\times 10^{-3}$, which is stronger than those obtained in previous studies of the LRSM.

8 pages, 3 figures