^{1}

^{2}

^{*}

^{3}

The constraints on the number of neutrinos generations,
g'
_{1} coupling and
*Z -*
* Z′ *mixing angle through the invisible width method, and in the framework of a U(1)
_{B-L} model are obtained. Based on the experimental value reported by the LEP for the rate
, we obtained a bound on the
g'
_{1} coupling,
. In addition, we derive 90% C.L. bounds on the
*Z - Z′* mixing angle
, improving the existing bounds by one order of magnitude.

The number of fermion generations, which is associated to the number of light neutrinos, is one of the most important predictions of the Standard Model of the electroweak interactions (SM) [

The most precise measurement of the number of light

where

In the SM the experimental value from the four LEP experiments for the number of light neutrinos species is

The existence of a heavy neutral

Our aim in this paper is to estimate constraints on the number of neutrinos generations,

This paper is organized as follows. In Section 2, we present the theoretical framework. In Section 3 we present the numerical computation. Finally, we summarize our conclusions in Section 4.

We consider a

where

The Lagrangian for the scalar sector of the

where the potential term is [

with

where the doublet and singlet scalars are

with

From the Lagrangian of the

where the couplings of the

where

In order to compare the respective expressions with the experimental result for the number of light neutrinos species

Since Equation (2) reduces the influence of the top quark mass, the expression

order to get information on the meaning of

The definition given in Equation (2) replaces the expression

top quarks mass. To get information on the meaning of

where

with

This new expression is a function of the mixing angle

In order to estimate a limit for the number of light neutrinos species

In

is a result of both factors in Equation (11). In this figure

broading. This analysis was done using the experimental value given in Equation (2) for

whose central value is quite close to the standard model of three active neutrinos species.

The correlation between the mixing angle

By reversing the process we determined a limit on the

which is consistent with that obtained through from a Renormalisation Group Equation (RGE) analysis [

Finally, is clear that the effects induced by the tree level

From the invisible width method and and in the framework of a _{v} for the SM previously reported in the literature [

0.2 | |

0.4 | |

0.6 | |

0.8 | |

1 |

We acknowledge support from CONACyT, SNI, PROMEP and PIFI (México).

A.González-Sánchez,A.Gutiérrez-Rodríguez,M. A.Hernández-Ruíz, (2015) Bounds on the Number of Light Neutrinos Species, g'_{1} Coupling and Z - Z′ Mixing Angle in a U(1)_{B-L} Model. Journal of Modern Physics,06,1077-1084. doi: 10.4236/jmp.2015.68112