CONSTRAINTS ON LEFT–RIGHT SYMMETRIC AND E₆ SUPERSTRING MODELS FROM THE NUMBER OF LIGHT NEUTRINO SPECIES

Abstract

Using the experimental value for the rate R LEP exp = Γ inv /Γ ll = 5.942±0.016, we derive constraints on the number of light neutrino species with the invisible width method in the framework of a leftright symmetric model (LRSM) and a E 6 superstring model as a function of their respective mixing angles for the neutral vector gauge bosons. Using the above LEP result we get the constraints −1.6 × 10 −3 ≤ φ ≤ 1.1 × 10 −3 and −1.3 × 10 −2 ≤ φ E 6 ≤ 0.4 × 10 −2 , which are stronger than those obtained in previous studies of these models. n E 6 f E 6 q = 37.8 , E 6 0 M M z z q = 7 1 A l l o w e d R e g i o n FIG. 3: The same as in Fig. 1, but for E 6 , with θ E 6 = 37.8 o and M Z θ = 7M Z 1 . FIG. 4: The same as in Fig. 2, but for E 6 , with θ E 6 = 37.8 o and M Z θ = 7M Z 1 .

Fermion Family Number and the Z–z′ Mixing in the 3-3-1 Model With Right-Handed Neutrinos

“…Analysis of the behaviour of N ν with the Z-Z ′ mixing angle in the left-right model were done in Refs. [2,3].…”

Bounds on the anomalous $HZγ$ vertex arising from the process $e^+e^-\to τ^+ τ^- γ$

“…In conclusion, we have analyzed the constraints imposed on the HZγ coupling from the known data for the process e + e − → τ + τ − γ obtained by the L3 Collaboration [16]. We have made similar analysis using LEP data in order to improve previous limits on the ZZγ and Zγγ vertices [23,24], the magnetic and electric dipole moments of tau neutrinos [25] and the tau lepton [26], as well as some of the parameters involved in L-R symmetric and E 6 superstring model [27]. In the present case, our bounds shown in Eqs.…”

Bounds on the anomalousHZγ vertex arising from the processe+e−→ τ+τ−γ

“…In conclusion, we have analyzed the constraints imposed on the H Zγ coupling from the known data for the process e + e − → τ + τ − γ obtained by the L3 Collaboration [16]. We have made similar analysis using LEP data in order to improve previous limits on the ZZγ and Zγ γ vertices [23,24], the magnetic and electric dipole moments of tau neutrinos [25] and the tau lepton [26], as well as some of the parameters involved in L-R symmetric and E 6 superstring model [27]. In the present case, our bounds shown in equations ( 8) and ( 9) are close to the limits expected in the annihilation process e + e − → H Z with polarized beams [14] and an order of magnitude better than the limits obtained for the same process by the L3 Collaboration [18].…”