Constraints onZ 1–Z 2 mixing from the decayZ 1→e− e + in the left-right symmetric model

Abstract

We examine the decay of Z 1 in electrons with recent data from LEP. The partial width Γ(Z 1 → e − e + ) is studied in the framework of a left-right symmetric model with standard electroweak corrections. Processes measured near the resonance has served to measure the neutral coupling constants very precisely, which is useful to set bounds on the parameters of the model. This partial decay occurs in the resonance zone. As a consecuence the process is independent of the mass of the additional Z 2 heavy gauge boson which appears in this kind of models and so we have the mixing angle φ between the left and the right bosons as the only additional parameter. In this paper we take advantage of this fact to set a bound for φ: −9 × 10 −3 ≤ φ ≤ 4 × 10 −3 , which is in agreement with other constraints previously reported.

LIMITS ON THE ELECTROMAGNETIC AND WEAK DIPOLE MOMENTS OF THE TAU-LEPTON IN E6 SUPERSTRING MODELS

“…which are consistent with those obtained recently from the LEP data on the number of light neutrino species in the LRSM [57], and they are about one order of magnitude stronger than the previous limit obtained from old LEP data [58]. Since we have calculated the cross section at the Z 1 pole, i.e.…”

“…Processes measured in the resonance serve to set limits on the tau electromagnetic and weak dipole moments. First, using as an input the results obtained by the L3 and OPAL Collaborations [51,52] for the tau MM and EDP in the process e + e − → τ + τ − γ, we will set a limit on the LRSM mixing angle φ which is similar to that obtained recently from the LEP data on the number of light neutrino species [57] but it is stronger by about one order of magnitude than the previous limit for this angle obtained from old LEP data [58]. We then use this limit on φ to get bounds on the weak dipole moments of the tau from the same L3/OPAL data.…”

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

“…On the other hand, the LEP result is about two sigmas away from the SM expectation, N ν = 3. While not statistically significant, this result suggests that the Zνν-couplings might be suppressed with respect to the SM value [6,14,15].…”

“…This definition replaces the expression N ν = Γ inv Γνν since (2) reduces the influence of the top quarks mass. To get information on the meaning of N ν in the LRSM model we should define the corresponding expression [14,15],…”

Bound on noncommutative standard model with hybrid gauge transformation via lepton flavor conservingZdecay

“…The gap between the experimental results and the theoretical prediction is of order 0.03% and exhibits possible existence of new physics beyond the standard model. Motivated by this, various models beyond the SM have been discussed [15][16][17]. In Ref.…”