We obtain limits on the electromagnetic and weak dipole moments of the tau-lepton in the framework of a Left-Right symmetric model (LRSM) and a class of E 6 inspired models with an additional neutral vector boson Z θ . Using as an input the data obtained by the L3 and OPAL Collaborations for the reaction e + e − → τ + τ − γ, we get a stringent limit on the LRSM mixing angle φ, −1.66 × 10 −3 < φ < 1.22 × 10 −3 , which in turn induces bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH Collaborations from the reaction e + e − → τ + τ − . We also get similar bounds for the weak dipole moments of the tau lepton in the framework of E 6 superstring models.

We study the Higgs pair production in the standard model of strong and electroweak interactions at future e ϩ e Ϫ collider energies, with the reaction e ϩ e Ϫ →t tHH. We evaluate the total cross section of t tHH and calculate the total number of events considering the complete set of Feynman diagrams at the tree level. The numerical computation is done for an energy which is expected to be available at a possible Next Linear e ϩ e Ϫ Collider with a center-of-mass energy 800, 1600 GeV and a luminosity of 1000 fb Ϫ1 .

We analyzed the triple Higgs boson self-coupling at future e + e − colliders energies, with the reactions e + e − → bbHH, ttHH. We evaluate the total cross-sections for both bbHH and ttHH, and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. We vary the triple coupling κλ 3H within the range κ = −1 and +2. The numerical computation is done for the energies expected to be available at a possible Future Linear e + e − Collider with a center-of-mass energy 800, 1000, 1500 GeV and a luminosity 1000 f b −1 . Our analysis is also extended to a center-of-mass energy 3 T eV and luminosities of 1000 f b −1 and 5000 f b −1 . We found that for the process e + e − → bbHH, the complete calculation differs only by 3% from the approximate calculation e + e − → ZHH(Z → bb), while for the process e + e − → ttHH, the expected number of events, considering the decay products of both t and H, is not enough to obtain an accurate determination of the triple Higgs boson self-coupling.

We obtain bounds on the anomalous magnetic and electric dipole moments of the t-quark from a future high-energy and high-luminosity linear electron-positron collider, as the CLIC, with polarized and unpolarized electron beams which are powerful tools for determining new physics. We consider the processes γe − →tbν e (γ is the Compton backscattering photon) and e + e − → e − γ * e + →tbν e e + (γ * is the Weizsacker-Williams photon) as they are one of the most important sources of single top-quark production. For systematic uncertainties of δ sys = 0% (5%), b − tagging efficiency = 0.8, center-of-mass energy of √ s = 3 T eV and integrated luminosity of L = 2 ab −1 the future e + e − collider may put bounds on the electromagnetic dipole momentsâ V andâ A of the top quark of the order of O(10 −2 − 10 −1 ) at the 2σ (3σ) level, which are competitive with those recently reported in previous studies at hadron colliders and the ILC.

Limits on the anomalous magnetic moment and the electric dipole moment of the τ lepton are calculated through the reaction e + e − → τ + τ − γ at the Z 1 -pole and in the framework of a left-right symmetric model. The results are based on the recent data reported by the L3 Collaboration at CERN LEP.Due to the stringent limit of the model mixing angle φ, the effect of this angle on the dipole moments is quite small.