No abstract

In the framework of the electroweak standard model, we have investigated the top quarks pair production from e − e + annihilation at the energies of a future compact linear collider in the presence of an intense circularly polarized laser field. We have analytically generated the detailed expression for the laser-assisted differential cross section using the lowest-order Dirac-Volkov formalism, including the γ t t ˉ and Z t t ˉ interactions, in the center-of-mass frame. A wide range of center-of-mass energies corresponding to the future e − e + collider has been covered to study the behavior of the total cross section (TCS); this future compact linear collider constitutes an important direction in the study of top quark physics in order to improve the measurements, and the limits of some physical parameters obtained so far at the LHC and the Tevatron. We have analyzed the dependence of the laser-assisted total and partial cross sections on the energy of the center-of-mass of the colliding system e − e + and also on the parameters of the laser field, such as the number of exchanged photons, the laser field strength, and its frequency. The results indicate that the laser field decreases the order of magnitude of the TCS as much as the laser field strength increases or decreases its frequency.

The top quark is distinct from all other fermions due to its high mass and short lifetime. Therefore, it decays rapidly almost exclusively into a light quark and a W + gauge boson. Through all of these properties, the top quark can reveal new details about the standard model and possibly about new physics. In this paper, we have investigated the two-body decay of the top quark ( t → q   W + ), where q represents one of the quarks d, s and b, in the presence of a monochromatic circularly polarized laser field. Using the lowest-order Dirac-Volkov formalism, we have analytically established the expression for the laser-assisted total decay width of the top quark. We have analyzed the dependence of the total decay width, as well as the lifetime and branching ratios (BRs) on the characteristic parameters of the laser. The results indicate that the laser has a decreasing effect on the decay width, leading to an extension of the lifetime. The lifetime behavior inside the laser field is explained by the quantum Zeno effect. More importantly, we find that the laser field with an appropriate frequency and electric field amplitude leads to a modification of the BRs either by the enhancement of the ( t → b   W + ) mode or by the suppression of the ( t → s   W + ) and ( t → d   W + ) modes.