Search

The effect of anomalous chromoelectric couplings of the gluon to the top quark are considered in e + e − →t t . The total cross section, as well as t and t polarizations are calculated to order α s in the presence of the anomalous couplings. One of the two linear combinations of t and t polarizations is CP even, while the other is CP odd. Limits that could be obtained at a future linear collider on CP-odd combinations of anomalous couplings are determined.

In this paper we investigate methods to study the $t\bar{t}$ Higgs coupling. The spin and CP properties of a Higgs boson are analysed in a model-independent way in its associated production with a $t\bar{t}$ pair in high-energy $e^+e^-$ collisions. We study the prospects of establishing the CP quantum numbers of the Higgs boson in the CP-conserving case as well as those of determining the CP-mixing if CP is violated. We explore in this analysis the combined use of the total cross section and its energy dependence, the polarisation asymmetry of the top quark and the up-down asymmetry of the antitop with respect to the top-electron plane. We find that combining all three observables remarkably reduces the error on the determination of the CP properties of the Higgs Yukawa coupling. Furthermore, the top polarisation asymmetry and the ratio of cross sections at different collider energies are shown to be sensitive to the spin of the particle produced in association with the top quark pair.

The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.

In an earlier work it was pointed out in the framework of a model field theory that the vanishing of wave function- and vertex-renormalization constants was not a sufficient condition to make an elementary particle equivalent to a three-particle bound state. In the present paper, this result is attributed to the lack of certain direct couplings amongst the multiple channels of the model. It is demonstrated that with the introduction of suitable extra couplings, the Z = 0 condition is sufficient for the compositeness of a particle in the model.

The data of recent single-tag two-photon experiments indicating noticeable excess in ( R γγ ) jet over fractionally charged quark-parton model-predictions is studied from the point of view of its implications on the gauge integer charge quark model. Focusing attention on the region of p T exceeding about 3 GeV, where higher order QCD and non-perturbative effects might be expected to be small, it is noted that this excess and its Q 2 dependence can be attributed to the presence of a colour component in the electromagnetic current provided the effective mass of the gluon lies between about 150 to 350 MeV. Accurate measurements of R γγ in the high p T region ( p T ⪆ 5 GeV ) are crucial for an unambiguous distinction between fcq and gauge-icq models.

Parity violating effects in PP → μ+μ−X and P P → μ + μ − X with the polarized targets have been calculated in the parton picture. The weak neutral currents used are based on an SU(2)L × SU(2)R × U(1) model. The result for the Weinbergy-Salam model occurs as a special case.

We study an SO(4) x U(1) extension of the standard model of weak and electromagnetic interactions, which accommodates the new leptons postulated as an explanation for trimuon events. Universality is shown to be natural in the model. A phenomenological analysis gives good agreement with present data.

We have considered production of Higgs bosons in the process qq→qqWW→qqH and qq→qqZZ→qqZZ→qqH. It is shown that the contribution σ T of the transversely polarized intermediate vector bosons (V) in the equivalent vector boson approximation (EVBA) is comparable to the contribution σ L of the longitudinal ones. σ T can be as large as 1.5–2 times σ L . We also find that for interme diate values of m H , viz. 0.3–0.6 TeV, the leading EVBA for σ = σ L + σ T overestimates the exact total cross section by a factor, up to 2–3, even at high energies. σ T is negligible compared to the leading contribution σ L only for m H ⩾0.6 TeV, where the EVBA is correct within 15–20%.

It is shown that angular distribution in e+e−→γ+2 jets can serve as a possible test of quark charges but only above color threshold.

The decay width of about 5 keV observed for psi ..-->.. ee implies that the SU(4) symmetry for the vector meson-photon coupling constant ..gamma../subV/ is broken, and that the quantity ..gamma../subV/m/subV//sup -1///sup 2/ (where m/subV/ is the mass of the vector meson V) obeys the symmetry. Using this experimental result in conjunction with vector dominance and broken SU(3), the author calculated the decay width for rho ..-->.. ..pi pi.., and obtains GAMMA (rho ..-->.. ..pi pi..) = 142 MeV, in improved agreement with experiment. (AIP)