CP Violation in the Decay of Neutral Higgs Boson into t−tˉt-{\bar t} or W+−W−W^+-W^-

We investigate a potentially large CP violating asymmetry in the neutral Higgs boson decay into a heavy quark pair or a $W^+$--$W^-$ pair. The source of the CP nonconservation is in the Yukawa couplings of the Higgs boson which can contain both scalar and pseudoscalar pieces. One of the interesting consequence is the different rates of the Higgs boson decays into CP conjugate polarized states. The required final state interactions can be either the strong or the electroweak interactions. The CP violating asymmetry can manifests itself in the asymmetry in the energies of the secondary decay products of these heavy quarks and $W$ bosons. Such asymmetry can be measureable in the future colliders such as SSC or LHC.Comment: 14 pages, 6 postscript figures, extended version of preprint FERMILAB-PUB-92/172-

Top quark production at threshold with O(alpha_s^2) accuracy

We calculate the next-to-next-to-leading order correction to the cross section for top quark pair production in e+e- annihilation in the threshold region, resumming all O [ (alpha_s/beta)^n (alpha_s^2, beta^2, alpha_s beta) ] terms of perturbation series. We find that the magnitude of the NNLO correction is comparable to the size of the NLO corrections.Comment: 15 pages, Latex, one figure, some misprints correcte

CP-Violatiing Asymmetries in e^+e^-\ra t\bar{t} with Longitudinally Polarized Elecrtons

New CP-violating asymmetries of decay leptons in e^+\,e^-\;\ra\;t\,\bar{t}, arising from electric and weak dipole couplings of $t\,\bar{t}$ to $\gamma$ and $Z$, are examined in the case of unpolarized and longitudinally polarized electrons. The new asymmetries measured together with the old ones can help to determine independently the real and imaginary parts of the electric as well as weak dipole couplings. Longitudinal beam polarization, if present, obviates the need for the simultaneous measurement of more than one asymmetry, and enhances considerably the sensitivity to the CP-violating parameters. Numerical results are presented for the Next Linear Collider with $\sqrt{s}=500$ GeV and $\int{\cal L}\,dt\;=\;10\,{\rm fb}^{-1}$.Comment: 12 pages LaTex,PRL-TH-94/3