An anomalous Wtb coupling at a linear collider

Differential cross sections of secondary particles in a process of top quark pair production and decay into six fermions at a linear collider with an unpolarized and a longitudinally polarized electron beam are computed to the lowest order in the standard model and in the presence of an anomalous Wtb coupling. It is illustrated that the latter has a little impact on the differential cross sections. In particular, it is shown that the angular distribution of a secondary lepton receives practically no contribution from the anomalous Wtb coupling, even if the top quark is produced off shell and the non-double resonance background contributions are taken into account. This finding is in accordance with the decoupling theorem that has been proven in literature in the narrow top quark width approximation.Comment: 11 pages, 9 figures, axodraw.st

SUSY-Induced CP Violation in tt Decays at e−e+e^-e^+ Colliders

CP violation in the decays $t \to \ell^+\nu b$ and $\bar t \to \ell^-\bar\nu \bar b$ from the production process e^-e^+ \to \ttbar is discussed. Since the asymmetry proposed as a measure of CP violation vanishes even at the one-loop level in the Standard Model (SM), it may be a useful tool to search for sources of CP violation outside of the SM. As an illustration the asymmetry has been computed within supersymmetric extensions of the SM. Prospects for its measurement at future high-energy linear colliders are discussed.Comment: 17 pages, corrected former postscript output mistake

Using Back-Scattered Laser Beams to Detect CP Violation in the Neutral Higgs Sector

We demonstrate that the ability to polarize the photons produced by back-scattering laser beams at a TeV scale linear \epem collider could make it possible to determine whether or not a neutral Higgs boson produced in photon-photon collisions is a CP eigenstate. The relative utility of different types of polarization is discussed. Asymmetries that are only non-zero if the Higgs boson is a CP mixture are defined, and their magnitudes illustrated for a two-doublet Higgs model with CP-violating neutral sector.Comment: 15 pages, UCD-92-18, 4 figures, postscript figure files available by request, uses phyzzx.te

Four-Fermi Effective Operators in Top-Quark Production and Decay

Effects of four-Fermi-type new interactions are studied in top-quark pair production and their subsequent decays at future e^+e^- colliders. Secondary-lepton-energy distributions are calculated for arbitrary longitudinal beam polarizations. An optimal-observables procedure is applied for the determination of new parameters.Comment: Polarized e^- plus unpolarized e^+ collisions were include

Gluon Fusion: A Probe of Higgs Sector CP Violation

We demonstrate that CP violation in the Higgs sector, \eg\ of a multi-doublet model, can be directly probed using gluon-gluon collisions at the SSC. % requires phyzzx.tex macro packageComment: UCD-93-

Electric Dipole Moments of Neutron and Electron in Two-Higgs-Doublet Model with Maximal CPCP violation

We study the electric dipole moments(EDM) of the neutron and the electron in the two-Higgs-doublet model, in the case that $CP$ symmetry is violated maximally in the neutral Higgs sector. We take account of the Weinberg's operator O_{3g}=GG\t G as well as the operator $O_{qg}=\bar q\sigma\tilde Gq$ for the neutron, and the Barr-Zee diagrams for the electron. It is found that the predicted neutron EDM could be considerably reduced by the destructive contribution of the two Higgs scalars to get the lower value than the experimental bound. As to the electron EDM, the predicted value is smaller in one order than the experimental one.Comment: 15pages, UWThPh-1994-48, AUE-08-94, US-94-06. The post-script files of figures will be sent by request by electric mai

Using Decay Angle Correlations to Detect CP Violation in the Neutral Higgs Sector

We demonstrate that decay angle correlations in \taum\taup and t\anti t decay modes could allow a determination of whether or not a neutral Higgs boson is a CP eigenstate. Sensitivity of the correlations is illustrated in the case of the \epem\rta Z \hn and \mupmum\rta \hn production processes for a two-doublet Higgs model with CP-violating neutral sector. A very useful technique for minimizing `depolarization-factor' suppressions of the correlations in the t\anti t mode is introduced.Comment: 13 pages, phyzzx.tex macro, full postscript file including embedded figure available at ftp://ucdhep.ucdavis.edu/gunion/cpasym.p

CP-Violating Lepton-Energy Correlation in e\bar{e}\to t\bar{t}

In order to observe a signal of possible CP violation in top-quark couplings, we have studied energy correlation of the final leptons in $e^+e^-\to t\bar{t} \to \ell^+\ell^-X / \ell^\pm X$ at future linear colliders. Applying the recently-proposed optimal method, we have compared the statistical significances of CP-violation-parameter determination using double- and single-lepton distributions. We have found that the single-lepton-distribution analysis is more advantageous.Comment: Final version (to appear in Phys.Lett.B

Probing Top-Quark Couplings at Polarized NLC

The energy spectrum of the lepton(s) in e^+e^- --> tt-bar --> l^{+-} ...../l^+l^-..... at next linear colliders (NLC) is studied for arbitrary longitudinal beam polarizations as a possible test of new physics in top-quark couplings. The most general non-standard couplings for gamma-tt-bar, Ztt-bar and Wtb vertices are considered. Expected precision of the non-standard-parameter determination is estimated applying the optimal-observable procedure.Comment: Final version, To appear in Phys. Rev.

Using Spin Correlations to Distinguish Zh from ZA at the International Linear Collider

We investigate how to exploit the spin information imparted to the Z boson in associated Higgs production at a future linear collider as an aid in distinguishing between CP-even and CP-odd Higgs bosons. We apply a generalized spin-basis analysis which allowsus to study the possibilities offered by non-traditional choices of spin projection axis. In particular, we find that the Z bosons produced in association with a CP-even Higgs via polarized collisions are in a single transverse spin-state (>90% purity) when we use the Zh-transverse basis, provided that the Z~bosons are not ultra-relativistic (speed <0.9c). This same basis applied to the associated production of a CP-odd Higgs yields Z's that are an approximately equal mixture of longitudinal and transverse polarizations. We present a decay angular distribution which could be used to distinguish between the CP-even and CP-odd cases. Finally, we make a few brief remarks about how this distribution would be affected if the Higgs boson turns out to not be a CP-eigenstate.Comment: 48 pages, 18 figures, revtex