Decoupling of Anomalous Top-Quark-Decay Vertices in Angular Distribution of Secondary Particles

Angular distribution of a secondary particle from top-quark decays is studied in a simple and general manner, paying careful attention to how relevant the top-quark production mechanism is. The conditions that lead to the distribution free from any possible anomalous top-quark decay interactions are specified. It is discussed how important the approximations adopted in earlier papers are.Comment: 9 pages, Latex, Final version (to appear in Phys.Lett. B

Optimal-Observable Analysis of the Angular and Energy Distributions for Top-Quark Decay Products at Polarized Linear Colliders

An optimal-observable analysis of the angular and energy distributions of the leptons and bottom quarks in the process e+e- --> tt-bar --> l^{+-}/b(b-bar)... has been performed in order to measure the most general top-quark couplings to gauge bosons at polarized linear colliders. The optimal beam polarization for determination of each coupling has been found. A very sensitive test of CP violation in tt-bar production and decay has been proposed.Comment: A typo found in Eq.(A.3), which affects Eqs.(4.13), (4.14) and related discussions. A note added to summarize resultant modification

Angular Distribution of Leptons in General ttbar Production and Decay

Angular distribution of the secondary lepton in top-quark production followed by subsequent semi-leptonic decay is studied assuming general top-quark couplings. It is shown that the distribution does not depend on any possible anomalous tbW couplings and is determined only by the standard V-A decay vertex for any production mechanism if certain well-justified conditions are satisfied.Comment: (1) PACS number changed (2) In Ref.[8], one typo corrected and one paper (Erratum) added (3) To appear in Phys.Lett.

How Valuable is Polarization at a Muon Collider? A Test Case: Determining the CP Nature of a Higgs Boson

We study the use of polarization asymmetries at a muon collider to determine the CP-even and CP-odd couplings of a Higgs boson to $\mu^+mu^-$. We determine achievable accuracy as a function of beam polarization and luminosity. The appropriate techniques for dealing with the polarization precession are outlined. Strategies especially appropriate for a two-Higgs-doublet model (including the MSSM) are given. Our general conclusion is that polarization will be very useful, especially if the proton source is such that full luminosity in the storage ring can be retained even after imposing cuts on the originally accepted muons necessary for P\gsim 0.4 for each beam.Comment: 33 pages, 10 figures, equations.st

Resonance enhancement of dark matter interactions: the case for early kinetic decoupling and velocity dependent resonance width

Motivated by the possibility of enhancing dark matter (DM) self-interaction cross-section $\sigma_{\rm self}$, we have revisited the issue of DM annihilation through a Breit-Wigner resonance. In this case thermally averaged annihilation cross-section has strong temperature dependence, whereas elastic scattering of DM on the thermal bath particles is suppressed. This leads to the early kinetic decoupling of DM and an interesting interplay in the evolution of DM density and temperature that can be described by a set of coupled Boltzmann equations. The standard Breit-Wigner parametrization of a resonance propagator is also corrected by including momentum dependence of the resonance width. It has been shown that this effects may change predictions of DM relic density by more than order of magnitude in some regions of the parameter space. Model independent discussion is illustrated within a theory of Abelian vector dark matter. The model assumes extra $U(1)$ symmetry group factor and an additional complex Higgs field needed to generate a mass for the dark vector boson, which provides an extra neutral Higgs boson $h_2$. We discuss the resonance amplification of $\sigma_{\rm self}$. It turns out that if DM abundance is properly reproduced, the Fermi-LAT data favor heavy DM and constraint the enhancement of $\sigma_{\rm self}$ to the range, which cannot provide a solution to the small-scale structure problems.}Comment: 17 pages, 5 figures, v2: minor changes in text, BBN and CMB constraints adde

Signals of CP Violation in Distributions of Top-Quark Decay Products at Linear Colliders

Angular and energy distributions for leptons and bottom quarks in the process e+e- --> t tbar --> l/b ... have been calculated assuming the most general top-quark couplings. The double distributions depend both on modification of the top-quark production and tbW decay vertices. However, the leptonic angular distribution turned out to be insensitive to non-standard parts of tbW vertex. The method of optimal observables have been used to estimate sensitivity of future measurements at linear e+e- collidersComment: 7 pages, LaTex, 1 figure, talk given at PASCOS '99, Lake Tahoe, California, December 10-16, 1999, typos in the reference list correcte

Brane modeling in warped extra-dimension

Five-dimensional scenarios with infinitesimally thin branes replaced by appropriate configurations of a scalar field were considered. A possibility of periodic extra dimension was discussed in the presence on non-minimal scalar-gravity coupling and a generalized Gibbons-Kallosh-Linde sum rule was found. In order to avoid constraints imposed by periodicity, a non-compact spacial extra dimension was introduced. A five dimensional model with warped geometry and two thin branes mimicked by a scalar profile was constructed and discussed. In the thin brane limit the model corresponds to a set-up with two positive-tension branes. The presence of two branes allows to address the issue of the hierarchy problem which could be solved by the standard warping of the four dimensional metric provided the Higgs field is properly localized. Stability of the background solution was discussed and verified in the presence of the most general perturbations of the metric and the scalar field.Comment: 38+1 pages and 5 figures; v2: some references added and matches the published version in JHE