984 research outputs found
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 . 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 , 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 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 . We discuss the resonance
amplification of . It turns out that if DM abundance is
properly reproduced, the Fermi-LAT data favor heavy DM and constraint the
enhancement of 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
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