381 research outputs found
Determining the top-antitop and Couplings of a Neutral Higgs Boson of Arbitrary CP Nature at the NLC
The optimal procedure for extracting the coefficients of different components
of a cross section which takes the form of unknown coefficients times functions
of known kinematical form is developed. When applied to \epem\to t\anti
t+Higgs production at \rts=1\tev and integrated luminosity of 200\fbi, we
find that the t\anti t\toHiggs CP-even and CP-odd couplings and, to a lesser
extent, the Higgs (CP-even) coupling can be extracted with reasonable
errors, assuming the Higgs sector parameter choices yield a significant
production rate. Indeed, the composition of a mixed-CP Higgs eigenstate can be
determined with sufficient accuracy that a SM-like CP-even Higgs boson can be
distinguished from a purely CP-odd Higgs boson at a high level of statistical
significance, and vice versa.Comment: 8 pages, full postscript file also available via anonymous ftp at
ftp://ucdhep.ucdavis.edu/gunion/eetottbh.p
CP Nonconservation in at the Tevatron
The reaction is found to be rather rich in exhibiting
several different types of CP asymmetries. The spin of the top quark plays an
important role. Asymmetries are related to form factors arising from radiative
corrections of the production vertex due to non-standard physics. As
illustrations, effects are studied in two Higgs Doublet Models and in
Supersymmetric Models; asymmetries up to a few percent may be possible.Comment: 14 pages, 3 figures. Note: replaced due to minor problems that
appeared on some postscript previewers. No change in conten
Effective-Field-Theory Approach to Top-Quark Production and Decay
We discuss new physics in top-quark interactions, using an effective field
theory approach. We consider top-quark decay, single top production, and
top-quark pair production. We identify 15 dimension-six operators that
contribute to these processes, and we compute the deviation from the Standard
Model induced by these operators. The results provide a systematic way of
searching for (or obtaining bounds on) physics beyond the Standard Model.Comment: 24 pages, 12 figures; references added, typos correcte
CP Violation from 5-dimensional QED
It has been shown that QED in (1+4)-dimensional space-time, with the fifth
dimension compactified on a circle, leads to CP violation (CPV). Depending on
fermionic boundary conditions, CPV may be either explicit (through the
Scherk--Schwarz mechanism), or spontaneous (via the Hosotani mechanism). The
fifth component of the gauge field acquires (at the one-loop level) a non-zero
vacuum expectation value. In the presence of two fermionic fields, this leads
to spontaneous CPV in the case of CP-symmetric boundary conditions.
Phenomenological consequences are illustrated by a calculation of the electric
dipole moment for the fermionic zero-modes.Comment: 11 pages, 2 figure
Top-spin analysis of new scalar and tensor interactions in e^+ e^- collisions with beam polarization
We utilize top polarization in the process e+ e-\rightarrow t\bar{t} at the
ILC with transverse beam polarization to probe interactions of the scalar and
tensor type beyond the standard model and to disentangle their individual
contributions. 90% confidence level limits on the interactions with realistic
integrated luminosity are presented and are found to improve by an order of
magnitude compared to the case when the spin of the top quark is not measured.
Sensitivities of the order of a few times 10^{-3} TeV^{-2} for real and
imaginary parts of both scalar and tensor couplings at \sqrt{s}=500 and 800 GeV
with an integrated luminosity of 500 fb^{-1} and completely polarized beams is
shown to be possible. A powerful model-independent framework for inclusive
measurements is employed to describe the spin-momentum correlations and their
C, P and T properties is presented in a technical appendix.Comment: 14 pages, 10 figures, uses revtex; replaced with version accepted for
publication in Physical Review D; significantly rewritten and reformulated,
section added, inclusive section moved to appendix, reference adde
Large Tree Level CP Violation in in The Two Higgs Doublet Model
We find a large CP violation effect within the Two-Higgs-Doublet-Model for
the reaction at future linear colliders. The
CP-asymmetry arises already at the tree level as a result of interference
between diagrams with emission from (and ) and its emission
from a and can be about 10--20\%. In the best case one needs a few
hundred events to observe CP violation at the 3 level.Comment: UU encoded tar compressed tex file with postscript figure
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 to and
, 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 GeV and
.Comment: 12 pages LaTex,PRL-TH-94/3
New results for a photon-photon collider
We present new results from studies in progress on physics at a two-photon
collider. We report on the sensitivity to top squark parameters of MSSM Higgs
boson production in two-photon collisions; Higgs boson decay to two photons;
radion production in models of warped extra dimensions; chargino pair
production; sensitivity to the trilinear Higgs boson coupling; charged Higgs
boson pair production; and we discuss the backgrounds produced by resolved
photon-photon interactions.Comment: 17 pages, 15 figure
Study of CP Property of the Higgs at a Photon Collider using
We study possible effects of CP violation in the Higgs sector on
production at a -collider. These studies are performed in a
model-independent way in terms of six form-factors which
parametrize the CP mixing in the Higgs sector, and a strategy for their
determination is developed. We observe that the angular distribution of the
decay lepton from produced in this process is independent of any CP
violation in the vertex and hence best suited for studying CP mixing in
the Higgs sector. Analytical expressions are obtained for the angular
distribution of leptons in the c.m. frame of the two colliding photons for a
general polarization state of the incoming photons. We construct combined
asymmetries in the initial state lepton (photon) polarization and the final
state lepton charge. They involve CP even ('s) and odd ('s) combinations
of the mixing parameters. We study limits up to which the values of and
, with only two of them allowed to vary at a time, can be probed by
measurements of these asymmetries, using circularly polarized photons. We use
the numerical values of the asymmetries predicted by various models to
discriminate among them. We show that this method can be sensitive to the
loop-induced CP violation in the Higgs sector in the MSSM.Comment: 15 pages, 9 figures added one referenc
Probing anomalous tbW couplings in single-top production using top polarization at the Large Hadron Collider
We study the sensitivity of the Large Hadron Collider (LHC) to anomalous tbW
couplings in single-top production in association with a W^- boson followed by
semileptonic decay of the top. We calculate top polarization and the effects of
these anomalous couplings to it at two centre-of-mass (cm) energies of 7 TeV
and 14 TeV. As a measure of top polarization, we look at various laboratory
frame distributions of its decay products, viz., lepton angular and energy
distributions and b-quark angular distributions, without requiring
reconstruction of the rest frame of the top, and study the effect of anomalous
couplings on these distributions. We construct certain asymmetries to study the
sensitivity of these distributions to anomalous tbW couplings. We find that
1\sigma limits on real and imaginary parts of the dominant anomalous coupling
Ref_{2R} which may be obtained by utilizing these asymmetries at the LHC with
cm energy of 14 TeV and an integrated luminosity of 10 fb^{-1} will be
significantly better than the expectations from direct measurements of cross
sections and some other variables at the LHC and over an order of magnitude
better than the indirect limits.Comment: 25 pages, 34 figure
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