5,846 research outputs found
Determining at Electron-Positron Colliders
Verifying is critical to test the three generation
assumption of the Standard Model. So far our best knowledge of is
inferred either from the unitarity of CKM matrix or from single
top-quark productions upon the assumption of universal weak couplings. The
unitarity could be relaxed in new physics models with extra heavy quarks and
the universality of weak couplings could also be broken if the coupling
is modified in new physics models. In this work we propose to measure
in the process of without prior knowledge of the number
of fermion generations or the strength of the coupling. Using an
effective Lagrangian approach, we perform a model-independent analysis of the
interactions among electroweak gauge bosons and the third generation quarks,
i.e. the , and couplings. The electroweak symmetry
of the Standard Model specifies a pattern of deviations of the --
and -- couplings after one imposes the known experimental
constraint on the -- coupling. We demonstrate that, making use of
the predicted pattern and the accurate measurements of top-quark mass and width
from the energy threshold scan experiments, one can determine from the
cross section and the forward-backward asymmetry of top-quark pair production
at an {\it unpolarized} electron-positron collider.Comment: publish versio
Uniqueness theorems for meromorphic mappings sharing hyperplanes in general position
The purpose of this article is to study the uniqueness problem for
meromorphic mappings from into the complex projective space
By making using of the method of dealing with
multiple values due to L. Yang and the technique of Dethloff-Quang-Tan
respectively, we obtain two general uniqueness theorems which improve and
extend some known results of meromorphic mappings sharing hyperplanes in
general position.Comment: 10 page
Simple non-Abelian extensions of the standard model gauge group and the diboson excesses at the LHC
The ATLAS collaboration reported excesses at around 2 TeV in the di-boson
production decaying into hadronic final states. We consider the possibility of
explaining the excesses with extra gauge bosons in two simple non-Abelian
extensions of the Standard Model. One is the so-called models with a
symmetry structure of and the other is
the models with an extended symmetry of . The and bosons emerge after the electroweak symmetry is
spontaneously broken. Two patterns of symmetry breaking in the models
are considered in this work: one is , the other is . The symmetry breaking of the model is
. We perform a global
analysis of and phenomenology in ten new physics models,
including all the channels of decay. Our study shows that
the leptonic mode and the dijet mode of decays impose a
very stringent bound on the parameter space in several new physics models. Such
tight bounds provide a useful guide for building new physics models to address
on the diboson anomalies. We also note that the Left-Right and Lepton-Phobic
models can explain the excess if the deviation in
the pair around 2~TeV were confirmed to be a fluctuation of the SM
backgrounds.Comment: Publish version; title changed as suggested by journal Edito
A General Analysis of Wtb anomalous Couplings
We investigate new physics effects on the Wtb effective couplings in a
model-independent manner. The new physics effects are summarized as four
independent couplings , , and . Using
single-top-quark productions and W-helicity fraction measurements at the LHC
and Tevatron, we perform a global fit to impose constraints on top quark
effective couplings. We introduce a set of parameters , , and
to study the correlations among Wtb effective couplings. We show that (i)
improving the measurements of and is important in
constraining the correlation of and ; (ii)
and are anti-correlated, which is sensitive to all the
experiments; (iii) and are also anti-correlated, which is
sensitive to the W-helicity measurements; (iv) the correlation between
and is sensitive to the precision of , and
measurements. The effective Wtb couplings are studied in three kinds of
new physics models: models, vector-like
quark models and Littlest Higgs model with and without T-parity. The Wtb
couplings in the left-right model and the un-unified model are sensitive to the
ratio of gauge couplings when the new heavy gauge boson's mass () is
less than several hundred GeV, but the constraint is loose if TeV.
The Wtb couplings in vector-like quark models and the Littlest Higgs models are
sensitive to the mixing angles of new heavy particles and SM particles. We also
include the constraints of the oblique T-parameter and Zbb couplings which
impose much tighter constraints on the mixing angles. We show that the Wtb
coupling constraints become relevant if the precision of single top production
cross section measurements could be reduced to 1\% relative to the SM
predictions in future.Comment: Chin. Phys. C in pres
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