1,805 research outputs found
Top-quark flavor-changing couplings and rare processes
We model-independently study the impacts of anomalous couplings
(), which lead to the decays, on low energy flavor physics.
It is found that the -coupling effect can significantly affect the rare
and decays, whereas the -coupling effect is small. Using the
ATLAS's branching ratio (BR) upper bound of ,
the influence of the anomalous -coupling on the rare decays can be found
as follows: (a) The contribution to the Kaon direct CP violation can be up to
; (b) and ; (c) the BR for
including the long-distance effect can be enhanced by with respect to
the standard model result, and (d) . In addition, although cannot be
synchronously enhanced with and in the same region of the CP-violating phase, the values of
, , and can be simultaneously increased.Comment: 19 pages, 3 figures, version to be published in the European Physical
Journal
Penguin and -meson anomalies in a gauged
The -gauge boson in an gauge symmetry has two
interesting features: one is its vector couplings to the charged leptons, and
the other is the decoupling from the electron. Based on these properties, we
investigate the feasibility to simultaneously resolve the and anomalies in an model, where the former is
expected to arise from the -penguin-induced process
and the latter from the tree-level decay. In order
to achieve the intended purpose, we employ one vector-like doublet lepton and
one singlet scalar leptoquark (LQ), in which the new particles all carry the
charges; the effective interaction is
generated from the vector-like lepton and LQ loop, and the decay is induced from the LQ. When the constraints from the , , , , and processes are included, it is found that
and can be enhanced to fit the experimental data, and the
Wilson coefficient from the LQ-loop can reach ,
which can explain the and anomalies. In addition, in this
simple model, the Higgs lepton-flavor violating decay can occur
at the tree level, and its branching ratio can be as large as the current
experimental upper limit.Comment: 21 pages, 6 figures, 1 table, version published in PL
Charged-Higgs on , polarization, and FBA
We study the influence of a charged-Higgs on the excess of branching fraction
ratio, , in a generic two-Higgs-doublet model. In order to
investigate the lepton polarization, the detailed decay amplitudes with lepton
helicity are given. When the charged-Higgs is used to resolve excesses, it is
found that two independent Yukawa couplings are needed to explain the and
anomalies. We show that when the upper limit of is included, can be significantly enhanced while
. With the constraint, we find
that the -lepton polarizations can be still affected by the charged-Higgs
effects, where the standard model (SM) predictions are obtained as: and , and they can be enhanced to be
and by the charged-Higgs.
The integrated lepton froward-backward asymmetry (FBA) is also studied, where
the SM result is , and they
can be enhanced (decreased) to be .Comment: 22 pages, 4 figures, version to be published in EPJ
2 TeV Higgs boson and diboson excess at the LHC
Diboson resonance with mass around 2 TeV in the dijet invariant mass spectrum
is reported by ATLAS experiment in proton-proton collisions at
TeV. We propose that the candidate of resonance is a heavy neutral Higgs
or charged Higgs and use the extended two-Higgs-doublet (THD) to
demonstrate the potentiality. We find that the large Yukawa coupling to the
first generation of quarks can be realized in THD and the required value for
producing the right resonance production cross section is of . Besides channels, we find that if the mass of
pseudoscalar satisfies the jet mass tagging condition GeV, the diboson excess could be also caused by or channel.Comment: 12 pages, 7 figures, title changed, Fig.2 corrected, comments and
references added, version to appear in PL
and in a diquark model
Based on the calculations using the lattice QCD by RBC-UKQCD collaboration
and a large dual QCD, the resulted , which is less
than the experimental data by more than a in the standard model (SM),
suggests the necessity of a new physics effect. In order to complement the
insufficient , we study the extension of the SM with a
colored scalar in a diquark model. In addition to the pure diquark box
diagrams, it is found that the box diagrams with one -boson and one diquark,
ignored in the literature, play an important role in the process.
The mass difference between and in the diquark model is well below
the current data, whereas the Kaon indirect CP violation gives a
strict constraint on the new parameters. Three mechanisms are classified in the
study of , and they include: tree-level diagram, QCD and
electroweak penguins, and chromomagnetic dipole. Taking the Kobayashi-Maskawa
phase as the unique CP source, we analyze each contribution of the three
mechanisms in detail and conclude that these diquark-mediated effects can
singly enhance to be of , depending on
the values of free parameters, when the bound from is satisfied.Comment: 44 pages, 10 figures, typos corrected, references added, and
charged-Goldstone-boson effects include
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