61 research outputs found
Can Up FCNC solve the puzzle?
We investigate the attempt using flavor violation gauge interaction in the up
sector to explain the LHCb recently observed large
(). We study an
Abelian model that only right-handed up quarks is charged under it and the 1-3
coupling is maximized. The simultaneous 1-3 2-3 mixing is realized by a quark
mixing of 1-2 generation. Given the easy identification of top quark, the model
can be directly tested by and processes at the hadron
colliders as associated top production or same-sign top
scattering . The direct search bounds are still consistent with the
assumption that and couplings are equal but the same-sign top
scattering bound is expected to be reached very soon. However, since there is
no CKM-like suppression, the corresponding parameter space for generating
is completely excluded by the mixing. We
conclude that the up FCNC type models cannot explain the while
to be consistent with the mixing constraint at the same
time. On the other hand, a model as SM with fourth family extension has better
chance to explain the large consistently.Comment: 10 pages, 2 figure
WIMPless dark matter and the excess gamma rays from the Galactic center
In this paper we discuss the excess gamma rays from the Galactic center, the
WMAP haze and the CoGeNT and DAMA results in WIMPless models. At the same time
we also investigate the low energy constraints from the anomalous magnetic
moment of leptons and from some lepton flavor violating decays. It is found
that, for scalar or vector WIMPless dark matter, neither the WMAP haze nor the
CoGeNT and DAMA observations could be explained simultaneously with the excess
gamma rays from the Galactic center. As to fermion WIMPless dark matter, it is
only marginally possible to accommodate the CoGeNT and DAMA results with the
excess gamma rays from the Galactic center with vector connector fields. On the
other hand, only scalar connector fields could interpret the WMAP haze
concerning the constraints of anomalous magnetic moment of leptons.
Furthermore, if there is only one connector field for all the charged leptons,
some lepton flavor violating decays could happen with too large branching
ratios severely violating the experimental bounds.Comment: 15 pages, 3 figures, accepted for publication in Phys. Rev.
A Revisit to Top Quark Forward-Backward Asymmetry
We analyze various models for the top quark forward-backward asymmetry
() at the Tevatron, using the latest CDF measurements on different
s and the total cross section. The axigluon model in Ref. \cite{paul}
has difficulties in explaining the large rapidity dependent asymmetry and mass
dependent asymmetry simultaneously and the parameter space relevant to
is ruled out by the latest dijet search at ATLAS. In contrast to
Ref. \cite{cp}, we demonstrate that the large parameter space in this model
with a flavor symemtry is not ruled out by flavor physics. The
-channel flavor-violating \cite{hitoshi},
\cite{waiyee} and diquark \cite{tim} models all have parameter
regions that satisfy different measurements within 1 .
However, the heavy model which can be marginally consistent with
the total cross section is severely constrained by the Tevatron direct search
of same-sign top quark pair. The diquark model suffers from too large total
cross section and is difficult to fit the invariant mass
distribution. The electroweak precision constraints on the model based on
- mixings is estimated and the result is rather weak (
GeV). Therefore, the heavy model seems to give the best fit for
all the measurements. The model predicts the signal
from production and is 10%-50% of SM at the 7 TeV LHC.
Such resonance can serve as the direct test of the model.Comment: 25 pages, 7 figures, 1 tabl
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