749 research outputs found
Up Sector of Minimal Flavor Violation: Top Quark Properties and Direct D meson CP violation
Minimal Flavor Violation in the up-type quark sector leads to particularly
interesting phenomenology due to the interplay of flavor physics in the charm
sector and collider physics from flavor changing processes in the top sector.
We study the most general operators that can affect top quark properties and
meson decays in this scenario, concentrating on two CP violating operators
for detailed studies. The consequences of these effective operators on charm
and top flavor changing processes are generically small, but can be enhanced if
there exists a light flavor mediator that is a Standard Model gauge singlet
scalar and transforms under the flavor symmetry group. This flavor mediator can
satisfy the current experimental bounds with a mass as low as tens of GeV and
explain observed -meson direct CP violation. Additionally, the model
predicts a non-trivial branching fraction for a top quark decay that would
mimic a dijet resonance.Comment: 27 pages, 7 figure
CP Violation Studies at Tevatron
We present an overview of a few recent results related to CP-violation from
the Tevatron. First, we discuss a measurement of the dimuon charge asymmetry
from D{\O}that extracts the CP-violation parameter of \Bo mixing and decay.
This is followed by the CDF measurement of the CP-violating asymmetry in
\bdkpi decays. Finally we give the CDF result on the ratio Comment: 4 pages. Talk given at BEACH 2006, Lancaster, Englan
Leptoquarks and Neutrino Masses at the LHC
The properties of light leptoquarks predicted in the context of a simple
grand unified theory and their observability at the LHC are investigated. The
SU(5) symmetry of the theory implies that the leptoquark couplings to matter
are related to the neutrino mass matrix. We study the resulting connection
between neutrino masses and mixing parameters and the leptoquark decays, and
show that different light neutrino hierarchies imply distinctive leptoquark
decay signatures. We also discuss low-energy constraints implied by searches
for charged lepton flavour violation, studies of meson decays, and electroweak
precision data. We perform a detailed parton-level study of the leptoquark
signals and the Standard Model backgrounds at the LHC. With the clean final
states containing a di-lepton plus two jets, the QCD production of the
leptoquark pair can be observed for a leptoquark mass of one TeV and beyond. By
examining the lepton flavor structure of the observed events, one could further
test the model predictions related to the neutrino mass spectrum. In
particular, b-flavor tagging will be useful in distinguishing the neutrino mass
pattern and possibly probing an unknown Majorana phase in the Inverted
Hierarchy or the Quasi-Degenerate scenario. Electroweak associated production
of the leptoquark doublet can also be useful in identifying the quantum numbers
of the leptoquarks and distinguishing between the neutrino mass spectra, even
though the corresponding event rates are smaller than for QCD production. We
find that with only the clean channel of mu+ E_T jets, one could expect an
observable signal for a leptoquark masses of about 600 GeV or higher.Comment: 46 pages, 52 figure
and colliding in noncommutative space
By studying the scattering process of scalar particle pion on the
noncommutative scalar quantum electrodynamics, the non-commutative amendment of
differential scattering cross-section is found, which is dependent of
polar-angle and the results are significantly different from that in the
commutative scalar quantum electrodynamics, particularly when . The non-commutativity of space is expected to be explored at around
TeV.Comment: Latex, 12 page
Constraints on charged Higgs bosons from D(s)+- -> mu+- nu and D(s)+- -> tau+- nu
The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been
used to measure the D(s)+- meson decay constant f_D(s). Recent measurements at
CLEO-c and the B factories suggest a branching ratio for both decays somewhat
higher than the Standard Model prediction using f_D(s) from unquenched lattice
calculations. The charged Higgs boson (H+-) in the Two Higgs Doublet Model
(Type II) would also mediate these decays, but any sizeable contribution from
H+- can only suppress the branching ratios and consequently is now slightly
disfavoured. It is shown that constraints on the parameters tan(beta) and m_H+-
from such decays can be competitive with and complementary to analogous
constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+-
-> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) <
250 MeV.Comment: 18 pages, 4 figure
Radiative and Leptonic B-meson Decays from the B-factories
Radiative and leptonic decays of B-mesons represent an excellent laboratory
for the search for New Physics. I present here recent results on radiative and
leptonic decays from the Belle and BABAR collaborations.Comment: 7 pages, 5 figures. To be published in the proceedings of the "Second
Workshop on Theory, Phenomenology and Experiments in Heavy Flavour Physics,
Capri, Italy, June 16-18,2008
Flavorful signatures at LHC and ILC
There are lots of new physics models which predict an extra neutral gauge
boson, referred as Z'-boson. In a certain class of these new physics models,
the Z'-boson has flavor-dependent couplings with the fermions in the Standard
Model (SM). Based on a simple model in which couplings of the SM fermions in
the third generation with the Z'-boson are different from those of the
corresponding fermions in the first two generations, we study the signatures of
Z'-boson at the Large Hadron Collider (LHC) and the International Linear
Collider (ILC). We show that at the LHC, the Z'-boson with mass around 1 TeV
can be produced through the Drell-Yan processes and its dilepton decay modes
provide us clean signatures not only for the resonant production of Z'-boson
but also for flavor-dependences of the production cross sections. We also study
fermion pair productions at the ILC involving the virtual Z'-boson exchange.
Even though the center-of-energy of the ILC is much lower than a Z'-boson mass,
the angular distributions and the forward-backward asymmetries of fermion pair
productions show not only sizable deviations from the SM predictions but also
significant flavor-dependences.Comment: 11 pages, 5 figures, some typos corrected, the version to appear in
PL
Loop Induced Flavor Changing Neutral Decays of the Top Quark in a General Two-Higgs-Doublet Model
Decays of the top quark induced by flavor changing neutral currents (FCNC)
are known to be extremely rare events within the Standard Model. This is so not
only for the decay modes into gauge bosons, but most notably in the case of the
Higgs channels, e.g. t-> H_{SM}+c, with a branching fraction of 10^{-13} at
most. Therefore, detection of FCNC top quark decays in a future high-energy,
and high-luminosity, machine like the LHC or the LC would be an indisputable
signal of new physics. In this paper we show that within the simplest extension
of the SM, namely the general two-Higgs-doublet model, the FCNC top quark
decays into Higgs bosons, t->(h^{0},H^{0},A^{0})+c, can be the most favored
FCNC modes -- comparable or even more efficient than the gluon channel t-> g+c.
In both cases the optimal results are obtained for Type II models. However,
only the Higgs channels can have rates reaching the detectable level (10^{-5}),
with a maximum of order 10^{-4} which is compatible with the charged Higgs
bounds from radiative B-meson decays. We compare with the previous results
obtained in the Higgs sector of the MSSM.Comment: 18 pages, LaTeX, 5 figures, 1 table. References adde
One Loop Beta Functions in Topologically Massive Gravity
We calculate the running of the three coupling constants in cosmological,
topologically massive 3d gravity. We find that \nu, the dimensionless
coefficient of the Chern-Simons term, has vanishing beta function. The flow of
the cosmological constant and Newton's constant depends on \nu, and for any
positive \nu there exist both a trivial and a nontrivial fixed point.Comment: 44 pages, 16 figure
Deformed Two-Mode Quadrature Operators in Noncommutative Space
Starting from noncommutative quantum mechanics algebra, we investigate the
variances of the deformed two-mode quadrature operators under the evolution of
three types of two-mode squeezed states in noncommutative space. A novel
conclusion can be found and it may associate the checking of the variances in
noncommutative space with homodyne detecting technology. Moreover, we analyze
the influence of the scaling parameter on the degree of squeezing for the
deformed level and the corresponding consequences.Comment: 11 pages, no figure
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