1,469 research outputs found
B_s ---> \gamma \gamma decay in the model III and 3HDM(O_2) with CP violating effects
We analyse the CP asymmetry for B_{s} -->\gamma\gamma in the two Higgs
doublet model with tree level flavor changing currents (model III) and three
Higgs doublet model with O_2 symmetry in the Higgs sector, including O_{7} type
long distance effects. Further, we study the dependencies of the branching
ratio Br(B_{s} --> \gamma\gamma)$ and the ratio of CP-even and CP-odd amplitude
squares, R=|A^{+}|^2/|A^{-}|^2, on the CP parameter sin \theta. We found that,
there is a weak CP asymmetry, at the order of 10^{-4}. Besides, the branching
ratio Br(B_{s} --> \gamma\gamma), and also R ratio, is not sensitive to the CP
parameter for |\frac{\bar{\xi}^{U}_{N,tt}}{\bar{\xi}^{D}_{N,bb}}|<1.Comment: 17 pages, 11 figure
QCD sum rules analysis of the rare B_c \rar X\nu\bar{\nu} decays
Taking into account the gluon correction contributions to the correlation
function, the form factors relevant to the rare B_c \rar X \nu\bar{\nu}
decays are calculated in the framework of the three point QCD sum rules, where
stands for axial vector particle, , and vector particles,
. The total decay width as well as the branching ratio of these
decays are evaluated using the dependent expressions of the form factors.
A comparison of our results with the predictions of the relativistic
constituent quark model is presented.Comment: 21 Pages, 2 Figures and 5 Table
Study of Bs-> \phi l^+ l^-$ Decay in a Single Universal Extra Dimension
Utilizing form factors calculated within the light-cone sum rules, we have
evaluated the decay branching ratios of and in a single universal extra dimension model (UED), which is
viewed as one of the alternative theories beyond the standard model (SM). For
the decay , the dilepton invariant mass spectra, the
forward-backward asymmetry, and double lepton polarization are also calculated.
For each case, we compared the obtained results with predictions of the SM. In
lower values of the compactification factor 1/R, the only parameter in this
model, we see the considerable discrepancy between the UED and SM models.
However, when 1/R increases, the results of UED tend to diminish and at , two models have approximately the same predictions.
Compared with data from CDF of , the 1/R tends to be
larger than . We also note that the zero crossing point of
the forward-backward asymmetry is become smaller, which will be an important
plat to prob the contribution from the extra dimension model. The results
obtained in this work will be very useful in searching new physics beyond SM.
Moreover, the order of magnitude for branching ratios shows a possibility to
study these channels at the Large Hadron Collider (LHC), CDF and the future
super-B factory.Comment: 13 pages, 16 figure
Floor plate and motor neuron induction by different concentrations of the amino-terminal cleavage product of sonic hedgehog autoproteolysis
AbstractThe differentiation of floor plate cells and motor neurons can be induced by Sonic hedgehog (SHH), a secreted signaling protein that undergoes autoproteolytic cleavage to generate amino- and carboxy-terminal products. We have found that both floor plate cells and motor neurons are induced by the aminoterminal cleavage product of SHH (SHH-N). The threshold concentration of SHH-N required for motor neuron induction is about 5-fold lower than that required for floor plate induction. Higher concentrations of SHH-N can induce floor plate cells at the expense of motor neuron differentiation. Our results suggest that the induction of floor plate cells and motor neurons by the notochord in vivo is mediated by exposure of neural plate cells to different concentrations of the amino-terminal product of SHH autoproteolytic cleavage
Statefinder diagnostic in a torsion cosmology
We apply the statefinder diagnostic to the torsion cosmology, in which an
accounting for the accelerated universe is considered in term of a
Riemann-Cartan geometry: dynamic scalar torsion. We find that there are some
typical characteristic of the evolution of statefinder parameters for the
torsion cosmology that can be distinguished from the other cosmological models.
Furthermore, we also show that statefinder diagnostic has a direct bearing on
the critical points. The statefinder diagnostic divides the torsion parameter
into differential ranges, which is in keeping with the requirement of
dynamical analysis. In addition, we fit the scalar torsion model to ESSENCE
supernovae data and give the best fit values of the model parameters.Comment: 18 pages, 15 figures, accepted paper in JCA
Lambda_b -> Lambda l+ l- decay within family non-universal Z' model
We perform a comprehensive analysis of the rare "Lambda_b -> Lambda l+ l-"
decay in the framework of family non-universal Z' model. It is shown that Z'
gives considerable contribution to the decay width. Zero positions of the
forward-backward asymmetry and alpha_theta parameter are shifted to the left
compared to the Standard Model result. The obtained results could be tested in
near future at LHC-b.Comment: 14 pages, 4 postscript figures, LaTeX formatte
The puzzle of 90 degree reorientation in the vortex lattice of borocarbide superconductors
We explain 90 degree reorientation in the vortex lattice of borocarbide
superconductors on the basis of a phenomenological extension of the nonlocal
London model that takes full account of the symmetry of the system. We propose
microscopic mechanisms that could generate the correction terms and point out
the important role of the superconducting gap anisotropy.Comment: 4 pages, 2 eps figure
Controlled dephasing of Andreev states in superconducting quantum point-contacts
We have studied the relaxation and dephasing processes in a superconducting
quantum point contact induced by the interaction with an electromagnetic
environment. Based on a density matrix approach we obtain the rates for the
dissipative dynamics as function of the transmission, the phase difference on
the contact and the external impedance. Our calculation allows to determine the
appropriate range of parameters for the observation of coherent oscillations in
the current through the contact.Comment: 8 pages, 2 figures. To appear in Physical Review
Is the `Finite Bias Anomaly' in planar GaAs-Superconductor junctons caused by point-contact like structures?
We correlate transmission electron microscope (TEM) pictures of
superconducting In contacts to an AlGaAs/GaAs heterojunction with differential
conductance spectroscopy performed on the same heterojunction. Metals deposited
onto a (100) AlGaAs/GaAs heterostructure do not form planar contacts but,
during thermal annealing, grow down into the heterostructure along
crystallographic planes in pyramid-like `point contacts'. Random surface
nucleation and growth gives rise to a different interface transmission for each
superconducting point contact. Samples annealed for different times, and
therefore having different contact geometry, show variations in
characteristic of ballistic transport of Cooper pairs, wave interference
between different point emitters, and different types of weak localization
corrections to Giaever tunneling. We give a possible mechanism whereby the
`finite bias anomaly' of Poirier et al. (Phys. Rev. Lett., {\bf 79}, 2105
(1997)), also observed in these samples, can arise by adding the conductance of
independent superconducting point emitters in parallel
Connecting Berry's phase and the pumped charge in a Cooper pair pump
The properties of the tunnelling-charging Hamiltonian of a Cooper pair pump
are well understood in the regime of weak and intermediate Josephson coupling,
i.e. when . It is also known that
Berry's phase is related to the pumped charge induced by the adiabatical
variation of the eigenstates. We show explicitly that pumped charge in Cooper
pair pump can be understood as a partial derivative of Berry's phase with
respect to the phase difference across the array. The phase fluctuations
always present in real experiments can also be taken into account, although
only approximately. Thus the measurement of the pumped current gives reliable,
yet indirect, information on Berry's phase. As closing remarks, we give the
differential relation between Berry's phase and the pumped charge, and state
that the mathematical results are valid for any observable expressible as a
partial derivative of the Hamiltonian.Comment: 5 pages, 5 figures, RevTeX, Presentation has been clarifie
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