99 research outputs found
Radiative and Semileptonic B Decays Involving the Tensor Meson K_2^*(1430) in the Standard Model and Beyond
We study semileptonic and radiative B decays involving the strange tensor
meson K_2^*(1430) in the final state. Using the large energy effective theory
(LEET) techniques, we formulate the B \to K_2^* transition form factors in
large recoil region. All the form factors can be parametrized in terms of two
independent LEET parameters \zeta_\perp and \zeta_\parallel. The magnitude of
\zeta_\perp is estimated from the data for Br(B \to K_2^*(1430)\gamma).
Assuming a dipole q^2-dependence for the LEET parameters and
\zeta_\parallel/\zeta_\perp = 1.0 \pm 0.2, we investigate the decays B \to
K_2^* \ell^+ \ell^- and B \to K_2^* \nu \bar{\nu}, where the contributions due
to $\zeta_\parallel are suppressed by m_{K_2^*}/m_B. For the B \to K_2^* \ell^+
\ell^- decay, in the large recoil region where the hadronic uncertainties are
considerably reduced, the longitudinal distribution d F_L/ds is reduced by
20-30 % due to the flipped sign of c_7^eff compared with the standard model
result. Moreover, the forward-backward asymmetry zero is about 3.4 GeV^2 in the
standard model, but changing the sign of c_7^eff yields a positive asymmetry
for all values of the invariant mass of the lepton pair. We calculate the
branching fraction for B \to K_2^* \nu \bar{\nu} in the standard model. Our
result exhibits the impressed resemblance between B \to K_2^*(1430)
\ell^+\ell^-, \nu \bar{\nu} and B \to K^*(892) \ell^+ \ell^-, \nu\bar{\nu}.Comment: 21 pages, 4 figures (v2) comments adde
A model of CP Violation from Extra Dimension
We construct a realistic model of CP violation in which CP is broken in the
process of dimensional reduction and orbifold compactification from a five
dimensional theories with gauge symmetry. CP
violation is a result of the Hosotani type gauge configuration in the higher
dimension.Comment: 5 page
Radiative and Semileptonic B Decays Involving Higher K-Resonances in the Final States
We study the radiative and semileptonic B decays involving a spin-
resonant with parity for and for
in the final state. Using the large energy effective theory (LEET)
techniques, we formulate transition form factors in the large
recoil region in terms of two independent LEET functions
and , the values of
which at zero momentum transfer are estimated in the BSW model. According to
the QCD counting rules, exhibit a dipole
dependence in . We predict the decay rates for ,
and . The
branching fractions for these decays with higher -resonances in the final
state are suppressed due to the smaller phase spaces and the smaller values of
. Furthermore, if the spin of
becomes larger, the branching fractions will be further suppressed due to the
smaller Clebsch-Gordan coefficients defined by the polarization tensors of the
. We also calculate the forward backward asymmetry of the decay, for which the zero is highly insensitive to the
-resonances in the LEET parametrization.Comment: 27 pages, 4 figures, 7 tables;contents and figures corrected, title
and references revise
Foxc Transcription Factors Directly Regulate Dll4 and Hey2 Expression by Interacting with the VEGF-Notch Signaling Pathways in Endothelial Cells
Recent studies have shown that in the developing embryo, arterial and venous identity is established by genetic mechanisms before circulation begins. Vascular endothelial growth factor (VEGF) signaling and its downstream Notch pathway play critical roles in arterial cell fate determination. We have recently shown that Foxc1 and Foxc2, two closely related Fox transcription factors, are essential for arterial cell specification during development by directly inducing the transcription of Delta-like 4 (Dll4), a ligand for Notch receptors. However, the basic mechanisms whereby the VEGF and Notch signaling pathways control transcriptional regulation of arterial-specific genes have yet to be elucidated.In the current study, we examined whether and how Foxc transcription factors are involved in VEGF and Notch signaling in induction of Dll4 as well as the Notch target gene Hey2 in endothelial cells. We found that Foxc1 and Foxc2 directly activate the Hey2 promoter via Foxc binding elements. Significantly, Foxc2 physically and functionally interacts with a Notch transcriptional activation complex containing Su(H) and Notch intracellular domain to induce Hey2 promoter activity. Moreover, activation of the Dll4 and Hey2 promoters is induced by VEGF in conjunction with either Foxc1 or Foxc2 more than by either component alone. VEGF-activated PI3K and ERK intracellular pathways modulate the transcriptional activity of Foxc proteins in Dll4 and Hey2 induction.Our new findings demonstrate that Foxc transcriptional factors interact with VEGF and Notch signaling to regulate arterial gene expression in multiple steps of the VEGF-Dll4-Notch-Hey2 signaling pathway
Vacuum Structure of Twisted Scalar Field Theories on M^{D-1} \otimes S^1
We study scalar field theories on M^{D-1} \otimes S^1, which allow to impose
twisted boundary conditions for the S^1 direction, in detail and report several
interesting properties overlooked so far. One of characteristic features is the
appearance of critical radii of the circle S^1. A phase transition can occur at
the classical level or can be caused by quantum effects. Radiative corrections
can restore broken symmetries or can break symmetries for small radius. A
surprising feature is that the translational invariance for the S^1 direction
can spontaneously be broken. A particular class of coordinate-dependent vacuum
configurations is clarified and the O(N) \phi^4 model on M^{D-1}\otimes S^1 is
extensively studied, as an illustrative example.Comment: 27 pages, 4 figures, LaTex2
Nonlinear optical phase shift obtained from two-level atoms confined in a planar microcavity
We investigate the nonlinear optical phase shift obtained from a thin atomic layer confined in a distributed Bragg reflector (DBR) microcavity with reflection geometry. The optical response of the atom-cavity system is numerically analyzed using finite-difference time-domain method with the optical Bloch equations. The optimal position of atomic layer, at which a maximal phase shift of π is realized, drastically changes with the quality factor Q of the cavity. We show that for high Q the maximal phase shift of π can be obtained anywhere in the cavity field independently of atomic layer position. This result is in contrast to that obtained from a one-dimensional atom model in the limit of bad cavity, where a maximal phase shift of π is obtained only at the antinode of the cavity field. We also show that the independence of phase shift on atom position realized in high-Q regime is due to an interference effect in the surface layers of the DBR cavity
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