10,112 research outputs found
Study of Decays in the Family Non-universal Models
In a combined investigation of the decays,
constraints on the related couplings in family non-universal
models are derived. We find that within the allowed parameter space, the
recently observed forward-backward asymmetry in the
decay can be explained, by flipping the signs of the Wilson coefficients
and . With the obtained constraints, we also calculate
the branching ratio of the decay. The upper bound of our
prediction is near the upper bound given by CDF Collaboration recently.Comment: 19 pages, 4 figures, some errors corrected; Journal versio
Nonperturbative Determination of Heavy Meson Bound States
In this paper we obtain a heavy meson bound state equation from the heavy
quark equation of motion in heavy quark effective theory (HQET) and the heavy
meson effective field theory we developed very recently. The bound state
equation is a covariant extention of the light-front bound state equation for
heavy mesons derived from light-front QCD and HQET. We determine the covariant
heavy meson wave function variationally by minimizing the binding energy
. Subsequently the other basic HQET parameters and
, and the heavy quark masses and can also be
consistently determined.Comment: 15 pages, 1 figur
Pair production of the T-odd leptons at the LHC
The T-odd leptons predicted by the littlest model with T-parity can
be pair produced via the subprocesses ,
, and (= or
) at the Large Hadron Collider . We estimate the hadronic
production cross sections for all of these processes and give a simply
phenomenology analysis. We find that the cross sections for most of the above
processes are very small. However, the value of the cross section for the
process can reach .Comment: 12 pages, 2 figure
Magnetic Pinning of Vortices in a Superconducting Film: The (anti)vortex-magnetic dipole interaction energy in the London approximation
The interaction between a superconducting vortex or antivortex in a
superconducting film and a magnetic dipole with in- or out-of-plane
magnetization is investigated within the London approximation. The dependence
of the interaction energy on the dipole-vortex distance and the film thickness
is studied and analytical results are obtained in limiting cases. We show how
the short range interaction with the magnetic dipole makes the co-existence of
vortices and antivortices possible. Different configurations with vortices and
antivortices are investigated.Comment: 12 pages, 12 figures. Submitted to Phys. Rev.
Evidence for Factorization in Three-body B --> D(*) K- K0 Decays
Motivated by recent experimental results, we use a factorization approach to
study the three-body B --> D(*) K- K0 decay modes. Two mechanisms are proposed
for kaon pair production: current-produced (from vacuum) and transition (from B
meson). The Bbar0 --> D(*)+ K- K0 decay is governed solely by the
current-produced mechanism. As the kaon pair can be produced only by the vector
current, the matrix element can be extracted from e+ e- --> K Kbar processes
via isospin relations. The decay rates obtained this way are in good agreement
with experiment. Both current-produced and transition processes contribute to
B- --> D(*)0 K- K0 decays. By using QCD counting rules and the measured B- -->
D(*)0 K- K0 decay rates, the measured decay spectra can be understood.Comment: 17 pages, 6 figure
Bounds on Heavy-to-Heavy Mesonic Form Factors
We provide upper and lower bounds on the form factors for B -> D, D^* by
utilizing inclusive heavy quark effective theory sum rules. These bounds are
calculated to leading order in Lambda_QCD/m_Q and alpha_s. The O(alpha_s^2
beta_0) corrections to the bounds at zero recoil are also presented. We compare
our bounds with some of the form factor models used in the literature. All the
models we investigated failed to fall within the bounds for the combination of
form factors (omega^2 - 1)/(4 omega)|omega h_{A2}+h_{A3}|^2.Comment: 27 pages, 10 figure
Quantifying and identifying the overlapping community structure in networks
It has been shown that the communities of complex networks often overlap with
each other. However, there is no effective method to quantify the overlapping
community structure. In this paper, we propose a metric to address this
problem. Instead of assuming that one node can only belong to one community,
our metric assumes that a maximal clique only belongs to one community. In this
way, the overlaps between communities are allowed. To identify the overlapping
community structure, we construct a maximal clique network from the original
network, and prove that the optimization of our metric on the original network
is equivalent to the optimization of Newman's modularity on the maximal clique
network. Thus the overlapping community structure can be identified through
partitioning the maximal clique network using any modularity optimization
method. The effectiveness of our metric is demonstrated by extensive tests on
both the artificial networks and the real world networks with known community
structure. The application to the word association network also reproduces
excellent results.Comment: 9 pages, 7 figure
Polarization Dependence of Born Effective Charge and Dielectric Constant in KNbO
The Born effective charge Z^{*} and dielectric tensor \epsilon_{\infty} of
KNbO_3 are found to be very sensitive to the atomic geometry, changing by as
much as 27% between the paraelectric cubic and ferroelectric tetragonal and
rhombohedral phases. Subtracting the bare ionic contribution reveals changes of
the dynamic component of Z^{*} as large as 50%, for atomic displacements that
are typically only a few percent of the lattice constant. Z^{*},
\epsilon_{\infty} and all phonon frequencies at the Brillouin zone center were
calculated using the {\it ab initio} linearized augmented plane-wave linear
response method with respect to the reference cubic, experimental tetragonal,
and theoretically determined rhombohedral ground state structures. The ground
state rhombohedral structure of KNbO_3 was determined by minimizing the forces
on the relaxed atoms. By contrast with the cubic structure, all zone center
phonon modes of the rhombohedral structure are stable and their frequencies are
in good agreement with experiment. In the tetragonal phase, one of the soft
zone center modes in the cubic phase is stablized. In view of the small atomic
displacements involved in the ferroelectric transitions, it is evident that not
only the soft mode frequencies but also the Born effective charge and
dielectric constants are very sensitive to the atomic geometry.Comment: 26 pages, revtex, no figures; to appear in Phys. Rev. B15 (Oct.),
199
New Physics in Bs -> J/psi phi: a General Analysis
Recently, the CDF and D0 collaborations measured indirect CP violation in Bs
-> J/psi phi and found a hint of a signal. If taken at face value, this can be
interpreted as a nonzero phase of Bs-Bsbar mixing (beta_s), in disagreement
with the standard model, which predicts that beta_s ~= 0. In this paper, we
argue that this analysis may be incomplete. In particular, there can be new
physics (NP) in the bbar -> sbar c cbar decay. If so, the value of beta_s is
different than for the case in which NP is assumed to be present only in the
mixing. We have examined several models of NP and found that, indeed, there can
be significant contributions to the decay. These effects are consistent with
measurements in B -> J/psi K* and Bd -> J/psi Ks. Due to the NP in the decay,
polarization-dependent indirect CP asymmetries and triple-product asymmetries
are predicted in Bs -> J/psi phi.Comment: 28 pages, JHEP, no figures. Considerable changes made. Abstract and
main text of paper modified to alter presentation. Appendix added. References
added. Conclusions unchanged
Lensless Fourier-Transform Ghost Imaging with Classical Incoherent Light
The Fourier-Transform ghost imaging of both amplitude-only and pure-phase
objects was experimentally observed with classical incoherent light at Fresnel
distance by a new lensless scheme. The experimental results are in good
agreement with the standard Fourier-transform of the corresponding objects.
This scheme provides a new route towards aberration-free diffraction-limited 3D
images with classically incoherent thermal light, which have no resolution and
depth-of-field limitations of lens-based tomographic systems.Comment: 14 pages, 4 figures, comments are welcom
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