71,535 research outputs found
"Hard-scattering" approach to very hindered magnetic-dipole transitions in quarkonium
For a class of hindered magnetic dipole () transition processes, such as
(the discovery channel of the meson),
the emitted photon is rather energetic so that the traditional approaches based
on multipole expansion may be invalidated. We propose that a "hard-scattering"
picture, somewhat analogous to the pion electromagnetic form factor at large
momentum transfer, may be more plausible to describe such types of transition
processes. We work out a simple factorization formula at lowest order in the
strong coupling constant, which involves convolution of the Schr\"odinger wave
functions of quarkonia with a perturbatively calculable part induced by
exchange of one semihard gluon between quark and antiquark. This formula,
without any freely adjustable parameters, is found to agree with the measured
rate of rather well, and can also reasonably
account for other recently measured hindered transition rates. The
branching fractions of are also
predicted.Comment: v3; 5 pages, 1 figure and 1 table; title changed, presentation
improve
Euclidean Dynamical Symmetry in Nuclear Shape Phase Transitions
The Euclidean dynamical symmetry hidden in the critical region of nuclear
shape phase transitions is revealed by a novel algebraic F(5) description. With
a nonlinear projection, it is shown that the dynamics in the critical region of
the spherical--axial deformed and the spherical-- soft shape phase
transitions can indeed be manifested by this description, which thus provides a
unified symmetry--based interpretation of the critical phenomena in the region.Comment: 5 pages, 2 figures, 2 table
Structural and electronic properties of ScnOm (n=1~3, m=1~2n) clusters: Theoretical study using screened hybrid density functional theory
The structural and electronic properties of small scandium oxide clusters
ScnOm (n = 1 - 3, m = 1 - 2n) are systematically studied within the screened
hybrid density functional theory. It is found that the ground states of these
scandium oxide clusters can be obtained by the sequential oxidation of small
"core" scandium clusters. The fragmentation analysis demonstrates that the ScO,
Sc2O2, Sc2O3, Sc3O3, and Sc3O4 clusters are especially stable. Strong
hybridizations between O-2p and Sc-3d orbitals are found to be the most
significant character around the Fermi level. In comparison with standard
density functional theory calculations, we find that the screened hybrid
density functional theory can correct the wrong symmetries and yield more
precise description for the localized 3d electronic states of scandium.Comment: 8 figure
Multiple Lifshitz transitions driven by short-range antiferromagnetic correlations in the two-dimensional Kondo lattice model
With a mean field approach, the heavy Fermi liquid in the two-dimensional
Kondo lattice model is carefully considered in the presence of short-range
antiferromagnetic correlations. As the ratio of the local Heisenberg
superexchange coupling to the Kondo coupling increases, the Fermi surface
structure changes dramatically. From the analysis of the ground state energy
density, multiple Lifshitz type phase transitions occur at zero temperature.Comment: 4 pages, 3 figures, contribution to SCES201
Magnetic rotations in 198Pb and 199Pb within covariant density functional theory
Well-known examples of shears bands in the nuclei 198Pb and 199Pb are
investigated within tilted axis cranking relativistic mean-field theory. Energy
spectra, the relation between spin and rotational frequency, deformation
parameters and reduced and transition probabilities are calculated.
The results are in good agreement with available data and with calculations
based on the phenomenological pairing plus-quadrupole-quadrupole tilted-axis
cranking model. It is shown that covariant density functional theory provides a
successful microscopic and fully self-consistent description of magnetic
rotation in the Pb region showing the characteristic properties as the shears
mechanism and relatively large B(M1) transitions decreasing with increasing
spin.Comment: 22 pages, 8 figure
Capital account liberalization in China: a cautionary tale
This repository item contains a policy brief from the Boston University Global Economic Governance Initiative. The Global Economic Governance Initiative (GEGI) is a research program of the Center for Finance, Law & Policy, the Frederick S. Pardee Center for the Study of the Longer-Range Future, and the Frederick S. Pardee School of Global Studies. It was founded in 2008 to advance policy-relevant knowledge about governance for financial stability, human development, and the environment.This policy brief synthesizes some of the main themes and policy recommendations discussed at a February 2014 workshop of the Pardee Task Force for Regulating Capital Flows at Boston University, and presented in this report, though the specific recommendations discussed in this brief are our own. The main message is that China would do well to draw lessons from both the economics literature and country experiences with capital account liberalization. Such an approach
would guide China to adopt a carefully sequenced and cautionary approach to capital account liberalization
Quantum transport in a curved one-dimensional quantum wire with spin-orbit interactions
The one-dimensional effective Hamiltonian for a planar curvilinear quantum
wire with arbitrary shape is proposed in the presence of the Rashba spin-orbit
interaction. Single electron propagation through a device of two straight lines
conjugated with an arc has been investigated and the analytic expressions of
the reflection and transmission probabilities have been derived. The effects of
the device geometry and the spin-orbit coupling strength on the
reflection and transmission probabilities and the conductance are investigated
in the case of spin polarized electron incidence. We find that no spin-flip
exists in the reflection of the first junction. The reflection probabilities
are mainly influenced by the arc angle and the radius, while the transmission
probabilities are affected by both spin-orbit coupling and the device geometry.
The probabilities and the conductance take the general behavior of oscillation
versus the device geometry parameters and . Especially the electron
transportation varies periodically versus the arc angle . We also
investigate the relationship between the conductance and the electron energy,
and find that electron resonant transmission occurs for certain energy.
Finally, the electron transmission for the incoming electron with arbitrary
state is considered. For the outgoing electron, the polarization ratio is
obtained and the effects of the incoming electron state are discussed. We find
that the outgoing electron state can be spin polarization and reveal the
polarized conditions.Comment: 7 pages, 8 figure
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