30,109 research outputs found
Anatomy of molecular structures in Ne
We present a beyond mean-field study of clusters and molecular structures in
low-spin states of Ne with a multireference relativistic energy density
functional, where the dynamical correlation effects of symmetry restoration and
quadrupole-octupole shapes fluctuation are taken into account with projections
on parity, particle number and angular momentum in the framework of the
generator coordinate method. Both the energy spectrum and the electric
multipole transition strengths for low-lying parity-doublet bands are better
reproduced after taking into account the dynamical octupole vibration effect.
Consistent with the finding in previous studies, a rotation-induced dissolution
of the O molecular structure in Ne is predicted.Comment: 6 pages with 6 figures, version to be published in Phys. Lett.
Exact O(g^2 alpha_s) top decay width from general massive two-loop integrals
We calculate the b-dependent self-energy of the top quark at O(g^2 \alpha_s)
by using a general massive two-loop algorithm proposed in a previous article.
From this we derive by unitarity the O(\alpha_s) radiative corrections to the
decay width of the top quark, where all effects associated with the quark
mass are included without resorting to a mass expansion. Our results agree with
the analytical results available for the O(\alpha_s) correction to the top
quark width
Heavy-to-light scalar form factors from Muskhelishvili-Omn\`es dispersion relations
By solving the Muskhelishvili-Omn\`es integral equations, the scalar form
factors of the semileptonic heavy meson decays ,
, and
are simultaneously studied. As input, we
employ unitarized heavy meson-Goldstone boson chiral coupled-channel amplitudes
for the energy regions not far from thresholds, while, at high energies,
adequate asymptotic conditions are imposed. The scalar form factors are
expressed in terms of Omn\`es matrices multiplied by vector polynomials, which
contain some undetermined dispersive subtraction constants. We make use of
heavy quark and chiral symmetries to constrain these constants, which are
fitted to lattice QCD results both in the charm and the bottom sectors, and in
this latter sector to the light-cone sum rule predictions close to as
well. We find a good simultaneous description of the scalar form factors for
the four semileptonic decay reactions. From this combined fit, and taking
advantage that scalar and vector form factors are equal at , we obtain
, and for the involved Cabibbo-Kobayashi-Maskawa (CKM) matrix
elements. In addition, we predict the following vector form factors at :
, ,
and , which might serve as alternatives to determine the CKM elements when
experimental measurements of the corresponding differential decay rates become
available. Finally, we predict the different form factors above the
regions accessible in the semileptonic decays, up to moderate energies
amenable to be described using the unitarized coupled-channel chiral approach.Comment: includes further discussions and references; matches the accepted
versio
Partitioning space for range queries
It is shown that, given a set S of n points in R3, one can always find three planes that form an eight-partition of S, that is, a partition where at most n/8 points of S lie in each of the eight open regions. This theorem is used to define a data structure, called an octant tree, for representing any point set in R3. An octant tree for n points occupies O(n) space and can be constructed in polynomial time. With this data structure and its refinements, efficient solutions to various range query problems in 2 and 3 dimensions can be obtained, including (1) half-space queries: find all points of S that lie to one side of any given plane; (2) polyhedron queries: find all points that lie inside (outside) any given polyhedron; and (3) circular queries in R2: for a planar set S, find all points that lie inside (outside) any given circle. The retrieval time for all these queries is T(n)=O(na + m) where a= 0.8988 (or 0.8471 in case (3)) and m is the size of the output. This performance is the best currently known for linear-space data structures which can be deterministically constructed in polynomial time
Transient response under ultrafast interband excitation of an intrinsic graphene
The transient evolution of carriers in an intrinsic graphene under ultrafast
excitation, which is caused by the collisionless interband transitions, is
studied theoretically. The energy relaxation due to the quasielastic acoustic
phonon scattering and the interband generation-recombination transitions due to
thermal radiation are analyzed. The distributions of carriers are obtained for
the limiting cases when carrier-carrier scattering is negligible and when the
intercarrier scattering imposes the quasiequilibrium distribution. The
transient optical response (differential reflectivity and transmissivity) on a
probe radiation and transient photoconductivity (response on a weak dc field)
appears to be strongly dependent on the relaxation and recombination dynamics
of carriers.Comment: 9 pages, 8 figure
Prewetting transition on a weakly disordered substrate : evidence for a creeping film dynamics
We present the first microscopic images of the prewetting transition of a
liquid film on a solid surface. Pictures of the local coverage map of a helium
film on a cesium metal surface are taken while the temperature is raised
through the transition. The film edge is found to advance at constant
temperature by successive avalanches in a creep motion with a macroscopic
correlation length. The creep velocity varies strongly in a narrow temperature
range. The retreat motion is obtained only at much lower temperature,
conforming to the strong hysteresis observed for prewetting transition on a
disordered surface. Prewetting transition on such disordered surfaces appears
to give rise to dynamical phenomena similar to what is observed for domain wall
motions in 2D magnets.Comment: 7 pages, 3 figures, to be published in Euro.Phys.Let
Hole Spin Coherence in a Ge/Si Heterostructure Nanowire
Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si
nanowire double quantum dot using a fast pulsed-gate method and dispersive
readout. An inhomogeneous dephasing time
exceeds corresponding measurements in III-V semiconductors by more than an
order of magnitude, as expected for predominately nuclear-spin-free materials.
Dephasing is observed to be exponential in time, indicating the presence of a
broadband noise source, rather than Gaussian, previously seen in systems with
nuclear-spin-dominated dephasing.Comment: 15 pages, 4 figure
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