6,242 research outputs found
Vector-pseudoscalar two-meson distribution amplitudes in three-body meson decays
We study three-body nonleptonic decays by introducing two-meson
distribution amplitudes for the vector-pseudoscalar pair, such that the
analysis is simplified into the one for two-body decays. The twist-2 and
twist-3 two-meson distribution amplitudes, associated with
longitudinally and transversely polarized mesons, are constrained by the
experimental data of the and branching
ratios. We then predict the and decay
spectra in the invariant mass. Since the resonant contribution in the
channel is negligible, the above decay spectra provide a clean test
for the application of two-meson distribution amplitudes to three-body
meson decays.Comment: 9 pages, 1 figure, Revtex4, version to appear in PR
Hybrid fuzzy and sliding-mode control for motorised tether spin-up when coupled with axial vibration
A hybrid fuzzy sliding mode controller is applied to the control of motorised tether spin-up coupled with an axial oscillation phenomenon. A six degree of freedom dynamic model of a motorised momentum exchange tether is used as a basis for interplanetary payload exchange. The tether comprises a symmetrical double payload configuration, with an outrigger counter inertia and massive central facility. It is shown that including axial elasticity permits an enhanced level of performance prediction accuracy and a useful departure from the usual rigid body representations, particularly for accurate payload positioning at strategic points. A special simulation program has been devised in MATLAB and MATHEMATICA for a given initial condition data case
Rare K decays in a model of quark and lepton masses
An extension of a model of neutrino masses to the quark sector provides an
interesting link between these two sectors. A parameter which is important to
describe neutrino oscillations and masses is found to be a crucial one
appearing in various ``penguin'' operators, in particular the so-called Z
penguin. This parameter is severely constrained by the rare decay process
. This in turn has interesting implications on the
decay rates of other rare processes such as , etc..., as well
as on the masses of the neutrinos and the masses of the vector-like quarks and
leptons which appear in our model.Comment: 34 pages, 10 figures, corrected some typos in the introductio
Experimental constraints on fourth generation quark masses
The existing bounds from CDF on the masses of the fourth generation quarks,
t' and b', are reexamined. The bound of 256 GeV on the t' mass assumes that the
primary decay of the t' is into q+W, which is not the case for a substantial
region of parameter space. The bound of 268 GeV on the b' mass assumes that the
branching ratio for b' --> b+Z is very large, which is not only not true for
much of parameter space, but is {\em never} true for b' masses above 255 GeV.
In addition, it is assumed that the heavy quarks decay within the silicon
vertex detector, and for small mixing angles this will not be the case. The
experimental bounds, including all of these effects, are found as a function of
the other heavy quark mass and the mixing angle.Comment: 4 double-column pages, 3 figures. Version to be published in PR
Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT
Two crystallized [FeFe] hydrogenase model complexes, 1 =
(μ-pdt)[Fe(CO)2(PMe3)]2 (pdt = SC1H2C2H2C3H2S), and their bridging-hydride
(Hy) derivative, [1Hy]+++ = [(μ-H)(μ-pdt)[Fe(CO)2 (PMe3)]2]+ (BF4−), were
studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by
density functional theory. Structural changes in [1Hy]+++ compared to 1
involved small bond elongations (<0.03 Å) and more octahedral Fe geometries;
the Fe–H bond at Fe1 (closer to pdt-C2) was [similar]0.03 Å longer than that
at Fe2. Analyses of (1) pre-edge absorption spectra (core-to-valence
transitions), (2) Kβ1,3, Kβ′, and Kβ2,5 emission spectra (valence-to-core
transitions), and (3) resonant inelastic X-ray scattering data (valence-to-
valence transitions) for resonant and non-resonant excitation and respective
spectral simulations indicated the following: (1) the mean Fe oxidation state
was similar in both complexes, due to electron density transfer from the
ligands to Hy in [1Hy]+++. Fe 1s→3d transitions remained at similar energies
whereas delocalization of carbonyl AOs onto Fe and significant Hy-
contributions to MOs caused an [similar]0.7 eV up-shift of Fe1s→(CO)s,p
transitions in [1Hy]+++. Fed-levels were delocalized over Fe1 and Fe2 and
degeneracies biased to Oh–Fe1 and C4v–Fe2 states for 1, but to Oh–Fe1,2 states
for [1Hy]+++. (2) Electron-pairing of formal Fe(d7) ions in low-spin states in
both complexes and a higher effective spin count for [1Hy]+++ were suggested
by comparison with iron reference compounds. Electronic decays from Fe d and
ligand s,p MOs and spectral contributions from Hys,p→1s transitions even
revealed limited site-selectivity for detection of Fe1 or Fe2 in [1Hy]+++. The
HOMO/LUMO energy gap for 1 was estimated as 3.0 ± 0.5 eV. (3) For [1Hy]+++
compared to 1, increased Fed (x2 − y2) − (z2) energy differences ([similar]0.5
eV to [similar]0.9 eV) and Fed→d transition energies ([similar]2.9 eV to
[similar]3.7 eV) were assigned. These results reveal the specific impact of
Hy-binding on the electronic structure of diiron compounds and provide
guidelines for a directed search of hydride species in hydrogenases
A synthetic electric force acting on neutral atoms
Electromagnetism is a simple example of a gauge theory where the underlying
potentials -- the vector and scalar potentials -- are defined only up to a
gauge choice. The vector potential generates magnetic fields through its
spatial variation and electric fields through its time-dependence. We
experimentally produce a synthetic gauge field that emerges only at low energy
in a rubidium Bose-Einstein condensate: the neutral atoms behave as charged
particles do in the presence of a homogeneous effective vector potential. We
have generated a synthetic electric field through the time dependence of an
effective vector potential, a physical consequence even though the vector
potential is spatially uniform
Dynamics of Binary Mixtures with Ions: Dynamic Structure Factor and Mesophase Formation
Dynamic equations are presented for polar binary mixtures containing ions in
the presence of the preferential solvation. In one-phase states, we calculate
the dynamic structure factor of the composition accounting for the ion motions.
Microphase separation can take place for sufficiently large solvation asymmetry
of the cations and the anions. We show two-dimensional simulation results of
the mesophase formation with an antagonistic salt, where the cations are
hydrophilic and the anions are hydrophobic. The structure factor S(q) in the
resultant mesophase has a sharp peak at an intermediate wave number on the
order of the Debye-Huckel wave number. As the quench depth is increased, the
surface tension nearly vanishes in mesophases due to an electric double layer.Comment: 24 pages, 10 figures, to appear in Journal of Physics: Condensed
Matte
Strong subadditivity and the covariant holographic entanglement entropy formula
Headrick and Takayanagi showed that the Ryu-Takayanagi holographic
entanglement entropy formula generally obeys the strong subadditivity (SSA)
inequality, a fundamental property of entropy. However, the Ryu-Takayanagi
formula only applies when the bulk spacetime is static. It is not known whether
the covariant generalization proposed by Hubeny, Rangamani, and Takayanagi
(HRT) also obeys SSA. We investigate this question in three-dimensional
AdS-Vaidya spacetimes, finding that SSA is obeyed as long as the bulk spacetime
satisfies the null energy condition. This provides strong support for the
validity of the HRT formula.Comment: 38 page
On Classical Equivalence Between Noncritical and Einstein Gravity : The AdS/CFT Perspectives
We find that noncritical gravity, a special class of higher derivative
gravity, is classically equivalent to Einstein gravity at the full nonlinear
level. We obtain the viscosity-to-entropy ratio and the second order transport
coefficients of the dual fluid of noncritical gravity to all orders in the
coupling of higher derivative terms. We also compute the holographic
entanglement entropy in the dual CFT of noncritical gravity. All these results
confirm the nonlinear equivalence between noncritical gravity and Einstein
gravity at the classical level.Comment: 19 pages, no figure
Spectral function of the electron in a superconducting RVB state
We present a model calculation of the spectral function of an electron in a
superconducting resonating valence bond (RVB) state. The RVB state, described
by the phase-string mean field theory is characterized by three important
features: (i) spin-charge separation, (ii) short range antiferromagnetic
correlations, and (iii) holon condensation. The results of our calculation are
in good agreement with data obtained from Angle Resolved Photoemission
Spectroscopy (ARPES) in superconducting Bi 2212 at optimal doping
concentration.Comment: 4 pages, 3 figure
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