1,790 research outputs found
Indirect determination of the Kugo-Ojima function from lattice data
We study the structure and non-perturbative properties of a special Green's
function, u(q), whose infrared behavior has traditionally served as the
standard criterion for the realization of the Kugo-Ojima confinement mechanism.
It turns out that, in the Landau gauge, u(q) can be determined from a dynamical
equation, whose main ingredients are the gluon propagator and the ghost
dressing function, integrated over all physical momenta. Using as input for
these two (infrared finite) quantities recent lattice data, we obtain an
indirect determination of u(q). The results of this mixed procedure are in
excellent agreement with those found previously on the lattice, through a
direct simulation of this function. Most importantly, in the deep infrared the
function deviates considerably from the value associated with the realization
of the aforementioned confinement scenario. In addition, the dependence of
u(q), and especially of its value at the origin, on the renormalization point
is clearly established. Some of the possible implications of these results are
briefly discussed.Comment: 25 pages, 10 figures; v2: typos corrected, expanded version that
matches the published articl
Hadronic Charmed Meson Decays Involving Tensor Mesons
Charmed meson decays into a pseudoscalar meson P and a tensor meson T are
studied. The charm to tensor meson transition form factors are evaluated in the
Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the
Cabibbo-allowed decay is dominated by the
W-annihilation contribution and has the largest branching ratio in
decays. We argue that the Cabibbo-suppressed mode
should be suppressed by one order of magnitude relative to . When the finite width effect of the tensor resonances is taken
into account, the decay rate of is generally enhanced by a factor of
. Except for , the predicted branching ratios
of decays are in general too small by one to two orders of magnitude
compared to experiment. However, it is very unlikely that the
transition form factors can be enhanced by a factor of within the
ISGW quark model to account for the discrepancy between theory and experiment.
As many of the current data are still preliminary and lack sufficient statistic
significance, more accurate measurements are needed to pin down the issue.Comment: 11 page
Hadronic B Decays Involving Even Parity Charmed Mesons
Hadronic B decays containing an parity-even charmed meson in the final state
are studied. Specifically we focus on the Cabibbo-allowed decays and , where denotes generically a p-wave charmed meson.
The transition form factors are studied in the improved version
of the Isgur-Scora-Grinstein-Wise quark model. We apply heavy quark effective
theory and chiral symmetry to study the strong decays of p-wave charmed mesons
and determine the magnitude of the mixing angle. Except
the decay to the predictions for agree
with experiment. The sign of mixing angle is found to be
positive in order to avoid a severe suppression on the production of
. The interference between color-allowed and color-suppressed
tree amplitudes is expected to be destructive in the decay . Hence, an observation of the ratio
can be used to test the relative signs of
various form factors as implied by heavy quark symmetry. Although the predicted
at the level of exceeds the
present upper limit, it leads to the ratio
as expected from the factorization
approach and from the ratio . Therefore, it is
crucial to have a measurement of this mode to test the factorization
hypothesis. For decays, it is expected that \bar
D_{s0}^*D\gsim \bar D_{s1}D as the decay constants of the multiplet
become the same in the heavy quark limit.Comment: 27 pages, Belle's new data on DD_s^{**} productions in B decays and
on the radiative decay D_{s1}-> D_s\gamma are updated and discussed. Add two
reference
Hadronic Charmed Meson Decays Involving Axial Vector Mesons
Cabibbo-allowed charmed meson decays into a pseudoscalar meson and an
axial-vector meson are studied. The charm to axial-vector meson transition form
factors are evaluated in the Isgur-Scora-Grinstein-Wise quark model. The dipole
momentum dependence of the transition form factor and the presence of
a sizable long-distance -exchange are the two key ingredients for
understanding the data of . The mixing angle of
the strange axial-vector mesons is found to be or
from decays. The study of decays excludes the positive mixing-angle
solutions. It is pointed out that an observation of the decay at the level of will rule out
and favor the solution .
Though the decays are color suppressed, they are
comparable to and even larger than the color-allowed counterparts: and . The finite width effect of the axial-vector resonance is
examined. It becomes important for in particular when its width is
near 600 MeV.Comment: 19 page
Spectrum of the Vortex Bound States of the Dirac and Schrodinger Hamiltonian in the presence of Superconducting Gaps
We investigate the vortex bound states both Schrodinger and Dirac Hamiltonian
with the s-wave superconducting pairing gap by solving the mean-field
Bogoliubov-de-Gennes equations. The exact vortex bound states spectrum is
numerically determined by the integration method, and also accompanied by the
quasi-classical analysis. It is found that the bound state energies is
proportional to the vortex angular momentum when the chemical potential is
large enough. By applying the external magnetic field, the vortex bound state
energies of the Dirac Hamiltonian are almost unchanged; whereas the energy
shift of the Schrodinger Hamiltonian is proportional to the magnetic field.
These qualitative differences may serve as an indirect evidence of the
existence of Majorana fermions in which the zero mode exists in the case of the
Dirac Hamiltonian only.Comment: 8 pages, 9 figure
Influence of constitution and charge on radical pairing interactions in tris-radical tricationic complexes
The results of a systematic investigation of trisradical tricationic complexes formed between cyclobis(paraquat-p-phenylene) bisradical dicationic (CBPQT2(•+)) rings and a series of 18 dumbbells, containing centrally located 4,4′-bipyridinium radical cationic (BIPY•+) units within oligomethylene chains terminated for the most part by charged 3,5-dimethylpyridinium (PY+) and/or neutral 3,5-dimethylphenyl (PH) groups, are reported. The complexes were obtained by treating equimolar amounts of the CBPQT4+ ring and the dumbbells containing BIPY2+ units with zinc dust in acetonitrile solutions. Whereas UV–Vis–NIR spectra revealed absorption bands centered on ca. 1100 nm with quite different intensities for the 1:1 complexes depending on the constitutions and charges on the dumbbells, titration experiments showed that the association constants (Ka) for complex formation vary over a wide range, from 800 M–1 for the weakest to 180 000 M–1 for the strongest. While Coulombic repulsions emanating from PY+ groups located at the ends of some of the dumbbells undoubtedly contribute to the destabilization of the trisradical tricationic complexes, solid-state superstructures support the contention that those dumbbells with neutral PH groups at the ends of flexible and appropriately constituted links to the BIPY•+ units stand to gain some additional stabilization from C–H···π interactions between the CBPQT2(•+) rings and the PH termini on the dumbbells. The findings reported in this Article demonstrate how structural changes implemented remotely from the BIPY•+ units influence their non-covalent bonding interactions with CBPQT2(•+) rings. Different secondary effects (Coulombic repulsions versus C–H···π interactions) are uncovered, and their contributions to both binding strengths associated with trisradical interactions and the kinetics of associations and dissociations are discussed at some length, supported by extensive DFT calculations at the M06-D3 level. A fundamental understanding of molecular recognition in radical complexes has relevance when it comes to the design and synthesis of non-equilibrium systems
Isotopic and spin selectivity of H_2 adsorbed in bundles of carbon nanotubes
Due to its large surface area and strongly attractive potential, a bundle of
carbon nanotubes is an ideal substrate material for gas storage. In addition,
adsorption in nanotubes can be exploited in order to separate the components of
a mixture. In this paper, we investigate the preferential adsorption of D_2
versus H_2(isotope selectivity) and of ortho versus para(spin selectivity)
molecules confined in the one-dimensional grooves and interstitial channels of
carbon nanotube bundles. We perform selectivity calculations in the low
coverage regime, neglecting interactions between adsorbate molecules. We find
substantial spin selectivity for a range of temperatures up to 100 K, and even
greater isotope selectivity for an extended range of temperatures,up to 300 K.
This isotope selectivity is consistent with recent experimental data, which
exhibit a large difference between the isosteric heats of D_2 and H_2 adsorbed
in these bundles.Comment: Paper submitted to Phys.Rev. B; 17 pages, 2 tables, 6 figure
Is the Sun Embedded in a Typical Interstellar Cloud?
The physical properties and kinematics of the partially ionized interstellar
material near the Sun are typical of warm diffuse clouds in the solar vicinity.
The interstellar magnetic field at the heliosphere and the kinematics of nearby
clouds are naturally explained in terms of the S1 superbubble shell. The
interstellar radiation field at the Sun appears to be harder than the field
ionizing ambient diffuse gas, which may be a consequence of the low opacity of
the tiny cloud surrounding the heliosphere. The spatial context of the Local
Bubble is consistent with our location in the Orion spur.Comment: "From the Outer Heliosphere to the Local Bubble", held at
International Space Sciences Institute, October 200
Neutralino Decays at the CERN LHC
We study the distribution of lepton pairs from the second lightest neutralino
decay \tchi^0_2\to\tchi^0_1 l^+l^-. This decay mode is important to measure the
mass difference between \tchi^0_2 and the lightest neutralino \tchi^0_1, which
helps to determine the parameters of the minimal supersymmetric standard model
at the CERN LHC. We found that the decay distribution strongly depends on the
values of underlying MSSM parameters. For some extreme cases, the amplitude
near the end point of the lepton invariant mass distribution can be suppressed
so strongly that one needs the information of the whole m_{ll} distribution to
extract m_{\tchi^0_2}-m_{\tchi^0_1}. On the other hand, if systematic errors on
the acceptance can be controlled, this distribution can be used to constrain
slepton masses and the Z\tchi^0_2\tchi^0_1 coupling. Measurements of the
velocity distribution of \tchi^0_2 from samples near the end point of the
m_{ll} distribution, and of the asymmetry of the p_T of leptons, would be
useful to reduce the systematic errors.Comment: 23 pages, latex2e, 9 figures, minor change, accepted to PR
Uptake of gases in bundles of carbon nanotubes
Model calculations are presented which predict whether or not an arbitrary
gas experiences significant absorption within carbon nanotubes and/or bundles
of nanotubes. The potentials used in these calculations assume a conventional
form, based on a sum of two-body interactions with individual carbon atoms; the
latter employ energy and distance parameters which are derived from empirical
combining rules. The results confirm intuitive expectation that small atoms and
molecules are absorbed within both the interstitial channels and the tubes,
while large atoms and molecules are absorbed almost exclusively within the
tubes.Comment: 9 pages, 12 figures, submitted to PRB Newer version (8MAR2K). There
was an error in the old one (23JAN2K). Please download thi
- …