12,685 research outputs found
An Implication on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the New BABAR Data
The new BABAR data on the pion-photon transition form factor arouses people's
new interests on the determination of pion distribution amplitude. To explain
the data, we take both the leading valence quark state's and the non-valence
quark states' contributions into consideration, where the valence quark part up
to next-to-leading order is presented and the non-valence quark part is
estimated by a phenomenological model based on its limiting behavior at both
and . Our results show that to be consistent with the
new BABAR data at large region, a broader other than the asymptotic-like
pion distribution amplitude should be adopted. The broadness of the pion
distribution amplitude is controlled by a parameter . It has been found that
the new BABAR data at low and high energy regions can be explained
simultaneously by setting to be around 0.60, in which the pion distribution
amplitude is closed to the Chernyak-Zhitnitsky form.Comment: 19 pages, 6 figures, 2 tables. Slightly changed, references updated.
To be published in Phys.Rev.
A Comprehensive Analysis on the Pion-Photon Transition Form Factor Beyond the Leading Fock State
We perform a comprehensive analysis of the pion-photon transition form factor
involving the transverse momentum corrections with the
present CLEO experimental data, in which the contributions beyond the leading
Fock state have been taken into consideration. As is well-known, the leading
Fock-state contribution dominates of at large momentum
transfer () region. One should include the contributions beyond the
leading Fock state in small region. In this paper, we construct a
phenomenological expression to estimate the contributions beyond the leading
Fock state based on its asymptotic behavior at . Our present
theoretical results agree well with the experimental data in the whole
region. Then, we extract some useful information of the pionic leading twist-2
distribution amplitude (DA) by comparing our results of
with the CLEO data. By taking best fit, we have the DA moments,
,
and all of higher moments, which are closed to the asymptotic-like behavior of
the pion wavefunction.Comment: 25 pages, 7 figures. Typo error correcte
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Semileptonic decays in the light-cone QCD sum rules
Semileptonic () decays are investigated systematically in the
light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on
weak form factors with an adequate chiral current correlator, which turns out
to be particularly effective to control the pollution by higher twist
components of spectator mesons. The result for each channel depends on the
distribution amplitude of the the producing meson. The leading twist
distribution amplitudes of the related heavy mesons and charmonium are worked
out by a model approach in the reasonable way. A practical scenario is
suggested to understand the behavior of weak form factors in the whole
kinematically accessible ranges. The decay widths and branching ratios are
estimated for several () decay modes of current interest.Comment: 8 pages, talk given by the first arthur at 4th International
Conference on Flavor Physics (ICFP 2007), Beijing, China, Sept 24-28, 200
Effect of edge decoration on the energy spectrum of semi-infinite lattices
Analytical studies of the effect of edge decoration on the energy spectrum of
semi-infinite one-dimensional (1D) lattice chain with Peierls phase transition
and zigzag edged graphene (ZEG) are presented by means of transfer matrix
method, in the frame of which the sufficient and necessary conditions for the
existence of the edge states are determined. For 1D lattice chain, the
zero-energy edge state exists when Peierls phase transition happens regardless
whether the decoration exists or not, while the non-zero-energy edge states can
be induced and manipulated through adjusting the edge decoration. On the other
hand, the semi-infinite ZEG model with nearest-neighbor interaction can be
mapped into the 1D lattice chain case. The non-zero-energy edge states can be
induced by the decoration as well, and we can obtain the condition of the
decoration on the edge for the existence of the novel edge states.Comment: 6 pages,4 figure
Disruption of mesoderm formation during cardiac differentiation due to developmental exposure to 13-cis-retinoic acid.
13-cis-retinoic acid (isotretinoin, INN) is an oral pharmaceutical drug used for the treatment of skin acne, and is also a known teratogen. In this study, the molecular mechanisms underlying INN-induced developmental toxicity during early cardiac differentiation were investigated using both human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs). Pre-exposure of hiPSCs and hESCs to a sublethal concentration of INN did not influence cell proliferation and pluripotency. However, mesodermal differentiation was disrupted when INN was included in the medium during differentiation. Transcriptomic profiling by RNA-seq revealed that INN exposure leads to aberrant expression of genes involved in several signaling pathways that control early mesoderm differentiation, such as TGF-beta signaling. In addition, genome-wide chromatin accessibility profiling by ATAC-seq suggested that INN-exposure leads to enhanced DNA-binding of specific transcription factors (TFs), including HNF1B, SOX10 and NFIC, often in close spatial proximity to genes that are dysregulated in response to INN treatment. Altogether, these results identify potential molecular mechanisms underlying INN-induced perturbation during mesodermal differentiation in the context of cardiac development. This study further highlights the utility of human stem cells as an alternative system for investigating congenital diseases of newborns that arise as a result of maternal drug exposure during pregnancy
A Model for the Twist-3 Wave Function of the Pion and Its Contribution to the Pion Form Factor
A model for the twist-3 wave function of the
pion has been constructed based on the moment calculation by applying the QCD
sum rules, whose distribution amplitude has a better end-point behavior than
that of the asymptotic one. With this model wave function, the twist-3
contributions including both the usual helicity components
() and the higher helicity components
() to the pion form factor have been studied within
the modified pQCD approach. Our results show that the twist-3 contribution
drops fast and it becomes less than the twist-2 contribution at . The higher helicity components in the twist-3 wave function will give
an extra suppression to the pion form factor. The model dependence of the
twist-3 contribution to the pion form factor has been studied by comparing
three different models. When all the power contributions, which include higher
order in , higher helicities, higher twists in DA and etc., have been
taken into account, it is expected that the hard contributions will fit the
present experimental data well at the energy region where pQCD is applicable.Comment: 22pages,4 figures. Phys.Rev. D70, 093013(2004) (in press
On the equivalence of strong formulations for capacitated multi-level lot sizing problems with setup times
Several mixed integer programming formulations have been proposed for modeling capacitated multi-level lot sizing problems with setup times. These formulations include the so-called facility location formulation, the shortest route formulation, and the inventory and lot sizing formulation with (l,S) inequalities. In this paper, we demonstrate the equivalence of these formulations when the integrality requirement is relaxed for any subset of binary setup decision variables. This equivalence has significant implications for decomposition-based methods since same optimal solution values are obtained no matter which formulation is used. In particular, we discuss the relax-and-fix method, a decomposition-based heuristic used for the efficient solution of hard lot sizing problems. Computational tests allow us to compare the effectiveness of different formulations using benchmark problems. The choice of formulation directly affects the required computational effort, and our results therefore provide guidelines on choosing an effective formulation during the development of heuristic-based solution procedures
Consistent Analysis of the Transition Form Factor in the Whole Physical Region
In the paper, we show that the transition form factor can be
calculated by using the different approach in the different regions and
they are consistent with each other in the whole physical region. For the
transition form factor in the large recoil regions, one can apply the
PQCD approach, where the transverse momentum dependence for both the hard
scattering part and the non-perturbative wavefunction, the Sudakov effects and
the threshold effects are included to regulate the endpoint singularity and to
derive a more reliable PQCD result. Pionic twist-3 contributions are carefully
studied with a better endpoint behavior wavefunction for and we find
that its contribution is less than the leading twist contribution. Both the two
wavefunctions and of the B meson can give sizable
contributions to the transition form factor and should be kept for a
better understanding of the B decays. The present obtained PQCD results can
match with both the QCD light-cone sum rule results and the extrapolated
lattice QCD results in the large recoil regions.Comment: 18pages, 6 figure
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