2,461 research outputs found
Problems of QCD factorization in exclusive decays of B meson to charmonium
We study the exclusive decays of meson into P-wave charmonium states
in the QCD factorization approach with light-cone
distribution functions describing the mesons in the processes. For decay, we find that there are logarithmic divergences arising from
nonfactorizable spectator interactions even at twist-2 order and the decay rate
is too small to accommodate the experimental data. For
decay, we find that aside from the logarithmic divergences arising from
spectator interactions at leading-twist order, more importantly, the
factorization will break down due to the infrared divergence arising from
nonfactorizable vertex corrections, which is independent of the specific form
of the light-cone distribution functions. Our results may indicate that QCD
factorization in the present form may not be safely applied to -meson
exclusive decays to charmonium states.Comment: Latex, 7 pages, 1 eps figure, final version to appear in Phys.Lett.B;
a few references are added, the expression of chi_c1 decay constant is give
and meson exclusive decay in QCD factorization
Belle has observed surprisingly copious production of in
meson decay , of which the rate is comparable to that of
. We study this puzzling process in the QCD factorization
approach with the effect of S-D mixing considered. We find that the soft
scattering effects in the spectator interactions play an essential role. With a
proper parametrization for the higher twist soft end-point singularities
associated with kaon, and with the S-D mixing angle , the
calculated decay rates can be close to the data. Implications of these soft
spectator effects to other charmonium production in exclusive decays are
also emphasized.Comment: journal versio
Constraints for the nuclear parton distributions from Z and W production at the LHC
The LHC is foreseen to finally bring also the nuclear collisions to the TeV
scale thereby providing new possibilities for physics studies, in particular
related to the electro-weak sector of the Standard Model. We study here the Z
and W production in proton-lead and lead-lead collisions at the LHC,
concentrating on the prospects of testing the factorization and constraining
the nuclear modifications of the parton distribution functions (PDFs).
Especially, we find that the rapidity asymmetries in proton-nucleus collisions,
arising from the differences in the PDFs between the colliding objects, provide
a decisive advantage in comparison to the rapidity-symmetric nucleus-nucleus
case. We comment on how such studies will help to improve our knowledge of the
nuclear PDFs.Comment: The version accepted for publication in JHEP. New figures has been
added, and we also discuss the single charged lepton productio
Mechanical Properties of End-crosslinked Entangled Polymer Networks using Sliplink Brownian Dynamics Simulations
The mechanical properties of a polymeric network containing both crosslinks
and sliplinks (entanglements) are studied using a multi-chain Brownian dynamics
simulation. We coarse-grain at the level of chain segments connecting
consecutive nodes (cross- or sliplinks), with particular attention to the
Gaussian statistics of the network. Affine displacement of nodes is not
imposed: their displacement as well as sliding of monomers through sliplinks is
governed by force balances. The simulation results of stress in uniaxial
extension and the full stress tensor in simple shear including the (non-zero)
second normal stress difference are presented for monodisperse chains with up
to 18 entanglements between two crosslinks. The cases of two different force
laws of the subchains (Gaussian chains and chains with finite extensibility)
for two different numbers of monomers in a subchain (no = 50 and no = 100) are
examined. It is shown that the additivity assumption of slip- and crosslink
contribution holds for sufficiently long chains with two or more entanglements,
and that it can be used to construct the strain response of a network of
infinitely long chains. An important consequence is that the contribution of
sliplinks to the small-strain shear modulus is about ⅔ of the
contribution of a crosslink
SDN-Actors:Modeling and Verification of SDN Programs
Software-Defined Networking (SDN) is a recent networking paradigm that has become increasingly popular in the last decade. It gives unprecedented control over the global behavior of the network and provides a new opportunity for formal methods. Much work has appeared in the last few years on providing bridges between SDN and verification. This paper advances this research line and provides a link between SDN and traditional work on formal methods for verification of distributed software—actor-based modelling. We show how SDN programs can be seamlessly modelled using actors, and thus existing advanced model checking techniques developed for actors can be directly applied to verify a range of properties of SDN networks, including consistency of flow tables, violation of safety policies, and forwarding loops.Depto. de Sistemas Informáticos y ComputaciónFac. de InformáticaTRUEpu
Reexamining radiative decays of quarkonium into and
Recently CLEO has studied the radiative decay of into and
an upper limit for the decay has been determined. Confronting with this upper
limit,most of theoretical predictions for the decay fails. After briefly
reviewing these predictions we re-examine the decay by separating
nonperturbative effect related to the quarkonium and that related to or
, in which the later is parameterized by distribution amplitudes of
gluons in . With this factorization approach we obtain theoretical
predictions which are in agreement with experiment. Uncertainties in our
predictions are discussed. The possibly largest uncertainties are from
relativistic corrections for and the value of the charm quark mass. We
argue that the effect of these uncertainties can be reduced by using quarkonium
masses instead of using quark masses. An example of the reduction is shown with
an attempt to explain the violation of the famous 14% rule in radiative decays
of charmonia.Comment: 9 Pages, Latex fil
Effects of gestational age at birth on cognitive performance : a function of cognitive workload demands
Objective: Cognitive deficits have been inconsistently described for late or moderately preterm children but are consistently found in very preterm children. This study investigates the association between cognitive workload demands of tasks and cognitive performance in relation to gestational age at birth.
Methods: Data were collected as part of a prospective geographically defined whole-population study of neonatal at-risk children in Southern Bavaria. At 8;5 years, n = 1326 children (gestation range: 23–41 weeks) were assessed with the K-ABC and a Mathematics Test.
Results: Cognitive scores of preterm children decreased as cognitive workload demands of tasks increased. The relationship between gestation and task workload was curvilinear and more pronounced the higher the cognitive workload: GA2 (quadratic term) on low cognitive workload: R2 = .02, p<0.001; moderate cognitive workload: R2 = .09, p<0.001; and high cognitive workload tasks: R2 = .14, p<0.001. Specifically, disproportionally lower scores were found for very (<32 weeks gestation) and moderately (32–33 weeks gestation) preterm children the higher the cognitive workload of the tasks. Early biological factors such as gestation and neonatal complications explained more of the variance in high (12.5%) compared with moderate (8.1%) and low cognitive workload tasks (1.7%).
Conclusions: The cognitive workload model may help to explain variations of findings on the relationship of gestational age with cognitive performance in the literature. The findings have implications for routine cognitive follow-up, educational intervention, and basic research into neuro-plasticity and brain reorganization after preterm birth
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