442 research outputs found
Relation between Light Cone Distribution Amplitudes and Shape Function in B mesons
The Bakamjian-Thomas relativistic quark model provides a Poincar\'e
representation of bound states with a fixed number of constituents and, in the
heavy quark limit, form factors of currents satisfy covariance and Isgur-Wise
scaling. We compute the Light Cone Distribution Amplitudes of mesons
as well as the Shape Function , that enters
in the decay , that are also covariant in this class of
models. The LCDA and the SF are related through the quark model wave function.
The former satisfy, in the limit of vanishing constituent light quark mass, the
integral relation given by QCD in the valence sector of Fock space. Using a
gaussian wave function, the obtained is identical to the so-called
Roman Shape Function. From the parameters for the latter that fit the spectrum we predict the behaviour of . We
discuss the important role played by the constituent light quark mass. In
particular, although for vanishing light quark mass, a
non-vanishing mass implies the unfamiliar result . Moreover,
we incorporate the short distance behaviour of QCD to ,
which has sizeable effects at large . We obtain the values for the
parameters GeV and
GeV. We compare with other theoretical approaches and illustrate the
great variety of models found in the literature for the functions ; hence the necessity of imposing further constraints as in the
present paper. We briefly review also the different phenomena that are
sensitive to the LCDA.Comment: 6 figure
Spatial distributions in static heavy-light mesons: a comparison of quark models with lattice QCD
Lattice measurements of spatial distributions of the light quark bilinear
densities in static mesons allow to test directly and in detail the wave
functions of quark models. These distributions are gauge invariant quantities
directly related to the spatial distribution of wave functions. We make a
detailed comparison of the recent lattice QCD results with our own quark
models, formulated previously for quite different purposes. We find a striking
agreement not only between our two quark models, but also with the lattice QCD
data for the ground state in an important range of distances up to about 4/GeV.
Moreover the agreement extends to the L=1 states [j^P=(1/2)^+]. An explanation
of several particular features completely at odds with the non-relativistic
approximation is provided. A rather direct, somewhat unexpected and of course
approximate relation between wave functions of certain quark models and QCD has
been established.Comment: 40 pages, 5 figures (version published in PRD
The structure of the atomic helium trimers: Halos and Efimov states
The Faddeev equations for the atomic helium-trimer systems are solved
numerically with high accuracy both for the most sophisticated realistic
potentials available and for simple phenomenological potentials. An efficient
numerical procedure is described. The large-distance asymptotic behavior,
crucial for weakly bound three-body systems, is described almost analytically
for arbitrary potentials. The Efimov effect is especially considered. The
geometric structures of the bound states are quantitatively investigated. The
accuracy of the schematic models and previous computations is comparable, i.e.
within 20% for the spatially extended states and within 40% for the smaller
^4He-trimer ground state.Comment: 32 pages containing 7 figures and 6 table
Semileptonic inclusive heavy meson decay: duality in a nonrelativistic potential model in the Shifman-Voloshin limit
Quark-hadron duality in the inclusive semileptonic decay in
the Shifman-Voloshin limit is
studied within a nonrelativistic potential model. The integrated semileptonic
decay rate is calculated in two ways: first, by constructing the Operator
Product Expansion, and second by a direct summation of the exclusive channels.
Sum rules (Bjorken, Voloshin, etc.) for the potential model are derived,
providing a possibility to compare the two representations for . An explicit difference between them referred to as duality-violation
effect is found. The origin of this effect is related to higher charm
resonances which are kinematically forbidden in the decay process but are
nevertheless picked up by the OPE.
Within the considered order the OPE and the sum over exclusive
channels match each other, up to the contributions of higher resonances, by
virtue of the sum rules. In particular this is true for the terms of order
and which are present in each of
the decay channels and cancel in the sum of these channels due to the Bjorken
and Voloshin sum rules, respectively. The size of the duality violation effects
is estimated to be of the order with
depending on the details of the potential. Constraints for a better accuracy
are discussed.Comment: revtex, 19 pages, a comment on the OPE in the potential model has
been added and several typoes correcte
Scalable and accurate causality tracking for eventually consistent stores
Lecture Notes in Computer Science 8460, 2014In cloud computing environments, data storage systems often rely on optimistic replication to provide good performance and availability even in the presence of failures or network partitions. In this scenario, it is important to be able to accurately and efficiently identify updates executed concurrently. Current approaches to causality tracking in optimistic replication have problems with concurrent updates: they either (1) do not scale, as they require replicas to maintain information that grows linearly with the number of writes or unique clients; (2) lose information about causality, either by removing entries from client-id based version vectors or using server-id based version vectors, which cause false conflicts. We propose a new logical clock mechanism and a logical clock framework that together support a traditional key-value store API, while capturing causality in an accurate and scalable way, avoiding false conflicts. It maintains concise information per data replica, only linear on the number of replica servers, and allows data replicas to be compared and merged linear with the number of replica servers and versions.(undefined
Organics preserved in anhydrous interplanetary dust particles: Pristine or not?
The chondritic‐porous subset of interplanetary dust particles (CP‐IDPs) are thought to have a cometary origin. Since the CP‐IDPs are anhydrous and unaltered by aqueous processes that are common to chondritic organic matter (OM), they represent the most pristine material of the solar system. However, the study of IDP OM might be hindered by their further alteration by flash heating during atmospheric entry, and we have limited understanding on how short‐term heating influences their organic content. In order to investigate this problem, five CP‐IDPs were studied for their OM contents, distributions, and isotopic compositions at the submicro‐ to nanoscale levels. The OM contained in the IDPs in this study spans the spectrum from primitive OM to that which has been significantly processed by heat. Similarities in the Raman D bands of the meteoritic and IDP OMs indicate that the overall gain in the sizes of crystalline domains in response to heating is similar. However, the Raman ΓG values of the OM in all of the five IDPs clearly deviate from those of chondritic OM that had been processed during a prolonged episode of parent body heating. Such disparity suggests that the nonaromatic contents of the OM are different. Short duration heating further increases the H/C ratio and reduces the δ13C and δD values of the IDP OM. Our findings suggest that IDP OM contains a significant proportion of disordered C with low H content, such as sp2 olefinic C=C, sp3 C–C, and/or carbonyl contents as bridging material
Variational Calculation on A=3 and 4 Nuclei with Non-Local Potentials
The application of the hyperspherical harmonic approach to the case of
non-local two-body potentials is described. Given the properties of the
hyperspherical harmonic functions, there are no difficulties in considering the
approach in both coordinate and momentum space. The binding energies and other
ground state properties of A=3 and 4 nuclei are calculated using the CD Bonn
2000 and N3LO two-body potentials. The results are shown to be in excellent
agreement with corresponding ones obtained by other accurate techniques.Comment: 12 pages, 6 tables, RevTex
Breakup reaction models for two- and three-cluster projectiles
Breakup reactions are one of the main tools for the study of exotic nuclei,
and in particular of their continuum. In order to get valuable information from
measurements, a precise reaction model coupled to a fair description of the
projectile is needed. We assume that the projectile initially possesses a
cluster structure, which is revealed by the dissociation process. This
structure is described by a few-body Hamiltonian involving effective forces
between the clusters. Within this assumption, we review various reaction
models. In semiclassical models, the projectile-target relative motion is
described by a classical trajectory and the reaction properties are deduced by
solving a time-dependent Schroedinger equation. We then describe the principle
and variants of the eikonal approximation: the dynamical eikonal approximation,
the standard eikonal approximation, and a corrected version avoiding Coulomb
divergence. Finally, we present the continuum-discretized coupled-channel
method (CDCC), in which the Schroedinger equation is solved with the projectile
continuum approximated by square-integrable states. These models are first
illustrated by applications to two-cluster projectiles for studies of nuclei
far from stability and of reactions useful in astrophysics. Recent extensions
to three-cluster projectiles, like two-neutron halo nuclei, are then presented
and discussed. We end this review with some views of the future in
breakup-reaction theory.Comment: Will constitute a chapter of "Clusters in Nuclei - Vol.2." to be
published as a volume of "Lecture Notes in Physics" (Springer
Measuring with B transitions
We propose the determination of the CKM matrix element by the
measurement of the spectrum of , dominated by the spectator
quark model mechanism . The interest of
considering versus the semileptonic decay is that more than 50
% of the spectrum for occurs above the kinematical limit for
, while most of the spectrum occurs below
the one. Furthermore, the measure of the hadronic mass
is easier in the presence of an identified than when a has been
produced. As a consistency check, we point out that the rate (including QCD corrections that we present elsewhere) is
consistent with the measured . Although the hadronic
complications may be more severe in the mode that we propose than in the
semileptonic inclusive decay, the end of the spectrum in is
not well understood on theoretical grounds. We argue that, in our case, the
excited , decaying into , do not contribute and, if there is
tagging of the meson, the other mechanisms to produce a of the right
sign are presumably small, of relative to the spectator amplitude,
or can be controlled by kinematical cuts. In the absence of tagging, other
hadronic backgrounds deserve careful study. We present a feasability study with
the BaBar detector.Comment: 22 pages, LaTe
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