30 research outputs found
Quantitative predictions for B semileptonic decays into D, D*, and the orbitally excited D** in quark models in the manner of Bakamjian and Thomas
Once chosen the dynamics in one frame, the rest frame in this paper, the Bakamjian and Thomas method allows to define relativistic quark models in any frame. These models have been shown to provide, in the infinite quark mass limit, fully covariant current form factors as matrix elements of the quark current operator. In this paper we use the rest frame dynamics fitted from the meson spectrum by various authors, already shown to provide a reasonable value for . From the general formulae for the scaling invariant form factors , and , we predict quantitavely the semileptonic branching ratios to the ground state and orbitally excited charmed mesons and . We check Bjorken's sum rule and discuss the respective contributions to it. We find , resulting from the fact that the ground state wave function is Coulomb-like. We also find and . Very small branching ratios into orbitally excited 's results. The overall agreement with experiment is rather good within the present accuracy which is poor for the orbitally excited charmed mesons. We predict a ratio as a mere consequence of the heavy quark symmetry. If some faint experimental indications that were confirmed, it would indicate a sizeable correction
Possible explanation of the discrepancy of the light-cone QCD sum rule calculation of g(D*Dpi) coupling with experiment
The introduction of an explicit negative radial excitation contribution in
the hadronic side of the light cone QCD sum rule (LCSR) of Belyaev, Braun,
Khodjamirian and Ruckl, can explain the large experimental value of g(D*Dpi),
recently measured by CLEO. At the same time, it considerably improves the
stability of the sum rule when varying the Borel parameter.Comment: 9 pages, 1 PostScript figure
Critical Analysis of Theoretical Estimates for to Light Meson Form Factors and the Data
We point out that current estimates of form factors fail to explain the
non-leptonic decays and that the combination of data
on the semi-leptonic decays and on the non-leptonic
decays (in particular recent po\-la\-ri\-za\-tion
data) severely constrain the form (normalization and dependence) of the
heavy-to-light meson form factors, if we assume the factorization hypothesis
for the latter. From a simultaneous fit to \bpsi and \dk data we find that
strict heavy quark limit scaling laws do not hold when going from to
and must have large corrections that make softer the dependence on the masses.
We find that should increase slower with \qq than .
We propose a simple parametrization of these corrections based on a quark
model or on an extension of the \hhs laws to the \hl case, complemented with an
approximately constant . We analyze in the light of these data and
theoretical input various theoretical approaches (lattice calculations, QCD sum
rules, quark models) and point out the origin of the difficulties encountered
by most of these schemes. In particular we check the compatibility of several
quark models with the heavy quark scaling relations.Comment: 48 pages, DAPNIA/SPP/94-24, LPTHE-Orsay 94/1
Entre nuisances et urbanisation : une méthode de lecture du bien-être : La ville industrielle de Gardanne (Bouches-du-Rhône)
International audienc
Entre nuisances et urbanisation : une méthode de lecture du bien-être : La ville industrielle de Gardanne (Bouches-du-Rhône)
International audienc
Designing distributed algorithms by means of formal sequentially phased reasoning (extended abstract)
Designers of network algorithms give elegant informal descriptions of the intuition behind their algorithms (see [GHS83, Hu83, MS79, Se82, Se83, ZS80]). Usually, these descriptions are structured as if tasks or subtasks are performed sequentially. From an operational point of view, however, they are performed concurrently. Here, we present a design principle that formally describes how to develop algorithms according to such sequentially phased explanations. The design principle is formulated using Manna and Pnueli's linear time temporal logic [MP83]. This principle, together with Chandy and Misra's technique [CM88] or Back and Sere's technique [BS89] for designing parallel algorithms, is applicable to large classes of algorithms, such as those for minimum-path, connectivity, network flow, and minimum-weight spanning trees. In particular, the distributed minimum-weight spanning tree algorithm of Gallager, Humblet, and Spira [GHS83] is structured according to our principle