23,873 research outputs found
Light-cone sum rules for form factors revisited
We reconsider and update the QCD light-cone sum rules for form
factors. The gluon radiative corrections to the twist-2 and twist-3 terms in
the correlation functions are calculated. The -quark mass is
employed, instead of the one-loop pole mass used in the previous analyses. The
light-cone sum rule for is fitted to the measured
-distribution in , fixing the input parameters with the
largest uncertainty: the Gegenbauer moments of the pion distribution amplitude.
For the vector form factor at zero momentum transfer we predict
. Combining it with the value of the
product extracted from experiment, we obtain
. In addition, the scalar
and penguin form factors and are
calculated.Comment: 33 pages, 7 figures, one figure and a few comments added, version to
appear in JHE
Analysis of B-> \phi K Decays in QCD Factorization
We analyze the decay within the framework of QCD-improved
factorization. We found that although the twist-3 kaon distribution amplitude
dominates the spectator interactions, it will suppress the decay rates
slightly. The weak annihilation diagrams induced by penguin
operators, which are formally power-suppressed by order , are
chirally and logarithmically enhanced. Therefore, these annihilation
contributions are not subject to helicity suppression and can be sizable. The
predicted branching ratio of is in
the absence of annihilation contributions and it becomes
when annihilation effects are taken into
account. The prediction is consistent with CLEO and BaBar data but smaller than
the BELLE result.Comment: 13 pages, 3 figures. A major change for the presentation of
branching-ratio predictions. Experimental data are update
Incompatible sets of gradients and metastability
We give a mathematical analysis of a concept of metastability induced by
incompatibility. The physical setting is a single parent phase, just about to
undergo transformation to a product phase of lower energy density. Under
certain conditions of incompatibility of the energy wells of this energy
density, we show that the parent phase is metastable in a strong sense, namely
it is a local minimizer of the free energy in an neighbourhood of its
deformation. The reason behind this result is that, due to the incompatibility
of the energy wells, a small nucleus of the product phase is necessarily
accompanied by a stressed transition layer whose energetic cost exceeds the
energy lowering capacity of the nucleus. We define and characterize
incompatible sets of matrices, in terms of which the transition layer estimate
at the heart of the proof of metastability is expressed. Finally we discuss
connections with experiment and place this concept of metastability in the
wider context of recent theoretical and experimental research on metastability
and hysteresis.Comment: Archive for Rational Mechanics and Analysis, to appea
Electromagnetic form-factor of the meson with light-cone QCD sum rules
In this article, we calculate the electromagnetic form-factor of the
meson with the light-cone QCD sum rules. The numerical value is in excellent agreement with the experimental data
(extrapolated to the limit of zero momentum transfer, or the normalization
condition ). For large momentum transfers, the values from the two
sum rules are all comparable with the experimental data and theoretical
estimations.Comment: 16 pages, 3 figures, 5 versio
Heavy-to-light transition form factors and their relations in light-cone QCD sum rules
The improved light-cone QCD sum rules by using chiral current correlator is
systematically reviewed and applied to the calculation of all the
heavy-to-light form factors, including all the semileptonic and penguin ones.
By choosing suitable chiral currents, the light-cone sum rules for all the form
factors are greatly simplified and depend mainly on one leading twist
distribution amplitude of the light meson. As a result, relations between these
form factors arise naturally. At the considered accuracy these relations
reproduce the results obtained in the literature. Moreover, since the explicit
dependence on the leading twist distribution amplitudes is preserved, these
relations may be more useful to simulate the experimental data and extract the
information on the distribution amplitude.Comment: 1+16 pages, no figure
Leading twist contribution to color singlet decays
In this paper the leading twist contribution to
decays in the color singlet approximation is considered. It is shown, that the
predictions for \Br(\chi_0\to\omega\omega) is in a good agreement with the
experimental data, while \Br(\chi_{c2}\to\omega\omega) differs from the
experiment significantly.Comment: 4 pages, RevTeX; minor changes, some refrences adde
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit of QCD
We argue that the Large Energy Effective Theory (LEET), originally proposed
by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative and
rare heavy-to-light transitions in the region where the energy release E is
large compared to the strong interaction scale and to the mass of the final
hadron, i.e. for q^2 not close to the zero-recoil point. We derive the
Effective Lagrangian from the QCD one, and show that in the limit of heavy mass
M for the initial hadron and large energy E for the final one, the heavy and
light quark fields behave as two-component spinors. Neglecting QCD
short-distance corrections, this implies that there are only three form factors
describing all the pseudoscalar to pseudoscalar or vector weak current matrix
elements. We argue that the dependence of these form factors with respect to M
and E should be factorizable, the M-dependence (sqrt(M)) being derived from the
usual heavy quark expansion while the E-dependence is controlled by the
behaviour of the light-cone distribution amplitude near the end-point u=1. The
usual expectation of the (1-u) behaviour leads to a 1/E^2 scaling law, that is
a dipole form in q^2. We also show explicitly that in the appropriate limit,
the Light-Cone Sum Rule method satisfies our general relations as well as the
scaling laws in M and E of the form factors, and obtain very compact and simple
expressions for the latter. Finally we note that this formalism gives
theoretical support to the quark model-inspired methods existing in the
literature.Comment: Latex2e, 25 pages, no figure. Slight changes in the title and the
phrasing. Misprint in Eq. (25) corrected. To appear in Phys. Rev.
A Simulator for LLVM Bitcode
In this paper, we introduce an interactive simulator for programs in the form
of LLVM bitcode. The main features of the simulator include precise control
over thread scheduling, automatic checkpoints and reverse stepping, support for
source-level information about functions and variables in C and C++ programs
and structured heap visualisation. Additionally, the simulator is compatible
with DiVM (DIVINE VM) hypercalls, which makes it possible to load, simulate and
analyse counterexamples from an existing model checker
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