1,107 research outputs found
Form factors of exclusive transitions
We present the form factors of the transitions induced by the
quark currents at all kinematically accessible . Our analysis is
based on the spectral representations of the form factors within the
constituent quark picture: we fix the soft meson wave functions and the
constituent quark masses by fitting and to the lattice
results at small recoils (). We then calculate
the transition form factors down to . For the
case the region however does not cover the whole
kinematically accessible range. Due to the smallness of the pion mass the
region of small recoils is close to the nearby resonance. We
develop a parametrization which includes the dominance of the form
factors and at small recoils and numerically reproduces the results
of calculations at . We find
ps and
ps.Comment: revtex, 6 pages, 1 figur
Quark-binding effects in inclusive decays of heavy mesons
We present a new approach to the analysis of quark-binding effects in
inclusive decays of heavy mesons within the relativistic dispersion quark
model. Various differential distributions, such as electron energy spectrum,
- and -distributions, are calculated in terms of the meson soft
wave function which also determines long-distance effects in exclusive
transition form factors. Using the quark-model parameters and the meson
wave function previously determined from the description of the exclusive transitions within the same dispersion approach, we provide numerical
results on various distributions in the inclusive decays.Comment: revtex, 18 pages, preprint HD-THEP-99-50 (Heidelberg) and
RM3-TH/99-13 (Roma
Can one control systematic errors of QCD sum rule predictions for bound states?
We study the possibility to control systematic errors of the ground-state
parameters obtained by Shifman-Vainshtein-Zakharov (SVZ) sum rules, making use
of the harmonic-oscillator potential model as an example. In this case, one
knows the exact solution for the polarization operator, which allows one to
obtain both the OPE to any order and the parameters (masses and decay
constants) of the bound states. We determine the parameters of the ground state
making use of the standard procedures of the method of QCD sum rules, and
compare the obtained results with the known exact values. We show that in the
situation when the continuum contribution to the polarization operator is not
known and is modelled by an effective continuum, the method of sum rules does
not allow to control the systematic errors of the extracted ground-state
parameters.Comment: RevTex, 7 pages, figure 4 modified, version to be published in Phys.
Lett.
A narrow "peanut" pentaquark
We analyse the decay in a non-relativistic Fock space
description using three and five constituent quarks for the nucleon and the
pentaquark, respectively. Following Jaffe and Wilczek \cite{jw}, we assume that
quark-quark correlations in spin-zero state play an important role for the
pentaquark internal structure. Within this scenario, a strong dynamical
suppression of the decay width is shown to be possible only if the pentaquark
has an asymmetric "peanut" structure with the strange antiquark in the center
and the two extended composite diquarks rotating around. In this case a decay
width of 1 MeV may be a natural possibility.Comment: Talk given at the Conference "Quark Confinement and Hadron Spectrum
VI", Villasimius (Cagliari) Sardinia, Italy, 21 - 25 September 200
Dispersion approach to quark-binding effects in weak decays of heavy mesons
Dispersion approach based on the constituent quark picture and its
applications to weak decays of heavy mesons are reviewed. Meson interaction
amplitudes are represented within this approach as relativistic spectral
integrals over the mass variables in terms of the meson wave functions and
spectral densities of the corresponding Feynman diagrams. Various applications
of this approach are discussed:
Relativistic spectral representations for meson elastic and transition form
factors at spacelike momentum transfers are constructed. Form factors at
are obtained by the analytical continuation. As a result of this
procedure, form factors are given in the full range of the weak decay in
terms of the wave functions of the participating mesons.
The 1/m_Q expansion of the obtained spectral representations for the form
factors for the particular limits of the heavy-to-heavy and heavy-to-light
transitions are analysed. Their full consistency with the constraints provided
by long-distance QCD for these limits is demonstrated. Predictions for form
factors for B, B(s), D, and D(s) decays to light mesons are given. The
B\to\gamma l\nu decay and the weak annihilation in rare radiative decays are
considered. Nonfactorizable corrections to the B^0-\bar B^0 mixing are
calculated. Inclusive weak B-decays are analysed and the differential
distributions are obtained in terms of the B-meson wave function.Comment: revtex, 119 pages. Summary of changes made: In Sect. V comparison
with the recent experimental data is added, in Sect. VI discussion of contact
terms in B->V\gamma is extended and comments on the recent publications are
given, in Sect. VII signs of the decay constants are brought in agreement
with other Sections, typoes correcte
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