508 research outputs found
Hyperon-nucleon coupling from QCD sum rules
The NKY coupling constant for and is evaluated in a
QCD sum rule calculation. We discuss and extend the result of a previous
analysis in the structure and compare it with the result
obtained with the use of the structure. We find a
huge violation of the SU(3) symmetry in the
structure.Comment: 4 pages, 2 figures, espcrc2.sty included. Talk presented at QCD99,
Montpellier, France (to appear in Nucl.Phys.B Proc.Suppl.
Pre-resonant Charmonium-Nucleon Cross Section in the Model of the Stochastic Vacuum
We calculate the nonperturbative charmonium - nucleon cross sections with the
model of the stochastic vacuum, which has been succesfully applied in many high
energy reactions. We also give a quantitative discussion of pre-resonance
formation and medium effects.Comment: Talk given at QCD Euroconference 99, Montpellier, 7-13 July 1999, 4
pages, Late
and form factors from QCD Sum Rules
The form factor for H = B and D mesons is evaluated in a QCD sum
rule calculation. We study the Borel sum rule for the three point function of
two pseudoscalar and one vector meson currents up to order four in the operator
product expansion. The double Borel transform is performed with respect to the
heavy meson momenta. We discuss the momentum dependence of the form factors and
two different approaches to extract the coupling constant.Comment: 12 pages, RevTeX including 6 figures in ps files, revised version
accepted for publication in Phys. Lett.
from QCD Sum Rules
The coupling constant is evaluated in a full QCD sum rule
calculation. We study the Borel sum rule for the three point function of one
pseudoscalar one nucleon and one current up to order seven in the
operator product expansion. The Borel transform is performed with respect to
the nucleon and momenta, which are taken to be equal, whereas the
momentum of the pseudoscalar vertex is taken to be zero. This coupling
constant is relevant in the meson cloud description of the nucleon which has
been recently used to explain exotic events observed by the H1 and ZEUS
Collaborations at HERA.Comment: 9 pages, Latex, 5 ps figure
Progress in the determination of the cross section
Improving previous calculations, we compute the cross section using QCD sum rules. Our sum rules for the , , and hadronic
matrix elements are constructed by using vaccum-pion correlation functions, and
we work up to twist-4 in the soft-pion limit. Our results suggest that, using
meson exchange models is perfectly acceptable, provided that they include form
factors and that they respect chiral symmetry. After doing a thermal average we
get mb at T=150\MeV.Comment: 22 pages, RevTeX4 including 7 figures in ps file
Chiral Symmetry in Charmonium - Pion Cross Section
We perform a non-perturbative calculation of the cross section
using a effective Lagrangian. Our results differ from those
of previous calculations, specially in the description of vertices involving
pions.Comment: 6 pages, RevTeX including 2 figures in eps file
J/psi D*D* vertex from QCD sum rules
We calculated the strong form factor and coupling constant for the vertex in a QCD sum rule calculation. We performed a double Borel sum
rule for the three point correlation function of vertex considering both
and mesons off--shell. The form factors obtained are very
different, but they give the same coupling constant.Comment: 7 pages and 4 figures, replaced version accepted for publication in
Phys. Lett.
Charmonium - Pion Cross Section from QCD Sum Rules
The , and cross sections as a function of are evaluated in a QCD sum rule
calculation. We study the Borel sum rule for the four point function involving
pseudoscalar and vector meson currents, up to dimension four in the operator
product expansion. We find that our results are smaller than the cross sections obtained with models based on meson exchange,
but are close to those obtained with quark exchange models.Comment: revised version accepted for publication in Phys. Lett.
A Comparative Study of Pentaquark Interpolating Currents
In a diquark-diquark-antiquark picture of pentaquarks, we use two
interpolating currents to calculate the mass of the recently measured
state in the framework of QCD sum rules. We show that, even though
yielding similar values for (and close to the experimental
value), these currents differ from each other in what concerns the strength of
the pole, convergence of the OPE and sensitivity to the continuum threshold
parameter.Comment: 19 pages, 8 figures, replaced version accepted for publication in
Phys. Lett.
How Hard Are the Form Factors in Hadronic Vertices with Heavy Mesons?
The and form factors are evaluated in a full
QCD sum rule calculation. We study the double Borel sum rule for the three
point function of one meson one nucleon and one current up to order
six in the operator product expansion. The double Borel transform is performed
with respect to the nucleon and momenta, and the form factor is
evaluated as a function of the momentum of the heavy meson. These form
factors are relevant to evaluate the charmonium absorption cross section by
hadrons. Our results are compatible with constant form factors in these
vertices.Comment: 12 pages, RevTeX including 5 figures in ps file
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