40 research outputs found
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.
and vertices in a QCD Sum Rule approach
We calculate the strong form factors and coupling constants of
and vertices using the QCD sum rules technique. In each case we
have considered two different cases for the off-shell particle in the vertex:
the ligthest meson and one of the heavy mesons. The method gives the same
coupling constant for each vertex. When the results for different vertices are
compared, they show that the SU(4) symmetry is broken by around 40%.Comment: 10 pages, 8 figures. Submitted to Phys. Lett.
Is hypoimmunogenic stem cell therapy safe in times of pandemics?
The manipulation of human leukocyte antigens (HLAs) and immune modulatory factors in "universal" human pluripotent stem cells (PSCs) holds promise for immunological tolerance without HLA matching. This paradigm raises concerns should "universal" grafts become virally infected. Furthermore, immunological manipulation might functionally impair certain progeny, such as hematopoietic stem cells. We discuss the risks and benefits of hypoimmunogenic PSCs, and the need to further advance HLA matching and autologous strategies.Toxicolog
Diquark-Antidiquark with open charm in QCD sum rules
Using the QCD sum rule approach we investigate the possible four-quark
structure of the recently observed charmed scalar mesons
(BELLE) and (FOCUS) and also of the very narrow
, firstly observed by BABAR. We use diquak-antidiquark
currents and work to the order of in full QCD, without relying on
expansion. Our results indicate that a four-quark structure is acceptable for
the resonances observed by BELLE and BABAR: and
respectively, but not for the resonances observed by FOCUS:
.Comment: 6 pages, 5 eps figures; Contribution to the 'Workshop on Light-Cone
QCD and Nonperturbative Hadron Physics 2005 (LC2005)', Cairns-Australi
\rho D^*D^* vertex from QCD sum rules
We calculate the form factors and the coupling constant in the
vertex in the framework of QCD sum rules. We evaluate the three point
correlation functions of the vertex considering both and mesons
off--shell. The form factors obtained are very different but give the same
coupling constant: . This number is 50% larger
than what we would expect from SU(4) estimates.Comment: 9 pages, 6 eps 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
Another tetraquark structure in the invariant mass distribution
In this article, we assume that there exists a scalar hidden charm tetraquark
state in the invariant mass distribution, and study its mass
using the QCD sum rules. The numerical result is
consistent with the mass of the Z(4250). The Z(4250) may be a tetraquark state,
other possibilities, such as a hadro-charmonium resonance and a
molecular state are not excluded.Comment: 14 pages, 14 figure, correct some type error
The meson as a tetraquark state
We test the validity of the QCD sum rules applied to the meson ,
by considering a diquark-antidiquark type of current with and
with . We find that, with the studied currents, it is possible to
find an acceptable Borel window. In such a Borel window we have simultaneously
a good OPE convergence and a pole contribution which is bigger than the
continuum contribution. We get m_Z=(4.52\pm0.09)\GeV and
m_Z=(4.84\pm0.14)\GeV for the currents with and
respectively. We conclude that the QCD sum rules results favors
quantum numbers for the meson.Comment: version accepted for publication at Phys. Lett.
Mass spectrum of the axial-vector hidden charmed and hidden bottom tetraquark states
In this article, we perform a systematic study of the mass spectrum of the
axial-vector hidden charmed and hidden bottom tetraquark states using the QCD
sum rules, and identify the as an axial-vector tetraquark state
tentatively.Comment: 24 pages, 38 figures, slight revisio
The transition form factors for semi-leptonic weak decays of in QCD sum rules
Within the Standard Model, we investigate the semi-leptonic weak decays of
. The various form factors of transiting to a single charmed
meson () are studied in the framework of the QCD sum rules.
These form factors fully determine the rates of the weak semi-leptonic decays
of and provide valuable information about the non-perturbative QCD
effects. Our results indicate that the decay rate of the semi-leptonic weak
decay mode is at order of .Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.