144 research outputs found
Improved Calculations of Quark Distributions in Hadrons: the case of pion
The earlier introduced method of calculation of quark distributions in
hadrons, based on QCD sum rules, is improved. The imaginary part of the virtual
photon forward scattering amplitude on some hadronic current is considered in
the case, when initial and final virtualities of the current , and
are different, . The operator product expansion (OPE)
in , is performed. The sum rule for quark distribution is
obtained using double dispersion representation of the amplitude on one side in
terms of calculated in QCD OPE and on the other side in terms of physical
states contributions. Double Borel transformation in , is
applied to the sum rule, killing background non-diagonal transition terms,
which deteriorated the accuracy in previous calculations. The case of valence
quark distribution in pion is considered, which was impossible to treat by the
previous method. OPE up to dimension 6 operators is performed and leading order
perturbative corrections are accounted. Valence -quark distribution in
was found at intermediate , and normalization point
. These results may be used as input for evolution equations.Comment: 29 pages, LaTeX 2e, 13 eps figures include
Quark distributions in QCD sum rules: unexpected features and paradoxes
Some very unusual features of the hadron structure functions, obtained in the
generalized QCD sum rules, like the surprisingly strong difference between
longitudinally and transversally polarized mesons structure functions
and the strong suppression of the gluon sea in longitudinally polarized
mesons are discussed. Also the problem of exact zero contribution of gluon
condensates to pion and longitudinally polarized meson quark
distributions is discussed.Comment: 9 pages, 5 fig
Pentaquark decay is suppressed by chirality conservation
It is shown, that if the pentaquark baryon can be
represented by the local quark current , its decay is forbidden in the limit of chirality conservation. The
decay width is proportional to , where , is quark condensate, and,
therefore, is strongly suppressed. Also the polarization operator of the
pentaquark current with isospin 1 is calculated using the operator product
expansion and estimation for it mass is obtained .Comment: 4 pages, 1 fig, typos correcte
Calculation of the pentaquark width by QCD sum rule
The pentaquark width is calculated in QCD sum rules. Result for
show, that can vary in the region less than
1. The main conclusion is, that if pentaquark is genuine states then sum
rules really predict the narrow width of pentaquark , and the
suppression of the width is both parametrical and numerical.Comment: 8 Ppages, 3 figures,the numerical error was corrected, two figures
are modified. In the limit of errors the result did not change significantl
Axial anomaly and mixing: from real to highly virtual photons
The relation for transition form factors of eta and eta' mesons is obtained
by combining the exact nonperturbative QCD sum rule, following from the
dispersive representation of axial anomaly, and quark-hadron duality. It is
valid at all virtual photon momenta and allows one to express the transition
form factors entirely in terms of meson decay constants. This relation is in a
good agreement with experimental data.Comment: 10 pages, 4 figures. Minor corrections, references added and updated;
to appear in Phys.Rev.
Quark-hadron duality, axial anomaly and mixing
Interplay between axial anomaly and quark-hadron duality in the presence of
strong mixing is considered. The anomaly sum rule for meson transition form
factors based on the dispersive representation of axial anomaly and
quark-hadron duality in octet channel is analyzed. The comparison of this sum
rule to the experimental data on and mesons transition form
factors shows that the interval of duality in this channel is rather small,
contradicting the usual understanding of quark-hadron duality. The same values
of interval of duality are supported by considering the two-point correlator in
the local duality limit. This contradiction may be resolved by introducing of
some nonperturbative non-OPE correction to the relevant spectral density. The
form and value of this correction are discussed.Comment: 9 pages, 1 figure, reference adde
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