136 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 $p^2_1$, and
$p^2_2$ are different, $p^2_1\not= p^2_2$. The operator product expansion (OPE)
in $p^2_1$, $p^2_2$ 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 $p^2_1$, $p^2_2$ 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 $u$-quark distribution in
$\pi^+$ was found at intermediate $x$, $0.15 < x < 0.7$ and normalization point
$Q^2=2 GeV^2$. These results may be used as input for evolution equations.Comment: 29 pages, LaTeX 2e, 13 eps figures include

### Small size pentaquark width: calculation in QCD sum rules

The pentaquark width is calculated in QCD sum rules. The higher dimension
operators contribution is accounted. It is shown, that $\Gamma_{\Theta}$ should
be very small, less than $1Mev$.Comment: 10 peges, 7 figure

### 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 $\rho$ mesons structure functions
and the strong suppression of the gluon sea in longitudinally polarized $\rho$
mesons are discussed. Also the problem of exact zero contribution of gluon
condensates to pion and longitudinally polarized $\rho$ meson quark
distributions is discussed.Comment: 9 pages, 5 fig

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