240 research outputs found
Baryon octet distribution amplitudes in Wandzura-Wilczek approximation
We study higher twist distribution amplitudes for the SU_F(3) baryon octet.
We identify independent functions for all baryons in the isospin symmetry limit
and calculate the Wandzura-Wilczek contributions to the twist-4 and 5
distributions amplitudes.Comment: 7 page
Nucleon Form Factors and Distribution Amplitudes in QCD
We derive light-cone sum rules for the electromagnetic nucleon form factors
including the next-to-leading-order corrections for the contribution of
twist-three and twist-four operators and a consistent treatment of the nucleon
mass corrections. The essence of this approach is that soft Feynman
contributions are calculated in terms of small transverse distance quantities
using dispersion relations and duality. The form factors are thus expressed in
terms of nucleon wave functions at small transverse separations, called
distribution amplitudes, without any additional parameters. The distribution
amplitudes, therefore, can be extracted from the comparison with the
experimental data on form factors and compared to the results of lattice QCD
simulations. A selfconsistent picture emerges, with the three valence quarks
carrying 40%:30%:30% of the proton momentum.Comment: 27 pages, 7 figures uses revte
Axial form factor of the nucleon at large momentum transfers
Motivated by the emerging possibilities to study threshold pion
electroproduction at large momentum transfers at Jefferson Laboratory following
the 12 GeV upgrade, we provide a short theory summary and an estimate of the
nucleon axial form factor for large virtualities in the range using next-to-leading order light-cone sum rules.Comment: A comparison to the new neutrino data analysis and several references
added. Final version to appear in Phys.Rev.
Tagging the pion quark structure in QCD
We combine the constraints on the pion quark structure available from
perturbative QCD, nonperturbative QCD (nonlocal QCD sum rules and light cone
sum rules) with the analysis of current data on F_{\pi\gamma\gamma^*}(Q^2),
including recent high-precision lattice calculations of the second moment of
the pion's distribution amplitude. We supplement these constraints with those
extracted from the renormalon approach by means of the twist-four contributions
to the pion distribution amplitude in order to further increase stability with
respect to related theoretical uncertainties. We show which regions in the
space of the first two non-trivial Gegenbauer coefficients a_2 and a_4 of all
these constraints overlap, tagging this way the pion structure to the highest
degree possible at present.Comment: V1: 6 pages, 2 figures, 1 table. V2: Two references added with
corresponding insertions in the text. Matches version published in PR
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