Photon distribution amplitudes and lightcone wave functions in chiral quark models
Abstract
The leading and highertwist distribution amplitudes and lightcone wave functions of real and virtual photons are analyzed in chiral quark models. The calculations are performed in the nonlocal quark model based on the instanton picture of the QCD vacuum, as well as in the spectral quark model and the Nambu JonaLasinio model with the PauliVillars regulator, which both treat interaction of quarks with external fields locally. We find that in all considered models the leadingtwist distribution amplitudes of the real photon defined at the quarkmodel momentum scale are constant or remarkably close to the constant in the x variable, thus are far from the asymptotic limit form. The QCD evolution to higher momentum scales is necessary and we carry it out at the leading order of the perturbative theory for the leadingtwist amplitudes. We provide estimates for the magnetic susceptibility of the quark condensate χ_{m} and the coupling f_{3γ}, which in the nonlocal model turn out to be close to the estimates from QCD sum rules. We find the highertwist distribution amplitudes at the quark model scale and compare them to the WandzuraWilczek estimates. In addition, in the spectral model we evaluate the distribution amplitudes and lightcone wave functions of the ρmeson.
 Publication:

Physical Review D
 Pub Date:
 September 2006
 DOI:
 10.1103/PhysRevD.74.054023
 arXiv:
 arXiv:hepph/0607171
 Bibcode:
 2006PhRvD..74e4023D
 Keywords:

 12.38.Lg;
 12.38.t;
 12.39.Fe;
 Other nonperturbative calculations;
 Quantum chromodynamics;
 Chiral Lagrangians;
 High Energy Physics  Phenomenology
 EPrint:
 24 pages, 15 figures