4 research outputs found
The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum
We investigate the leading-twist light-cone distribution amplitudes for the
pion and kaon, based on the nonlocal chiral quark model from the instanton
vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into
account. The Gegenbauer moments are computed, analyzed and compared with those
of other models. The one-loop QCD evolution of the moments is briefly
discussed. The transverse momentum distributions are also discussed for the
pion and kaon light-cone wave functions.Comment: 17 pages, 12 figures. Accepted for publication in Physical Review
Photon distribution amplitudes and light-cone wave functions in chiral quark models
The leading- and higher-twist distribution amplitudes and light-cone 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 QCD vacuum, as well as in the spectral quark model and the
Nambu--Jona-Lasinio model with the Pauli-Villars regulator, which both treat
interaction of quarks with external fields locally. We find that in all
considered models the leading-twist distribution amplitudes of the real photon
defined at the quark-model momentum scale are constant or remarkably close to
the constant in the 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 leading-twist amplitudes.
We provide estimates for the magnetic susceptibility of the quark condensate
and the coupling , which in the nonlocal model turn out
to be close to the estimates from QCD sum rules. We find the higher-twist
distribution amplitudes at the quark model scale and compare them to the
Wandzura-Wilczek estimates. In addition, in the spectral model we evaluate the
distribution amplitudes and light-cone wave functions of the -meson.Comment: 24 pages, 15 figure
Generalized Quark Transversity Distribution of the Pion in Chiral Quark Models
The transversity generalized parton distributions (tGPDs) of the the pion,
involving matrix elements of the tensor bilocal quark current, are analyzed in
chiral quark models. We apply the nonlocal chiral models involving a
momentum-dependent quark mass, as well as the local Nambu--Jona-Lasinio with
the Pauli-Villars regularization to calculate the pion tGPDs, as well as
related quantities following from restrained kinematics, evaluation of moments,
or taking the Fourier-Bessel transforms to the impact-parameter space. The
obtained distributions satisfy the formal requirements, such as proper support
and polynomiality, following from Lorentz covariance. We carry out the
leading-order QCD evolution from the low quark-model scale to higher lattice
scales, applying the method of Kivel and Mankiewicz. We evaluate several
lowest-order generalized transversity form factors, accessible from the recent
lattice QCD calculations. These form factors, after evolution, agree properly
with the lattice data, in support of the fact that the spontaneously broken
chiral symmetry is the key element also in the evaluation of the transversity
observables.Comment: 17 pages, 17 figures, regular pape