705 research outputs found
Parton Distributions Functions of Pion, Kaon and Eta pseudoscalar mesons in the NJL model
Parton distributions of pseudoscalar pi,K and eta mesons obtained within the
NJL model using the Pauli-Villars regularization method are analyzed in terms
of LO and NLO evolution, and the valence sea quark and gluon parton
distributions for the pion are obtained at Q^2 = 4 GeV^2 and compared to
existing parametrizations at that scale. Surprisingly, the NLO order effects
turn out to be small compared to the LO ones. The valence distributions are in
good agreement with experimental analyses, but the gluon and sea distributions
come out to be softer in the high-x region and harder in the low-x region than
the experimental analyses suggest.Comment: (Latex, epsfig) 17 pages, 7 figure
Pion transition form factor in the Regge approach and incomplete vector-meson dominance
The concept of incomplete vector-meson dominance and Regge models is applied
to the transition form factor of the pion. First, we argue that variants of the
chiral quark model fulfilling the chiral anomaly may violate the Terazawa-West
unitarity bounds, as these bounds are based on unverified assumptions for the
real parts of the amplitudes, precluding a possible presence of polynomial
terms. A direct consequence is that the transition form factor need not
necessarily vanish at large values of the photon virtuality. Moreover, in the
range of the BaBar experiment, the Terazawa-West bound is an order of magnitude
above the data, thus is of formal rather than practical interest. Then we
demonstrate how the experimental data may be properly explained with incomplete
vector-meson dominance in a simple model with one state, as well as in more
sophisticated Regge models. Generalizations of the simple Regge model along the
lines of Dominguez result in a proper description of the data, where one may
adjust the parameters in such a way that the Terazawa-West bound is satisfied
or violated. We also impose the experimental constraint from the Z -> pi0 gamma
decay. Finally, we point out that the photon momentum asymmetry parameter may
noticeably influence the precision analysis.Comment: 11 pages, 7 figure
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