Constituent-quark and baryon loops in pseudoscalar-meson transitions

Predictions for the coupling, the pion charge radius r+2, the q2 dependence of the pion decay constant near q2=0 [f(0)], and the ratio describing radiative pion decay are obtained in the context of two related models: the constituent-quark model and a baryon-loop model with nf=2, 3, or 4 flavors. All these models lead to two relations among the four above-mentioned parameters, which are satisfied by the data. A sort of equivalence or duality for the two models is observed, particularly for nf=4. © 1984 The American Physical Society.