Modified Three-Pole VMD Model with Two-Branch-Point Analytic Structure and Approved Asymptotic Behaviour for the Pion Electromagnetic Form Factor

摘要

A modification of three-pole VMD model for electromagnetic pion form factor was carried out, first by means of its transformation into the pion c.m. momentum variable and subsequently by using the inverse Zhukovsky transformation into another variable. In such a procedure, a common normalized factor for all three vector mesons, rho(770), rho'(1250) and rho''(1600), is singled out, by means of which it is possible to settle a specific freedom in the choice of the pion form factor asymptotic behaviour. An explicit incorporation of nonzero vector meson widths creates a real analytic model, defined on the four-sheeted Riemann surface. It includes inelastic contributions effectively, depends just on the parameters with a clear physical meaning, conserves the normalization of the original VMD parametrization, and provides a perfect fit of all existing pion form factor data, in which all parameters of the model are determined and the presence of rho'(1250) in e/sup +/e/sup -/ -> pi /sup +/ pi /sup -/ is again established. 15 refs. (Atomindex citation 19:074780)