Meson Physics

Different ways to express the vector meson dominance (VMD) assumption are examined by analysing a wide set of data. These data cover e + e − → π + π − and e + e − → µ + µ − cross sections, the I = l = 1 ππ phase shift and the near threshold predictions of chiral perturbation theory (ChPT). We find that, of the models 1 Permanent address. 2 Present address. considered here, only that proposed by Bando et al. is able to consistently account for all information, provided one allows its parameter a to vary from 2 to 2.4. Consequently, we can propose motivated values for the ρ mass and partial widths to π + π − and e + e − and for Br(ω → π + π −). As a consequence of allowing universality violation, we show that data provide evidence for a point–like coupling γπ + π − of magnitude ≃ −e/6, while the common formulation of VMD excludes such a term.