The dipion mass spectrum in e+e- annihilation and tau decay: Isospin symmetry breaking effects from the (rho, omega, phi) mixing

A way to explain the puzzling difference between the pion form factor as measured in e{sup +}e{sup -} annihilations and in {tau} decays is discussed. We show that isospin symmetry breaking, beside the already identified effects, produces also a full mixing between the {rho}{sup 0}, {omega} and {phi} mesons which generates an isospin 0 component inside the {rho}{sup 0} meson. This effect, not accounted for in current treatments of the problem, seems able to account for the apparent mismatch between e{sup +}e{sup -} and {tau} data below the {phi} mass.