Lengths of ππ-scattering

Pion-pion scattering lengths are estimated in a composite meson model based upon the four-quark interactions. Form factors of the rho → 2π and S* → 2π, epsilon → 2π decays have been used in the calculations, and the q2-dependence of the tetragonal quark diagrams has been taken into account (where q2 are final parts of quark loops, so called q2-terms). The calculations qualitatively reproduce well the experimental picture, which testifies to the correct selection of form factors