Meson-meson scattering: $K\overline{K}$-thresholds and $f_{0}(980) -   a_{0}(980)$ mixing
  We study the influence of mass splitting between the charged and neutral pions and kaons in the Juelich meson exchange model for $\pi\pi$ and $\pi\eta$ scattering. The calculations are performed in the particle basis, which permits the use of physical masses for the pseudoscalar mesons and a study of the distinct thresholds associated with the neutral and the charged kaons. Within this model we also investigate the isospin violation which arises from the mass splitting and an apparent violation of G-parity in $\pi\pi$ scattering which stems from the coupling to the $K\overline{K}$ channel. Nonvanishing cross sections for $\pi\pi \rightarrow \pi^{0}\eta$ indicate a mixing of the $f_{0}(980)$ and $a_{0}(980)$ states. 
O. Krehl (1), R. Rapp (2), J. Speth (3,1) ((1) IKP, KFA-Juelich, (2)   Dept. of Physics, Stony Brook, (3) CEBAF, Newport News)