In a combined analysis of the experimental data on the coupled processes $\pi\pi\to\pi\pi,K\bar{ K}$ in the channel with $I^GJ^{ PC}=0^+0^{ ++}$, the following results are obtained in a model-independent way: 1) The $f_0(665)$ state with properties of the $\sigma$-meson is proved to exist; 2) it is shown that the ${ f_0}(980)$ and especially ${ f_0}(1370)$ (if exists) have a dominant $s{ \bar s}$ component; 3) indications of the glueball nature of the $f_0(1500)$ and of a considerable $s{ \bar s}$ component in the ${ f_0}(1710)$ are obtained; 4) conclusion on the linear realization of chiral symmetry is drawn.
Categories: hep-ph