The $f_0$ Mesons in Processes $\pi \pi \to \pi \pi ,K\bar{K}$ and Chiral Symmetry

In a combined analysis of the experimental data on the coupled processes $\pi \pi \to \pi \pi ,K\bar{K}$ in the channel with $I^G{J}^{PC}=0^{+}{0}^{++}$, 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.