Nonperturbative Approach to Effective Chiral Lagrangians and Meson Interactions

We develop a coupled channel unitary approach describing the behavior at higher energies of systems whose low-energy dynamics is given by effective $O\left(p^2\right)$ and $O\left(p^4\right)$ chiral Lagrangians. Our free parameters are those of the $O\left(p^4\right)$ Lagrangian. When applied to the meson-meson interaction, it yields a remarkable agreement with data up to $\sqrt{s}\simeq 1.2\mathrm{GeV}$, dynamically generating the $\sigma$, $f_0$, $a_0$, $\rho$, and $K^{*}$ resonances. Further applications are also proposed.