Pion Resonances

A self-consistent calculation of some features of the low-energy pion resonances is performed by a "boot-strap" method which preserves unitarity and the analytic properties of scattering amplitudes and satisfies crossing symmetry approximately. The interaction of two-pion states with pion-omega meson states is decisive for the properties of the $\rho$ meson. Values of the $\rho$-meson mass and width and the $\omega$-meson width are obtained in terms of the pion and $\omega$-meson masses and are in fair agreement with experiment.