Consistency of Low-Energy Parameters and Soft-Pion Scattering Theory

The parameters of low-energy $\pi \pi$, $\pi N$, and $\pi N\to \pi \pi N$ scattering and their consistency with current-algebra predictions are discussed. It is found that the isospin-zero $\pi \pi$ scattering length is $(0.24\mathrm{}\pm 0.03){m_{\pi }}^{-1\mathrm{}}$ quite independent of the exact value of $f_{\pi }$. An effective value of $f_{\pi }$ near 85 MeV seems to be preferred. Experiments are suggested which will clarify the situation further.