What π-π scattering tells us about chiral perturbation theory

A rearrangement of the standard expansion of the symmetry breaking part of the QCD effective Lagrangian is described that includes into each order additional terms which in the standard chiral perturbation theory χPT, are relegated to higher orders. The new expansion represents a systematic and unambiguous generalization of the standard χPT and is more likely to converge rapidly. It provides a consistent framework for a measurement of the importance of additional 'higher order' terms whose smallness is usually assumed but has never been checked. A method of measuring, among other quantities, the QCD parameters m-circumflex(q-barq) and the quark mass ratio ms/m-circumflex is elaborated in detail. The method is illustrated using various sets of available data. The importance of new, more accurate, experimental information on low-energy π-π scattering is stressed. (author) 33 refs.; 6 figs.; 5 tabs