Chiral perturbation theory: An effective field theory

The concept of an effective field theory (EFT), i.e. a theory which is valid only in a limited range of parameter space, is one which has become highly developed recently. After presenting familiar examples from the realms of classical and quantum mechanics together with condensed matter physics, we show that QCD has an intriguing parallel with superconductivity in that, by using quark–antiquark (mesonic) degrees of freedom and exploiting the symmetries of the theory, a useful and powerful theory–chiral perturbation theory–results, which offers a complete and rigorous description of low energy particle and nuclear physics.