The pion-nucleon interaction as an effective field theory

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After a brief survey of effective field theories, the linear sigma model is discussed as a prototype of an effective field theory of the standard model below the chiral-symmetry-breaking scale. Although it can serve as a toy model for the pion-nucleon interaction, the linear sigma model is not a realistic alternative to chiral perturbation theory. The heavy-baryon approach to chiral perturbation theory allows for a systematic low-energy expansion of Green functions and amplitudes with baryons. The chiral-invariant renormalization of the effective field theory for the pion-nucleon system to O(p³) in the chiral expansion is reviewed.