Meson Exchange Effects in Two-Nucleon States

It is suggested that the most fruitful study of meson exchange effects requires a unified treatment of all processes in which they occur. A new representation of the eigenstates of the two-nucleon system, based on the Heitler-London method, is proposed as being particularly useful for this purpose. Heitler-London states have the property that they become equal to the exact eigenstates when the two nucleons are far apart. Matrix elements between Heitler-London states can be expressed in terms of the properties of isolated nucleons, by means of expansions in the number of exchanged mesons. The Heitler-London method affords a mathematically precise method of incorporating phenomenological isobar effects into a field-theoretical model. Most of the discussion of the details of the formalism is confined to the fixed-source model, but in the final part of the paper the application to a more general model is discussed briefly.