ABSTRACT
The most characteristic feature of the behavior is rapid changes in angular distributions with energy. This chapter discusses the general "theory" of resonances. The same resonances appear in many reactions at the same mass and width. There are examples of narrow resonances in other fields: atomic systems; and nuclei. In atomic systems the excited levels of atoms are stable except for coupling with light. The narrowness of the observed resonances in the emission spectrum of an atom, for example, is known to be due to the small value of the coupling e2. In nuclei the coupling is known to be large but narrow resonances are observed. In this case the origin of the narrowness of the resonances can still be understood. The meaning of the appearanc of resonances in strong interactions is not understood. At first theoretical physicists did not expect resonances from strong coupling field theory.
