ELECTROMAGNETIC INTERACTIONS OF COMPOSITE SYSTEMS

Starting from Lagrangian field theory, we derive the interaction Hamiltonian of a composite system with an external electromagnetic field. Upon this basis, we develop the theoretical foundations of the atomic Zeeman effect, with specific reference to the fine structure and Lamb shift measurements. We also explicitly verify the Drell-Hearn-Gerasimov sum rule and the low energy theorem for Compton scattering for composite systems. An essential result of our investigation is that the interaction of a loosely bound composite system with an external electromagnetic field can be well approximated by the sum of the relativistic interaction Hamiltonians appropriate to the free constituents, but that in general the nonrelativistic reduction of this Hamiltonian does not yield the sum of the corresponding free reduced (e.g. Foldy-Wouthuysen) Hamiltonians. New features of this work include an extended Salpeter equation which includes interactions with an external electromagnetic field, explicit wave packet solutions to a two-body relativistic equation, and a calculational approach to perturbation theory with composite systems in which sums over intermediate or final states preceed nonrelativistic approximations. Our explicit calculation of the DHG sum rule illustrates its super-convergent nature. © 1969.