A Relativistic equation for bound state problems

  title={A Relativistic equation for bound state problems},
  author={E. Salpeter and H. Bethe},
  journal={Physical Review},
The relativistic $S$-matrix formalism of Feynman is applied to the bound-state problem for two interacting Fermi-Dirac particles. The bound state is described by a wave function depending on separate times for each of the two particles. Two alternative integral equations for this wave function are derived with kernels in the form of an expansion in powers of ${g}^{2}$, the dimensionless coupling constant for the interaction. Each term in these expansions gives Lorentz-invariant equations. The… Expand