Relativistic Oscillator Model and Delbr\"uck scattering
  Elastic scattering of photons in a Lorentz-scalar potential via virtual spin-zero particle-antiparticle pairs (`` Delbr\"uck scattering") is considered. An analytic expression for the Delbr\"uck amplitude is found exactly in case of an oscillator potential. General properties of the amplitude and its asymptotics are discussed. 
A.I. L'vov and A.I. Milstein