Key points are not available for this paper at this time.
Virtual pair creation in a strong, virtual, bremsstrahlung field is considered in QED as a model for parton saturation. In a weak field the virtual pair density increases quadratically in the external field; however, at large values of the field the number density becomes independent of the strength of that field. A similar effect is found in scalar electrodynamics.
A.H. Mueller (Thu,) studied this question.