Lamm, Valluri, Jentschura and Weniger comment on "A Convergent Series   for the QED Effective Action" by Cho and Pak [Phys. Rev. Lett. vol. 86, pp.   1947-1950 (2001)]
  Complete results were obtained by us in [Can. J. Phys. 71, 389 (1993)] for convergent series representations of both the real and the imaginary part of the QED effective action; these derivations were based on correct intermediate steps. In this comment, we argue that the physical significance of the "logarithmic correction term" found by Cho and Pak in [Phys. Rev. Lett. 86, 1947 (2001)] in comparison to the usual expression for the QED effective action remains to be demonstrated. Further information on related subjects can be found in Appendix A of hep-ph/0308223 and in hep-th/0210240. 
D. R. Lamm, S. R. Valluri, U. D. Jentschura and E. J. Weniger