A new look at the pair-production width in a strong magnetic field
  We reexamine the process $\gamma\to e^++ e^-$ in a background magnetic field comparable to $B_c\equiv m_e^2/e$. This process is known to be non-perturbative in the magnetic-field strength. However, it can be shown that the {\it moments} of the above pair production width is proportional to the derivatives of photon polarization function at the zero energy, which is perturbative in $B$. Hence, the pair-production width can be easily obtained from the latter by the inverse Mellin transform. The implications of our approach are discussed. 
W. F. Kao, Guey-Lin Lin and Jie-Jun Tseng