On relativization of the Sommerfeld-Gamow-Sakharov factor
  The Sommerfeld-Gamow-Sakharov factor is considered for the general case of arbitrary masses and energies. It is shown that the scalar triangular one-loop diagram gives the Coulomb singularity in radiative corrections at the threshold. The singular part of the correction is factorized at the complete Born cross section regardless of its partial wave decomposition. Different approaches to generalize the factor are discussed. 
Andrej B. Arbuzov and Tatiana V. Kopylova
hep-ph