Phase of the Scattering Amplitude for Charged Bosons

A calculation, to order $\alpha$, of the phase of the scattering amplitude for charged bosons is shown to involve the double spectral function for the box graph. At small angles the result agrees with a (Bakamjian-Thomas) equivalent-potential calculation and reduces to the potential-scattering-theory result in the nonrelativistic limit; the infrared-divergent part agrees with that obtained for a Yukawa potential, as the shielding radius approaches infinity.