The counterterm lagrangian:
The counterterm amplitude:
The photon selfenergy correction:
The above non-renormalization condition implies the following value of :
With this substitution, the full amplitude is ultraviolet finite, but remains infrared divergent:
Mathematica cannot take the limit of ampinf+ampct
. Instead we notice that the coefficients of cancel, and find the limit by omitting this term and setting δ = 0:
Converted by Mathematica (July 10, 2003)