Two-loop Sudakov form factor in a theory with a mass gap.

The two-loop Sudakov form factor is computed in a U(1) model with a massive gauge boson and a U(1)xU(1) model with mass gap. We analyze the result in the context of hard and infrared evolution equations and establish a matching procedure which relates the theories with and without mass gap, setting the stage for the complete calculation of the dominant two-loop corrections to electroweak processes at high energy.