The two-loop Sudakov form factor is computed in a U(1) model with a massive
gauge boson and a U(1)×U(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.Comment: Latex, 5 pages, 2 figures. Bernd Feucht is Bernd Jantzen in later
publications. (The contents of the paper is unchanged.