Calculability of the N-P mass difference in gauge theories

The requirement of a calculable N-P mass difference leads to a consideration of unified gauge theories. Future developments in grand unified models may provide a realistic framework for the calculation of the N-P mass difference. The possibility that the relatively soft ultraviolet behavior of QCD softens the divergence in the lowest order electromagnetic mass shift is considered in detail. It is shown that if the bare mass and QCD coupling are constrained to be independent of the electromagnetic coupling, as is natural, then the lowest order electromagnetic shifts of the renormalized mass and QCD coupling are infinite