ABSTRACT
The unification of electromagnetic and weak interactions into electroweak theory leaves something to be desired. First, there are two independent coupling constants in the theory. Second, no unification with the strong interactions has occurred. The aim of grand unified theory is to rectify this by unifying strong, weak and electromagnetic interactions in a grand unified gauge theory with a single coupling constant. The scale at which grand unification occurs, with a single coupling constant for all gauge field interactions, may be determined using the renormalisation group equation to extrapolate the known values of the electroweak coupling constants at an ‘ordinary’ renormalisation scale. This chapter illustrates that in electroweak theory, it is not possible to introduce fermion mass terms directly into the grand unified theory consistently with the gauge symmetry.
