FERMION MASSES AND THE STANDARD MODEL GROUP AS A DIAGONAL SUBGROUP

We argue that if the Standard Model is viewed as the effective low-energy remnant of some extended group, and if the observed fermion masses are to be naturally produced as this larger group is spontaneously broken, then the extended group should possess certain characteristics. Specifically, its irreducible fermion representations should be no bigger than those of the Standard Model Group, the Standard Model Group should be embedded within it as a diagonal subgroup and its non-abelian part should be gauged. We analyse how well some groups of this type can satisfactorily account for the fermion mass and mixing hierarchies, at least order-of-magnitude wise.