Horizontal SU(2) symmetry revisited

One possible approach to understanding the pattern of masses and mixing angles in the quark sector is the concept of horizontal symmetry. We consider the SU(2) horizontal symmetry candidate, and examine the possibility of assigning the three generations of fermions to the doublet and singlet representations of SU(2)H. This assignment allows a natural explanation of the near masslessness of the first generation, and the smallness of the Kobayashi-Maskawa matrix elements connecting the third and first generation, and the second and third generation. We suggest that these masses and mixings may arise radiatively, and an example is given to illustrate how this may come about. In this example the inequality mu < md arises naturally. (orig.)