GAUGE UNIFICATION, YUKAWA HIERARCHY AND THE MU PROBLEM

The hierarchy in the Yukawa couplings may be the result of a gauged horizontal U(1)(H) symmetry. If the mixed anomalies of the Standard Model gauge group with U(1)H are cancelled by a Green-Schwarz mechanism, a relation between the gauge couplings, the Yukawa couplings and the mu-term arises. Assuming that at a high energy scale g(3)(2) g(2)(2) = 5/3g(1)(2) and (m(e)m(mu)m(tau))/(m(d)m(s)m(b)) similar to lambda (where lambda is of the order of the Cabibbo angle), the U(1)(H) symmetry solves the mu-problem with mu similar to lambda m(3/2).