An improved supersymmetric SU(5)

By supplementing minimal supersymmetric SU(5) (MSSU(5)) with a flavor U(1) symmetry and two pairs of 15+15 `matterʹ supermultiplets, we present an improved model which explains the charged fermion mass hierarchies and the magnitudes of the CKM matrix elements, while avoiding the undesirable asymptotic mass relations ms=mμ, mdms=memμ. The strong coupling αs(MZ) is predicted to be approximately 0.115, and the proton lifetime is estimated to be about five times larger than the MSSU(5) value. The atmospheric and solar neutrino puzzles are respectively resolved via maximal νμ−ντ and small mixing angle νe−νs MSW oscillations, where νs denotes a sterile neutrino. The U(1) symmetry ensures not only a light νs but also automatic `matterʹ parity.