Efficacious Extra U(1) Factor for the Supersymmetric Standard Model
  The totality of neutrino-oscillation phenomena appears to require the existence of a light singlet neutrino. As pointed out recently, this can be naturally accommodated with a specific extra U(1) factor contained in the superstring-inspired E$_6$ model and its implied particle spectrum. We analyze this model for other possible consequences. We discuss specifically the oblique corrections from Z-Z' mixing, the phenomenology of the two-Higgs-doublet sector and the associated neutralino sector, as well as possible scenarios of gauge-coupling unification. 
E. Keith and Ernest Ma