Relaxing the Landau-pole constraint in the NMSSM with the Abelian gauge symmetries

In order to relax the Landau pole constraint on "\lambda", which is a coupling constant between a singlet S and the MSSM Higgs, \lambda Sh_uh_d in the next-to-MSSM (NMSSM), and also maintain the gauge coupling unification, we consider U(1) gauge extensions of the NMSSM. For relatively strong U(1) gauge interactions down to low energies, we assign U(1) charges only to the Higgs and the third family of the chiral matter among the MSSM superfields. In the U(1)_Z [U(1)_Z\times U(1)_X] extension, the low energy value of \lambda can be lifted up to 0.85-0.95 [0.9-1.0], depending on the employed charge normalizations, when \lambda and the new gauge couplings are required not to blow up below the 10^{16} GeV energy scale. Introduction of extra vector-like superfields can induce the desired Yukawa couplings for the first two families of the chiral matter. We also discuss various phenomenological constraints associated with extra U(1) breaking.Comment: 22 pages, 2 eps figures, version to appear in Phys. Rev.