U(1)′ symmetry breaking in supersymmetric E₆ models

We study the electroweak and U(1)′ symmetry breaking patterns in models with the particle content of supersymmetric E₆, including standard model singlets S and exotic quarks D, D̄. Motivated by free fermionic string models, we do not require E₆-type relations between Yukawa couplings. In particular, we assume that baryon and lepton numbers are conserved, so that the exotic quarks can be light. Gauge invariance allows Yukawa interactions between S and Higgs doublets, and between S and the exotic quarks, allowing radiative U(1)′ symmetry breaking and the generation of an effective μ parameter at the electroweak scale. For both the E₆ ψ and η models, universal soft supersymmetry breaking parameters and Yukawa universality at the high (string) scale do not yield acceptable low energy phenomenology. Relaxing universality, we find solutions with phenomenologically acceptable values of M_Z′ and the Z-Z′ mixing angle. In addition, by varying the U(1)′ charge assignments due to the mixing of U(1)_χ and U(1)_ψ of E₆, it is possible to have acceptable low energy phenomenology with universal boundary conditions.