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The lightest Higgs scalar boson mass in supersymmetry can be raised by extra vector-like quark and lepton supermultiplets with large couplings but dominantly electroweak-singlet masses. I consider models this type that maintain perturbative gauge coupling unification. The impact the new particles on precision electroweak observables is found to be, with the fit to Z-pole data as good or better than that of the Model even if the new Yukawa couplings are as large as their-point values and the extra vector-like quark masses are as light as 400. I study the size of corrections to the lightest Higgs boson mass, taking account the fixed-point behavior of the scalar trilinear couplings. I also the decay branchings ratios of the lightest new quarks and leptons and features of the resulting collider signatures.
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Stephen P. Martin (2010) studied this question.
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