Relaxing the Upper Bound on the Mass of the Lightest Supersymmetric Higgs Boson

We present a class of supersymmetric models in which the lightest Higgs-boson mass can be as large as a few hundred GeV (200 - 300 GeV) while the successful MSSM prediction for gauge coupling unification is preserved. The theories are formulated on a 5D warped space truncated by two branes, and a part of the Higgs sector is localized on the infrared brane. The structure of the Higgs sector in the four dimensional effective theory below the Kaluza-Klein mass scale is essentially that of the next-to-minimal supersymmetric standard model (NMSSM), or related theories. However, large values of the NMSSM couplings at the weak scale are now possible as these couplings are required to be perturbative only up to the infrared cutoff scale, which can in general be much lower than the unification scale. This allows the possibility of generating a large quartic coupling in the Higgs potential, and thereby significantly raising the Higgs-boson mass bound. We present two particularly simple models. In the first model, the quark and lepton fields are localized on the ultraviolet brane, where the grand unified symmetry is broken. In the second model, the quark and lepton fields are localized on the infrared brane, and the unified symmetry is broken both on the ultraviolet and infrared branes. Our theories potentially allow the possibility of a significant reduction in the fine-tuning needed for correct electroweak symmetry breaking, although this is somewhat model dependent.