Supersymmetric Higgs Bosons in a 5D Orbifold Model

We analyze the phenomenology of the Higgs sector in a 5D model compactified on an $S_1/Z_2$ orbifold where the compactification scale $M_C$ is around the TeV scale. We show that the conventional MSSM Higgs boson mass bounds in 4D can be violated when we allow the gauge sector, Higgs and third family multiplets to live in the fifth extra dimension. Supersymmetry is broken at an orbifold fixed point which is spatially separated from the Yukawa brane where two chiral families are localized. When the brane-localized supersymmetry breaking term for the stop sector is arbitrarily large, we find that the stop KK-mode mass spectrum is completely independent of the Higgs fields. Hence, the Higgs masses only receive radiative contributions from the top KK-modes. The 1-loop effective potential is insensitive to the cutoff scale of the theory and yields a negative Higgs squared-mass contribution that triggers electroweak symmetry breaking in the range $1.5\simlt\tan\beta\simlt 20$, where bottom/sbottom loop effects can be ignored. The recent LEP Higgs bound at $m_{h^{0}} > 114.1$ GeV, in conjunction with naturalness arguments, allows us to bracket the compactification scale $1.5 \simlt M_{C} \simlt 4$ TeV. Within this parameter space, we find that the lightest Higgs boson mass has an upper bound $m_{h^{0}} \simlt 160$ GeV with the magnitude of the $\mu$-parameter restricted to the range $33 \simlt | \mu | \simlt 347$ GeV.