Higgs boson mass limits in perturbative unification theories

Motivated in part by recent demonstrations that electroweak gauge coupling unification may occur at a low scale, we analyze the requirements on the Higgs mass if the gauge coupling unification is to be perturbative. We consider an infinite set of possible unification scenarios parametrized by the value of sin θW at the unification scale Λ, and show the Higgs boson mass limits based on the minimal standard model, the standard model with the fourth generation, the minimal SUSY standard model, and the next-to-minimal SUSY standard model with an additional singlet field. One of our interesting results is that the Higgs boson can be as heavy as 500 GeV in the non-SUSY and non-minimal SUSY models if the unification scale is low (Λ ∼ 1− 10 TeV). Future Higgs discovery will tell us which unification scenarios are consistent with the perturbativity of the theory.