Vacuum stability bounds in the two-Higgs doublet model

In the standard model, the requirements of vacuum stability and the validit y of perturbation theory up to the unification scale force the mass of the Higgs boson to be approximately between 130 GeV and 180 GeV. We re-examine these requirements in the (non-supersymmetric) two-Higgs doublet model, in the light of the large top quark mass, and constrain the masses of the Higg s bosons in this model. It is found that the mass of the charged Higgs boso n must be lighter than 150 GeV. This bound is below the lower bound in the popular model-II two-Higgs doublet model, and thus we conclude that this mo del cannot be valid up to the unification scale. The bounds on the neutral Higgs scalars are also discussed. (C) 1999 Published by Elsevier Science B. V. All rights reserved.