Mass bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet model
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The upper and the lower bounds of the lightest CP-even Higgs-boson mass ($m_h$) are discussed in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. They are obtained as a function of a cut-off scale $Λ$ ($\leq 10^{19}$ GeV) by imposing the conditions in which the running coupling constants neither blow up nor fall down below $Λ$. In comparison with the standard model (SM), although the upper bound does not change very much, the lower bound is considerably reduced. In the decoupling regime where only one Higgs boson ($h$) becomes much lighter than the others, the lower bound is given, for example, by about 100 GeV for $Λ= 10^{19}$ GeV and $m_t = 175$ GeV, which is smaller by about 40 GeV than the corresponding lower bound in the SM. In generic cases, $m_h$ is no longer bounded from below by these conditions. If we consider the $b \to s γ$ constraint, small values of $m_h$ are excluded in Model II of the 2HDM.
13 pages, 5 figures, extend the analysis to the case without restriction among self-coupling constants. Conclusions unchanged. To appear in Phys. Lett. B
13 pages, 5 figures, extend the analysis to the case without restriction among self-coupling constants. Conclusions unchanged. To appear in Phys. Lett. B