Upper and lower bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet model
Abstract
By imposing validity of the perturbation and stability of vacuum up to an energy scale
Λ
(
≤
10
19
GeV), we evaluate mass bounds of the lightest CP-even Higgs-boson mass (
m
h
) in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. The most general bounds are obtained as a function of
Λ
vering all the free parameters under the experimental constraint from the
rho
parameter and the b \to s \gamma
results.Wefindthat,whiletheupperboundisalmostthesameasintheSM,thelowerboundissignificantlyreduced.InthedecouplingregimewherethemodelbehavesliketheSMatlowenergy,thelowerboundisgiven,forexample,byabout100GeVfor
\Lambda = 10^{19}
GeVand
m_t = 175
GeV,whichissmallerbyabout40GeVthanthecorrespondinglowerboundintheSM.Ingeneralcase,the
m_h
isnolongerboundedfrombelowbytheseconditions.Ifweconsidertheexperimental
b \to s \gamma
constraint,small
m_h$ are excluded in Model II of the 2HDM.