@misc{oai:ir.soken.ac.jp:00000608,
 author = {笠井, 隆志 and カサイ, タカシ and KASAI, Takashi},
 month = {2016-02-17, 2016-02-17},
 note = {In the Standard Model (SM) of particle physics, the Higgs sector is introduced　in order to explain the mass of gauge bosons and fermions without conflict with　the gauge principle. In the Higgs sector, the Higgs field φ, which have a non-zero　vacuum expectation value, is introduced, and then the existence of Higgs boson is　predicted. After the discovery of the top quark, the Higgs sector is the last　remaining part yet to be confirmed in the SM. Experimental search for the Higgs　boson has been continued at the Fermilab Tevatron experiments and will be succeeded　by the CERN Large Hadron Collider (LHC) and future linear colliders (LC's). 　Discovery of the Higgs boson is important not only in confirming the mechanism of the electroweak gauge-symmetry breaking but also in providing us useful information on physics beyond the SM. As such a physics, some models are proposed. For each　model, allowed properties of the Higgs boson is obtained. When the Higgs boson is　discovered, its mass and various decay properties will be measured to test the SM　and to distinguish models of new physics at high energy scales. In this thesis we　obtain allowed properties of the Higgs boson theoretically in various extensions　of the SM, e.g. two-Higgs-doublet model (2HDM) with a softly-broken discrete　symmetry, Zee-Model which requires the existence of a SU (2) charged Higgs singlet　in order to generate the small neutrino mass, and Minimal super-symmetric Standard　Model (MSSM).<br /><br />　　The most interesting property of the Higgs boson is its mass value. Although　the mass of the Higgs boson is a free parameter in the SM, we can obtain its mass　bounds by demanding the considered theory to be a valid effective theory all the　way up to some cut-off energy scale (Λ); if we require the vacuum stability and　the validity of perturbation theory below a given cut-off scale Λ, we can determine　the lower and the upper bounds of the Higgs boson mass as a function of Λ, 　respectively, using renormalization group equations (RGE's). In the SM, for the　Planck scale m<SUB>p1</SUB>～10<SUP>19</SUP> GeV as Λ, the lower and the upper bounds become about　145 and 175 GeV at m<SUB>t</SUB>＝175 GeV, respectively.<br /><br />　　In the MSSM which is the most popular in the particle models beyond the SM,　the theoretical upper bound on the lightest CP-even Higgs boson mass is given by　about 120 GeV for m<SUB>t</SUB>＝175 GeV and m<SUB>stop</SUB>＝1 TeV.<br /><br />　　The lightest CP-even Higgs-boson mass for the 2HDM is investigated. This model　includes one more Higgs doublet compared to the SM Higgs sector. This is the most　simple extension of the SM. Through spontaneous symmetry breaking, five physical　Higgs bosons appear, i.e. two CP-even, one CP-odd and a pairs of charged Higgs bosons.　In the 2HDM, the mass upper bound is the same as that of the SM, whereas the lower　bound is reduced to zero. Specially, in the decoupling regime, where only one neutral　Higgs boson is light as compared to the other physical states of Higgs bosons, the　lower bound of the lightest Higgs boson mass is given by 100 GeV for Λ＝10<SUP>19</SUP>　GeV and m<SUB>t</SUB>＝175 GeV. This is considerably smaller as compared to the SM value.<br /><br />　　Next, the Higgs boson mass bounds for the Zee-Model is investigated. From the　observations of atmospheric and solar neutrinos, there are increasing evidences　for neutrino oscillations. If this is a correct interpretation, the SM has to be　extended to incorporate the small masses of the neutrinos suggested by data. There　has been several ideas proposed in literature to generate small neutrino masses. The　Zee-model is one of such attempts. In this model, the three different flavor　neutrinos are massless at the tree level, and their small masses are induced　radiatively through one-loop diagrams. For such a mass-generation mechanism to work,　it is necessary to extend the Higgs sector of the SM to contain at least two weak-doublet fields and one weak-singlet charged scalar field. The Higgs sector　of the Zee-model is similar to that of the 2HDM except for the existence of an　additional weak-singlet charged Higgs field, so that the physical scalar-bosons　include two CP-even, one CP-odd and two pairs of charged Higgs bosons. We show that　the mass bounds for the lightest CP-even Higgs boson are almost the same as those　in the 2HDM.<br /><br />　　For the Zee-Model, although the allowed mass range is the same as that of the　2HDM, other properties can be different from that in the usual Higgs doublet model.　We examine effects of the additional loop contribution of the singlet charged Higgs　boson to the partial decay width of h→γγ. If we assume Λ＝10<SUP>19</SUP> GeV, the　deviation of the decay width from the SM prediction can be about 20% within the　allowed range of the Higgs self-coupling constants which is obtained by the RGE　analysis. This amount of deviation could be tested at the future LC or photon-photon　LC experiments. We also discuss phenomenology of the singlet charged Higgs boson　at present and future collider experiments, which is found to be completely　different from that of the ordinary 2HDM-like charged Higgs bosons., 総研大甲第504号},
 title = {Phenomenology of Higgs bosons in variousextensions of the Standard Model},
 year = {}
}