| The predictions of Standard Model (SM) of particle physics are always con-sistent with results of the high energy experiment excellently, so it can be said that the SM is one of the most successful theoretical models until now. In the SM, electroweak symmety breaking (EWSB) is achieved by introducing the Higgs mechanism, which gives masses to the elementary particles and implies the ex-istence of a SM Higgs boson. A giant step of particle physics was made with a new boson with mass of around126GeV observed both by the ATLAS and CMS collaborations at the Large Hadron Collider (LHC) in July2012. This particle is tentatively identified as a Higgs boson. The more precision measurements on its properties are still going on at the LHC. And in light of the current data, it is very likely to be the SM Higgs boson. The next important task is to investigate and measure the nature of this new particle, and finally to determine whether it is really the SM Higgs boson.Due to the strong and complex hadronic backgrounds, there are intrinsic limitations for hadron collider in precision measurements of the nature of par-ticles. Therefore, physicists anchor their hopes of more precision determination of this Higgs boson on the proposed International Linear Collider (ILC), which is a positron-electron collider with more clean background and higher accuracy measurement. Among the nature of Higgs particle, the determinations of its total decay width and branching ratio for each decay channel are very important. The H→γγ decay width is very sensitive to the theoretical model. Any deviation between the SM prediction and the exprimental measurement may possibly pro-vide hints for new phycics. In the chapter3of thesis, we provide the precision study on the process e+e-→γγ at the ILC, which is one of the most seri-ous and irreducible background to determine the H→γγ decay width and can also be used to investigate the gauge boson coupling. We present a calculation of the complete one-loop electroweak (EW) corrections to the diphoton plus Z production in the SM at the ILC, and give out the leading order (LO) and next-to-leading order (NLO) EW corrected cross sections and kinematic distributions of final products. We find that the NLO EW relative correction exhibits a strong dependence on phase space. With the study and comparison of the signal process e+e-→ZH→Zγγ as well as the background process e+e-→Zγγ, we conclude that the background events can be suppressed significantly if we take some proper kinematic cuts on the final products. The Higgs boson coupling with top quarks can help to shed light on in the electroweak symmetry breaking (EWSB) mechanism, which is of particular phe-nomenological and theoretical interest all the time. The Higgs boson production associated with a top quark pair at the hadron collider can provide an opportunity unequivocally to determine the Yukawa coupling of top quark, since its production rate is directly proportional to the square of this coupling. In the chapter4of this thesis, we report on our calculations of the NLO QCD and NLO EW corrections to the process pp→Htt with sequential top quark decays in the SM. We provide the integrated cross sections at the14TeV LHC and even at the future proton-proton colliders with1/2S=33and100TeV. We present some kinematic distributions of final products for the process pp→Htt→HW+bW-b+X→Hl+l-bbvv+X. We conclude that the NLO EW corrections are quantitatively comparable with the NLO QCD corrections in some kinematic region.The innovations in this thesis are listed as follows:· We firstly provide the calculation of full NLO EW corrections for the dipho-ton plus Z production at the ILC, and present the most precision theoret-ical predictions so far. It provides theoretical foundation to determine the H→γγ decay channel and to probe gauge boson coupling.· In the precision study on the e+e-→Zγγ and pp→Htt processes, we have to adopt quadruple precision arithmetic, which would consume much more computer CPU time, to solve the serious unstable problem in the calculation of one-loop integrals. In order to treat the unstable problem and improve the efficiency in the numerical calculation, we developed program coded with double precision and quadruple precision united.· We firstly meet the demand listed in the Les Houches wishlist about the deep investigations on the Htt with sequential top quark decays at high energy hadron collider, that is, present the calculation for pp→Htt→HW+bW b+X→H1+1-bbvv+X process at the hadron collider up to NLO QCD and NLO EW, which is the most precision theoretical prediction until now. Our study as theoretical reference is helpful for the measurement of top quark Yukawa coupling.· We solve the specific complex IR divergence cancellation problem appearing in the calculation of NLO EW corrections for the pp→Htt process, in which there exist both the photonic and gluonic IR divergences. |
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