The on-shell renormalization scheme for electroweak theory is well studied in the standard model （SM）, but a consistent on-shell renormalization scheme for the minimal supersymmetric standard model （MSSM） is still unknown. In the MSSM, we study the on-shell scheme for three vertexes： with virtual SUSY particles （chargino, sneutrino, neutralino and slepton） at one-loop order. Instead of the amplitude of a single triangle diagram, the sum of the amplitude of triangle diagrams belonging to one suit can be renormalized in the on-shell scheme. One suit points out that the internal virtual particles are consistent. The zero-momentum scheme is also used for the renormalization. The two schemes can make the renormalized results decoupled, and in the MSSM some of the special characters of the on-shell scheme are shown. This work is propitious in completing the on-shell renormalization scheme in the MSSM.
A sizable difference in top quark pair forward backward asymmetry （AFB） is observed at Tevatron. The discrepancy triggers many new physics beyond the standard model （SM） and then constrains the parameter spaces in them. In this article we calculate the AFB of the top-pair production at Tevatron up to next to leading order （NLO） in the little Higgs model （LHM）. We find that the contribution of ZH can be large enough to make up the gap between SM prediction and experimental data. Then, the parameter space for the couplings between ZH and quarks are constrained. Thus, this model can fulfill the experimental data, both in AFB and in cross section.
We discuss the production of ηc （2S） through the process e＋e- -→γηc （2S）, where the leading contributionoriginates from l-loop electroweak corrections. Adopting some reasonable light-cone distribution amplitudes, we analyze the cross section of this process. As the electron-positron center of mass energy √s=3770 MeV, the typicalproduction cross section of this process is about 1 fb.
We analyze the theoretical prediction on the branching ratio of B→Xsγ to order ∧^2EW/∧^2KK in extension of the standard model with a warped extra dimension and the custodial symmetry SU（3）c×SU（2）L×SU（2）R×U（1）××PLR, where AKK denotes the energy scale of low-lying Kaluze-Klein excitations and AEW denotes the electroweak energy scale. Contributions from the infinite series of Kaluze-Klein excitations are summed over through the residue theorem. The numerical result indicates that the present experimental data constrain the parameter space of the concerned model strongly.
Applying an effective Lagrangian method and an on-shell scheme, we analyze the electroweak corrections to the rare decay b→, s＋γ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in the inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of B → Xsγ can reach 5% as the energy scale of new physics ANp=200 GeV.
