高能物理的精确计算和精确测量

随着近半个世纪高能物理的实验装置和测试手段的飞速发展,相应的理论也达到新的高度,人们更深入地认识了自然界最基本的组成结构并了解了它们之间的相互作用,从而建立了非常成功的'标准模型'。然而,像19世纪末物理学家那样盲目乐观的态度却是不可取的,在各领域中仍存在现有理论无法解释的现象。于是,寻找超越标准模型的新物理成为促进理论和实验向新层次发展的动力。众所周知,新物理的能标可能超出目前能取得的能量范围(LHC),因而要在精确测量中寻找新物理发现的蛛丝马迹。因此,对理论计算的精度的要求也在大幅度提升。精确测量和精确计算是探求超越标准模型新物理的两个侧面,缺一不可。它们的进展不仅增进我们对自然界的认识,而且带动了相应高技术的发展。

Kaluza-Klein Corrections to the μ Anomalous Magnetic Moment in the Appelquist-Cheng-Dobrescu Model

Applying the effective Lagrangian method,we analyze the radiative contributions of the Kaluza–Klein(KK)modes to the muon magnetic dipole moments in the Appelquist–Cheng–Dobrescu model.Summing over the infinite series composed by the KK towers,we verify the final results satisfying the decoupling theorem in the limit R^(-1)→∞.For the compactification scale R^(-1)=300 GeV,we obtain the electroweak radiative corrections from the KK modes to the muon MDM amount to 6.72×10^(-12) at one loop level.

最小超对称模型中希格斯势的真空稳定性

讨论了量子场论对希格斯有效势的单圈阶修正与重整化群方程的改进方法,并将这些理论应用于最小超对称模型(minimum supersymmetric model,MSSM).在MSSM框架下讨论了稳定的希格斯有效势对敏感参数tanβ的限制,通过重整化群方程的双圈阶数值解,在不同能标下对希格斯势的真空稳定性进行了研究并作出了分析.结果表明,随能标增长希格斯势行为有所变化,但没有出现标准模型那样的不稳定势.

Leptonic di-flavor and di-number violation processes at high energyμ^(±)μ^(±)colliders

The leptonic di-flavor violation (LFV) processes μ^(±)μ^(±)→e^(±)e^(±) and μ^(±)μ^(±)→τ^(±)τ^(±) and leptonic di-number violation (LNV) processes μ^(±)μ^(±)→W_(i)^(±)W_(j)^(±) (i,j=1,2) at same-sign high energy μ^(±)μ^(±) colliders are studied. The new physics (NP) factors that may play roles in these processes are highlighted by cataloging them into three types. Taking into account the experimental constraints, the processes at μ^(±)μ^(±) colliders are computed, and the results are presented properly. The results lead to the conclusion that observing the NP factors through the LFV and LNV processes at TeV-energy μ^(±)μ^(±) colliders has significant advantages that cannot be achieved elsewhere. Therefore, once the techniques for muon acceleration and collision are developed successfully, the option of building same-sign high energy muon colliders should be seriously considered.

在加速器上探测周围的超对称暗物质(英文)

探讨了在加速器上直接检测周围超对称暗物质的可能性,计算了暗物质与e^+e^-和强子对撞机上束粒子碰撞的弹性和非弹性散射截面．

量子世界中寻找新物理的基础理论研究

本项目属于量子世界中粒子物理学的基础理论研究,依托于国家自然科学基金项目,进行了寻找量子世界新物理的基础理论研究,主要的研究对象是粒子物理新物理理论的候选者——超对称标准模型。具体在以下超对称标准模型中进行理论研究:μν超对称标准模型,该模型解决了最小超对称标准模型的μ问题与中微子质量问题;B-L超对称标准模型与BL最小超对称标准模型,这两个模型可以很好地解释宇宙中物质与反物质不对称问题。本项目在以下几方面展开具体研究,取得了一系列重要科学成果。

Neutrino Mixing in the BLMSSM

In recent years, a nonzero value for the neutrino mixing angle θ13has been successively measured by the international famous reactor oscillation experiments, which is greater than 5 standard deviations. Our study is in the framework of the MSSM, where baryon and lepton numbers are local gauged symmetries(BLMSSM). This model can generate three tiny neutrino masses at the tree level through TeV scale seesaw mechanism. In our paper, we analyze the neutrino masses and their corresponding mixing angles with a "top-down" method, assuming neutrino mass spectrum with normal ordering(NO) and inverted ordering(IO).

t→cγ and t→cg in Local Gauged Baryon and Lepton Numbers

In this paper,we calculate the top quark rare decays t→cγ and t→cg in an extension of the standard model,where baryon number and lepton number are local gauge symmetries.Adopting reasonable assumptions on the parameter space,we find that the branching ratios of t→cγ and t→cg can reach 10 6and 10 5respectively,which can be detected in near future.

B^0-B^0 Mixing in Local Gauged Baryon and Lepton Numbers

Using the efective Hamiltonian method, we analyze the B0-ˉB0mixing in the extension of the standard model(SM) where baryon number and lepton number are local gauge symmetries. The numerical results indicate the correction from the extra particles to the mass diference mB is significant. There is a 60% enhancement compared to the SM prediction for mB at most, which agrees with the current experimental result.

Neutrino Production via e^-e^+ Collision at Z-Boson Peak

The production of the three normal neutrinos via e-e+ collision at Z-boson peak(neutrino production in a Z-factory) is investigated thoroughly. The differences of νe-pair production from νμ-pair and ντ-pair production are presented in various aspects. Namely the total cross sections, relevant differential cross sections and the forwardbackward asymmetry etc. for these neutrinos are presented in terms of figures as well as numerical tables. The restriction on the room for the mixing of the three species of light neutrinos with possible externals(heavy neutral leptons and/or sterile neutrinos) from refined measurements of the invisible width of Z-boson is discussed.

Constraining parameter space of the little Higgs model using data from tera-Z factory and ILC

STYLE=“word-wrap： break-word”〉The Standard Model（SM） prediction on the forward-backward asymmetry for bˉb production（A^bFB） is well consistent with the data of LEP at the Z-pole, but deviates from the data at√s =89.55 and 92.95 Ge V which are slightly away from the pole. This deviation implies that there is still room for new physics. We calculate the A^bFB at the vicinity of the Z-pole in the little Higgs model as well as other measurable parameters such as R b and R c,by which we may constrain the parameter space of the little Higgs model. This can be further tested in the newly proposed tera-Z factory. With the fitted parameters we further make predictions on A^bFB and A t FB for tˉt production at the International Linear Collider（ILC）.

Top quark forward-backward asymmetry in the little Higgs model

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.

125 GeV Higgs decay with lepton flavor violation in the μνSSM

Recently,the CMS and ATLAS collaborations have reported direct searches for the 125 GeV Higgs decay with lepton flavor violation,h→μτ.In this work,we analyze the signal of the lepton flavour violating（LFV） Higgs decay h→μτ in the μ.from γ Supersyninietric Standard Model（μνSSM） with slepton flavor mixing.Simultaneously,we consider the constraints from the LFV decay τ→μγ,the muon anomalous magnetic dipole moment and the lightest Higgs mass around 125 GeV.

Feynman rules for neutrinos and new neutralinos in the BLMSSM

In a supersymmetric extension of the Standard Model where baryon and lepton numbers are local gauge symmetries（BLMSSM）, we deduce the Feynman rules for neutrinos and new neutralinos. We briefly introduce the mass matrices for the particles and the related couplings in this work, which are very useful to research the neutrinos and new neutralinos.

Top quark decay to a 125 Ge V Higgs in the BLMSSM

In this paper, we calculate the rare top quark decay t → ch in a supersymmetric extension of the Standard Model where baryon and lepton numbers are local gauge symmetries. Adopting reasonable assumptions on the parameter space, we find that the branching ratios of t→ch can reach 10-3, which could be detected in the near future.

Comprehensive analysis of e^+e^-→γηc(2S)

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.

One-loop on-shell renormalization of MSSM vertexes

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.

Constraint on the warped space from → X_s γ

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.

Muon anomalous Muon anomalous Muon anomalous magnetic dipole moment in theμνSSM

Recently,the Muon g-2 experiment at Fermilab measured the muon anomalous magnetic dipole moment(MDM),aμ=(gμ-2)/2,and reported that the new experimental average increases the difference between the experiment and the standard model(SM)prediction to 4.2σ.In this work,we reanalyze the muon anomalous MDM at the two-loop level in theμfrom theνSupersymmetric Standard Model(μνSSM)combined with the updated experimental average.TheμνSSM can explain the current difference between the experimental measurement and the SM theoretical prediction for the muon anomalous MDM,constrained by the 125 GeV Higgs boson mass and decays,the rare decayˉB→Xsγ,and so on.We also investigate the anomalous MDM of the electron and tau lepton,ae=(ge-2)/2 and aτ=(gτ-2)/2,at the two-loop level in theμνSSM.In addition,the decaying of the 125 GeV Higgs boson into a pair of charged leptons in theμνSSM is analyzed.

Scalar neutrino dark matter in the BLMSSM

The BLMSSM is an extension of the minimal supersymmetric standard model(MSSM).Its local gauge group is SU(3)C×SU(2)L×U(1)Y×U(1)B×U(1)L.Supposing the lightest scalar neutrino is a dark matter candidate,we study the relic density and the spin independent cross section of sneutrino scattering off a nucleon.We calculate the numerical results in detail and find a suitable parameter space.The numerical discussion can confine the parameter space and provide a reference for dark matter research.