Radiative Decay Bc → Ds*γ in the Technicolor with a Massless Scalar Doublet Model

Applying perturbative QCD, we study the process Bc → Dsγ in the technicolor with a massless scalar doublet model (TCMLSM). There are mainly two mechanisms contributing to the Bc → D*sγ process. One proceeds through the short distance b → sγ transition and the other through weak annihilation accompanied by a photon emission.We find that, compared with the standard model, the modification of Bc → D*sγ from πρ (the physical pions in the TCMLSM) is so small that can be neglected for the allowed mass ofπρ. The weak-annihilation contribution is found to be about one order larger than that of the electromagnetic penguin diagrams.     

顶色辅助的人工色模型下顶夸克极化效应的研究

在顶色辅助的人工色(TC2)理论下, 在强子对撞机上研究了顶夸克-反顶夸克对的产生过程中顶夸克的极化效应, 在计算过程中, 运用了MRS set A'部分子分布函数和螺旋度投影算符的方法. 研究结果表明: 在Tevatron上顶夸克的极化效应太小不可探测; 参数选取得当, 该效应在LHC上可以探测到, 其值可达16%. 因此, 顶夸克的极化效应提供了一种切实可行的检验顶色辅助的人工色模型的方法.     

Lepton-Flavor Violating Processes li → ljγ in Topcolor-Assisted Technicolor Models

We consider the lepton-flavor violating (LFV) processes li → ljγ in the framework of topcolor-assistedtechnicolor (TC2) models. We find that the new gauge boson Z‘ predicted by TC2 models can give significantlycontributions to these processes via the flavor-changing couplings Z‘lilj. The present experimental bound on the LFVprocess μ→ eγ gives severe constraints on the TC2 models. Using other experimental constraints on the Z‘ mass Mz,we obtain constraints on the lepton mixing factors KTμ and KTe. The future LFV experiments will probe into TC2models.     

TC2模型下的顶夸克稀有衰变t→cV

在顶色辅助的人工色(TC2)理论框架下,研究了顶夸克稀有衰变t→cV过程.结果表明TC2模型预言的标量粒子top-pions和top-Higgs对顶夸克稀有衰变分支比的贡献可以使其比标准模型预言值大6—9个数量级.在大多数参数范围内,分支比的数量级为:Br(t→cg)～10^－5,Br(t→cZ)～10^－5,Br(t→cγ)～10^－7.在合理的参数范围内,顶夸克稀有衰变t→cV过程能够被未来的对撞机实验探测到.因此,顶夸克稀有衰变过程为我们提供了一种检验TC2理论的方法.     

Single t-Quark Productions via Flavor-Changing Processes in Topcolor-Assisted Technicolor Model at Hadron Colliders

In the framework of topcolor-assisted technicolor （TC2） model, there exist tree-level flavor-changing （FC） couplings, which can result in the loop-level FC coupling tcg. Such tcg coupling can contribute significant clues at the forthcoming Large Hadron Collider （LHC） experiments. In this paper, based on the TC2 model, we study some single t-quark production processes involving tcg coupling at the Tevatron and LHC： pp（pp） → tq （q = u, d, s）, tg. We calculate the cross sections of these processes. The results show that the cross sections at the Tevatron are too small to observe the signal, but at the LHC it can reach a few pb. With the high luminosity, the LHC has considerable capability to find the single t-quark signal produced via some FC processes involving coupling tcg. On the other hand, these processes can also provide some valuable information of the coupling tcg with detailed study of the processes and furthermore provide the reliable evidence to test the TC2 model     

Rare Decays B → XS,dνν and XS,d → l+l- in the,Topcolor-Assisted Technicolor Model

We calculate the contributions to the rare decays B → X_S,dνν and X_S,d → l⁺l^- from one-loop Z^o -penguin diagrams in the framework of topcolor-assisted technicolor model. Within the parameter space, we find that: (a) the new contribution from technipions is less than 2% of the standard model prediction; (b) the top-pions can provide a factor of 10 to 30 enhancement to the ratios in question; (c) the topcolor-assisted technicolor model is consistent with the current experimental'data.     

Semileptonic Decays B＊→ηclυl with QCD Sum Rules

In this article, we calculate the B＊→ηc form-factors with the three-point QCD sum rules, then study the semileptonic decays B＊→ηclυl. The tiny decay widths may be observed experimentally in the future at the LHCb, while the B＊→ηc form-factors can be taken as basic input parameters in other phenomenologieal analysis.     

Top Quark Pair Production at e^＋e^— Colliders in the Topcolor—Assisted Technicolor Model

In the framework of topcolor-assisted technicolor model we calculate the contributions from the preudo Goldstone bosons and new gauge bosons to e^ e^-→ttk.We find that for reasonable ranges of the parameters,the preudo Goldstone bosons afford dominate contribution,the correction arising from new gauge bosons is negligibly small,the maximum of the relative corrections is-10% with the center-of-mass energy √s=500GeV;whereas in the case of √s=1500 GeV,the relative corrections could be up to 16%.Thus large new physics might be observable at the experiments of next-generation linear colliders.     

TOPCMTC模型中PGBs对top夸克稀有衰变的贡献

计算了top人工色援助的多标度人工色模型下top夸克稀有衰变t→cV(V=Z,γ,g)的单圈过程.发现在这个模型下,扩展的人工色相互作用对这些衰变提供主要的贡献,总的贡献能够把它们在标准模型下的分支比提高大约5–6个量级,对于一般的参数值,这些的结果分别是:B(t→cZ)～10^－6,B(t→cγ)～10^－7,B(t→cg)～10^－5.     

Constraints on Technicolor Models from Inclusive Decay of B Meson

Corrections to the branching ratio BR (B → X_s γ) from technipions and top pions appeared in technicolor models are investigated. We found that: (a) the multiscale walking technicolor model is ruled out since it is conflict with the CLEO data; (b) the topcolor-assisted technicolor model is consistent with the CLEO data of BR(B → X_s γ) for a certain range of parameters.     

Radiative Decay Bc→ Ds*γ in the Technicolor with a Massless Scalar Doublet Model

Applying perturbative QCD, we study the process B_c→D_s^*γ in the technicolor with a massless scalar doublet model (TCMLSM). There are mainly two mechanisms contributing to the B_c→ D_s^*γ process. One proceeds through the short distance b→sγ transition and the other through weak annihilation accompanied by a photon emission. We find that, compared with the standard model, the modification of B_c→ D_s^*γ from π_p (the physical pions in the TCMLSM) is so small that can be neglected for the allowed mass of π_p. The weak-annihilation contribution is found to be about one order larger than that of the electromagnetic penguin diagrams.     

TC2理论中tc夸克的联合产生

在TC2理论框架下,计算了在高能正负电子对撞机(LC)上,TC2动力学对味改变中性流过程e⁺e^－→tc产生截面的修正和TC2理论预言的中性top–pionπ0t对该过程产生截面的贡献.计算结果表明:TC2理论对LC实验中tc夸克联合产生的贡献主要来自中性top-pion π0t.在TC2理论的绝大部分参数空间内,可达10^－2ph.若假设LC的积分亮度为500fb^－1,则每年可产生数千个tc事例.因此,将来的LC实验可作为检验TC2理论的重要工具.     

The Analytical Helicity Amplitudes for Z → 3γ, γγ → γZ and γZ → γγ via W-Loop,Charged Scalar-Loop

The analytic helicity amplitudes of Z → 3γ, γγ → γZ and γZ → γγ via W-loop and charged scalar-loop are presented. There is some difference between our results and those in Z. Phys. C60 (1993) 175 (E.W.N. Glover and A.G. Morgan) for Z → 3γ via W-loop and fermion-loop, which has different physical meanings.     

Chiral Extrapolation of Lattice Data of Λ_b→Λ_c Form Factors

An extrapolation to the physical limit for the lattice data of Λ_b →Λ_c form factors computed in the nonphysical region is made in this work through a class of fitting functions proposed by us with nonlinear dependence on m2/π derived in the chiral perturbative theory(ChPT) and the heavy quark effective theory(HQET) framework. Then the results are applied to calculate the differential and integrated Λ_b →Λ_c semileptonic decay rates. Meanwhile, a comparison between our results and those obtained through the extrapolation functions with naive linear dependenceon m2/π is made.It is shown that the difference between the extrapolated central values of these two cases is about 5%.The total uncertainties(depending on the momentum transfer q~2) in the linear case are about 5% ～10%(caused by the uncertainties of lattice data) and those in the nonlinear case are about 10% ～ 20%(caused by the uncertainties of both lattice data and input parameters in Ch PT and HQET). More accurate lattice data and parameters in ChPT and HQET are needed to reduce the uncertainties of the extrapolated results.     

The Polarization Tensors of Z → 3γ and γγ → γγ via W-Loop in the Standard Model

The polarization tensors of Z → 3γ and γγ → γγ W-Boson loops are calculated in the standard model. The constrained equations for the tensors are deduced from the crossing symmetry and gauge invariance. These equations are numerically checked by the polarization tensor of γγ → γγ to the first three lowest orders in its low energy expansion.     

微扰QCD方法计算稀有衰变B+→D+s(-K)*0

在标准模型中,稀有衰变道B+→D+s(-K)*0只有通过纯湮没图才可以发生.这样这个衰变道的分支比很小.利用基于kT因子化的微扰方法给出分支比的预测,发现它在10-8的量级上.这个衰变道估计在将来的LHC上得到测量,对检验标准模型以及探寻新物理有着重要的意义.     

Pure annihilation decays of B_s~0→a_0~+a_0~- and B_d~0→K_0~(*+)K_0~(*-) in the PQCD approach

We study the CP-averaged branching fractions and the CP-violating asymmetries in the pure annihilation decays ofB _s~0→a_0~+a _0~-andB _d~0→K_0~(*+)K_0~(*-),where a_0[K_0~*]denotes the scalar a_0(980) and a_0(1450)[K_0~*(800)(ork)and K_0~*(1430)],with the perturbative QCD factorization approach under the assumption of two-quark structure for the a_0and K_0~*states.The numerical results show that the branching ratios of theB _d~0→K_0~(*+)K_0~(*-)decays are in the order of 10~(-6),while the decay rates of theB_s~0→a_0~+a _0~-modes are in the order of 10~(-5).In light of the measured modes with the same quark components in the pseudoscalar sector,namely,B _d~0→K~+K~-and B_s~0→p p~(+-),the predictions for the considered decay modes in this work are expected to be measured at the Large Hadron Collider beauty and/or Belle-Ⅱ experiments in the (near) future.Meanwhile,it is of great interest to find that the twist-3 distribution amplitudes φ~S and φ~T with inclusion of the Gegenbauer polynomials for the scalar a_0(1450) and K_0~*(1430)states in scenario2 contribute slightly to the branching ratios while significantly to the CP violations in the B_d~0→K_0~*(14 30)~+K_0*(14 30)~-and B_s~0→a_0(1450)~+a_0(1450)~-decays,which indicates that,compared to the asymptotic φ~Sand φ~T,these Gegenbauer polynomials could change the strong phases evidently in these pure annihilation decay channels.These predictions await for the future confirmation experimentally,which could further provide useful information to help explore the inner structure of the scalars and shed light on the annihilation decay mechanism.     

Production of a neutral scalar associated with a photon at the LHC in the topcolorassisted technicolor model

In the context of the topcolor-assisted technicolor (TC2) model, we consider the production of the neutral scalar S(π_t⁰ or h_t⁰) associated with a photon at the LHC and compare our results with those given by the minimal supersymmetric extension of the Standard Model (MSSM). We find that its production cross section is larger or smaller than that of the scalar particle predicted by the MSSM model, depending on the values of the relevant free parameters.     

ILC上Z玻色子与荷电top-pion对联合产生过程的研究

在国际直线对撞机(ILC)上顶色辅助的人工色(TC2)模型下对Z玻色子与荷电top-pion对联合产生过程e⁺e^- → Zπ_t⁺π_t^-进行了研究. 计算了过程e⁺e^- → Zπ_t⁺π_t^-的产生截面, 发现在TC2模型所允许的参数空间范围之内该过程的截面最大可达到1 fb. 考虑到荷电top-pion的主要的衰变模式π_t⁺ → tb, 发现该截面在ILC能产生很可观的事例数.     

The Signatures of the Neutral Top-Pion at the NLC and the Tevatron in Topcolor-Assisted MWTC Model

The neutral top-pion π_t⁰ can couple to the gluons and the photons through the top quark triangle-loop. we calculate the corrections of the neutral top-pion π_t⁰ to the tt production cross section in topcolor-assisted multiscale walking technicolor model. We find that, for a heavy neutral top-pion, the corrections are quite significant. For m_t = 175 GeV, 5 GeV ≤ m_t¹ ≤ 20 GeV and M_πt = 350 GeV, the relative correction Δσ/σ₀ is larger than 10% which might be observed at a high-luminosity Tevatron. We further estimate the production cross section of π_t⁰ at the NLC experiment. We find that the production rate is significantly large. The neutral top-pion π_t⁰ may be detected in future e⁺e^- linear collider experiments.