Charmless Hadronic Decays B→VV in the Topcolor-Assisted Technicolor Model

Based. On the effective Hamiltonian with the generalized factorization approach, we calculate the branchingratios and CP asymmetries of B → VV decays in the Topcolor-assisted Technicolor (TC2) model. Within the consideredparameter space we find that: (a) for the penguin-dominated B → K* φ and K*0 φ decays, the new physics enhancementsto the branching ratios are around 40%; (b) the measured branching ratios of B →K* φ and K*0φ decays prefer therange of 3 Neffc 5; (c) the SM and TC2 model predictions for the branching ratio B(B →ρ ρ0) are only about halfof the Belle‘s measurement; and (d) for most B → VV decays, the new physics corrections on their CP asymmetries are generally small or moderate in magnitude and insensitive to the variation of mπ and Neffc.     

B→ηK and B→φKs Decays in the Two Higgs Doublet Model Ⅲ

Using the QCD factorization approach, we investigate the large branching ratios of B→ηK^＊ decays and the SCKs anomaly of B→φKs decay in the two Higgs doublet model Ⅲ. With the contributions of flavour-changing neutral current mediated by the neutral Higgs bosons H^0, h^0 and A^0 at the tree level, we provide a coherent resolution to these anomalies within the constrained parameter spaces, which are 120 〈｜λbs λss｜ 〈136. This will be really interesting in searching for the signs of new physics.     

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 Z_H can be large enough to make up the gap between SM prediction and experimental data. Then, the parameter space for the couplings between Z_H and quarks are constrained. Thus, this model can fulfill the experimental data, both in AFB and in cross section.     

Searching for new physics in D~0→μ~+ μ~-,e~+e~-,μ~±e~■ at BES and/or the super charm-tau factory

In contrast with B0-ˉB0, Bs-ˉBs mixing where the standard model(SM) contributions overwhelm that of the new physics beyond standard model(BSM), a measured relatively large D0-ˉD0mixing where the SM contribution is negligible, definitely implies the existence of the new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the decay mode D0→μ+μ-could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of the new physics BSM in the leptonic decays of D0. Concretely we discuss the contributions of unparticle or an extra gauge boson Z while imposing the constraints set by fitting the D0-ˉD0mixing data. We find that the long-distance SM effects for D0→lˉl still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as D0→μ±e, the new physics contribution would be significant.     

Bos(d)-(-B)os(d) Mixing and New Physics Effects in a Top Quark Two-Higgs Doublet Model

We calculate the new physics contributions to the neutral B0d and B0s meson mass splitting △Md and △Ms induced by the box diagrams involving the charged-Higgs bosons in the top quark two-Higgs doublet model (T2HDM).Using the precision data, we obtain the bounds on the parameter space of the T2HDM: (a) For fixed MH = 400 Ge V and δ = [0°,60°], the upper bound on tanβ is tanβ≤ 30 after the inclusion of major theoretical uncertainties; (b) For the case of tanβ≤ 20, a light charged Higgs boson with a mass around 300 Ge V is allowed; and (c) The bounds on tanβ and MH are strongly correlated: a smaller (larger) tanβ means a lighter (heavier) charged Higgs boson.     

B→Kη~(,) decays in the SM with fourth generation fermions

By employing the perturbative QCD(pQCD) factorization approach, we calculate the new physics contributions to the four B→Kη()decays in the Standard Model(SM) with a fourth generation of fermions(SM4),induced by the loop diagrams involving t quark. Within the considered parameter space of the SM4 we find that:(a) the next-to-leading order(NLO) pQCD predictions for the branching ratios and CP-violating asymmetries in both the SM and SM4 generally agree with the data within one standard deviation;(b) for Br(B→Kη), the inclusion of the fourth generation contributions can improve the agreement between the theoretical predictions and the data effectively;(c) however, for Br(B → Kη) the decrease due to t loops is disfavored by the data; and,(d) the new physics corrections to the CP-violating asymmetries of the considered decays are only about 10%.     

Probing magnetic moment operators in H_γ production and H→τ~+τ~-γ rare decay

The magnetic moment(a_γ) and weak magnetic moment(a_W) of charged leptons and quarks are sensitive to quantum effects of new physics heavy resonances.In effective field theory,a_γ and a_W are induced by two independent operators.Therefore,one has to measure both ay and aw to shed light on new physics.The aw's of the SM fermions are measured at the LEP.In this work,we analyze the contributions from magnetic and weak magnetic moment operators in the processes of pp→H_γ and gg→H→τ~+τ~-γ at the High-Luminosity Large Hadron Collider.We demonstrate that the two processes can cover most of the parameter space that cannot be probed at the LEP.     

Two loop electroweak corrections from heavy fermions to b→s＋γ

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.     

Littlest Higgs Model and Spin Correlation of Top Quark Production at High Energy Linear e^＋e^- Colliders

Based on the littlest Higgs model, we investigate the spin correlation of the top quark pair production via the process e^＋e^- →tt at the high energy linear e^＋e^- collider （ILC） with a centre-of-mass energy √S = 800 GeV. Our numerical results show that the gauge boson ZH generates very small corrections to the spin correlation observable C in all the parameter space allowed by the electroweak data. However, with reasonable values of the free parameters, the value of the relative correction parameter RBH = （CBH-CSM）/CSM can reach 10%, which might be detected in future ILC experiments.     

A private SUSY 4HDM with FCNC in the up-sector

We present a SUSY model with four Higgs doublets of the"private type,"in which all fermion types(up,down,and charged leptons)obtain their masses from a different Higgs doublet H_f(f=u_1,d,e) .The conditions for anomaly cancellation imply that the remaining Higgs doublet of the model( H_{u_2} )must have the same hypercharge as H_{u_1} ,and thus,can only couple to up-type quarks,which opens the possibility to have FCNCs only in this sector.We study the Lagrangian of the model,and in particular,the Higgs potential,to identify the Higgs mass-eigenstates and their interactions;for the Yukawa matrices,we consider the four-texture case.We obtain constraints on the model parameters by using LHC measurements on the properties of the 125 GeV Higgs boson(h),and identify viable regions of the parameter space.Subsequently,these constraints are used to evaluate the prospects for detecting the FCNC decay mode t→ch at the future high-luminosity(HL)option for the LHC,which are compared with current limits from LHC-run2.Moreover,we evaluate the FCNC decay of the next heavier Higgs boson H₂→tc ,which can typically reach BR(H_2→tc)≈(10^-4-10^-5) .The search for the signal at HL-LHC is also studied,and it is found that it may be detectable for specific regions of the model parameter space.     

Searching for new physics in D^0→μ^＋ μ^-,e^＋e^-,μ^±e at BES and/or the super charm-tau factory

In contrast with B0-ˉB0, Bs-ˉBs mixing where the standard model（SM） contributions overwhelm that of the new physics beyond standard model（BSM）, a measured relatively large D0-ˉD0mixing where the SM contribution is negligible, definitely implies the existence of the new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the decay mode D0→μ＋μ-could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of the new physics BSM in the leptonic decays of D0. Concretely we discuss the contributions of unparticle or an extra gauge boson Z while imposing the constraints set by fitting the D0-ˉD0mixing data. We find that the long-distance SM effects for D0→lˉl still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as D0→μ±e, the new physics contribution would be significant.     

LHCb anomaly in B→K~*μ~+μ~- optimised observables and potential of Z' model

Over the last few years LHCb found some discrepancies in b → sl~+l~-FCNC transitions, including anomalies in the angular observables of B→K~*μ~+μ~-, particularly in P′_5, in the low dimuon mass region. Recently,these anomalies have been confirmed by Belle, CMS and ATLAS. As direct evidence of physics beyond the Standard Model is absent so far, these anomalies are being interpreted as indirect hints of new physics. In this context, we study the implications of the family non-universal Z′ model for the angular observables P_(1,2,3), P′_(4,5,6) and newly proposed lepton flavor universality violation observables, Q_(4,5), in the B → K~*(→Kπ)μ~+μ~-decay channel in the low dimuon mass region. To see the variation in the values of these observables from their Standard Model values, we have chosen different scenarios for the Z′ model. It is found that these angular observables are sensitive to the values of the parameters of the Z′ model. We have also found that with the present parametric space of the Z′ model,the P′_5-anomaly could be accommodated. However, more statistics on the anomalies in the angular observables are helpful to reveal the status of the considered model and, in general, the nature of new physics.     

Process e-γ→ e-H in Littlest Higgs Model

In the context of the littlest Higgs (LH) model, we estimate the production cross section of the process e-γ→ e-H in the future high-energy linear e e- collider (ILC) with the center-of-mass (CM) energy √S= 500 GeV. Our numerical results show that the contributions of the LH model to this process are very small in most of the parameter space allowed by the electroweak precision measurement data, and are very difficult to be detected in the future ILC experiments.     

Benchmarking the simplest slave-particle theory with Hubbard dimer

Slave-particle method is a powerful tool to tackle the correlation effect in quantum many-body physics. Although it has been successfully used to comprehend various intriguing problems, such as Mott metal–insulator transition and Kondo effect, there is still no convincing theory so far on the availability and limitation of this method. The abuse of slave-particle method may lead to wrong physics. As the simplest slave-particle method, Z2 slave spin, which is widely applied to many strongly correlated problems, is highly accessible and researchable. In this work, we will uncover the nature of the Z2 slave-spin method by studying a two-site Hubbard model. After exploring aspects of properties of this toy model, we make a comparative analysis of the results obtained by three methods:(i) slave-spin method on mean-field level,(ii) slave-spin method with gauge constraint, and(iii) the exact solution as a benchmark. We find that, protected by the particle–hole symmetry, the slave-spin mean-field method can recover the static properties of ground state exactly at half filling. Furthermore, in the parameter space where both U and T are small enough, the slave-spin mean-field method is also reliable in calculating the dynamic and thermal dynamic properties. However, when U or T is considerably large, the mean-field approximation gives ill-defined behaviors, which result from the unphysical states in the enlarged Hilbert space.These findings lead to our conclusion that the accuracy of slave particle can be guaranteed if we can exclude all unphysical states by enforcing gauge constraints. Our work demonstrates the promising prospect of slave-particle method in studying complex strongly correlated models with specific symmetry or in certain parameter space.     

Top Quark Flavor Changing Decay t→ cH^0 in Little Higgs Model

We study theoretically the quantum effects of the littlest Higgs model （LH） mediated by flavor changing one-loop Feynman diagrams on the rare decay process t→ cH^0. The comparison of the decay width in the LH model with that in the standard model （SM） is made. We find that the decay branch ratio of t→ cH^0 in the LH model is at most of the order-10^-12, which is two order larger than in the SM. The numerical results show that the difference between the branch ratios in the LH model and the SM is generally sensitive to the LH model parameters, such as symmetry breaking scale f, Higgs boson mass mH0, and x=v＇4f/v^2 in our chosen parameter space, but relatively insensitive to the value choice of the cosine of the mixing angle c and the ratio λ1/λ2.     

Oblique parameters in gauged baryon and lepton numbers with a 125 GeV Higgs

In an extension of the standard model,where baryon number and lepton number are local gauge symmetries,we analyze the effect of corrections from exotic fermions and scalars on the oblique parameters S,T,U.Because a light neutral Higgs ho with mass around 124-126 GeV strongly constrains the corresponding parameter space of this model,we also investigate the gluon fusion process gg→h_0 and two photon decay of the lightest neutral Higgs ho→γγ at the Large Hadron Collider.     

Lepton-number-violating decays of singly-charged Higgs bosons in the type-(Ⅰ+Ⅱ) seesaw model

The lepton-number-violating decays of singly-charged Higgs bosons H± are investigated in the minimal type-(Ⅰ+Ⅱ) seesaw model with one SU(2)L Higgs triplet Δ and one heavy Majorana neutrino N1 at the TeV scale.We find that the branching ratios B(H+ → lα+ ν)(for α = e,μ,τ) depend not only on the mass and mixing parameters of three light neutrinos νi(for i=1,2,3) but also on those of N1.Assuming that the mass of N1 lies in the range of 200 GeV to 1 TeV,we figure out the generous interference bands for the contributions of νi and N1 to B(H+ →lα+ ν).We illustrate some salient features of such interference effects by considering three typical mass patterns of νi,and show that the relevant Majorana CP-violating phases can affect the magnitudes of B(H+ →l+αν) in this parameter region.     

Oblique parameters in gauged baryon and lepton numbers with a 125 GeV Higgs

In an extension of the standard model, where baryon number and lepton number are local gauge sym- metries, we analyze the effect of corrections from exotic fermions and scalars on the oblique parameters S, T, U. Because a light neutral Higgs h0 with mass around 12-126 GeV strongly constrains the corresponding parameter space of this model, we also investigate the gluon fusion process gg→h0 and two photon decay of the lightest neutral Higgs h0→yy at the Large Hadron Collider.     

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 v 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^-6 and 10^-5 respectively, which can be detected in near future.     

The littlest Higgs model with T-parity and some lepton flavor violation decay processes

The new particles predicted by the littlest Higgs model with T-parity (called LHT model) can induce the lepton flavor violation (LFV) couplings at the one-loop level,which can add contributions to some LFV processes.Taking into account the constraints of the experimental data on the relevant free parameters,we calculate the branching ratios of the LFV decay processes Z → l ˉl and τ-→μ-P 1 P 2 with P 1 P 2 = π + π-,K + K-,and K0 ˉK 0 in the context of this new physics model.We find that the LHT model can indeed make significant contributions to some of these LFV decay processes.The Z factory option for the future high energy e + e-collider experiments will give severe constraints on the LHT model.